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The environmental effects of underwater explosions with methods to mitigate impacts

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THE ENVIRONMENTAL EFFECTS OF
UNDERWATER EXPLOSIONS
WITH
METHODS TO MITIGATE IMPACTS
By
Thomas M Keevin, Ph.D.
and
Gregory L. Hempen, Ph.D., P.E., R.G.
U.S. Army Corps of Engineers
St. Louis District
1222 Spruce Street
St. Louis, Missouri 63103-2833
August 1997
ACKNOWLEDGEMENTS
Preparation of this manual and the original research that made parts of this
possible were funded by the LEGACY Program and by the St. Louis District, U.S. Army
Corps of Engineers.
We owe a special note of thanks to Dr. David Schaeffer (University of Illinois) who
was extremely helpful in the development of study designs, statistical analysis,
and publication of reports. Dr. Schaeffer participated in much of the original
research effort.
We appreciate the assistance of the St. Louis District Library, Arthur Taylor
(Director), Sandra Argabright, Phyllis Thomas and Hazel Schnatzmeyer. They were
given the task of obtaining hundreds of reports and publications, most very
obscure.
TABLE OF CONTENTS
INTRODUCTION
REFERENCES CITED
CHAPTER 1
UNDERWATER EXPLOSIVES USE: NATURAL RESOURCE AGENCY CONCERNS AND
REGULATORY AUTHORITY
RATIONAL FOR NATURAL RESOURCE AGENCY CONCERNS
NATURAL RESOURCE AGENCY REGULATORY AUTHORITY
CHAPTER 2
M
ECHANICS OF UNDERWATER EXPLOSIONS
INTRODUCTION
EXPLOSIONS
MEDIA CONSIDERATIONS
TRANSMITTING MEDIA
PRESSURE-WAVES
CHAPTER 3
THE ENVIRONMENTAL EFFECTS OF UNDERWATER EXPLOSIONS: AQUATIC PLANTS
INTRODUCTION
DAMAGE AND MORTALITY OF AQUATIC PLANTS EXPOSED TO UNDERWATER EXPLOSIONS
MITIGATION TECHNIQUES TO PROTECT AQUATIC PLANTS FROM UNDERWATER EXPLOSIONS
CHAPTER 4
THE ENVIRONMENTAL EFFECTS OF UNDERWATER EXPLOSIONS: AQUATIC
INVERTEBRATES
INTRODUCTION
APPROACH
INVERTEBRATE LITERATURE REVIEW
SUMMARY AND DISCUSSION
CHAPTER 5
THE ENVIRONMENTAL EFFECTS OF UNDERWATER EXPLOSIONS: AMPHIBIANS AND
REPTILES
INTRODUCTION
INJURY AND MORTALITY OF REPTILES EXPOSED TO UNDERWATER EXPLOSIONS
INJURY AND MORTALITY OF AMPHIBIANS EXPOSED TO UNDERWATER EXPLOSIONS
MITIGATION TECHNIQUES TO PROTECT REPTILES AND AMPHIBIANS FROM UNDERWATER
EXPLOSIONS
CHAPTER 6
THE ENVIRONMENTAL EFFECTS OF UNDERWATER EXPLOSIONS: FISH
INTRODUCTION
PRESSURE RELATED MORTALITY OF FISH
EXPLOSIVE PRESSURE RELATED ORGAN DAMAGE
EFFECT OF FISH SIZE
EFFECTS OF UNDERWATER EXPLOSIONS ON LARVAL FISH AND EGGS
SUBLETHAL INTERNAL DAMAGE TO FISH FROM UNDERWATER EXPLOSIONS
UNDERWATER EXPLOSIVE FISH MORTALITY MODELS
MITIGATION TECHNIQUES TO PROTECT FISH FROM UNDERWATER EXPLOSIONS
CHAPTER 7
THE ENVIRONMENTAL EFFECTS OF UNDERWATER EXPLOSIONS: MARINE MAMMALS
INTRODUCTION
INJURY AND MORTALITY OF MARINE MAMMALS EXPOSED TO UNDERWATER EXPLOSIONS
BEHAVIORAL EFFECTS OF UNDERWATER BLASTING ON MARINE MAMMALS
MITIGATION TECHNIQUES TO PROTECT MARINE MAMMALS FROM UNDERWATER EXPLOSIONS
CHAPTER 8
MITIGATING THE ADVERSE ENVIRONMENTAL EFFECTS OF UNDERWATER EXPLOSIONS
ON FISH
INTRODUCTION
DEVELOPMENT OF MITIGATIVE STRATEGIES: THE BLASTING DESIGN
DEVELOPMENT OF MITIGATIVE STRATEGIES: BIOLOGICAL CRITERIA
DEVELOPMENT OF MITIGATIVE STRATEGIES: USE OF PHYSICAL MITIGATION FEATURES
MITIGATION RECOMMENDATIONS
A TIERED MITIGATION PLANNING PROCESS
INTRODUCTION
In- or near-water use of explosives (i.e., construction or demolition projects;
ordinance testing and disposal; as well as, harbor maintenance projects; and use of
explosives during training exercises) can adversely affect significant aquatic
ecosystems or organisms. Many of the potential environmental problems associated
with use of explosives in aquatic environments are unique to the Department of
Defense (i.e. ordinance testing & training). The literature on blasting effects is
obscure and would be difficult to gather in a timely fashion by environmental
planners and resource managers attempting to practice good stewardship of
Department of Defense managed water resources. The goal of this manual is to
provide resource planners/managers with information, which allow quick assessments
of potential problems associated with underwater explosive use.
This handbook summarizes available literature (e.g., published, state and Federal
reports) on the environmental effects of underwater explosions and provides
information on the potential use of mitigative strategies to reduce impacts to
significant biological systems and species. Chapter 1 outlines natural resource
agency concerns and regulatory authority concerning explosive use. Chapter 2
provides information concerning explosives, the physics of explosions, and how
explosives react in various media. It is not the intent of this chapter to provide
an exhaustive review of the physics of explosions. We have attempted to provide
enough information to make the chapters on environmental effects more
understandable. The effects of underwater explosions on aquatic plants (Chapter 3
)
,
aquatic invertebrates (Chapter 4), fish (Chapter 5), amphibians and reptiles
(Chapter 6), aquatic mammals (Chapter 7) are reviewed. Chapter 8 provides
information on mitigation techniques to reduce adverse environmental effects of
underwater explosions.
A user-friendly computer program with users manual for planners/managers which
allows quick assessments of potential environmental problems is also being
developed under this LEGACY project. The computer program will provide impact
analysis (kill radius for fish) based on the amount, depth, and use (open-water
versus confined blast) of the explosive being detonated.
There is a considerable amount of research on the environmental effects of
underwater explosions still in progress by the authors. In addition, the authors
have established a Natural Resources Working Group within the International Society
of Explosives Engineers to tackle some of the outstanding questions in this field,
such as standardization of pressure transducer calibration, standardization of
pressure measurement and reporting, standardization of experimental designs for
mortality assessment, and identification of data gaps and prioritization of data
collection needs. As such, this manual should be considered a working document. If
you have any comments or questions, please feel free to contact the authors. Dr.
Thomas Keevin is an Aquatic Ecologist and Dr. Gregory Hempen is a Geophysical
Engineer.
Thomas M. Keevin, Ph.D. and Gregory L. Hempen,
Ph.D., P.E., R.G.
U.S. Army Corps of Engineers
St. Louis District
1222 Spruce Street
St. Louis, MO 63103-2833
Phone: TMK (314-331-8462); GLH (314-331-8441)
E-mail: keevin@smtp.mvs.usace.army.mil
Hempen@smtp.mvs.usace.army.mil
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CHAPTER 1
UNDERWATER EXPLOSIVES USE:
NATURAL RESOURCE AGENCY
CONCERNS AND REGULATORY AUTHORITY
RATIONAL FOR NATURAL RESOURCE AGENCY CONCERNS
Population growth and economic development have resulted in frequent changes in our
hometown landscapes and their waterways due to housing developments, shopping
malls, industrial development, and roadways. Population growth and development have
resulted in a loss of aquatic habitat and a general decline in water quality, both
important factors in sustaining aquatic species. For example, since 1850, 67% of
the fish species from the Illinois River and 44% from the Maumee River have become
less abundant or have disappeared (Kerr et al. 1985). These are just two examples
of aquatic degradation and loss of fish species that are occurring throughout the
United States (Warren and Burr 1994). The list of aquatic invertebrates and
vertebrates that are federally protected or under consideration for protection
(candidates) continues to increase and totals more than l,O00 taxa (Williams and
Neves 1992). In fact, 27 species and 13 subspecies of fish have become extinct in
North America during the past 100 years (Miller et al. 1989).
Marine resources are suffering similar assaults on their biological integrity as
described for freshwater ecosystems. Overharvesting, toxic and nutrient pollution,
costal development, and increasing ultraviolet radiation threaten marine species
(Upton 1992).
Habitat degradation has jeopardized the continued existence of many species. Both
federal and state laws afford protection to numerous aquatic organisms. The
following listing makes it clear that it is difficult to utilize explosives
underwater, in a major river basin or in the marine environment, without the
potential for adversely impacting a federally threatened or endangered species or a
species of special concern to federal and state natural resource agencies.
Aquatic Mammals. The U.S. Fish and Wildlife Service (1993) lists 15 species of
marine mammals that occur in U.S. coastal waters or near our trust territories as
threatened and endangered, including such species as the West Indian manatee
(Florida manatee), Southern sea otter, Steller sea lion, 3 species of seals, and
eight species of whales.
Reptiles. Of special concern for the blaster, in U.S. coastal marine environments
there are 6 sea turtle species listed as either threatened or endangered (U.S. Fish
and Wildlife Service 1993).
Fish. Williams et al. (1989) considered 364 fish species and subspecies in North
America that warrant protection because of their rarity. Their list consists of 147
fishes classified as special concern, 114 as threatened, and 103 as endangered.
Twenty-two of the fishes occur in Canada, 254 in the United States, and 123 in
Mexico. Some occur along international borders and, therefore, inhabit two
countries.
Freshwater mussels. Of the 297 native freshwater mussels of the United States and
Canada, Williams et al. (1993) considered 213 taxa (71.7%) as endangered,
threatened, or of special concern; only 70 (23.6%) were considered as currently
stable. Twenty-one taxa (7.1%) were listed as possibly extinct, 77 (26.0%) as
endangered, 43 (14.5%) as threatened, 72 (24.2%) as of special concern, and 14
(4.7%) as undetermined.
Crayfish. Of the 338 crayfish of the United States, Taylor et al. (1996) considered
162 taxa (48%) as possibly extinct, endangered, threatened or of special concern.
Of these, 2 (<1%) are possibly extinct, 65 (19.2%) are endangered, 45 (13.3%) are
threatened, and 50 (14.8%) are of special concern. Taxa classified as currently
stable total 176 (52%).
The above litany of extinctions and aquatic species classified as threatened,
endangered or of special concern form the basis of natural resource agency concerns
over aquatic resources. As population growth and economic development continues,
there will be more and more habitat degraded and species placed in jeopardy.
Underwater explosives use is often considered by natural resource agencies as
another assault on the resources that the agency is mandated to protect.
Natural resource agencies are challenged with permitting, under various regulatory
authorities, underwater explosive use while at the same time protecting aquatic
resources. Deciding on whether or not to allow use of explosives requires striking
a balance between development and aquatic resources protection. On a positive note,
natural resource personnel are generally willing to work with and accommodate the
blaster.
NATURAL RESOURCE AGENCY REGULATORY AUTHORITY
In the United States, there currently are no national guidelines or regulations
concerning mitigation of explosive use impacts. Decisions are left to individual
state agencies and regulatory authority may rest with more than one state agency.
In Canada, National guidelines for the use of explosives in Canadian fisheries
waters have been prepared by the Department of Fisheries and Oceans under the
Fisheries Act (Wright In press).
Keevin (In press) reviewed state natural resource agency permit requirements for
underwater explosive use within waters under their jurisdiction (Table 1.1). To
determine current agency policies on the use of explosives, a questionnaire was
sent to fish and wildlife agency directors in each state. Questions were developed
to determine current state fish and wildlife agency policies concerning the use of
explosives for legitimate purposes (i.e., military testing programs, demolition,
construction) within waters under their jurisdiction. Questions targeted three
areas of concern for fish and wildlife agencies: (1) what type permit, if any, was
required; (2) what information did the agency provide to the applicant; and (3)
what mitigative techniques were required of the applicant by a agency or
recommended to protect aquatic 1ife from explosive pressures (Issue #3 is covered
in Chapter 8).
1. Permit Requirements. Thirty three state natural resource agencies require
permits to conduct underwater blasting. There is often more than one agency
responsible for permitting within a given state, depending on the location of the
blasting, (freshwater, marine, or wetland), or the type of project, (demolition or
seismic exploration).
Most agencies require permits based on existing fish and wildlife codes, codes that
are nonspecific to underwater blasting (i.e. fishing codes, stream protection acts,
or wetland protection laws). For example, the Montana Department of Fish, Wildlife
and Parks' permitting authority rests with the Stream Protection Act and The
Natural Streambed and Land Preservation Act. However, many states permitting or
review authority is based on fishing codes; since many codes specifically indicate
that it is illegal to take fish with explosives. In some states taking fish with
explosives is illegal by default, since explosives are not listed as an approved
fishing method.
Two states, Oregon and Pennsylvania, have permit application forms specific to
underwater explosive use and resource protection. The Oregon Department of Fish and
Wildlife's In-Water Blasting Permit Application Form requires that the applicant
provide detailed information on explosive type, amount, size and number of charges
to be detonated, detonation delay information, and estimated start and completion
data. The Oregon applicant is also required to provide information concerning
project impacts and proposed mitigation measures including: fish and wildlife
species which occur in the blast area and predicted effects of the blasting on
these species, fish and wildlife habitat within the affected area and the predicted
effects of blasting on these habitats, estimated distance of impacts and area
affected, and measures the blaster (before and after construction) will use to
prevent injury to fish and wildlife and their habitats including an analysis of
their effectiveness under the environmental conditions at the project site.
The "Guidelines for the Use of Explosives in Canadian Fisheries Waters" require
that the blaster prepare an environmental impact assessment of the project
describing the potential adverse effects on the fish and marine mammal resources
and their habitats in the project area. This document is submitted to the
Department of Fisheries and Oceans regional/area authority. The blaster is also
required to prepare a plan to mitigate adverse effects on fish and fish habitat
identified in the environmental impact assessment. The blaster must complete a
detailed application form, specific to underwater explosive use, for authorization
to kill fish by means other than fishing. Detailed information is required on the
type, weight and weight per delay of explosives, shot pattern, detonation depth,
delay period (msec), and method of detonation. The environmental impact assessment
and mitigation plan are required as part of the application submittal. Although
these guidelines are draft they are currently in use by the Department of Fisheries
and Oceans.
Seventeen state natural resource agencies responded that they do not require
permits for the use of explosives in waters under their jurisdiction. However,
these agencies may provide input to other agencies within their state and to
federal agencies. Under the Fish and Wildlife Coordination Act, state natural
resource agencies have the authority to review and comment on applications for U.S.
Army Corps of Engineers' Section 404 (Clean Water Act) permits as a means of
providing input to the decision making process. Federal explosive use projects
(including any military related activities), projects requiring federal permits or
receiving federal funding also fall under the jurisdiction of the National
Environmental Policy Act (NEPA) and the Endangered Species Act. The NEPA requires
Environmental Assessments of project impacts and possibly Environmental Impact
Statements.
The Endangered Species Act requires a Biological Assessment of potential impacts to
Federally threatened and endangered species and species Proposed for listing.
2. Information package on explosive-use provided to applicant by agencies. Only
five states provide an information package to the blaster (Table 1.1). The majority
of the information packages are related to use of explosives for seismic
exploration. For example, the Mississippi Department of Natural Resources provides
a booklet outlining rules and regulations governing geophysical and seismic
exploration on state-owned lands. The Louisiana Department of Wildlife and
Fisheries provides information outlining regulations governing explosive use for
seismic exploration within the state. Both packages, which are not lengthy, provide
information concerning requirements for observers, explosive charge size limits,
minimum shot hole depths for a range of explosive sizes, and measures to mitigate
impacts. The Canadian Department of Fisheries and Oceans provides the blaster with
their "Guidelines for the Use of Explosives in Canadian Fisheries Waters," which
explains environmental impact assessment and mitigation planning requirements and
contains permit application forms.
Table 1.1 Summary of State Natural Resource Agency Responses
AL AK AZ AR CA CO CT DE FL GA
AGENCY PERMIT YYNNYNYYYN
AGENCY PROVIDES
INFORMATION PACKG NYNNNNNNNN
HI ID IL IN IA KS KY LA ME MD
AGENCY PERMIT YNYYNNNYYY
AGENCY PROVIDES
INFORMATION PACKG NNNNNNNYNN
MA MI MN MS MO MT NE NV NH NJ
AGENCY PERMIT YYYYNYYNYY
AGENCY PROVIDES
INFORMATION PACKG NNNYNNNNNN
NM NY NC ND OH OK OR PA RI SC
AGENCY PERMIT NYYYYNYYYY
AGENCY PROVIDES
INFORMATION PACKG NNNNNNYYNN
SD TN TX UT VT VA WA WV WI WY
AGENCY PERMIT NNYNYYYNYN
AGENCY PROVIDES
INFORMATION PACKG NNNNNNNNNN
CHAPTER 2
MECHANICS OF UNDERWATER EXPLOSIONS
INTRODUCTION
Underwater blasting is a science well understood in direct terms. The chemical and
physical effects of detonation are well known. Wave passage is accurately developed
in theory. The application of explosives and blasting agents is an art, because it
is expensive to study in detail and because the variability of the media exposed to
detonation waves is extremely complex. Testing explosives or utilizing the
detonation in some manner can easily be accomplished by the art of blasting without
fully understanding, or needing to understand, the science and details of
detonations and wave passage. The physical aspects of underwater blasting are
described herein; more complete treatments of underwater blasting may be found in
Cole (1948) and Mellor (1986).
Three aspects of blasting are the detonation, the media transmitting the blast
effects, and the effects of blast on its ambient environment. Some blast effects
may be the desirable reasons for the shooting (examples, removing a bridge pier,
explosive/ordnance testing, producing seismic waves). Other effects may be adverse
impacts, resulting in damage to the natural and/or built environment. The primary
interest of this document is the passage of the water-borne pressure waves and its
negative impacts. These pressure waves are produced in water when the explosive
charge is in the water column or when the shot is beneath or adjacent to the body
of water.
Underwater blasting is conducted for a number of uses: rock excavation, demolition,
grade preparation for foundations, structural rehabilitation, waterway applications
(deepening channels/harbors, dike removal, and emergency levee-raises during
extreme flooding), geophysical exploration, fish sampling, metal forming, military
operations, and other uses. Shock-
w
ave pressures in column from explosions can have
adverse impacts on nearby submerged structures and on aquatic life. Regulatory
agencies, depending on the circumstances, do not permit underwater blasts (nor
blasts near aquatic environments) without mitigation of the adverse effects of
pressures.
EXPLOSIONS
Modern blasting products release energy in two forms: detonation and burning.
Detonation is the term for the rapid pressure front moving through the explosive
ahead of a chemical transition front. The property of detonation makes that
particular formulation an explosive, such as Cyclonite (RDX) and Trinitrotoluene
(TNT). RDX is a primary explosive, only a small quantity of RDX is required to
begin detonation. TNT, like dynamite, is a high explosive, which start to detonate
only when a greater amount than critical volume or critical diameter is present. A
blasting agent is a term for a material that can be made to detonate when initiated
properly, examples are Ammonium Nitrate with Fuel Oil (ANFO) and Water Gel
Slurries. A minimum charge diameter is required to achieve and sustain detonation.
Dick et al. (1993a) shows that some dynamites require less than 20 mm diameter to
initiate detonation, ANFO requires a 50 mm diameter with confinement to detonate.
Burning (deflagration) releases the chemical energy of the materials, including
explosives, but more slowly. Deflagration occurs without the rapidly expanding,
detonation pressures. Black powder is a material that only deflagrates and has been
called a low explosive. High explosives and blasting agents burn when their charge
diameter is less than the critical diameter to achieve detonation.
The chemical energy of a detonating explosive is released as physical, thermal, and
gaseous products. The detonation wave rapidly densifies the explosive material.
This physical shock front moves faster than the acoustic velocity of the explosive
material. The detonation is only sustained within the limits of the explosive. The
detonation ceases at the boundary with the medium containing the explosive. The
shock wave passes into the medium. The thermal and detonation effects are only
important near the explosion. Consideration of the thermal and detonation impacts
may usually be ignored beyond a short distance (three to ten diameters of the
explosive's volume) from the blast. The two main impacts in the far field (beyond
the zone where thermal and detonation effects are important) from an explosion are
the shock waves and the expanding gaseous reaction products. The original shock
wave is the primary cause of damage to aquatic life or other structures at great
distance from the shot point. The expanding gaseous products can cause: a noisy
airblast pressure concussion when exploded in the air, but produce little shock
wave amplitude in surface water or earthen media; a water plume and/or a gas bubble
for blasts in the water column, and less intense, recurring pressure waves when a
pulsating gas bubble occurs; and, lengthening of fractures and displacement of
solids when a confined explosion occurs in sediment or rock.
Water is displaced and pressurized both by burning and detonation within the water
column. Water is somewhat compressible in the near-blast region by extremely
elevated pressure due to the explosion. The water column depth and work
accomplished by the blasting (due to its confinement) are significant conditions in
determination of the explosion's effects. Besides the compression waves produced by
the explosion, other impacts could include noise, projectiles and gaseous chemical
products, which are vented to the water or air. Water is nearly incompressible at
standard temperature and pressure and cannot support shear waves. The extreme
pressures and temperatures of explosives' detonation complicates the analysis of
their adverse effects.
Use of explosives within or beneath or adjacent to the water column requires a
greater effort of safety and planning, relative to blasting under dry conditions.
The greatest concern is worker safety. The safety of underwater blasting is
directly related to planning and safe work practices. Worker safety must be
paramount in mitigation planning to avoid the severe potential that could result in
accidental detonation. Accidental detonation could shoot a large quantity of
explosives, cause worker mortality, and create greatly increased losses in the
natural environment. The variety of other concerns includes water flow rate,
turbidity, floating debris, and working depth beneath the water surface.
Maintenance of exact horizontal spacing within and between rows of shotholes and
loading explosives overwater increases the difficulty of accurate shooting. These
limitations also compound the potential for misfires and overshooting. With
submerged shooting, the chance of crossfiring closely spaced holes or overloading
voids/crevices in the material contribute to the increased pressure and energy in
the shot.
Important underwater blasting parameters include, but are not limited to: types of
explosives and their properties; energy releases from underwater explosions -
amplitude, duration, frequency, pressure, impulse, energy flux density; charge
weight and explosive-gas diameter versus water column depth; unconfined test
explosion properties versus confined blasting to perform work; scaling laws of
underwater blasting; wave mechanisms - spherical, cylindrical and planar wave
propagation; and, measuring equipment and its calibration.
Explosives perform two types of mechanical work: material fracturing (crushing and
extending fractures) or material displacement. Both shock and gas energy are
released by the detonation process. Varying explosive types release differing total
energy and fractions of the shock and gas component energies. All detonations have
some fraction of both brisant (shock) energy and expansion (gas) energy. The shock
component may be used for unconfined explosions, as the gas energy is lost to the
ambient environment without confinement. Common, unconfined applications in the
water column include explosives/ordnance testing, severing steel members, seismic
exploration sources, and boulder breakage. The more useful component for more
typical blast applications is gas development. These typical applications are
mineral production or mass demolition by placement of explosives in boreholes with
stemming. Stemming is the (normally granular) fill material placed in the boring
over the explosives material and extending to the surface. [For rock quarrying, the
impedance (density times velocity) are matched between the rock and the explosive.
Higher impedance explosives typically have more shock energy.] The expanding gases
displace material volumes when placed in such confinement that the gaseous reaction
products are not quickly vented to the atmosphere or marine environments.
Commercial explosives and blasting agents are designed as oxygen-balanced chemical
reactions (Dick et al. 1993b). The explosive's fuel and the oxidizing agent achieve
the greatest energy of reaction when there is neither an oxygen debt nor surplus.
The importance to underwater shooting is that a poor reaction is further water
cooled or "dampened" to make the reaction energy lower than if conducted above the
water surface. Unbalanced, water-cooled detonations may produce excess amounts of
toxic gaseous products, besides not achieving the desired work.
Two factors are important to underwater blasting: increasing charge weights and
lowering shock energy. Brower (1977) cites the need to displace both the blast's
host material and water to produce the desired outcome in typical work. The placed
weight of explosives is commonly increased several multiples in comparison to the
same work effort above the water surface. Oriard (1983) questions the need for
greater charge weights and recommends increased burden for greater water depths.
While shock energy may be important to fracture the media to be displaced, gas
energy must be capable of moving the material and the water load. Explosives in
underwater blasting obviously should be selected, in part, by the fraction of
available gas energy. Further, the shock energy component causes the peak, shock
pressures. For underwater blasting, this brisant pressure wave and its negative,
reflected pressure component at the air-water surface are the chief parameters in
undesirable damage to structures and aquatic life.
Optimized blasting is the environmental awareness of the impact of blasting on the
objective and ambient media. It also recognizes the host medium has a primary
effect on the blasting efficiency. Controlled blasting (Konya and Walter 1985) is
an industry term that is similar to, but different from, optimized blasting.
Optimized blasting utilizes the media's properties, i.e. varying the shooting
pattern to take advantage of the bedding and jointing of the removed rock, to
achieve efficient production. Optimized blasting attempts to optimize the
production and diminish the effects on the surroundings. Optimized blasting for
underwater programs: reduces the total weight of explosive by carefully considering
the media and the blasting pattern's relationship to the material's properties;
increases the number of delays used to allow movement of material (reducing the
burden) prior to causing additional material to displace; and, increases
confinement with added stemming to assure that premature venting of gases does not
occur.
Blasting materials are rated by a variety of factors, many of which have little
commonality between manufacturers. The producers provide the values of common
properties to the purchasers of explosives and blasting agents. Konya and Walter
(1985) and Persson et al. (1994) describe the array of explosives' and blasting
agents' properties. The properties of selected explosives can enhance performance
and reduce the hazards of blasting. For the considerations herein, the shock energy
should be diminished to limit the pressure pulse reaching the surrounding media.
The maximum shock pressure at some distance from the blast is related to the
detonation pressure, the travel path and the media of passage.
a. Density. The density is the mass of the product per unit volume, usually
expressed by Specific Gravity (SGe). The more dense the explosive the greater the
power of the shot. SGe can vary from 0.5 to 1.7 (Dick et al. 1993a). An explosive is
easier to handle and place submerged, if it is heavier than water, SGe > 1.0.
Density is one of two factors contributing to the detonation pressure within the
detonating material.
b. Detonation Velocity The detonation velocity (ve), by title, is the propagation
rate through the detonating media. The ve ranges from 1,900 to 7,500 meters/second
(mps). Konya and Walter (1985) provide an equation for the detonation pressure, Pd,
[converted to metric units]
where the pressure units are megapascals (Mpa, see Table 2.1 for common pressure
conversions) for Ve in mps. The peak pressure at the wall of the explosive's
containment (typically a borehole) may be one half the Pd , while Konya and Walter
(1985) feel that the detonation state does not exist at this boundary. The shock
pressure due to the Pd must extend to the surrounding media, and is related
empirically to the wall pressure and, ultimately, to the Pd.
The compression-wave pressure at any location in the water column is related to the
shock pressure in the detonating material. Since the maximum pressure, Pm, within
the water is the cause of hazard, its relation to Pd and to the square of Ve is
extremely relevant. The need to fracture a mass prior to its displacement (an
explosive with large shock energy) is an argument some authors and blasters make.
Contrarily, Dick et al. (1993a) indicates that "typical of most operations, it is
of little importance." Given two explosives of the same charge weight, A with a Ve
of 4,250 mps and B with a Ve of 6,000 mps, the Pmfor explosive B would be twice the
Pm value at the same distance as for A. Thus, an explosive with a low Ve should be
considered for submerged shooting when the hazard of shock pressure is a concern.
The doubling of pressure is contrary to unpublished data by Keevin (1995) that
three commercial explosives of differing Ve produced similar pressures and the same
mortality in fish for unconfined, shallow, water-
c
olumn shots. Other factors may be
more important in reduction of the shock-wave pressures (Oriard 1983).
c. Fumes. Fumes are the toxic gaseous by-products (chiefly carbon monoxide and
nitrous/nitric oxides) of the detonation reaction. The fume class or quality for
each blasting compound is a relative measure from poor (excessive toxic gas
creation) to excellent (insignificant toxic gas production). Some of these toxic
products remain as a dissolved hazard in the ambient water body, which may have a
detrimental effect on aquatic life. Underwater blasting creates conditions that may
Pd = 4.50e-4 SGe Ve2 / (1. + O.80 SGe){1}
Table 2.1. Pressure Unit Conversions
kPa bar psi atm
1 kPa 1
0100
.
1450 .009869
1 bar 100 1
1
4.50 .9869
1 psi 6.895
.
06895 1.06803
1 atm
1
01.3
.013 14.70 1
lead to increased fume production: inadequate water resistance and inadequate
priming (Konya and Walter 1985). "Permissible explosives" used in underground coal
mining should not be considered an alternative explosive for underwater blasting.
Permissible explosives are purposely less efficient, cooler reactions to avoid
igniting coal dust, and have worse fume quality than other blasting materials.
MEDIA CONSIDERATIONS
Blasting in solids beneath or adjacent to the water column is normally conducted to
remove obstacles. [Some removal methods may have the charge resting on the solid's
surface in air or in water.] Explosives are placed typically in boreholes drilled
into the mass to be removed. The shock front travels most rapidly down the
centerline of the explosive column. Detonation proceeds more slowly at the boundary
of the explosive with its container and passes into the surrounding medium. The
shock wave, after passage into the enclosing material, does work crushing,
fracturing and/or compressing the material. The loss of the energy supply, use of
energy to produce work on the medium, and the ever-expanding surface of the
compression front causes the shock wave to slow to the sonic velocity of the
medium. Particle disturbance at this transition distance from the explosive becomes
the commonly known compression or Primary wave (P-wave). The shock wave within the
supersonic zone, called the near field, exceeds the elastic strength of the medium
producing fractures and permanent deformation. The P-wave beyond the transition
distance, termed the far field, remains within the elastic limits of the material
(causing no lasting effects in rigid solids).
Seismic exploration, fish sampling, military use and explosives research may be
conducted by blasting in the water column (open-water shot) of natural
environments. Explosions in the water column produce P-waves in the far field. The
P-waves originate from the shock wave. P-waves also are created from the
contraction points of the pulsating gas bubble of gaseous reaction products, when
the gas bubble does not reach the air-water surface before reaching its contracted
state.
The more important differences between water-borne blasting and shooting within
solids are the properties of water. Water's elastic moduli are not nearly as great
as solids and, by its nature, water (like all fluids and gases) does not support
shear waves.
The shock wave emanating from the explosive's detonation is "converted suddenly
into potential energy of compression and kinetic energy of outward motion in the
water medium" (Kramer et al. 1968). Cole (1948), in his landmark publication,
describes the important processes and subsequently develops analytical and
empirical equations of state for the expanding waves. The shock wave expands into
the surrounding water medium applying a compressive load to the water. In a planar
shock front, the amplitude of the pressure pulse will retain its size for some
distance. Cole (1948) indicates that the particle velocity, u, is related to
pressure, P. by
where the hydrostatic pressure is Po and the acoustic impedance, Zw, is the density
times the velocity of water.
The pressure amplitude for cylindrical and spherical wave forms diminishes with
radial distance from the explosive. The nonplanar explosions produce two elements
of the original waveform: the shock wave (or compressive flow) and the afterflow,
or surge. The ever-expanding radial volume affected by the shock front must act
u = (P - Po) / Zw,{2}
also tangentially to compensate for the "side load," called spherical divergence.
It is this side pressure accommodation that contributes to the second term, surge.
These two effects, shock and surge, occur simultaneously along the shock wave path
to the transition distance. Beyond the transition distance, the velocity of the
disturbance falls to the P-wave velocity for water and the surge term has become
infinitesimal. The transition distance bounds the near-field region where acoustic
radiation and afterflow are important from the far-field where only compressive
flow is a factor.
A gas bubble or, as Cole (1948) terms it, gas sphere expands from the gaseous
products of detonation well after the shock wave has passed. The gas bubble with
its momentum expands to a maximum value, if the explosion is sufficiently deep so
that the bubble does not break the water surface with the atmosphere. Bjarnholt
(1978) provides a term for the maximum bubble radius, ab, in m:
for Q as the heat of detonation in megajoules/kilogram (MJ/kg), W being the charge
weight in kg, and dw is the explosive's water depth in m. Bjarnholt (1980) gives Q
for a variety of explosives; for an estimate of abuse a Q of 4.44 or 4.27 MJ/kg for
Nitromethane or TNT, respectively.
The gas expansion forms an oscillating system with the gas' momentum and
hydrostatic pressure of water. The gas bubble initially extends beyond the
equilibrium state with the water load. The gas sphere cannot easily rise toward the
air-water surface while in its larger size, because of the great volume of water
that must be displaced for the bubble to rise. The surrounding water pressure
causes the bubble to rapidly shrink to a minimum size of much greater dimensions
than the original solid explosive's volume. The gas sphere at this contraction has
greater internal pressure than the ambient water pressure, and expands a second
time. A smaller shock wave is released at the instant the bubble is at its minimum
diameter, in transition to its expansion phase. The gas bubble rises quickly while
in the compressed volume. The oscillation in size continues until the gas sphere
breaks the surface with episodic releases of energy and rapid vertical displacement
at gas-volume minima. Cole (1948) shows that the period of bubble oscillation is a
function of dw, Q. W and fraction of remaining energy for the nth bubble
oscillation, fn. Cole indicates that the energy remaining is merely 14% and 7.6% for
f1 and f2, compared to the total energy.
Pressure. The pressure between the dominant shock energy and the pulse from the gas
sphere takes a declining exponential form. Depending on the distance from the
blast, the pressure outside the explosive rises to a maximum pressure, Pm , in
microseconds ( s). USACE (1991) and Joachim and Welch (1997), in a form similar to
that provided by Cole (1948), give the value of pressure in time after reaching the
peak (Pm) as
for ta as the arrival time and , the time constant. USACE (1991) and Joachim and
Welch (1997) give the equations for the parameters of {4} [which herein have been
converted to metric units].
ab = [l.3 Q W / (1 + 0.1 dw)]1/3 {3}
P(t) = Pme -(t - ta)/{4}
Pm = 53.1 Rs -1.13 [MPa] {5}
Equations {5} through {8} use the lateral distance, r, in m, pressure in MPa, time
in seconds (s), velocity in mps, and equivalent weights of TNT in kg. Rs is the
scaled range, the distance normalized by the explosive weight factor. USACE (1991)
and Joachim and Welch (1997) give the TNT-equivalence for several explosives types
and, in particular, the 1.1 weight conversion for Nitromethane. Medwin (1975)
provides an equation for the sonic velocity of water (in mps) as a function of
depth (dw), temperature (T), and salinity (S) in parts per thousand (ppt).
for O m dw 1,000 m, 0 ppt S 45 ppt, and 0° T 35°C.
Scaled range, Rs, is an important term. Rs allows the comparison of differing
explosive weights. It provides the means to "scale" the pressure, vibration, and
mortality effects of blasts. The distance of comparison will need to be large
enough to be well beyond the transition distance, in the far field, for the larger
explosive weight. Equation {8} indicates that the same effect will occur at double
the distance when the charge weight, W. is cube of two, or eight times, greater.
The blast effect (pressure or mortality) will be the same at about twice the
distance for: 16 kg replacing 2 kg of the same explosive material; 80 pounds (lb)
substituted for 10 lb; and, 3,200 kg replacing 400 kg.
Equation {4} is an empirical form and does not resolve the variation of pressure
due to boundary effects nor time duration to the bubble pressure arrival. The
pressure in very deep water without nearby surfaces will fall below Po termed
"negative pressure," due to the inflow of water on the collapsing gas sphere.
Negative pressure merely indicates that the ambient pressure falls below the gage
hydrostatic level. The pressure does not decline below zero absolute pressure, as
water has minuscule tension capacity. Other travel paths of the shock wave can
complicate the waveform, when approaching other surfaces. Figure 2.1, reproduced
from USACE (1991), shows the four major wave types affecting pressure at a point.
The first arrival at some location in the water column due to a blast also in water
(when the shot is well removed from a higher velocity bottom material) is the
direct wave. The upper wave of Figure 2.1 shows its rapid rise and the decay form
of equation {4}. After some additional time there will be two (or many more
multiple) reflections. The reflection off the air-water interface is negative, due
to yielding (displacement) of the surface. The air-surface reflection is of nearly
the exact amplitude as the direct wave, because of the impedance contrast with air.
As shown in Figure 2.1, the air-surface reflection arrives later than the direct
arrival, due to the added distance traveled in reflection. The bottom surface is
not a perfect reflector; this surface accepts energy, so the bottom-reflection's
amplitude is less than the direct wave's. The amplitude from the bottom reflector
is in the same positive sense as the direct wave for the bottom and will not yield
in displacement, like the air-water surface. The bottom reflection is shown third
in Figure 2.1. The arrival of the two reflections depends upon where in the water
the shot and receiver are located. For Figure 2.1, the shot/receiver locations are
much nearer the air surface than the solid bottom. The bottom medium refracts some
energy and, at a critical refraction distance (for a bottom medium's acoustical
velocity exceeding the speed in water), induces a refraction wave that imparts
ta = r / cw {6}
= 9.2e-5 W1/3 Rs 0.18 [s] {7}
Rs = r / W1/3 [m/kg1/3]{8}
cw = 1449.2 + 4.6 T - 0.055 T2 + 2.9e-4 T3
+ (1.34 - 0.01 T)(S - 35) + 0.016 dw [mps] {9}
energy back into the water. The refraction wave is the fourth in Figure 2.1. The
resultant wave for the assumed geometry of the example is the lowest graph. This
example does not show possible multiple reflections between the air surface and the
bottom, nor arriving bubble sphere peaks.
Figure 2.1. Shock-wave components and resultant wave (USACE, 1991)
Blasts created by an explosion located near the air surface have no oscillating
bubble of explosion gases. The gases will be vented to the air as a column or
plume, when dw < ab. There will be no latter pressure wave arrivals in this case
from a gas sphere. Bottin and Outlaw (1987) provide an estimate of the water plume
radius, ap, [converted to a metric relation]
for W in kg and dw in m. A column of water and gas is ejected into the air of radius
apt The displaced water column extends to the hemisphere of like radius, centered
at dw. The water rushing to replace the vented plume volume can cause adjacent
negative gage pressures from the venting gas and water displacement long after the
shock-wave's passage.
The explosive's shock energy, when sufficient, can produce a sizable "cavitation
hat" near the air surface just beneath the water. Cavitation is the negative gage
pressure effect exhibited by explosives near the air-water surface and by boat
propellers. The cavitation is caused by the tensile movement in the water toward
the air. The proximity to the air surface assures that there will be a negative
pressure reflection as part of the wave form. The Pm using equation {4}, is 9 MPa
for just 10 g (not kg) of high explosive. In perspective, this is 90 times the
atmospheric pressure of 0.1 MPa; thus, the air-surface reflection of a tiny
explosive weight will produce negative pressures. The water near the surface can
only accommodate a gage pressure of -0.1 MPa, but the reflection attempts to
produce pressures to -9 MPa and results in cavitation. Christian (1973) defined the
cavitation's cylindrical volume of radius, Rc, and thickness from the air-water
surface to depth Do (not to be confused with the explosive's charge depth, dw
)
. This
"cavitation hat" is a flattened disc of diameter 2Rc, centered vertically above the
ap = 18.9 W1/3 (dw+ 1O m) [m] {10}
midpoint of the blast. There is a potential within the cavitation hat for
overextending air-filled organs due to the negative pressure; this damage potential
can produce organ damage or mortality. By equations, Christian reports [converted
to metric units]:
0.036 dw1/2
for dw < 15 m and W < 450 kg.
Impulse. Empirical estimates of pressure, strength and energy were required prior
to the recent development of accurate and inexpensive recording equipment.
Piezoelectric pressure transducers, commercially available only recently, can
measure these large, rapid pressure wave variations. The strength, or impulse, of
the wave is its momentum as it crosses a surface. The integral of pressure over
time is momentum per unit area and is called impulse, I.
The units of impulse are merely pressure-time, e.g. Pa-s. The impulse is the area
under the pressure-time curve, for example the bottom graph of Figure 2.1. The
length of time to evaluate the integral depends on the purposes and geometry of the
blast. Cole (1948) recommends (t' - ta) be 6.7 , but he accepts that this is
arbitrary. Cole (1948) chose 6.7 to resolve the strength in only the wave's
exponential-decay portion prior to the bubble pulse. Gaspin (1975) and some
subsequent authors use a long integration time without clearly stating their method
of period evaluation. Different authors calculate impulse over varying periods and
use either or both the positive pressure interval and the negative gage pressure
duration. The decision for the integration period must account for the blasting's
intent and waveform complexities. Cole (1948) estimates [converted to metric form]
for W in kg and Rs in m/kg1/3. USACE (1991) and Joachim and Welch (1997) furnish an
impulse estimate without specifying an integration interval [converted for metric
values]:
for W in kg and Rs in m/kg1/3. A much more accurate determination of strength is
provided by obtaining pressure readings at about 1. s intervals for the full
pressure range and integrating the pressure record in time by {13}. While this
latter method is preferred, there are many difficulties in properly recording the
pressure wave with pressure transducers (USACE 1991, Joachim and Welch 1997, and
Hempen and Keevin 1997).
Energy. Shock-wave intensity is assessed by determining the energy flux density, E.
The intensity is a measure of flow or change of energy across a unit surface
"normal to the direction of [wave] propagation" (Cole, 1948). Cole develops E for
Rc 40 dw1/2 (2.2 W) [m] {11}
Dc 3 W0.3 [m] {12}
I = tat' P dt {13}
I(6.7 ) = 7.41 W1/3 Rs -1.05 [kPa-s] {14}
I(t) = 5.75 W1/3 Rs-0.89 [kPa-s] {15}
both shock-wave terms of compressive flow and afterflow as components of one
formula. He proves that the surge term theoretically is negligible beyond 10 to 20
times the effective explosive's charge radius (ae). Cole (1948) gives
the intensity as for P < 135 MPa. E is in units of J/m2 for Zw in SI units. The
units of intensity are energy or work per unit area. Cole recommends the same
integration period of 6.7 for E. The integration period should be determined by
the intent of the blasting, like the discussion above for impulse. Cole (1948)
approximates the intensity as [converted for metric values]
for W in kg and Rs in m/kg1/3
The integrals of equations {13} and {16} accurately resolve the strength and
intensity of the shock wave at any point in the water column where pressure is
measured. Both formulae are correct when the explosion is mid-water or when the
shot is embedded, because each measures its parameter based on the pressure wave
recording at the point of interest. The empirical formulae are estimates for the
water-column shots at best, and are not intended to represent explosions in solids
overlain by a water mass.
TRANSMITTING MEDIA
Explosive shooting is conducted in solids beneath the water surface for removal or
demolition uses. The work accomplished by the gas expansion phase is energy
consumed. Less gas energy can be converted to P-
w
aves to enter the water, since the
gas bubble will not pulsate as it rises. Conversely, the shock energy rapidly
disturbs all surrounding environs. The P(r,t) for the first arrival must be
resolved by the properties of the blasted medium, blast geometry, and wave
transmissions across boundary surfaces.
The propagation of waves across surfaces between media has been developed by text
authors, such as Kinsler and Frey (1950) and Grant and West (1965). Oriard (1985)
shows that the energy transmitted to water from rock of specified properties varies
from 0.0 to 0.37 of the total shock energy for varied angles of incidence (Figure
2.2). Oriard (1985) shows that for land-
b
ased blasting adjacent to a water body the
pressure wave's amplitude "is about 1/40 to 1/400 of" that amplitude which would be
calculated for perpendicular (0.°) incidence between water and ideal rock. Shock-
wave energy would be considerably greater when the blasted medium is directly
beneath the water column. In this latter case, 30% to 37% (for 30° down to 0°
incidence, respectively) of the generated energy enters the water. Blasting would
not usually be accomplished in weak material of low P-wave velocity and Elastic
Modulus. The solid's properties would almost always be significantly greater than
water's, thus the pressures and energies should be comparable to those of Figure
2.2, in general. At large incidence angles (greater lateral distances from the
blast within a submerged solid), less energy enters the water from the solid, but
the water-borne energies from directly above the shot persist in the water beyond
the critical refraction angle. For the case cited by Oriard in Figure 2.2, this
angle is 19.1° (Grant and West 1965). The water column acts as a wave guide at
incident angles within the water greater than the refraction angle while continuing
to receive energy from the solid. In other words, some energy at large lateral
distances from the shot is captured and retained by the water column.
E = Zw-1 tat' P2 dt {16}
E(6.7 ) = 105 W1/3 Rs-2.12 [J/m2]{17}
Figure 2.2. Relative energy entering the water column from a rock material versus
the incident angle at the boundary (Oriard, 1985)
Another consideration of the shock wave from a solid-confined blast is the
direction of the explosive's detonation. Initiation of shots is normally at the
deepest part of the explosive charge. The detonation begins near the bottom of the
boring and continues to propagate up the explosive column toward the surface. The
detonation wave is focused toward a narrow cone in the direction of travel. Less
shock energy is transmitted radially and only a small percentage of shock
disturbance emanates opposite the detonation direction (Konya and Walter 1985). The
shock wave from the completed upward detonation is focused toward the water column.
Thus, the strongest intensity of shock energy in the water column is directly above
the blast for a confining solid. The shock energy crossing the boundary, which is
generally normal to the explosive's placement borings, into the water is the
largest (0.37 for the cited example) of all the transmission angles.
Blasting in a solid beneath the water surface allows gas energy to be released to
the water. The extreme cases for gas energy production are comparable to two
scenarios: the blast detonated in the water column (maximum gas energy
contribution) and the explosive shot within a material of sufficient strength to
retain the blast products. There is no gas energy component for a mid-water
explosion, if the explosion occurs within a container that totally contains the
reaction gases. There would also be no oscillating gas bubble since the container
retained the expansion products. All the work (in actual production blasting)
accomplished by the detonation's gases in moving the solid mass is work that cannot
contribute to bubble oscillation energy release in the water column. Premature
venting of the explosives' gases reduces the displacement of the mass and imparts
this gas energy to the water column. Having sufficient stemming (the granular
filling from the top of the blasting material to the top of the borehole) length
eliminates the early release of the detonation's gases.
Shallow Water Environments. The term "shallow water" may be defined for several
circumstances. A useful consideration relates water to its sonic velocity.
Relationships to blasting could be used to define what is shallow. Lastly, shallow
can be defined by the blasting objective and limitations on the depths of
mitigation.
Equation {9} shows that velocity is heavily dependent on water temperature and
pressure, or depth. Several naturally occurring temperature layers exist in bodies
of water. Urick (1983) indicates that four major layers may exist: surface layer,
seasonal thermocline, main thermocline and deep thermocline. A thermocline is a
unit of water which has a uniform gradient of temperature (and dissolved oxygen)
with depth. The surface layer produces a daily variation of water's sonic velocity;
It's velocity may be constant or variable with depth. Beneath the surface layer
lies the tier of the seasonal thermocline, which has an annual variation and a
negative thermal (and velocity) gradient. In deeper bodies of water, the main
thermocline develops with a nearly permanent, uniform negative gradient. The deep
isothermal layer occurs in waters below the main tier (occasionally below 1,000-m
depth - Urick 1983). The deep isotherm has a roughly constant temperature of 4.°C
and its increasing velocity with depth is due to hydrostatic pressure. Shallow
water depth may mean the level above the interface of the main and deep
thermoclines, if they exist. At this surface, water's velocity is a minimum and
refractions above or below this horizon tend to remain on their increasing velocity
side. Shallow may mean the depths of water bodies that do not develop a main
thermocline. For impoundments without main thermoclines, shallow may be the depth
of the winter velocity minimum.
Shallow water depth in conjunction with blast parameters may apply to depths above
which no gas sphere develops or may be considered the lowest depth of the
cavitation hat. Both of these shallow depth definitions depend on the explosive's
weight. The greater the instantaneously shot charge weight, the deeper the
allowable depth to avoid venting of the reaction gases or by equation {20} the
greater is Dc . A reduced environmental impact occurs for low detonation velocity
explosives with sizable gas energy components. None of the vented reaction gases
may oscillate in the water column for these reduced impact explosives with
significant confinement. By this gas energy definition of "shallow," the correct
choice of explosive and confinement parameters would result in great depths with no
gas energy contribution of pressure to the water column.
Shallow water depth may be defined by the working limit of typical underwater
blasting. Only occasional, special purpose blasting for engineering work would
require blasting deeper than 20 m for even oceanic harbors. Location of borehole
positions would be more difficult at this 20-m water depth. Harbor depths are
infrequently maintained below 15 m. Tunnel or mineral blasting beneath water bodies
is conducted at much greater depths, but the blast displaced solid mass is not
exposed to the water body. Shallow water at depths within (an arbitrary) 20 m of
the water surface represents herein the relative ease of conducting blasting work,
or its more frequent use, and the zone of increased environmental harm.
PRESSURE-WAVES
Shock waves from underwater blasting are of interest not only from an academic
sense, but also because they may be important to blast production and damage due to
explosive use. The explosive selection has a bearing on both the production and
damage potential. The hole diameter, for example, for charge placement is related
to the minimum removal height, called the bench height, by the "Rule of
Five" (Konya and Walter 1985). Minimum bench heights of 3. m require 50. mm, or
smaller, diameter holes. There are fewer blasting agents with small critical-
diameter sensitiveness that will detonate in this hole size. Both dynamites and
water gels meet the sensitiveness criterion and are water resistant; however,
dynamites have higher detonation velocities (Dick et al. 1993a). The choice of a
water gel blasting agent would lead to less shock energy, and therefore less
aquatic mortality potential, while allowing proper rock breakage.
In practice, nearly all underwater blasting will be done with holes
larger than 50 mm, regardless of depth. The greatest expense is that
associated with drilling, and that expense is dramatically reduced by
drilling holes of larger diameter on wider spacings (Oriard, 1983).
Brower (1977) was one of the earlier authors to recognize:
The two basic reasons for restricting or limiting the water shock levels
are: (a) preventing damage to nearby structures and (b) minimizing
environmental damage.
Brower was concerned with both structures and fauna. While other authors had one
concern or the other, Brower recognized the need to mitigate both. Brower provides
Cole's estimate for Pm like equation {6}. Brower's provisions to moderate water
shock were limited to care with the actual blasting measures.
Effects on Structures. Several authors estimated blast effects on structures by
pressure waves, as related to the Pm and impulse (I). Langefors and Kihlstrom
(1978) emphasized that the reduction of both Pmand I are important to the safety of
structures. Oriard (1983) presented:
...the damage potential of underwater waves is not directly related to
the peak pressure, but to impulse... it may be more damaging to lengthen
the duration of the pressure pulse than to lower its peak pressure
depending on the characteristics of the structure in question.
Oriard (1992) suggests that dynamic strain cannot be related to the static stress
regime of most analyses. He also implies that negative pressures from venting (and
from cavitation) cause plucking from tension at the concrete-water interface.
Structures should be addressed like the Oriard (1985) analysis to estimate dynamic
stress and strains on the submerged form. Oriard (1985) chose a procedure of
conducting small production shots to evaluate "the pressures in the water adjacent
to the powerhouse walls and stoplogs." This allowed the development of one program
to full scale without damage to the extremely important adjoining structures.
CHAPTER 3
THE ENVIRONMENTAL EFFECTS OF
UNDERWATER EXPLOSIONS:
AQUATIC PLANTS
INTRODUCTION
Aquatic plants, both submerged and emergent, have great importance as a food source
and shelter for both aquatic (Rozas and Odum 1988; Lubbers et al. 1988) and
terrestrial organisms (Bellrose et al. 1979). Extensive damage and mortality to
aquatic plant beds resulting from an underwater explosion could possibly upset the
balance of the ecosystem being altered.
DAMAGE AND MORTALITY OF AQUATIC PLANTS EXPOSED TO UNDERWATER EXPLOSIONS
Data on the effects of underwater explosions on aquatic plants are very limited.
Ludwig (1977) used explosives as a "herbicide" to remove eelgrass (Zostera marina)
to create a channel within the Niantic Estuary at Waterford, Connecticut in an
attempt to improve water quality and containment of egg and larval stages of the
bay scallop (Argopectens irradians). A contractor demonstrated the efficiency of
eelgrass removal techniques with in situ observations being performed on the
detonation of single and multiple charges as well as a weighted length of
detonation cord alone. During an eight week period following the explosions, the
eelgrass experienced an orderly dieback. In no instance was the disappearance less
than complete along an expanding circle of defoliation. In the case of the single
charged detonations, the circular defoliation had a final diameter of approximately
seven to eight meters. The chain or string detonations created overlapping rings of
impact ultimately clearing a rectangular area approximately 40 m long and 7 to 8 m
wide. The detonation cord created a similar impact but the final zone of influence
was limited to approximately 2 to 4 m of total width. Unfortunately no information
was provided concerning the charge type or weight.
Removal was restricted to eelgrass, with green algae (Codium sp.) and rockweek
(Fucus sp.) thriving in the defoliated areas following eight weeks. Ludwig (1977)
hypothesized that the orderly species-specific defoliation was the result of a
disruption of the cellular structures within the rhizomes. As the cellular
destruction radiated outward the thallus structures separated in a manner
reminiscent of normal exfoliation during the late autumn or winter period.
Examination of the rhizomes, however, clearly indicated cell wall failure
internally while the epidermal fibers continued to hold the structure together.
Without explosive weight information or pressure wave data it is impossible to
compare aquatic plant mortality levels with other aquatic organisms.
Smith (1996) examined the effects of underwater explosions on two types of aquatic
vascular plants (emergent and submerged), and three algal species. Two species of
vascular plants (Ludwigia peploides (HBK) Raven and Myriophyllum heterophyllum
(Michx.)) and three algal species (Chara zelandica (Willd.), Chara contraria (A.
Braun), and Nitella acuminate (A. Braun)) were exposed to 2 kg of T-100 Two
Component (green stick) explosive with a #8 instantaneous electric blasting cap.
Explosive charges were suspended from a float to a depth of 1.5 m below the water
surface. Plants were placed in hardware cloth cages and set out at 2.5, 4.5, 6.5,
8.5 and 10.5 m from the blast. Cages were attached to a buoyed rope of appropriate
length to maintain the cage centers at a depth of 1.5 m below the water surface. A
control cage contain each of the plant species was used for each blast. Controls
received the same treatment (i.e., transported to and from the blast area) as
experimental plants with the exception of exposure to blast pressures. Each test
was replicated (test blast 1 and test blast 2).
Plants were weighed pre-test and exposed to the test blast on September 30, 1996.
All plant material remaining after the explosions was transported back to the
laboratory and re-weighed, using the same procedures as before the blast. Plants
were maintained in 10-gallon aquaria in a greenhouse. At the end of the first week,
plants were removed from the tanks and all dead tissue was removed. Remaining plant
tissue was weighed and recorded. This procedure was repeated on October 8, 17, 24,
and November 26 at which time the project was concluded.
Aqueous phase measurements of photosynthesis were made in the laboratory using the
methods of Walker (1987) with the Hansatech DW2/2 (Hansatech, Inc., UK) oxygen
electrode and a 2.5 ml chamber.
Effect of the explosion on biomass: Individual species
Chara zelandica lost an average of 18.06% of its biomass over all distances. The
greatest loss was seen at 6.5 m (24.3%) and the least at 2.5 m (15.5%) for blast 1.
The greatest loss of biomass for blast 2 occurred at 6.5 m (19.3%) and the least at
2.5 m (10.3%). Plants for blast 1 had survival at 6.5 m, 8.5 m and lO.5 m. Plant
survival for blast 2 was seen only at 4.5 m. No surviving plants regained 100% of
their original biomass while the control plants had 109% of their original biomass
at the end of the project, a net gain of 9.3%.
Ludwigia peploides gained biomass in some
i
nstances, as high as 5.3% for blast 2 at
4.5 m. Biomass losses ranged from 10.7% at 4.5 m and less than 1% at 8.5 m for
blast 1. Blast 2 losses were seen only at 4.5 m (1.5%). Plants at 2.5 m for blast 1
were the only group of L. peploides to have 100% mortality. The surviving test
plants had a greater increase in biomass than the control plants, which gained only
1.7%; however, none of the surviving plants regained 100% of their original
biomass.
Myriophyllum heterophyllum lost biomass in both test blasts. Blast 1 had the
greatest loss at 2.5 m (24.3%) and the least at 4.5 m (<1%). Greatest loss of
biomass for blast 2 was also at 2.5 m (19.3%) and the least at 4.5 m (1.5%).
Mortality was 100% for both test shots at 2.5 m, 4.5 m and 6.5 m. Mortality was
also 100% in blast 1 at 8.5 m. None of the surviving test groups regained 100% of
their original biomass. The control group had a net gain of 17.9% for both tests.
Plants at 4.5 m for blast 2 had a small gain in biomass (3.2%) after the test.
Biomass loss for blast l ranged from 13.2% (6.5 m) to 8.6% (4.5 m). Biomass losses
for blast 2 ranged from 23.9% (10.5 m) to 8.9% (6.5 m). Growth curves for all test
groups became positive after the second week. The control group had a net gain of
19.9% over its original biomass by the end of the study. Five of the ten test
groups had greater biomass than before the test. The group at 2.5 m in blast 1
gained more biomass than the control (39.4%).
Nitella acuminata lost biomass in all test groups as a result of the explosion.
Losses for blast 1 ranged from 9.6 (10.5 m) to 5. 5% (8.5 m), while blast 2 ranged
from 14.0% (2.5 m) to 2. 8% (6.5 m). All plants at 2.5 m for both test blasts and
at 4.5 m for test 2 had 100% mortality. The control group had 26.2% greater biomass
at the end of the project. For blast 1, groups at 87.5 m and 10.5 m had greater
biomass than their original biomass. Biomass for test 2 was greater at 8.5 m than
originally, although other surviving groups had greater than 95% of their original
biomass.
Effect of the explosion on photosynthetic rates
All species responded to the explosion in a similar manner, i.e., a reduction in
photosynthetic rate in the treatment group of plants, relative to the control. The
effect on photosynthesis was greatest nearest the blast (2.5 m), and became
progressively less severe with each increment in distance (4.5 m, 6.5 m, 8.5 m, and
10.5 m). Two species, N. acuminata and C. contraria, maintained positive, but low,
rates of photosynthesis at 2.5 m. At 4.5 m, M. heterophyllum began to show
photosynthetic activity, followed by C. zelandica at 6.5 m. By 8.5 m, all species
demonstrated photosynthetic activity. As a percent of the photosynthetic rate of
the Control the species ranked as follows:
2.5 m, NA CC MH=LP=CZ;
4.5 m, NA MH CC LP=CA;
6.5 m, NA MH CC CZ LP;
8.5 m, NA MH CC CZ LP;
10.5 m, NH=NA CC CZ LP.
These results are preliminary and are currently being prepared for publication.
Work is currently in progress to establish the relationship between pressure
waveform and plant damage and mortality.
MITIGATION TECHNIQUES TO PROTECT AQUATIC PLANTS FROM UNDERWATER EXPLOSIONS
Mitigation techniques described for fish are also applicable to aquatic plants (see
Chapter 8). Any attempt to reduce the pressure waveforms will reduce the potential
kill zone of aquatic plants.
CHAPTER 4
THE ENVIRONMENTAL EFFECTS OF
UNDERWATER EXPLOSIONS:
AQUATIC INVERTEBRATES
INTRODUCTION
The potential for injury and mortality to aquatic invertebrates, resulting from
underwater blasts, has been well documented in agency and contractor reports and
the scientific literature. However, with the exception of brief literature reviews
concerning the effects of seismic exploration (Alperin 1967, Linton et al. 1985b)
and ordnance testing (O'Keeffe and Young 1984), a comprehensive critical review of
the literature does not exist.
The purpose of this review is to provide a comprehensive description of the
experimental designs for each reported investigation. The study design aspects
reviewed are: species tested, how organisms were caged, type and weight of the
explosive charge, location of the explosive charge and test organisms in the water
column, duration of the mortality test, pressure wave recording techniques and
author's conclusions. This review also provides a critical evaluation of the
studies based on their experimental designs and analysis of data.
A
PPROACH
Existing literature was reviewed in chronological order based on publication date.
This approach was taken rather than a phylogenetic analysis in order to best
evaluate study results for each investigation based on their experimental design.
In addition, inadequacies in study design (e.g., small sample size, inadequate or
no controls, differences in post-explosion mortality observation periods, and
differences in cage material) make comparison among studies difficult, if not
impossible. All of the studies, with the exception of Linton et al. (1985a), were
originally designed and conducted using English measurements. To maintain the
integrity of the original studies, all data are reported in English measurements
and followed with metric equivalents in parentheses. Conversions were rounded to
one decimal place. Metric conversions have been made to reproduce the English unit;
added significant digits of the metric conversions do not represent the precision
of the original research.
Common and scientific names follow Cairns et al. (1991) for Cnidaria, Turgeon et
al. (1988) for mollusks, and Williams et al. (1989) for decapod crustaceans. Common
and scientific names not covered in American Fisheries Society publications are
used as given in the original publication. In some instances, either the common or
scientific name of the organism being tested was given in the original publication,
but not both. In such cases the appropriate common/scientific name has been
provided in parentheses with an equal sign to indicate that the name has been added
and was not part of the original publication.
INVERTEBRATE LITERATURE REVIEW
The first published investigation of invertebrate mortality resulting from
underwater explosions was conducted by Knight (1907) in response to a "doleful tale
of a poor lobster fisherman" related to Knight by a young seaman. The young
seaman's story was that "when the lobster fisherman had accumulated about 500
animals in his pound (a pound is a cubical box made of wooden slats, anchored from
shore, which allows water to pass through), some mischievous or ignorant person put
off a dynamite blast about 150 or 200 yd (137.2 or 182.9 m) away, and killed every
lobster." As the young seaman first told the tale, "the lobster pound was 500 yards
[457.2 m] away, but on cross-examination he was compelled to reduce the distance."
To test the accuracy of this story, six lobsters (=American lobster, Homarus
americanus) were obtained from a local fisherman and tested with varying charge
sizes and distances from the blast in water 12 to 15 ft (3.7 to 4.6 m) deep. In the
first experiment, 3 large sticks of dynamite (of undefined weight) were detonated
at a distance of 80 ft (24.4 m) from a lobster trap containing 2 lobsters, and at a
distance of 40 ft (12.2 m) from a small lobster that was tethered by a piece of
twine. The explosion produced no effect upon any of the lobsters.
In a second experiment, 2 large sticks of dynamite (of undefined weight) were
exploded at a distance of 20 ft (6.1 m) from the small lobster. The animal was
uninjured. The third experiment consisted of detonation of two sticks of dynamite
within 10 ft (3.0 m) of a medium sized lobster. Knight (1907) indicated that there
was "No result." In the last experiment, 3 sticks (of undefined weight) were
exploded 15 ft (4.6 m) away from a trap which contained 5 lobsters which had all
been used in previous experiments. The explosion overturned the trap, nearly
overturned one of the piles on which the wharf was built, but "it seemed to have no
effect on the lobsters."
Knight (1907) concluded that the 500 lobsters of the sailor's yarn had died, not
from the effects of a dynamite explosion, but from suffocation. He surmised that
the lobsters had been confined in too small a pound for too long a period, and the
explosion was coincident with the fisherman's discovery of the dead lobsters.
The next published series of experiments evaluating the effects of explosives on
invertebrate mortality occurred in response to a request from the Magnolia
Petroleum Company to utilize dynamite charges up to 800 lb (362.9 kg) during the
course of a refraction seismograph survey in waters off the coast of Louisiana. The
area involved was in the heart of Louisiana's "jumbo" shrimp fishing grounds.
Descriptions of the study design and results are presented in various degrees of
detail in five separate non-refereed publications (Gowanloch and McDougall 1944,
1945, 1946; Gowanloch 1946a, 1950)
The first series of experiments, best described in Gowanloch and McDougall (1945),
involved the firing of one 200 lb (90.7 kg) and two 800 lb (362.9 kg) charges of 60
percent gelatin dynamite unconfined and placed on the sea bottom in 18 ft (5.5 m)
of water. Forty-five shrimp (Peneus setiferus) and thirty oysters (Ostrea
virginica) were placed in 30 inch (762 mm) cubicle cages, positioned at 50, 100,
150, 200, 300, and 400 ft (15.2, 30.5, 45.7, 61.0, 91.4 and 121.9 m) from the shot
point, and suspended midway between the surface and bottom in 18 ft (5.5 m) of
water. Test animal were held in their positions for 48 hours before the charges
were fired, were examined immediately before the shot, immediately after the shot,
and at 24 and 48 hours post detonation exposure. Gowanloch and McDougall (1946)
state that "adequate controls were established located far beyond any possible
influence from the dynamite blasts." However, no details are given concerning
control handling or subsequent mortality. Geophones, located at selected cages,
recorded "the amplitudes of each charge." However, no pressure data were presented.
Gowanloch and McDougall (1945) concluded that shrimp were uninjured at 50 ft (15.2
m) by the 800 lb (362.9 kg) charge. They noted that "the shrimp still remained
normal six days after the explosion. Yet the shock shook an oyster tugger ten miles
away, and threw water 300 ft [91.4 m] into the air." They concluded that "No
differential mortality could be found among the oysters, but for various biological
reasons the authors consider that more experimental work is necessary before a
satisfactory definite decision can be reached." No statistical basis for their
conclusions or supporting data in tabular form are given on which statistical
analysis could be conducted by the present authors.
A second series of experiments was conducted, "Since oysters constitute a highly
valuable aquatic resource, damage to which was not apparent, when the experimental
oysters were suspended as individuals in cages it was decided to re-examine effects
of dynamite blasting on oysters where the oysters were part of an integrated
reef" (Gowanloch and McDougall 1946). Descriptions of the study design and results
are again presented in various degrees of detail in four separate non-refereed
publications (Gowanloch and McDougall 1946; Gowanloch 1946b, 1948, 1950). It was
concluded that the "seismographic explosions caused no subsequent mortality to the
oysters."
Gowanloch and McDougall (1945) used cages that were 30 in (760 mm) cubes,
constructed with a strong external wooden slatted frame (picture of cage on page
303 of Gowanloch (1948)). Specimen confinement was accomplished by attaching 1/2 in
(13 mm) shrimp netting to the inside of the frame. Each cage was divided into two
compartments by a vertical wall of shrimp netting. Anonymous (1948) questioned
Gowanloch and McDougall's (1945) results since slatted wooden cages had been used
in their experiments. Anonymous (1948) contended that use of the slatted wooden
cages would "tend to produce a decrement in the shock and pressure reaching the
enclosed animals." In addition, Aplin (1947) noted that during experiments
previously conducted in Louisiana (presumably by Gowanloch and McDougall) "it was
found wooden cages would be broken up by the explosions unless so heavily built as
to give the impounded fish definite protection from the shock." Neither Anonymous
(1948) nor Aplin (1947) provided experimental support for their contention.
Linton et al. (1985b) make reference, in their annotated bibliography, to a paper
by Gowanloch and McDougall published in Louisiana Conservationist 4(12):13-16. The
publication date, title, volume, and page numbers are identical to Gowanloch and
McDougall (1945) published in Oil. A check of the Louisiana Conservationist
indicates that this article does not exist.
Aplin (1947) conducted a series of experiments to determine the effects of
explosives used in geophysical survey work to locate oil deposits along the
California Coast. Four rough abalones (Haliotis corrugata) and four green abalones
(Haliotis fulgens) were exposed to a 20 lb (9.1 kg) charge of 60 percent petrogel,
fired 4 ft (1.2 m) below the surface. The abalone were on the bottom, 55 ft (16.8
m) from the explosion. An hour after exposure the abalones were able to move when
given tactile stimulation. However, none of them extended their mantles when put
into an aquarium and all were dead within a few hours. Aplin (1947) noted "that
further experiments will have to be made as they may have been killed by handling
and transportation."
Aplin (1947) exposed eight lobsters (Panulirus interruptus
)
270 to 300 mm long to a
20 lb (9.1 kg) charge of 60 percent petrogel, fired 4 ft (1.2 m) below the surface.
The lobsters were on the bottom, 55 ft (16.8 m) from the shot and almost directly
below it. Five hours post exposure the lobsters were all alive and active. In a
second test shot, 13 lobsters ranging from 170 to 230 mm in length were exposed to
a 20 lb (9.1 kg) charge of 60 percent petrogel, fired 4 ft (1.2 m) below the
surface. The lobsters were positioned 4 ft (1.2 m) below the surface and 50 ft
(15.2m) away from the shot. Three hours post exposure the test lobsters were alive
and examination of internal organs found no signs of damage. Aplin (1947) concluded
that "Apparently lobsters are very resistant to concussion..." Aplin, as with his
abalone test, did not use controls. However, since there was no mortality in the
test lobsters it can be assumed that those factors which would be controlled for
(i.e., handling, transportation, and water quality) did not cause mortality.
Both the abalone and lobster studies suffer from serious experimental design flaws
including extremely small sample sizes, no replicate tests, and complete lack of
controls. No description of how the abalones and lobsters were caged is provided in
the text; although, fish were held in 3 ft (910 mm) square and 18 in (460 mm) deep
cages made of welded iron frames covered with 1/2-in (13 mm) mesh wire hardware
cloth. Because of the small sample sizes and lack of controls, no conclusions can
be made from this study.
Anonymous (1948, pp. 16-18) conducted a series of tests utilizing oysters (=eastern
oyster) (Ostrea virginica) held in wire bags placed on the bottom. Table 4.1
provides data on two tests conducted with the largest explosive charge, 300 lb
(136.1 kg) of TNT. They concluded that "Deaths among these over the two-week period
all occurred within the 200 ft (61.0 m) radius except for a single dead oyster
found in a bag exposed at a distance of about 960 ft (292.6 m). Excluding this one,
it was found that the two week's loss was 5.4%, or a little more than double that
observed immediately after the explosion." No attempt was made to measure explosive
pressure waves during mortality testing. No statistical analysis of the data was
conducted by the authors.
An analysis of the oyster data provided in Anonymous (1948) using a Cochran-
Armitage Trend Test on a 2 X C stratified contingency table (strata = shot) were
not significant (P>0.2) for distances to 960 or 400 ft (292.6 or 121.9 m) from the
blast. It is concluded that the relatively low numbers of dead oysters did not
change with distance from the blast. Furthermore, some mortality occurred in the
controls and it is likely that some oysters dying at 2 or 16 weeks died from causes
not related to the blast.
Table 4.1- Immediate, 2-week and 6-week live/dead counts for oysters (=eastern
oyster, Ostrea Virginica) placed on bottom at 30 ft (9.1 m) depth and exposed to a
300 lb (136.1 kg) charge of TNT suspended 15 ft (4.6 m) (From Anonymous 1948).
Anonymous (1948) conducted a series of tests utilizing blue crabs (Callinectes
sapidus). They provided data, shown in Table 4.2, that summarizes four tests where
blue crabs were held in cages placed on the bottom (depth not given) and exposed to
SHOT 16
Distance from Explosion
Initial Observation
10-5-1945
2 Week Observation
10-18-45
6 Week Observation
11-16-45
Feet Meters Live Dead Live Dead Live Dead
25 7.6 19 1 17 2 15 2
50 15.2 19 0 16 3 13 3
100 30.5 23 1 21 2 19 2
200 61.0 20 0 19 1 18 1
400 121.9 20 0 20 0 18 2
960 292.6 20 0 19 1 16 3
Control 20 0 20 0Lost
SHOT 17
Distance from Explosion
Initial Observation
10-6-1945
2 Week Observation
10-19-45
6 Week Observation
11-17-45
Feet Meters Live Dead Live Dead Live Dead
25 7.6 21 0 21 0 20 1
50 15.2 23 1 22 1 22 0
100 30.5 26 0 25 1 23 2
200 61.0 29 1 29 0 25 4
400 121.9 26 0 26 0 21 5
Control 292.6 30 0 30 0 27 3
a 30 lb (13.5 kg) charge of TNT. Based on the results presented in Table 4.2,
Anonymous (1948) noted that about 90% of the blue crabs were killed at 25 ft (7.6
m), under peak pressures exceeding 800-900 pounds/square inch, psi (5,516-6,206
kPa), and very few died at 150 ft (45.7 m), where pressure reached about 270 psi
(1,862 kPa). Anonymous (1948) noted that intermediate distance gave surprising
results, marked by the absence of any trend. This was confirmed by the present
authors, utilizing a chi-square test. However, first value, and last value, differ
from intervening four values (P<0.001), and first and last values differ (P<0.001).
The second and third values do not differ (P>0.1), and values (2, 4, and 5) versus
value (3) has P=0.05. Anonymous (1948) suggested that the erratic variation may be
due to the irregular transmission of the shock wave along the bottom or to other
unestablished causes. Although, external and internal damages were not quantified,
they observed loss of part or all of the carapace, cracking of the carapace, heart
rupture, broken spines and, autonomous loss of one or both claws. However, many of
the crabs killed showed no macroscopic changes. Anonymous (1948) provided no data
for control mortality, nor did they indicate that controls were used. Although the
true mortality levels due to the blast cannot be known exactly, the data at 150 ft
(45.7 m) give an upper bound of 7% on the "control" (e.g., handling) mortality.
No discussion is provided describing pressure recording. It is not clear if
pressures were recorded specifically for this set of four experiments or if they
used generic pressures given in Figure 7
.
This is an important point since pressure
readings may vary with depth of charge, depth of pressure gauges and nearness of
gauges to either the water-air (surface) interface or water-substrate (bottom)
interface. In addition, Anonymous (1948) used copper ball crusher gages, which only
record peak pressure.
The authors provide no information on how long crabs were held prior to determining
mortality (i.e., instantaneous, 24 hr. 48 hr. or 96 hr. mortality). Period of
observation could easily affect mortality levels, with longer periods having higher
mortality, especially with no controls to evaluate the effect of holding time.
Table 4.2- Effect of 30 lb (13.5 kg) charges of TNT on blue crabs (Callinectes
sapidus) held in cages on the bottom (bottom depth not given). Summary of four
tests (From Anonymous 1948).
Tollefson and Marriage (1949) evaluated the effects of channel blasting on three
species miscellaneous crab species (Cancer sp.), and Pacific oysters (Ostera
gigis). Cockles were captured the week prior to testing and held in an aquarium.
They ranged in size from 60 to 79 mm rib length, average 70 mm. Oysters were
clusters, ranging from 4-12, average 8.4 per cluster, of one and two year old taken
from adjacent beds. Crabs used were small miscellaneous specimens brought from the
Newport laboratory where they had been held for several months or more. They ranged
in back width from 115 to 144 mm, average width 129 mm.
All specimens, except oysters, which were placed at 20 ft (6.1 m) or less from the
center of the blast were placed in separate canvas sample bags with labels to
facilitate locating and to prevent any mixing of specimens following the blast. It
Distance from charge No. held % killed % surviving
Feet Meters
25 7.6 37 89% 11%
50 15.2 55 38% 62%
75 22.9 22 55% 45%
100 30.5 37 38% 62%
125 38.1 23 48% 52%
150 45.7 14 7% 93%
is not clear how oysters and organisms beyond 20 ft (6.1 m) were handled. Tollefson
and Marriage (1949) noted that they did not believe the canvas bags would affect
the results. No control organisms were used. Four cases of 50 percent dynamite were
fired as a single shot along a 95 ft (29.0 m) line in a sandy mud bottom intertidal
area at Bayocean, Oregon. The mean depth of planting of dynamite was about 3 ft
(0.9 m) below the surface. Water depth was 1 to 3 ft (0.3 to 0.9 m). No pressure
measurements were taken.
Tollefson and Marriage (1949) found that a number of miscellaneous organisms, crabs
(Cancer magister), a small snail (Thais Ep.), a small mud clam (Macoma sp.), and a
single specimen of a commensal clam (Pseudopythina rugifera), were unaffected,
while three sand worms (Nereis sp.) and several ribbon worms (Nemertinea) were
found dead within 25 ft (7.6 m) of the blast. A number of ghost shrimp were found
within 25 ft (7.6 m) of the blast. Seven of nine Callianassa sp. and 39 of 76
Upogebia pugettensis were found dead or died within 24 hours of the blast. The
authors concluded:
1. "Little or no damage to surface cockles located 10 ft [3.0 m] or
further from the center.
2. No damage to sub-surface cockles located 15 ft [4.6 m] or further from
the center.
3. No damage to crabs located 30 ft [9.1 m] or further from the center.
4. No damage to oysters located 10 ft [3.0 m] or further from the center.
(The foregoing does not consider any possible after-effects such as
silting.)
5. A 50 to 75 percent mortality of ghost shrimp was found within 25 ft
[7.6 m] of the center.
6. In the case of the invertebrates involved it is likely that almost all
damage done by blasting is grossly physical in nature, that there is
little shock or other after effects."
This study suffers from a number of serious design flaws and omissions of
methodology information. Sample sizes were extremely small. There were no control
animals. No information is provided on total weight of explosive detonated, other
than "four cases" were exploded. A typical case of dynamite contains 50 lb (22.5
kg) of explosives; however, the strength and size of each cartridge causes the
weight of each "stick" to have considerable variation. No information is provided
on the canvas sample bags. Contrary to the authors' statement that the bags would
not have "exerted any appreciable cushioning effect", the bags could have reduced
pressure wave transmission and thereby reduced mortality levels. In addition, no
information is provided on how test organisms were held beyond 20 ft (6.1 m).
Pressure wave measurements were not made. The lack of explosive weight data, use of
a linear charge pattern, and burial of the explosive, make prediction of explosive
pressures using existing empirical relationships, for example Cole (1948),
impossible. As such, it is impossible to determine the magnitude of pressure
experienced by the organisms. Thus, the results are, at best, lower trend estimates
of the mortality that unconfined organisms would experience.
Fry and Cox (1953) made casual observations on the effects of black powder on
invertebrates off the coast of California during seismic exploration activities.
The major objective of the study was to determine if fish were being killed by
seismic exploration charges. A 45 lb (20.4 kg) charge of E.P. 138 Seismograph Black
Powder was detonated within 6 ft (1.8 m) of the surface and divers were sent down
to make observations of damage. The authors noted that "Clams and tube worms were
found, none of which had suffered ill effects from the blast. These animals all
responded in the normal manner by quickly withdrawing siphons and tentacles when
touched by the divers." After the second day of testing, the authors noted that
"None of the invertebrates seemed to be affected; the sea anemones were extended,
as were the tube worms; none of the corals had been broken; the sea urchins were
still on the rocks and the sea cucumbers had not contracted."
Fry and Cox (1953) gave no information concerning the distance of the explosion
from the invertebrates being observed by the divers. As such, it is impossible to
even conclude that the invertebrates were unaffected at a given distance from a
known size explosion.
It is quite possible that Fry and Cox's (1953) observations are related to the type
of explosive utilized. It had been previously observed that black powder, a
combusting medium and not an explosive, has little effect on fish (Baldwin 1954;
Fry and Cox 1953; Ferguson 1962; Hubbs and Rechnitzer 1952) when compared to high
explosives such as dynamite. For example, Hubbs and Rechnitzer (1952) found that in
marine fish species tested, the lethal threshold peak pressure from dynamite
explosions varied from 276 to 483 kPa. Peak pressures from slowly detonating black
powder, producing pressures as high as 855 to 1,103 kPa, did not kill caged fishes.
The difference in fish mortality between black powder, a low explosive, and high
explosives appears to be related to the waveform produced by each explosive type.
Black powder produces a pressure waveform with a slow rise time and low amplitude
whereas high explosives have an abrupt rise time, high amplitude, and short
frequency. In addition, high explosives have a much higher negative pressure than
black powder, as shown in Figures 8 and 9 in Hubbs and Rechnltzer (1952). The
amplitude and short frequency of the negative pressure wave and resulting damage to
the swim bladder may be the causative factor of mortality in fish exposed to high-
explosive pressure waveforms.
Sieling (1954) conducted two experiments, carried out in separate locations during
1949-1950, to evaluate the effects of seismic exploration for oil on oysters in the
Barataria Bay, Louisiana, region. Work in Bay de Chene was referred to as
Experiment 1 and Bay Batiste work was referred to as Experiment 2.
Two explosive charges were used in each shot hole, one of 50 lb (22.7 kg) and one
of 20 lb (9.1 kg) of Nitranon (nitro-carbonitrate), and these were exploded at a
depth of 50 ft (15 2 m) and 30 ft (9.1 m) respectively. Charges were placed in
pipes which were in holes drilled into the bottom. The general procedure was to
drill the hole from a drilling barge, then move to the next location. A barge
carrying shooting equipment and explosive would then move in and load the first
charge into the pipe and fire it, then as quickly as was safe load the second
charge in the pipe and fire that. The two pieces of equipment would then move
around the other four shot holes and fire the charges at each hole in the same
manner.
Shot points formed a diamond with the points 1,000 ft (304.8 m) apart and one shot
point in the middle. Sieling (1954) noted that this distance simulated the worst
operating conditions possible under the law as when two lines of seismographic
explosions cross at right angles. There was no attempt to measure pressures.
Oysters (=eastern oyster, Ostrea virainica) were placed at 20, 60, 130 and 250 ft
(6.1, 18.3, 39.6 and 76.2 m) from the point of explosions and in a staggered line.
Control stations were located 750 ft (228.6 m) from the nearest shot point. At both
the experimental and control stations oysters were put in trays and placed on racks
above the bottom in Experiment 1 and placed on the bottom in Experiment 2. Water
depth was not given. Additional controls, which are not described here, were
established to evaluate the influence of various other environmental factors.
Results of this study are presented in Table 4.3. Sieling (1954) concluded that
there was no correlation between the distance of the oysters from the explosions
and the survival rate.
Kemp (1956) evaluated the effects of seismograph explosions by conducting a series
of three tests with fish, shrimp (=Penaeus sp.
,
three possible species occur in the
area), oysters (=eastern oyster, Crassostrea virginica) and blue crab (=Callinectes
sapidus) under actual exploration conditions. Test 1 was conducted in Corpus
Christi Bay in water 13 ft (4.0 m) deep with a bottom of very soft, gray, mud. Test
2 was also conducted in Corpus Christi Bay in water 2 1/2 to 3 ft (0.8 to 0.9 m)
deep with a bottom of hard sand. Test 3 was conducted in Aransas Bay in water 7 ft
(2.1 m) deep with a bottom of soft, gray mud.
Specimens were held in 1/2 in (13 mm) mesh hardware cloth cages, except oysters
which were in heavy wire trays. In each test one set of specimens was placed at the
shot hole and 25, 50, 100 and 200 ft (7.6, 15.2, 30.5 and 61.0 m) from the shot
hole. A set was also placed 1/4 to 1/2 mile (0.4 to 0.8 km) away as a control.
Organisms were held on the bottom in all tests reported here. In test 1, organisms
were also suspended 3 ft (0.9 m) below the surface; however, numbers were so small
and at sporadic distances from the blast, that results are not presented here.
Test organisms were exposed to a 40 lb (18.1 kg) charge of Nitramon, the maximum
allowed by law, at a depth of 20 ft (6.1 m) below the bay bottom, which is the
minimum depth allowed. Charge weight and burial depth were the worst possible
conditions permissible under the law. Pressure waves were not measured.
Kemp (1956) provides no indication of the waiting time period used prior to making
live-dead counts. The results are shown in Table 4.4.
Table 4.3- Percent survival of oysters (=eastern oyster, Ostrea virginica) at Bay
de Cene (Experiment 1) and Bay Bastiste (Experiment 2). Two explosive charges were
used in each shot hole (see text for description of shot design), one of 50 lb
(22.7 kg) and one of 20 lb (9.1 kg) of Nitranon (nitro-carbonitrate), and these
were exploded at a depth of 50 ft (15.2 m) and 30 ft (9.1 m) respectively. Oysters
were on the bottom (depth not given) (Modified from Seiling 1954, Tables 1 and 2).
Distance from
Explosion Number Tested
Number
Surviving
4 Months
Percent
Survival
4 Months
Number
Surviving
7.5 Months
Percent
Survival
7.5 Months
Experiment 1 - Bay de Chene
Feet Meters
20 6.1 345 289 83.7 --- ---
60 18.3 348 302 86.7 --- ---
130 39.6 336 287 85.3 --- ---
250 76.2 333 281 84.4 --- ---
Control 338 257 76.0 --- ---
Experiment 2 - Bay Batiste
Feet Meters
20 6.1 334 275 82.3 253 75.7
60 18.3 326 269 82.4 256 78.5
130 39.6 324 281 86.8 255 78.7
250 76.2 329 280 85.1 242 73.5
Control 341 294 86.2 264 77.4
Table 4.4- Live-Dead counts for shrimp (=Penaeus sp., three possible species occur
in the area), oysters (=eastern oyster, Crassostrea virginica), and blue crab
(Callinectes sapidus) in cages placed on the bottom of Corpus Christi Bay, TX and
exposed to a 40 lb (18.1 kg) charge of nitramon buried 20 ft (6.1 m) below the bay
bottom. For shot 1, organisms were in 13 ft (4 m) of water, bottom type was very
soft gray mud. For shot 2, organisms were in 2 1/2 to 3 ft (0.8-0.9 m) of water
depth, bottom type was hard sand (Modified from Tables 1 and 2 in Kemp (1956)).
Kemp (1956) concluded that shrimp and crabs were "found to be completely immune to
underwater explosions, since they suffered no ill effects whatsoever during the
tests." The sample sizes for shrimp and crabs are adequate but they are too small
to accurately estimate mortality. However, from the data provided, the upper 95%
bound on the shrimp mortality at a given distance is 0.06 (n=50 by pooling both
shots) to 0.11 (n=25 for individual shots). For blue crab the upper 95% bounds are
0.95 (n=1) and 0.78 (n=2). Pooling the data for both shots, the upper 95% bound on
blue crab mortality is 0.63 (n=3) at distances 550 ft (167.6 m). The data suggest
that the death of 2/2 blue crabs in shot 1 is an artifact and does not represent
the effects of the blast. Pooling the data from both shots at < 50 ft (15.2 m), the
upper bound is 0.28 (n=9). Kemp noted that damage to oysters was most severe within
a 25 ft (7.6 m) radius of the blast and some oysters were found as far as 200 ft
(61.0 m). Based on these results he concluded "If the minimum distance (from the
shot) from an oyster reef were extended from 300 to 500 ft (91.4 to 152.4 m), it
would probably afford a more comfortable safety margin." Statistical analysis
supports this conclusion. Pooling the data at 200 ft (61.0 m), the mortality is
1/62 = 0.016 + 0.016. For shot 1, the mortality is 1/24 = 0.042 + 0.040. For shot
2, the upper 95% bound on the proportion (12/38) is 0.075.
Anonymous (1962) conducted a series of tests with Dungeness crabs (=Cancer
magister) to evaluate the effects of underwater explosions from oil seismic
exploration. Tests were conducted off the Oregon coast north of the Alsea River in
an area normally fished for crabs. Small crabs, less than 80 mm maximum carapace
width, were caught in tide pools six weeks previous to testing. Adult crabs, over
130 mm minimum carapace width, were caught in commercial crab pots in Yaquina Bay a
few days prior to the experiments. All were held in live tanks. Commercial crab
pots were used as cages (12 test and 3 control). Eight crabs were placed in each of
14 pots -3 large hard shell, 3 large soft shell, and 2 small soft shell to a pot. A
similar assortment was used for the remaining pot, excluding 1 large soft shell.
Small crabs were placed inside a hardware cloth box, 6 x 6 x 12 in (150 x 150 x 305
mm) dimensions. Chelae of all crabs were tied with rubber bands prior to placement
SHOT 1
Distance Shrimp Oysters Blue Crab
Feet Meters Live Dead Live Dead Live Dead
<5 <1.5 25 0 18 7 2 0
25 7.6 25 0 34 4 2 0
50 15.2 25 0 30 1 2 0
100 30.5 25 0 25 1 2 0
200 61.0 25 0 24 1 2 2
Control 250320 2 0
<5 <1.5 25 0 37 4 1 0
25 7.6 24 1 41 1 1 0
50 15.2 25 0 38 1 1 0
100 30.5 25 0 47 0 1 0
200 61.0 25 0 38 0 1 0
Control No control due to boat mechanical problems
in pots.
Two series of tests were conducted. In the first series, one 5 lb (2.3 kg) charge
of nitro-carbonitrate suspended 2 ft (0.6 m) beneath the surface was fired between
two crab pots placed about 50 ft (15.2 m) apart on the bottom at each of two
depths, 8 and 15 fathoms (14.6 and 27.4 m). A 25 lb (11.3 kg) charge was exploded
at a depth of 4 ft (1.2 m) over two additional pots similarly spaced in 35 fathoms
(64.0 m) of water. In the second series, equivalent size charges and number of pots
were used. All other conditions were similar to the first experiment except that
the charges were detonated 20 ft (6.1 m) beneath the surface in the 8 and 15 fathom
(14.6 and 27.4 m) depths and 40 ft (12.2 m) in the 35 fathom (64.0 m) depth.
Pressure measurements were not made.
One pot was recovered and crabs were examined at each depth in both series within
30 min after the explosion. The remaining pots were recovered at 96 hr. Divers
examined the condition of crabs on the bottom and at the 8 and 15 fathom (14.6 and
27.4 m) depths of both series prior to recovery immediately following the blasts.
Three of 15 pots were placed on the bottom in the study area and retrieved at 96
hr. After the blast one pot was placed about 100 ft (30.5 m) from the remaining
test pot at each depth in the first series.
The results for all charge sizes, cage depths, carapice condition (soft or hard),
and crab sizes tested are combined and summarized in Table 4.5. Totals of 37 live
undamaged and 11 dead or damaged (including 3 live) crabs were observed in test
pots recovered immediately after the explosions. The test pots recovered at 96 hr
contained 31 live undamaged and 16 dead or damaged (including 5 live) crabs. The
control pots, examined at 96 hr. contained 16 live undamaged and 8 dead or damaged
(including 2 live) crabs. No small crabs were found dead or damaged in any group. A
Kruskal-Wallace test, utilizing data in Table 4.5, on a singly ordered r x c
(treatment+day x response, where for response = alive, injured, dead) was not
significant (P>0.4). Anonymous (1962) concluded the following:
1. There was no significant difference in the mortalities or damage
between the test and control groups.
2. There was no significant difference in mortalities or damage with the
crab pots placed at different depths.
3. There was no significant difference in numbers of mortalities or
damage between surface and submerged shots.
4. There was no significant difference in numbers of crabs dead or
damaged between 5 and 25 lb (2.3 and 11.3 kg) charges.
Brown and Smith (1972) evaluated the effects on marine life of three charges, 40 to
60, 400 and 2,170 lb (18.1 to 27.2, 181.4 and 984.3 kg) of C-4, used to clear a
beach area and create a boat lane on in a cove at Cross Cay, a small island located
east of Roosevelt Roads, Puerto Rico.
Table 4.5- Blast related mortality and injury of Dungeness crabs (=Cancer
magister). The results for all charge sizes, cage depths, carapice condition (soft
or hard), and crab sizes tested are combined and summarized. A Kruskal-Wallace
test, utilizing the combined data, on a singly ordered r x c (treatment+day x
response, where for response = alive, injured, dead) was not significant (P>0.4)
(Modified from Anonymous 1962, Table 5, page 12).
A single large snail (conch type) and a sea urchin (Lytechinus sp.) were placed in
one of three cages containing fish. Pressure measurements were taken at three
locations for the largest shot. Casual observations of the cove were made after the
explosion.
Neither the caged snail or sea urchin were killed by the blast. However, the
hydrophone nearest the cage was apparently defective so no pressures were measured
for these two animals. Two hours after the last explosion, turbidity in the cove
had cleared sufficiently for an in-water survey. Live sea urchins and chitons were
observed. Almost all of the staghorn coral (Acropora palmata) colonies were broken
off near their bases and encrusting coral (Millepora complanta) appeared to have
suffered some abrasion.
Small sample sizes, lack of adequate pressure readings, and lack of information
concerning charge distance from the staghorn coral and encrusting coral make it
impossible to form any quantitative conclusions from this observational study.
However, the original authors concluded: "...[B]ased on the results of the
experiment and the observations of the environmental effects of the explosions, it
is felt that the proper precautions were taken to keep the damage to the
environment to a minimum." Considering the study and report production costs, the
present authors question why this poorly designed study was conducted.
Gaspin (1975) and Gaspin et al. (1976) conducted a series of tests using blue crabs
(Callinectes sapidus) and eastern oysters (Crassostrea virginica) to investigate
the effects of naval ordnance testing in Chesapeake Bay.
In 1973, explosive effects were conducted (Gaspin 1975). Test animals were
collected in the Patuxent River in the vicinity of Solomons Island. Crabs were
collected in the Patuxent River with a 25 ft (7.6 m) semiballoon otter trawl with a
1/2 in (13 mm) stretch mesh liner. Oysters were collected with a 48 in (1.2 m)
oyster dredge at an unspecified site. Organisms were held in cages until used. No
information on holding time prior to testing was provided. Cages, constructed with
plastic mesh fabric on steel frames, were cylinders 20 in (510.0 mm) long and 12 in
(305.0 mm) in diameter. Organisms were placed in cages and positioned at a depth of
5 ft (1.5 m), referred to as surface cages, and on the bottom in 25 ft (7.6 m) of
water, at horizontal standoff distances from the charge (Table 4.6). Crabs were
placed in both the surface and bottom cages, while oysters were placed only on the
bottom. Sample size was small and variable, ranging from 9-20 individuals per
distance tested. There is no indication that controls were utilized.
The organisms were exposed to 200 lb (90.7 kg) Mk 82 general purpose bomb, placed
on the bottom. Shot #532 was loaded with tritinol and shot #533 was loaded with H-
6. The pressure wave was recorded. However, the gain on some of the recording
Aliv e Injured Dead Total
Day 0 Treatment 37 (77.08 %) 3 (6.25 %) 8 (16.67 %) 48 (100 %)
Day 4 Treatment 31 (65.96 %) 5 (10.64 %) 11 (23.40 %) 47 (100 %)
Day 4 Control 16 (66.67 %) 3 (12.50 %) 5 (20.83 %) 24 (100 %)
system channels was set too high and the records were clipped. As such, good
pressure measurements were not made.
Crabs and oysters were examined for obvious external damage and those still alive
after an explosion were held in flowing water for 24 hours to detect any delayed
mortality. Results are given in Table 4.6. Gaspin (1975) stated "Little can be
concluded... Some oysters and crabs were killed at stations nearest the explosions
but many survived."
In 1975, (Gaspin et al. 1976) a single shallow water test was conducted in
approximately 25 ft (7.6 m) of water in the Patuxent River. Test oysters
(Callinectes sapidus) were collected with an oyster dredge in the vicinity of
Solomons Island. Blue crabs (Ostrea virginica) were either captured by otter trawl
and oyster dredge, or purchased. Organisms were placed in cages and positioned at a
depth of 5 ft (1.5 m), referred to as surface cages, and on the bottom, at six
horizontal standoffs from the charge. Crabs were placed in both the surface and
bottom cages, while oysters were placed only on the bottom. A description of the
cages was not provided. The organisms were exposed to a 106 lb (48.1 kg) spherical
pentolite charge, placed on the bottom. Peak pressure measurements were recorded.
After exposure, crabs and oysters were examined for obvious external damage and
then the test cages were immediately submerged in holding tanks, later to be
transferred and held in wet tables at the Chesapeake Biological Laboratory. A small
sample of test crabs was dissected and examined for internal damage, but all
examinations were inconclusive and the procedure was later abandoned. With the
exception of the severed muscle tissue and ruptured organs that resulted from
massive fractures in the carapace, no internal damage was discernable.
Percentage of cumulative blue crab mortality for test distances and controls is
presented in the original text as a figure (p. A4). However, total numbers of test
and control organisms are not given in the text or figure. As such, it is
impossible to determine if adequate sample sizes were employed. In addition,
control mortality exceeded or closely approached exposure mortalities, which
questions the usefulness of the results. Gaspin et al. (1976) noted that the high
mortalities which occurred within the control groups might be (in part)
attributable to the differences in handling between controls and test crabs. Due to
space limitations within the holding tanks, the cages containing the controls were
held out of water several hours longer than the control cages during transfer to
the laboratory.
Table 4.6.-Blast related mortality of blue crabs (Callinectes sapidus) and eastern
oysters (Crassostrea virginica). Charges erer 200 lb (90.7 kg) Mk 82 general
purpose bombs. Shot 532 was loaded with tritinol and Shot 533 was loaded with H-6
(Modified from Gaspin 1975, Table A-1).
The only oyster mortality occurred at the 20 ft (6.1 m) bottom station. Twenty
hours after the shot, 5 of 20 oysters were dead. Between 20 and 41 hours, one
additional oyster died. There was no change after 140 hours, giving 6 of 20 dead
(30% mortality). It was indicated that there were no other oyster mortalities in
140 hours of observation.
Gaspin et al. (1976) concluded: "The great resistance exhibited by the test oysters
is, therefore, a good indication of the reaction that can be expected to occur in
natural oyster populations. However, there is at least one problem with
methodology. No indication of sample sizes at each exposure distance or control are
given, other than 20 oysters were used at the 20 ft (6.1 m) location. During the
1974 testing program (Gaspin 1974), variable sample sizes ranging from 9 to 20
individuals were used for both crabs and oysters. As such, it is impossible to say
that the sample size was 20 individuals for each exposure distance and control.
Linton et al. (1985a) conducted a test with both fish and invertebrates, with the
intention of determining adequacy of regulations imposed by governmental agencies
that permit geophysical exploration intended to minimize detrimental effects of
geophysical exploration on marine organisms. American oysters (=eastern oyster)
(Crassostrea virginica), white shrimp (Penaeus setiferus) and blue crab
(Callinectes sapidus) were used as test invertebrates.
All test organisms were collected in Trinity Bay, north of Smith Point, Texas
within one kilometer of the detonation site. Blue crabs were captured with
commercial traps, oysters with a commercial dredge, and white shrimp with an otter
trawl. Test organisms were selected for uniform size within species. Range and
average were: white shrimp, 7-11, 85 mm total length; blue crab 14-18, 170 mm-
carapace width. Oysters were not measured individually, but none was less than 150
mm in total shell length.
Crabs and oysters were transported in aerated tanks to open-water holding pens
immediately after capture. They were held there for at least 24 hr prior to the
experiment to monitor injuries and mortalities resulting from capture and handling.
Shrimp were captured the day of the experiment and transferred directly to test
cages. No attempt was made to determine shrimp mortality or injury resulting from
Species Distance Cage Depth Pmax Survival Mortality
Feet Meters Feet Meters (kPa)
Shot 532
crabs 50 15.2 25 7.6 1,679 7 2
110 33.5 5 1.5 484 15 5
110 33.5 25 7.6 1,264 10 0
oysters 50 15.2 25 7.6 1,679 10 0
110 33.5 25 7.6 1,264 12 0
Shot 533
crabs 40 12.2 25 7.6 1,600 11 1
75 22.9 5 1.5 1,206 9 1
75 22.9 25 7.6 1,637 7 3
oysters 40 12.2 25 7.6 1,600 6 7
75 22.9 25 7.6 1,673 11 2
capture or handling. All organisms were acclimated to test-cage conditions for at
least one hour prior to detonation.
During testing, organisms were held in cylindrical holding cages, 900 by 750 mm,
and enclosed with 18 mm nylon mesh webbing. Cages holding shrimp also contained a 5
mm mesh liner. Ten crabs and 10 oysters were caged together. White shrimp were
caged alone, 10 individuals per cage. Shrimp were held in paired cages at surface
and bottom locations (4 cages per location), whereas crabs and crabs and oysters
were only deployed in paired bottom cages.
Linton et al. (1985a) stated that surface and bottom cages were deployed at five
stations arranged perpendicular to, and at logarithmic distances of 1, 11, 23, and
46 m from the detonation line. However, based on their Figure 2 (p. 345) showing
the test array of cages, distances are from the explosive to the vertical line
maintaining both surface and bottom cages. Actual or slant distances from the
explosion to the surfaces cages would have been 24.0, 26.4, 33.2 and 51.9 m.
Distances from explosion to bottom cages are as stated.
Bottom cages were deployed at 24 m depth and surface cages were floated at the
surface. Controls were established at a distance of 136 m from the detonation site.
Control organisms received the same treatment (that is, method of capture, and
holding time as test organisms), with the exception that they were not in the water
at the time of the explosion.
Test organisms were exposed to a 33 m strand of 100 g/33 cm Primacord detonation
cord laid perpendicular to the transect of test cages. It was positioned to form
the top of the letter "T" and the line of cages forming the base. Both Primacord
ends were weighed to hold the cord on the bottom, 24 m depth. A blasting cap was
used to initiate the detonation. No pressure measurements were made.
After the test, observers raised the cages and recorded mortality among test
animals. Criteria used to denote death were: oysters-shell permanently agape;
shrimp-cessation of gill movement; and crabs-cessation of movement of chela,
appendages, and mouth parts. Dead organisms were removed from their cages. Cages
with living organisms were returned to the position they occupied at the time of
detonation and observed 24 hours later and separated as to living or dead.
The results are presented in Table 4.7. Surface cage distances are corrected from
those presented in the original publication (Table 1, p. 346) to reflect actual
distance from the explosion.
White shrimp exhibited no well-defined pattern relative to survival and distance
from the detonation site (Table 4.7).
Without pressure wave measurements it is impossible to determine if cages received
variable pressures that would explain the observed mortality pattern.
Blue crab mortality, immediately following the blast, ranged from 40 percent at 1 m
to 10 percent at 47 m. Twenty-four hour mortality ranged from 60 percent at 1 m to
10 percent at 47 m.
No mortality was observed in control cages.
Eastern oyster mortality, immediately following the blast, was minimal with 1 (5%)
dead oyster at 1 and 11 m and two (10%) dead at 23 and 46 m. There was 1 (5%) dead
oyster at 1 and 11 m and 3 (15%) dead at 23 and 46 m. There was no control
mortality.
Table 4.7.- Percent mortality for white shrimp (Penaeus setiferus), American
oysters (=eastern oyster, Crassostrea virginica) and blue crab (Callinectes
sapidus) as a function of cage depth (surface and bottom = 24 m), lapsed time, and
distance from detonation site. Test organizms were exposed to a 33m strand of 100
g/33 cm Primacord detonation cord laid on the bottom at 24 m depth and
perpendicular to the transect of test cages (Modified from Linton et al. 1985a)
Percent mortality at 24 hours is cumulative (e.g., 0 hr + 24 hr) to reflect total
mortality at 24 hr. Linton et al. (1985a, Table 1) removed from their cages and
counted dead organisms at O hr (instantaneous mortality). Living organisms were
returned to the position they occupied at the time of detonation and observed 24 hr
later. Their 24 hr values were not cumulative. For surface shots Linton et al.
(1985a) gave distances from the explosive to the vertical line maintaining both
surface and bottom cages. These values have been modified to provide the actual or
slant distances from the explosion to the surfaces cages.
SUMMARY AND DISCUSSION
The results of all the studies reviewed indicate that invertebrates are insensitive
to pressure related damage from underwater explosions. This may be due to the fact
that all the invertebrate species tested lack gas-
c
ontaining organs which have been
implicated in internal damage and mortality in vertebrates. Underwater explosion
produce a pressure waveform with rapid oscillations from positive pressure to
negative pressure which results in rapid volume changes in gas-containing organs.
In fish, the swimbladder, a gas-containing organ, is the most frequently damaged
organ (Christian 1973; Faulk and Lawrence 1973; Kearns and Boyd 1965; Linton et al.
1985a; Yelverton et al. 1975). It is subject to rapid contraction and overextension
in response to the explosive shock waveform (Wiley et al. 1981). Species lacking
swimbladders or with small swimbladders are highly resistant to explosive pressures
(Aplin 1947; Fitch and Young 1948; Goertner 1994). For example, Wiley et al. (1981)
and Goertner et al. (1994) noted that hogchokers (Trinectes maculatus), which lack
swimbladders, were extremely tolerant of underwater explosions, and greatly
exceeded the tolerance of any species with swimbladders that they had tested.
Goertner et al. (1994) found that hogchokers were not killed beyond a distance of 1
m from a 4.5 kg charge of pentolite.
Gas-containing organs have also been implicated as a causative factor of internal
damage and mortality in other vertebrate species exposed to underwater explosions.
Sailors exposed to depth charges and torpedo explosions, while escaping their
sinking ships during World War II, suffered damage to gas-containing organs
(Cameron et al. 1944; Ecklund 1943; Gage 1945; Palma and Uldall 1943; Yaguda 1945).
Percent Mortality
Number Cage Lapsed Distance (m) from Detonation Site
Species Per Cage Depth Time(hr) 24 26.4 33.2 51.9 control
White shrimp 20 Surface 0050205
2451025205
Distance (m) from Detonation Site
1 11 23 46 control
White shrimp 20 Bottom 0 5 30 5 0 0
2453510--0
Blue crab 20 Bottom 0 40 35 35 10 0
24 60 50 35 10 0
Eastern
oyster 20 Bottom 0 5 5 10 10 0
24 5 5 15 15 0
The lungs, stomach, and intestines, all gas-containing organs, were ruptured or
hemorrhaged, while other organs were relatively unaffected. Similar results have
been observed in underwater explosion tests with other mammalian species (Richmond
et al. 1973).
Experimental design has progressed little since the early investigative study
conducted by Knight (1907). Invertebrate mortality studies have used inadequate
sample sizes, lacked adequate controls, and failed to conduct pressure waveform
analysis of the explosion (Table 4.8). In addition, investigators have failed to
give adequate information concerning testing conditions (e.g., type and weight of
explosive, cage type, testing site conditions, post-test invertebrate holding
times).
It is essential to not only record invertebrate mortality at given distances from
an explosion but to also record the pressure waveform at each test distance. Three
parameters of underwater explosive waveforms have been implicated as being
responsible for fish mortality: pressure (Teleki and Chamberlain 1978), impulse
(Gaspin 1975; Gaspin et al. 1976; Yelverton et al. 1975), and energy flux density
(Ogawa et al. 1976, 1977, 1978; Sakaguchi et al. 1976). Peak pressure has been
dismissed as a causative mortality factor by Hubbs and Rechnitzer (1952) and
Yelverton et al. (1975).
The pressure waveform parameter responsible for invertebrate mortality has not been
experimentally determined. The pressure (force per unit area), impulse (strength)
and energy flux density (intensity) of the shock-
w
ave are complex physical measures
that vary in time. With recent technological advancements in recording equipment
and computer programs for waveform analysis, there is no reason why peak pressure,
impulse, and energy flux density can not be analyzed and reported. Investigators
would make a substantial contribution to the "state of the science" by reporting
all aspects of the waveform or by making digital information available to other
researchers. This is extremely important, since waveforms change considerably under
various test settings (i.e., depth, bottom type, embedment, etc.). In addition,
investigators attempting to duplicate study designs to test additional species need
precise details of how waveform analysis was conducted.
Pressure waveform-mortality relationships can be used to develop models to predict
invertebrate mortality at untested charge sizes and distances from the explosion
based on scaling laws of explosives (Cole 1948). It is essential that adequate test
distances from the explosion be used and pressure measurements be made at each
distance to construct mortality-pressure waveform relationships, or LD50 curves.
Without such data collection, little useful information is gained.
Table 4.8.- Summary of study type (experimental or observational), study design,
and type of publication for each study reviewed.
Adequate
Type Sample Adequate Measured Type of
Species Study Size Control Pressures Publication Reference
sea anemone-- Obs. No No No Refereed Fry and Cox 1953
corals-- Obs. No No No Refereed Fry and Cox 1953
staghorn coral
(Acropora palmata)-- Obs. No No No Gray Brown and Smith
1972
encrusting coral
(Millepora
complanta)-- Obs. No No No Gray Brown and Smith
1972
ribbon worms
(Nemertinea sp).-- Obs. No No No Gray Tollefson &
Marriage 1949
sand worms
(Nereis sp.)-- Obs. No No No Gray Tollefson &
Marriage 1949
tube worms-- Obs. No No No Refereed Fry and Cox 1953
Rough abalones
(Haliotis
corrugata)-- Exp. No No No Refereed Alpin 1947
Green abalones
(Haliotis fulgens)-- Exp. No No No Refereed Alpin 1947
snail
(Thais sp.)-- Obs. No No No Gray Tollefson &
Marriage 1949
snail (conch type)-- Exp. No No No Gray Brown and Smith
1972
cockles
(Cardium corbis)-- Exp. No No No Gray Tollefson &
Marriage 1949
muc clam
(Macoma sp.)-- Obs. No No No Gray Tollefson &
Marriage 1949
commensal clam
(Pseudopythina
rugifera).-- Obs. No No No Gray Tollefson &
Marriage 1949
oysters
(Ostrea gigas)-- Exp. No No No Gray Tollefson &
Marriage 1949
oyster bed
(Ostrea virginica)-- Exp. ? ? No Gray
Gowanloch and
McDougal 1946;
Gowanloch 1946b,
1948, 1950
oysters
(Ostrea virginica)-- Exp. Yes No No Gray Gowanloch and
McDougal 1946;
Gowanloch 1946b,
1948, 1950
oyster
(Ostrea virginica)-- Exp. Yes No No Gray Sieling 1954
oysters
(Ostrea virginica)-- Exp. Yes No No Gray Kemp 1956
oysters
(Ostrea virginica)-- Exp. No No Yes1Gray Gaspin 1975
oysters
(Ostrea virginica)-- Exp. ?2?2No Gray Gaspin et al. 1976
American oyster
(Ostrea virginica)-- Exp. Yes Yes No Refereed Linton et al.
1985a
shrimp
(Peneus setiferus)-- Exp. Yes No No Gray
Gowanloch and
McDougal 1946;
Gowanloch 1946a,
1950
white shrimp
(Peneus setiferus)-- Exp. Yes Yes No Refereed Linton et al.
1985a
shrimp
(Peneus sp.)-- Exp. Yes No No Gray Kemp 1956
ghost shrimp
(Upogebia
pugettensis)-- Obs. No No No Gray Tollefson &
Marriage 1949
blue crab
(Callinectes
sapidus)-- Exp. Yes No Yes3? Anonymous 1948
blue crab
(Callinectes
sapidus)-- Exp. Yes No No Gray Kemp 1956
blue crab
(Callinectes
sapidus)-- Exp. Yes No Yes1Gray Gaspin 1975
blue crab
(Callinectes
sapidus)-- Exp. ?2?2No Gray Gaspin et al. 1976
blue crab
(Callinectes
sapidus)-- Exp. Yes Yes No Refereed Linton et al.
1985a
Dungeness crabs
(Cancer magister)-- Exp. Small Yes No Gray Anonymous 1962
crabs
(Cancer sp.)-- Exp. No No No Gray Tollefson &
Marriage 1949
lobster
(Homarus
americanus)-- Exp. No No No ? Knight 1907
lobsters
(Panulirus
interuptus)-- Exp. No No No Refereed Aplin 1947
sea urchins-- Obs. No No No Refereed Fry and Cox 1953
1The pressure wave was recorded. However, the gain on some of the recording system
channels was set too high and the records were clipped. As such, good pressure
measurements were not made.
2Mortality is provided as percent mortality. Number of organisms exposed at each
distance tested is not provided.
3Peak Pressure is provided for the distance nearest and farthest from the explosion.
For example, Aplin (1947) tested only one distance from the explosion and did not
record the pressure waveform. It is only possible to conclude that at the distance
from the explosion and water depth tested there was no mortality. The data can not
be used to extrapolate to other charge sizes or distances from the explosion.
All of the invertebrate studies reviewed were conducted with organisms suspended in
the water column or on the substrate and with open-water explosions. Explosives in
open water, which are not contained completely by rigid structures, will produce
both higher amplitude and higher frequency shock waves than contained detonation.
Thus, the use of blasting in structure demolition, when the explosives are enclosed
within the structure being razed, should result in lower mortality than when the
same explosive detonated in open water. For example, "burning" a steel beam
underwater with perimeter charges to sever it would cause higher mortality than the
severance of a concrete pier using an explosive of the same weight placed within
the pier by drilling and covering. The more work accomplished by a detonation in
cracking and moving a rigid volume, and the greater the energy dissipated into
solid media, the lower the capacity of the water-borne shock wave will have to
cause mortality. Explosives buried in the substrate or placed in bore holes and
adequately stemmed (Keevin, In press) produce less impact than open-water
explosions. For example, Traxler et al. (1992) found no mortality or internal
injuries in largemouth bass (Micropterus salmoides), bluegill (Lepomis macrochirus
)
or channel catfish (Ictaluris punctatus) in a cage 7.6 m from each of two shot
holes drilled 27.4 and 33.5 m into the sediment and charged with 4.5 and 9.1 kg of
dynamite.
Natural resource managers making impact assessments based on the existing
literature should consider that explosive demolition and seismic testing using
explosives buried in the sediment will produce effects less than open-water shots.
sea cucumbers-- Obs. No No No Refereed Fry and Cox 1953
sea urchin
(Lytechinus sp.)-- Exp. No No No Gray Brown and Smith
1972
CHAPTER 5
THE ENVIRONMENTAL EFFECTS OF
UNDERWATER EXPLOSIONS:
AMPHIBIANS AND REPTILES
INTRODUCTION
To date, there has not been a single comprehensive study to determine the effects
of underwater explosions on either amphibians or reptiles that defines the
relationship between distance/pressure and mortality or damage.
INJURY AND MORTALITY OF REPTILES EXPOSED TO UNDERWATER EXPLOSIONS
There have been a number of studies which demonstrate that sea turtles are killed
and injured by underwater explosions (Duronslet et al 1986; Gitschlag 1990;
Gitschlag and Herozeg 1994 ; Gitschlag and Renaud 1989 ; Klima et al. 1988;
O'Keeffe and Young 1984) . Currently, there is no information available for
amphibians (i.e., frogs, salamanders, etc.). There are few reports of turtle
mortality because turtles can be difficult to observe, and turtles killed by
explosions may not float to the surface until sufficient bacterial activity has
occurred, which takes several days (NRC 1990). The NRC has concluded that data on
the effects of underwater explosions, in relation to oil and gas platform explosive
removal, are inadequate and that further research is needed.
In March and April of 1986, 51 dead sea turtles, primarily Kemp's ridleys, washed
ashore on Texas beaches after the removal of platforms that involved 22 underwater
explosions. Because shrimp fishing (another cause of sea turtle mortality) was at a
very low level in the area, the explosions were identified as the probable cause
(Klima et al. 1988).
To document the effects of underwater explosions on sea turtles, the National
Marine Fisheries Service undertook an experiment to determine the extent of
injuries to sea turtles placed at 700 ft. 1,200 ft. 1,800 ft. and 3,000 ft (213.4,
365.8, 548.6, and 914.4 m) from an explosive removal of an oil platform (Klima et
al. 1988). On June 21, 1986, a platform in 30 ft (9.1 m) of water was removed by
detonating 50 lb (22.7 kg) of nito-methane inside each of four jacket legs 15 ft
(4.6 m) below mudline. One Kemp's ridley and one loggerhead were placed in a cage
at each of the four distance. Just before detonation, the cages were lowered to a
mid-water depth of 15 ft (4.6 m). The cages were retrieved shortly after
detonation. The four turtles within 1,200 ft (365.8 m) of the explosion were
unconscious, as was the loggerhead in the cage at 3,000 ft (914.4 m). If they had
been left in the water these turtles may have drowned. Turtles in all of the cages
were affected. Some suffered averted cloaca and vasodilation, which lasted for two
to three weeks.
Two observations of sea turtles severely wounded by explosive removals of platforms
have been made. A dead or injured turtle drifting about 10 ft below the surface was
sighted 1.5 hr after the explosive removal of a structure in 1986 (Gitschlag and
Renaud 1989). At a removal site of a caisson in 1991, a loggerhead with a fracture
down the length of its carapace surfaced within one minute of detonation
(Gitschlag, personal communication in NRC 1996).
Two immature green turtles (100 to 150 ft) (30.5 to 45.7 m) were killed when 20 lb
(9.1 kg) of plastic explosives (C-4) were detonated in open water by a U.S. Navy
Ordnance Disposal Team. Necropsies revealed extensive internal damage, particularly
to the lungs (Schroeder, personal communication in NRC 1996).
Three sea turtles were unintentionally exposed to underwater shock tests by the
Naval Coastal Systems Center in 1981 off the coast of Panama City, Florida. Three
detonations of 1,200 lb (544.3 kg) of TNT at mid-depth (in approximately 120 ft
(36.6 m) of water) injured one turtle at a distance of 500 to 700 ft (152.4 to
213.4 m) and another at 1,200 ft (365.8 m). A third turtle at 2,000 ft (609.6 m)
was apparently uninjured (O'Keeffe and Young 1984; Klima et al. 1988).
Young (1991) developed the following equation to estimate sea turtle safe ranges.
Rt = 560 WE1/3
Rt = Range in feet
W= Weight of explosive in pounds
The metric form of this equation for the safe sea turtle range is
Rt (m) = 222 W(in kg)1/3
The estimated sea turtle safe range equation was based on Gulf of Mexico oil
platform criteria established by the National Marine Fisheries Service (NMPS). As
the sea turtle literature review indicated, there has not been a single study
establishing the relationship between underwater explosive pressures and mortality.
Young (1991) suggested that the calculated sea turtle safe ranges should only be
used for preliminary planning purposes.
There are no data on nonlethal damage from underwater explosions or delayed
mortality, both of which may have a greater impact on sea turtle populations than
immediate death from explosions.
INJURY AND MORTALITY OF AMPHIBIANS EXPOSED TO UNDERWATER EXPLOSIONS
There currently is no data available on the effects of underwater explosions on
amphibians (i.e., frogs, salamanders, etc.). Although untested, amphibians with
air-containing organs, such as lungs, probably have mortality comparable to fish
with swimbladders. For impact assessment purposes, the relationship between
distance/pressure and fish mortality/injury are probably fairly close (See Chapter
6 for details). Although untested, amphibians without air-containing organs, are
probably immune to underwater explosives as are benthic fish species without
swimbladders (Goertner et al. 1994).
MITIGATION TECHNIQUES TO PROTECT REPTILES AND AMPHIBIANS FROM UNDERWATER
EXPLOSIONS
Reptiles
The simplest method to protect sea turtles from underwater explosions is to either
avoid periods when they are in the blasting zone or to remove the sea turtles.
Avoidance of sea turtles can be achieved in two manners. Depending on location,
there may be time periods when sea turtles are not in the project area due to their
life history characteristics (e.g. migration patterns). This can be determined by
coordination with the state natural resource agency or NMFS. Blasting can be
planned during time periods of low sea turtle abundance. If sea turtles are
potentially in the area during blasting, an aerial survey using a light plane or
helicopter can be conducted prior to detonation. If sea turtles are observed in the
project area, blasting can be halted until they move out of a pre-determined blast
zone. As a last resort, turtles can be physically captured and removed from the
blast zone prior to detonation.
The NMFS developed a series of mitigation features for a Incidental Take Statement
under the auspices of the Endangered Species Act to protect sea turtles from the
use of underwater explosives during salvage of offshore oil and gas structures
(Table 5.1).
An example of the above strategy is in place for explosive removal of oil and gas
structures in state and federal waters of the Gulf of Mexico (Gitschlag 1990). For
at least 48 hr prior to detonation, NMFS observers watch for sea turtles from the
surface. Helicopter aerial surveys within a mile radius of the removal site are
conducted 30 min prior to and after detonation (Gitschlag and Herczeg 1994). If sea
turtles are observed, detonations are delayed until the sea turtles have been
safely removed or have left the area.
A
mphibians
Mitigation techniques described for fish in Chapter 8 are applicable to amphibians
with air-containing organs.
Table 5.1.- Summary of "generic" incidental take statement. From Gitschlag and
Herczeg (1994)
1. Qualified observers monitor for sea turtles beginning 48 hours prior to
detonations.
2. Thirty minute aerial surveys within one hour prior to and after detonation.
3. If sea turtles are observed within 914 meters of the structure, detonations
will be delayed and the aerial survey repeated.
4. No detonations will occur at night.
5. During salvage-related diving, divers must report sea turtle and dolphin
sightings. If sea turtles are thought to be resident, pre- and post-
d
etonation
diver surveys must be conducted.
6. Detonation of sequential explosive charges must be staggered by at least 0.9
seconds to minimize cumulative effects of the explosions.
7. Avoid use of "scare" charges to frighten away sea turtles which may actually
be attracted to feed on dead marine life.
8. Removal company must file a report summarizing the results.
CHAPTER 6
THE ENVIRONMENTAL EFFECTS OF
UNDERWATER EXPLOSIONS:
FISH
INTRODUCTION
The potential for injury and mortality to both marine and freshwater fishes,
resulting from underwater blasts, has been well documented (Hubbs and Rechnitzer
1952; Ferguson 1962; Teleki and Chamberlain 1978).
PRESSURE RELATED MORTALITY OF FISH
Three parameters of underwater explosive waveforms have been implicated as being
responsible for fish mortality: pressure (Teleki and Chamberlain 1978), impulse
(Gaspin 1975; Gaspin et al. 1976; Yelverton et al. 1975), and energy flux density
(Ogawa et al. 1976, 1977, 1978; Sakaguchi et al. 1976). Peak pressure has been
dismissed as a causative mortality factor by Hubbs and Rechnitzer (1952) and
Yelverton et al. (1975). Hubbs and Rechnitzer (1952) found that in marine fish
species tested, the lethal threshold peak pressure from dynamite (DV =
approximately 17,000 m/s) explosions varied from 276 to 483 kPa. Peak pressures
from slowly detonating black powder (DV = 1,709 m/s), producing pressures as high
as 855 to 1,103 kPa, did not kill caged fishes.
Based on the findings of Hubbs and Rechnitzer (1952), Teleki and Chamberlain (1978)
concluded that the lethality of an explosive is directly related to its detonation
velocity. Detonation velocity (DV) is the rate at which a blasting agent ignites.
It ranges from about 1,650 to 7,650 m/s for products used commercially today (Dick
et al. 1993a). Teleki and Chamberlain (1978) suggested that the more rapid the
detonation velocity the more abrupt was the resultant hydraulic pressure gradient
and the more difficulty fish had adjusting to the pressure changes. They felt that
a knowledge of the detonation velocity is critical to a true understanding of the
impact of blasting on fish.
Keevin (1995) tested Teleki and Chamberlain's (1978) suggestion by comparing the
mortality of bluegill (Lepomis macrochirus) exposed to three high-explosive types
(T-100 Two Component, Pellite, and Apex 260) spanning the range of detonation
velocities within commercially available explosives (Table 6.1).
Table 6.1.- Characteristics of explosives used during testing. (Atlas Powder
Company 1990a,b; Slurry Explosive Corporation 1991)
Using equivalent weights of explosives, there was no significant difference in
mortality curves based on distance from the explosive charge. The results suggest
that detonation velocity of commercially available explosives, with the exception
of black powder, is not an important factor in fish mortality. The misconception
concerning the relationship between lethality and detonation velocity is "probably"
based on field observations and research (Baldwin 1954; Fry and Cox 1953; Ferguson
1962; Hubbs and Rechnitzer 1952) which indicated that black powder, a low
Pellite APEX 260 T-100
Detonation Velocity (m/s) 3,6 5,033 6,314
Density (gm/cm3) 0.81-0.85 1.25 1.22
Relative Bulk Strength 1.00
(ANFO=1) 1.00 1.45 1.60
detonation velocity explosive, had little effect on fish. Ferguson (1962) found
that caged yellow perch (Perca flavescens) were unaffected by 45 kg charges of
black powder, fired with an electric squib (detonator). Black powder charges
detonated with a nitrone detonator, itself a high explosive, were damaging to fish.
Even a 0.45 kg nitrone charge killed caged perch up to 60.7 m away. Fry and Cox
(1953) reported that fish and game observers, attached to seismic operations which
normally used 40 to 50 shots of 20.3 or 40.5 kg charges of black powder per day,
reported almost no damage to fish. On one occasion, three divers located a school
of rockfish (Sebastodes sd.) in approximately 16.7 m of water. A 20.3 kg charge was
detonated above the school at a depth of 1.8 m. The divers descended and found no
mortality in the school. Baldwin (1954) observed "many salmon (Oncorhynchus)
swimming about in the blasting area prior to detonation" of either a 20.3 or 40.5
kg charge of black powder at a depth of 1.8 m. None were harmed by the explosion.
The difference in fish mortality between black powder, a low explosive, and high
explosives appears to be related to the waveform produced by each explosive type.
Black powder produces a pressure waveform with a slow rise time and low amplitude
whereas high explosives have an abrupt rise time, high amplitude, and short
frequency. In addition, high explosives have a much higher negative pressure than
black powder, as shown in Figures 8 and 9 in Hubbs and Rechnitzer (1952). The
amplitude and short frequency of the negative pressure wave and resulting damage to
the swim bladder may be the causative factor of mortality in fish exposed to high-
explosive pressure waveforms.
The exact pressure waveform measurement responsible for fish mortality is unknown.
As previously noted, peak pressure is not a good predictor of mortality when
comparing very different types of explosives (Hubbs and Rechnitzer 1952). Baxter et
al. (1982) reviewed overpressure waves versus damage effects data and concluded
that impulse strength was the most predictive damage parameter for water depths of
less than 3 m. Energy flux density was found to be more accurate in predicting
effects on fish in water depths greater than 3 m. Yelverton et al. (1975) compared
peak pressure and impulse as mortality predictors by keeping the depth of charge
and slant range constant and by varying the depth of the fish, thus varying the
impulse levels and keeping the peak pressure constant. The impulse for 50-percent
lethality in carp (Cyprinus carpio) was 189 Pa-s (at 52. m), 162 Pa-s (at 305. m)
and 181 Pa-s (at 3.05 m). In contrast, the corresponding peak pressures associated
with these LD50 impulses varied markedly, 5.58 Mpa (at 52 m), 2.31 Mpa (at 305. m)
and 1.21 Mpa (at 3.05 m) for carp tested at 3.05 m depths.
Keevin (1995) compared mortality of bluegill (Lepomis macrochirus) exposed to a 2
kg charge of T-100 detonated at 2 m depth with various measurements of the pressure
waveform. He demonstrated that there was a significant correlation (P > 0.05)
between all values of impulse and energy flux density and mortality, with the
exception of impulse calculated as 50 (Table 6.2). However, Keevin exposed the
bluegill to explosive pressures at only one depth.
Table 6.2.- Spearman correlation matrix of number of dead (n=25) versus waveforms.
Spearman correlations larger than 0.619 are significant at p < 0.05. (Modified from
Keevin (1995))
The rapid oscillation in the pressure waveform between a high overpressure and
underpressure associated with detonation of high explosives is most probably
responsible for fish mortality. This oscillation in waveform is responsible for the
rapid contraction and overextension of the swimbladder resulting in internal damage
and mortality. Any waveform value that provides a good predictor of mortality over
a wide range of conditions (i.e., organism depth, explosive size, explosion depth)
would be a suitable measure. Currently, it appears that impulse provides the best
measurement for shallow shots and energy flux density provides the best measurement
for deep water shots. However, this is an area that needs further evaluation.
EXPLOSIVE PRESSURE RELATED ORGAN DAMAGE
Investigators have found the swimbladder to be the most frequently damaged organ
(Christian 1973; Faulk and Lawrence 1973; Kearns and Boyd 1965; Linton et al.
1985a; Yelverton et al. 1975). The swimbladder, a gas-containing organ is subject
to rapid contraction and overextension in response to the explosive shock waveform
(Wiley et al. 1981). Gas-containing organs have also been implicated as a causative
factor of internal damage and mortality in other vertebrate species exposed to
underwater explosions. Sailors exposed to depth charges and torpedo explosions,
while escaping their sinking ships during World War II, suffered damage to gas-
containing organs (Cameron et al. 1944; Ecklund 1943; Gage 1945; Palma and Uldall
1943; Yaguda 1945). The lungs, stomach, and intestines were ruptured or
hemorrhaged, while other organs were relatively unaffected. Similar results have
been observed in underwater explosions tests with other mammalian species (Richmond
et al. 1973).
Because the swimbladder was burst outward, some investigators have suggested that
negative phase (relative to ambient) of the pressure wave is responsible for damage
to the swimbladder (Anonymous 1948; Hubbs and Rechnitzer 1952; Wiley et al. 1981).
For example, postmortem observation of striped bass (Roccus saxatilis) and trout
(Cynoscion regalis) found "the edges of holes in the swim bladder were turned
outward and that blood from broken vessels in the wall of the bladder had been
blown into the abdominal cavity" (Anonymous 1948).
Laboratory tests have demonstrated that small negative pressures can injure
swimbladders. Tsvetkov et al. (1972) applied pressure of 1-6 atmospheres (101.4-
608.4 kPa) above the surface of water containing fish in a closed container over a
period of 2-5 min. After the pressure was applied, fish were allowed to adapt until
they reached neutral buoyancy. Pressure was then released at rates of 0.1-
6
.0 atm/s
(10.1-608.4 kPa/s). One hundred percent mortality of roach (Rutilus rutilus) was
observed when the rate of discharge was 3 atm/s (304.1 kPa/s), 40-72% at a rate of
0.1-0.5 atm/s (10.1-50.7 kPa/s), and 10% at a rate of less than 0.1 atm/s (10.1
kPa/s). Rupture to the swimbladder walls was observed at their weakest point in
Waveform Shot 1 Shot 2
Peak pressure 0.903 0.651
Impulse (first positive wave) 0.9 0.806
Impulse (calculated by the greatest difference of
peak pressure to pressure low) 0.878 0.892
Impulse (5e) -0.195 -0.554
Impulse 6.7e -0.805 -0.843
Energy Flux Density 0.878 0.892
response to the large increase in volume. Hubbs and Rechnitzer (1952) found that
negative pressures of only one atmosphere (101.4 kPa) killed marine fish. Brown
(1939) showed that the guppy could not successfully adapt to decompressions of more
than about one-half atmosphere (50.7 kPa). Hogan (1941) applied negative pressures
of up to one atmosphere (101.4 kPa) to a variety of fish species, for periods of 10
to 30 seconds and found that physoclistous fish suffered hemorrhage in the
circulatory system and often died. Muir (19S9) found that young salmon could
usually survive decompressions of about one atmosphere (101.4 kPa); but when the
pressure was lowered to the vapor pressure so that the water cavitated, mortality
was high.
The rate and magnitude of pressure change in laboratory studies, both positive and
negative, does not approach those observed in underwater explosions. In addition,
laboratory studies do not duplicate the rapid oscillation from positive pressure to
negative pressure which result in rapid volume changes in the swim bladder.
Underwater explosions should be far more damaging.
Species lacking swimbladders or with small swimbladders are highly resistent to
explosive pressures (Aplin 1947; Fitch and Young 1948; Goertner et al. 1994). For
example, Aplin (1947) noted that two opal-eye perch (Girella nigricans), 15.24 m
from a 9 kg charge of 60% petrogel, were killed and their viscera reduced to a
"pulp". However, 4 sculpin (Scorpaena guttata) and a cabezone (Scorpoenicthys
marmoratus), which both lack swimbladders, in the same cage were not injured nor
was there any damage to their internal organs. Wiley et al. (1981) and Goertner et
al. (1994) noted that hogchokers (Trinectes maculatus), which lack swimbladders,
were extremely tolerant of underwater explosions, and greatly exceeded the
tolerance of any species with swimbladders that they had tested. Goertner et al.
(1994) found that hogchokers were not killed beyond a distance of 1 m from a 4.5 kg
charge of pentolite. Immediate death appeared to be caused by loss of blood
resulting from hemorrhaging in the gills. Goertner et al. (1994) suggest that the
lack of hogchoker injuries, except when close to an explosive charge, is probably
due to the absence of obvious air cavities. They imply that the observed damage may
be caused by the presence of microbubbles. Microbubbles have not been confirmed for
fish but are known to occur in humans, where they have a radii of a few micrometers
(Lewin and Bjorno 1981). Microbubble response to microsecond pulses of ultrasound
has become a concern in the field of diagnostic medicine using ultrasound (Flynn
and Church 1988). Investigators have defined a "transient cavity" as one that
expands to a critical maximum radius and then collapses violently. The gas
temperature and pressure reach extremely high values and a shock wave is generated
in the surrounding medium during collapse and rebound. Ayme-Bellegarda (1990) and
Holland and Apfel (1990) suggest that a bubble in the presence of a boundary can be
more damaging because of the formation of a jet in the collapsing bubble which is
directed toward the boundary.
Keevin et al. (In preparation) exposed 25 caged bluegill placed 2 m below the water
surface to a 2 kg charge of T-100 explosive detonated at 2 m depth. Pressure
waveform values (Table 6.3) can be compared with internal damages (Table 6.4) or
mortality (Table 6.5) to determine damaging pressure levels. An abrupt increase in
internal damage (ruptured swimbladder, kidney, liver, and spleen damage) occurred
at values above approximately 700 kPa peak pressure, 50 Pa-s impulse (first
positive wave), and 40 J/m2 energy flux density. Mortality abruptly increased at
approximate values above 500 kPa peak pressure, 40 Pa-s impulse (first positive
wave), and 20 J/m2 energy flux density. The lower threshold values for mortality
reflect the mortality scoring system which scores minor injuries as "dead". LD50
values are presented for each pressure waveform measurement are given in Table 6.6.
Table 6.3.-Pressure waveform values resulting from the underwater detonation of a
2kg charge of T-100 at a depth of 2m. Independent duplicate trials are reported.
(Keeven et al. (In preparation))
1 Peak pressure for the first positive waveform
2 Impulse was calculated by integrating the pressure-time curve for the first
positive wave.
Table 6.4.- Bluegill damage counts for each distance tested and controls (n=25 at
each distance) based on necropsies of fish preserved 1 hr post blast. Bluegill were
exposed to a 2 kg charge of T-100 at 2 m. Independent duplicate trials are
reported. (Keevin et al. (In preparation))
DISTANCE (Meters) FROM EXPLOSION
30.0 32.5 35.0 37.5 40.0 42.5 45.0 47.5 Control
SHOT 1
Peak Pressure (kPa)11300.0 860.0 900.0 693.0 572.0 518.0 340.0 368.0 0
Impulse (Pa-s)298.6 59.1 49.7 56.1 39.2 38.1 23.6 23.1 0
Energy Flux Density (J/m2)134.0 63.9 62.8 45.5 28.1 17.7 9.1 8.1 0
SHOT 2
Peak Pressure (kPa)1 1130.0 861.0 869.0 899.0 383.0 577.0 398.0 410.0 0
Impulse (Pa-s)2113.0 60.6 67.9 55.4 23.8 45.7 28.3 25.8 0
Energy Flux Density (J/m2)128.0 69.4 65.0 42.2 19.0 24.6 10.6 10.0 0
DISTANCE (Meters) FROM EXPLOSION
30.0 32.5 35.0 37.5 40.0 42.5 45.0 47.5 Control
SHOT 1
External Damage 9 3100000 0
Ruptured Swimbladder 22 14 1391000 0
Free Blood In Swimbladder 21 24 23 17 2 0 0 0 0
Free Blood In Coelom 12 4 1266000 0
Kidney Damage 16 8800000 0
Liver Damage 13 14 1400000 0
Spleen Damage 13 17 1900000 0
Heart Damage 1 0000000 0
Free Blood in Pericardium 2 0000000 0
Brain Damage 0 0000000 0
SHOT 2
External Damage 12 4500000 0
Ruptured Swimbladder 23 21 1940000 0
Free Blood In Swimbladder 21 25 25 16 6 0 0 0 0
Free Blood In Coelom 13 5788300 0
Kidney Damage 21 12 1000000 0
Liver Damage 14 15 1700000 0
Spleen Damage 9 11 1710000 0
Heart Damage 0 0000000 0
Free Blood in Pericardium 5 0000000 0
Brain Damage 0 0000000 0
Table 6.5.- Percent mortality of bluegill (n=25 at each distance) exposed to a 2 kg
charge of T-100 detonated underwater at 2 m depth. Independent duplicate trials are
reported. (Keevin et al. (In preparation))
Table 6.6.- Bluegill LD50 values resulting from detonation of a 2 kg charge of T-
100 at 2 m depth. Independent duplicate trials are reported. Keevin et al. (In
preparation)
1Impulse was calculated by integrating the pressure-time curve for first positive
wave.
Necropsy results for bluegill in this study agree with those of other investigators
who found the swimbladder to be the most frequently damaged organ (Christian 1973;
Faulk and Lawrence 1973; Kearns and Boyd 1965; Linton et al. 1985a; Yelverton et
al. 1975). The direction of rupture of bluegill swimbladders could not be
determined; probably due to the thin and delicate nature of the swimbladder wall
and fixation. Damage to the kidney, liver and spleen was extensive and possibly
related to the rapid contraction and expansion of the swim bladder. In bluegill,
the swimbladder is in close contact with the kidney located dorsally and the
alimentary system ventrally. Table 6.4 shows that at distances where swimbladder
ruptures occur, other internal damages also occur (i.e., liver kidney and spleen),
and as the rate of swimbladder damage falls so do other injuries.
Ogawa et al.(1978) found that in fish with less well-developed swimbladders,
neither the kidneys nor air bladder are injured, indicating that the presence of a
swimbladder plays an important role with reference to injuries to other organ
systems. Wiley et al. (1981) suggested that susceptibility to injury was related to
body rigidity and swimbladder position relative to other organs. For example,
oyster toadfish (Opsanus tau), a species which is extremely resistant to damage,
have swimbladders that are less adherent to the dorsal body wall and therefore were
DISTANCE (Meters) FROM EXPLOSION
30.0 32.5 35.0 37.5 40.0 42.5 45.0 47.5 Control
SHOT 1
Percent Mortality 100.0 88.0 92.0 96.0 36.0 0.0 0.0 0.0 0.0
SHOT 2
Percent Mortality 96.0 100.0 100.0 80.0 40.0 12.0 0.0 0.0 0.0
LD50 Lower Limit Upper Limit
SHOT 1
Distance(m) 38.96 37.95 40.00
Peak Pressure(KPa) 625.80 591.60 661.90
Impulse(Pa-s)144.09 39.00 49.00
Energy Flux Density(J/m2 )33.30 29.40 37.60
SHOT 2
Distance(m) 39.23 38.21 40.28
Peak Pressure(KPa) 583.23 131.00 957.94
Impulse(Pa-s)149.00 46.30 51.80
Energy Flux Density(J/m2 )28.00 10.42 56.06
less in direct contact with the kidney. Wiley et al. (1981) suggested that the
thick walls of their swimbladders reduced the incidence of rupture and the inherent
flexibility of their bodies cushioned the internal organs from damage caused by
rapid fluctuations in the size of the swimbladders. Incidence of internal
hemorrhaging and bruising of the kidneys was much greater in the more rigidly built
fish in which the swimbladder was closely adherent to the kidney. Apparently, the
rapid expansion and contraction of the swimbladder is also responsible for damage
to other organs. Knight (1907) and Fitch and Young (1948) have also suggested that
the thickness of the swimbladder may also be an important factor in determining
mortality levels, with species having thin swimbladders being most susceptible to
blasts.
Teleki and Chamberlain (1978) suggested that physoclistous fish species (swim
bladder attached to the circulatory system allowing slow change in bladder
pressure) are more sensitive to blast pressures than either physostomus species
(swim bladder attached to the esophagus allowing quick release of air) or species
with no swimbladder. In their testing program, pumpkinseed (Lepomis gibbosus),
white bass (Morone chrysops), and crappie (Pomoxis annularis), all physoclistic,
were the most sensitive to blasting than physostomus species i.e., rainbow trout
(Salmo gairdneri), white suckers (Catostomus commersoni), and yellow bullheads
(Ictalurus natalis). In tests with a number of species, Yelverton et al. (1975)
concluded there was little or no difference between the impulse required for 50%
mortality for fish having dusted swimbladders and fish having non-ducted
swimbladders. Christian (1973) suggested that intuitively he would expect that at
the outer limits of the lethal zone a physostomous species might be more capable of
adapting to the pressure changes than would a physoclistous species, but that under
more severe shock conditions the two types might suffer about equal damage. He also
stated that it may not matter in the explosion damage process, since pressure
changes occur within microseconds, too rapidly for the normal gas-exchange
mechanisms to operate. Baxter et al. (1982) suggested that the small duct of a
physostomous species would not pass a significant amount of gas during the transit
of shock waves.
External damage appears to be species specific and related to the magnitude of the
pressure wave (e.g., charge size and distance from explosion). Linton et al.
(1985a) noted that external injury to black drum (Pogonias cromis) exposed to
primacord detonations was minor, whereas internal injury was substantial. The only
visible external damage was loss of opercular scales. Red drum (Sciaenops
ocellatus) exhibited no visible external injuries. The presence of a swimbladder
may be a causative factor of some types of external damage. A bright red circle was
observed on both sides of bluegill, presumably dermal capillary rupture caused by
the rapid expansion and contraction of the swim bladder (Keevin et al. In
preparation). After preservation, the circle appeared as an area of pallor or
discoloration. Tyler (1960) observed a loss of small patches of scales in the
vicinity of the swimbladder from each side of red salmon (Oncorhynchus nerka)
exposed to 40-percent gelatin dynamite charges.
EFFECT OF FISH SIZE
There is limited information that fish weight may also influence vulnerability.
Yelverton et al. (1975) tested a number of different fish species and found that a
higher impulse was required to kill larger fish (body weight) than small fish. This
was true both within a species and between species tested. Other factors such as
age, general health, water temperature, and reproductive condition may influence
mortality.
EFFECTS OF UNDERWATER EXPLOSIONS ON LARVAL FISH AND EGGS
Kostyuchenko (1973) exposed anchovy, blue runner and carucian carp eggs to a 50 g
charge of TNT. The TNT charge produced structural abnormalities in the anchovy eggs
at a distance of 2 to 20 m from the source, in the blue runner eggs up to 10 m
away, and in the crucian carp eggs up to 5 m away. Only 20% of the eggs used in the
experiment survived at a distance of 2 m, 58.2% at a distance of 10 m; only at a
distance of 20 m were there no sharp differences from the control.
The "Guidelines for the Use of Explosives in Canadian Fisheries Waters" (Wright In
press) have a guideline for protecting eggs on spawning beds. "No explosive may be
use that produces, or is likely to produce, a peak particle velocity greater than
13 mm-sec-1 in a spawning bed during egg incubation." The guidelines provide the
following table of set-back distances to achieve the standard (Table 6.7).
There have been no comprehensive studies determining the relationship between
underwater pressures and larval fish mortality.
Table 6.7.- Set-back distance (meters) from center of detonation to spawning
habitat to achieve 13mm-sec-1 standard for all types of substrate. (From Wright (In
press))
SUBLETHAL INTERNAL DAMAGE TO FISH FROM UNDERWATER EXPLOSIONS
Sverdrup et al. (1994) conducted laboratory studies to determine the effects of
underwater explosions on the vascular endothelium and on primary stress hormones of
farmed Atlantic salmon (Salmo salar
)
. Acclimated salmon were exposed to a series of
10 underwater explosions over 70 min. each of 2 MPa in pressure amplitude, in a
laboratory tank. No mortality occurred immediately or during the subsequent 7 days
of observation.
Structurally, the vascular endothelium of the ventral aorta and the coeliaco
mesenteric artery revealed signs of injury within the first 30 min after the
experimental shock. The endothelial impairment was temporary, persisting throughout
the first days while being restored after 1 week.
Functionally, the cholinergic and adrenergic vasoconstrictor responses in the
coeliaco mesenteric artery were markedly reduced during the first day after the
shock. The loss of structural integrity and the reduced functional response
indicated a temporary impairment of the vascular endothelium in response to the
underwater explosion.
The primary stress hormones, adrenaline and cortical, were not immediately elevated
in plasma, but revealed different patterns of delayed increases. The head kidney
content of catecholamines was not altered by the acoustic shock, while the atrial
uptake of both catecholamines declined progressively during the 48 h of
observation. Plasma chloride was not affected.
Explosive Charge
Weight (kg) 0.5 1 5 10 25 50 100
Set-back Distance
(m) 15 20 45 65 100 143 200
UNDERWATER EXPLOSIVE FISH MORTALITY MODELS
Based on predictive equations, the kill radius for an underwater explosion can be
calculated prior to commencement of the project. Three such predictive models are
available: the energy flux density model (Sakaguchi et al. 1976), the impulse
strength model (Baxter et al. 1982; Hill 1978; Munday et al. 1986; Wright 1982;
Yelverton et al. 1975), and the dynamical model (Wiley et al. 1981). A user-
friendly computer program was developed by COASTLINE Environmental Services Ltd.
(1986) that uses the impulse strength model (IBlast) and the energy flux energy
flux density model (EBlast) to predict effects for both midwater charges and
charges that are drilled and buried in rock substrate. Although there are problems
associated with these models (Hempen and Keevin 1995; Keevin 1995), they do give an
approximation of the potential fish kill radius of a given explosive charge.
O'Keeffe (1984) and Young (1991) provide kill probability contours for various fish
sizes and charge weights based on the predicted results obtained by the dynamical
model.
Young (1991) developed an equation to estimate safe ranges for fish with
swimbladders. He noted that the prediction model was based on experimental data and
an injury mechanism related to the response of swimbladder gas to the direct and
reflected shock waves. Estimated range of vulnerability based on 90 percent
probability of survival at a relatively shallow depth. He indicated that small fish
are more vulnerable than large fish and fish near the surface are more vulnerable
than deep fish.
Young (1991) suggested that the following fish (with swimbladder) safe range (Table
6.8) be used for preliminary planning purposes. He suggestedthat the equations are
technically correct but they do not cover all possible conditions or marine
environments.
Table 6.8.- Safety zone range calculations for fish with swimbladders. (From Young
1991)
ENGLISH MEASUREMENTS
Rsafe = 95 Wf-0.13W0.28dW0.22
------------------------------
Rsafe = Safe range in feet
W = Weight of explosive in pounds
Wf = Weight of fish in pounds
dW = Depth of burst in feet
METRIC MEASUREMENTS (Conversions)
Rsafe = 43 Wf-0.13W0.28dW0.22
------------------------------
Rsafe = Safe range in feet
W = Weight of explosive in pounds
Wf = Weight of fish in pounds
dW = Depth of burst in feet
Hill (1978) developed a model to predict lethal ranges for fish based on data in
Yelverton et al. (1973). The model has been reproduced in Wright (1982) and has
been reproduced here. Hill (1978) indicated that the model will "underestimate
lethal ranges if the water depth is shallow (less than five times either the
detonation depth or target depth, whichever is greater), and the bottom is rocky.
In cases like this, there may be a considerable bottom-reflected shock wave which
will increase the impulse at any point. If the charge is to be detonated under
thick ice, a positive rather than negative surface-reflected wave may result. Once
again, this increases the impulse and, in turn, the lethal range. Under these
conditions, the calculated lethal ranges or safe distance should be doubled to
ensure a conservative safety margin."
To use Hill's model to calculate lethal ranges or safe distance, the following
information is required:
1. typical size (weight) of the fish species likely to be in the area,
2. depth of the target fish,
3. depth of detonation of the charge, and
4. weight of the charge.
To determine the slant range, the following steps are required:
1. From Figure 6.1, determine the impulse (I) corresponding to the assumed damage
level.
2. Calculate the scaled impulse by dividing the impulse found in Step 1 by the
cube root of the charge weight.
(Isc = I/wt l/3 )
3. Calculate parameter 'A', which is derived from the depth of the target fish,
the depth of the detonation and the charge weight such that:
4. From Figure 6.2 find the best-fit curve to the calculated value of 'A' and
using this curve, determine the value of the Scaled Range (Rsc) corresponding
to the Scaled Impulse (ISE ) determined in Step 2.
5. Calculate the range (R) in meters by multiplying the Scaled Range by cube root
of the charge weight.
R(m) = Rsc x charge wtl/3
A = target depth (m) x detonation depth (m)
charge weight (kg)2/3
Figure 6.1.-Lethal impulse versus weight for fish (from Hill ; after Yelverton et
al. 1975).
Figure 6.2.-Curves for calculating lethal range from impulse (from Hill 1978 after
Yelverton et al. 1975).
EXAMPLE CALCULATION
For instructive purposes Wright (1982) provides the following sample calculation
based on Hill's (1978) model.
What is the lethal range (50% mortality) for a 5 kg charge, detonated at a depth of
5 m? The fish in the area are Pacific herring Clupea harengus pallasii weighing 300
g, feeding on zooplankton at depths shallower than 10 m.
Weight of target fish = 300 g
Depth of target fish = 10 m
Depth of detonation = 5 m
Weight of charge = 5 kg
1. From Figure 6.1, an impulse of 2.3 bar-msec causes 50% mortality to 300 g
fish;
2. The scaled impulse is calculated
impulse =2.3 = 1.35
(weight of charge)1/3 51/3
3. Calculate the parameter 'A' using 10 m as the target depth This is a worst
case since fish at shallow depth will experience a lower, less damaging
impulse:
Therefore, we use the curve for A = 20 in Figure 6.2.
4. Using the curve A = 20 in Figure 6.2 the scaled range corresponding to a
scaled impulse of 1.35 will be 48.
5. Lethal range is given by:
R1 = scaled range x charge weight1/3
= 48 x 51/3 = 82.1 m
Thus, 50% of all 300 g Pacific herring at depths of 10 m and at 82.1 m from the
explosion will be killed outright.
Table 6.9 lists those factors which potentially influence fish mortality modeling.
Development of a precise model would add little to the accuracy of mortality
predictions, since fish community structure (species specific mortality), precise
fish location in the water column and size would not be known with any accuracy. At
best, a "worst case" impact assessment provides a conservative prediction of
mortality. As such, the impulse or energy flux density models may be adequate for
those purposes.
Table 6.9.- Parameters that can affect fish mortality making precise predictions of
mortality difficult (From Keevin (1995)).
Biological Parameters
1. Depth of fish
2. Weight of fish
3. Species specific mortality
Environmental Parameters
1. Air-water roughness
2. Water-bottom roughness
3. Water/bottom acoustic impedance (bottom type)
4. Water temperature
Explosive Parameters
1. Depth of explosive
2. Relative bulk strength of explosive
3. Surface, mid-column, or drillhole shot
4. Pressure reduction from confined shot
A= target depth x detonation depth =10 x 5 = 17.1
52/3
(charge weight)2/3
Data Acquisition Parameters
1. Accuracy of pressure transducers and recording equipment
2. Pressure wave processing techniques
3. Standardization of pressure waveform calculations
MITIGATION TECHNIQUES TO PROTECT FISH FROM UNDERWATER EXPLOSIONS
Mitigation techniques are described in detail in Chapter 8.
CHAPTER 7
THE ENVIRONMENTAL EFFECTS OF
UNDERWATER EXPLOSIONS:
MARINE MAMMALS
INTRODUCTION
In mammals, gas containing organs (e.g., lungs, intestinal tract) are most affected
by underwater detonation of explosives (Cameron, Short and Wakeley 1943; Clark and
Ward 1943). Hill (1978) and Ketten (1995) provide the most recent reviews of
existing literature.
INJURY AND MORTALITY OF MARINE MAMMALS EXPOSED TO UNDERWATER EXPLOSIONS
The potential for marine mammal mortality has been documented in the scientific
literature. Fitch and Young (1948) indicated that on at least three occasions
California sea lions (Zalophus californianus) were killed by underwater explosions
used in geophysical survey work. California grey whales (Rhachianects glaucus) were
seemingly unaffected and were not even frightened from the area. No information was
provided on the location of the charge (open water or jet shot), size of the
charge, or distance from the charge. Fur seals were reportedly killed by an 11.4 kg
dynamite charge exploded 23 m away (H. F. Hanson, in Wright 1982). Reiter (1981)
reported without further details that "there was evidence of [fur] seals....killed
from concussion in the immediate area of demolition" when a grounded ship was
broken up by about 454 kg of explosives.
Sea otter studies done in association with underground nuclear tests have provided
data on the susceptibility of marine mammals to shock waves. Wright (1971) reported
that sea otters (Enhydra lutris)were injured by pressures of 100 psi (0.69 MPa) and
killed outright by 300 psi (2.07 MPa).
Richmond et al. (1973) and Yelverton et al. (1973) conducted a series of tests to
assess the effects of underwater explosions on injury using sheep, dogs, and
monkeys. Based on the results of their studies, Yelverton et al. (1993) developed
underwater-blast criteria for aquatic and marine mammals (Table 7.1). An impulse of
40 psi-msec (275.8 Pa-s) would result in a high incidence of moderately severe
immersion-bast injuries including a high probability of eardrum rupture. They
suggested at that impulse the animals should recover on their own. An impulse of 20
psi-msec (137.9 Pa-s) would cause slight blast injuries and a high incidence of
eardrum rupture. An impulse of 5 psi-msec (34.5 Pa-s) should not cause any injury
and can be considered a safe level for mammals.
Richmond et al. (1973) also ran a series of tests with dogs beneath the surface to
evaluate eardrum rupture. A probit analysis of the data yielded an impulse of 22.6
psi-msec (155.8 Pa-s) for 50% eardrum rupture. Yelverton and Richmond suggested
that impulse (integral pat) in the underwater blast wave was the parameter that
governed biological damage and not peak pressure of energy.
Table 7.1. Underwater-blast damage criteria for mammals diving beneath the water
surface (From Yelverton et al. 1973).
Young (1991) developed equations to estimate marine mammal safe ranges based on
experiments with land mammals, presumably Richmond et al. (1973) and Yelverton et
al. (1973). Injury was related to the response of air cavities, such as the lungs
and bubbles in the intestines, to the shock wave. The estimated mammal safe ranges
were based on absence of injury. Young (1991) suggested that the following marine
mammal safe ranges (Table 7.2) be used for preliminary planning purposes. He
suggested that the equations are technically correct but they do not cover all
possible conditions or marine environments.
Table 7.2. Marine mammal safety zone range calculations (From Young 1991)
R = Range in feet
W = Weight of explosive in pounds
dw = Depth of burst in feet
R = Range in meters
W = Weight of explosive in kg
dw = Depth of burst in meters
Hill (1978) developed a model to predict lethal ranges for marine mammals based on
data in Yelverton et al. (1975). The model has been reproduced in Wright (1982) and
has been reproduced here. Hill (1978) indicated that the model Will "underestimate
lethal ranges if the water depth is shallow (less than five times either the
detonation depth or target depth, whichever is greater), and the bottom is rocky.
In cases 1lke this, there may be a considerable bottom-reflected shock wave which
will increase the impulse at any point. If the charge is to be detonated under
thick ice, a positive rather than negative surface-reflected wave may result. Once
again, this increases the impulse and, in turn, the lethal range. Under these
Impulse Criteria
psi-msec kPa-sec
40 275.8 No mortality. High incidence of
moderately severe blast injuries
i
ncluding eardrum rupture. Animals should
recover on their own.
20 137.9 High incidence of slight blast injuries
including eardrum rupture. Animals would
recover on their own.
10 69.0 Low incidence of trivial blast injuries.
No eardrum ruptures.
5 34.5 Safe level. No injuries.
ENGLISH MEASUREMENT
Calf Porpoise, 200-ft dwRep = 578 W0.28
Adult Porpoise, 200-ft dwRap = 434 W0.28
20-ft Whale, 200-ft dwRw = 327 W0.28
METRIC MEASUREMENTS (Conversions)
Calf Porpoise, 61.0-meters dwRep (m) = 220 W0.28 (kg)
Adult Porpoise, 61.0-meters dwRap(m) = 165 W0.28(kg)
20-ft Whale, 61.0-meters dwRw (m) = 124 W0.28 (kg)
conditions, the calculated lethal ranges or safe distance should be doubled to
ensure a conservative safety margin."
To use Hill's model to calculate lethal ranges or safe distance, the following
information is required:
1. depth of the target mammal;
2. depth of detonation of the charge, and
3. weight of the charge.
To determine the range, the following steps are required:
1. Determine the impulse (I) corresponding to the degree of protection required
for mammals from Table 7.1.
2. Calculate the scaled impulse by dividing the impulse found in Step 1 by the
cube root of the charge weight.
(Isc = I/wtl/3 )
3. Calculate parameter 'A', which is derived from the depth of the target fish or
marine mammal, the depth of the detonation and the charge weight such that:
4. From Figure 7.1 find the best-fit curve to the calculated value of 'A' and
using this curve, determine the value of the Scaled Range (Rsc) corresponding
to the Scaled Impulse (Isc) determined in Step 2.
5. Calculate the range (R) in meters by multiplying the Scaled Range by cube root
of the charge weight.
R(m) = Rsc x charge wt1/3
EXAMPLE CALCULATION
For instructive purposes Hill (1978) provides the following sample calculation.
What is the safe distance from a 5 kg charge detonated at a depth of 5 m for ringed
seals? We wish to ensure that no harm is done to these animals by the explosion.
Noting that the seals are feeding on small crustacea, and assuming that these are
concentrated at depths less than 25 m, we can calculate the safe distance as
follows:
1. According to Table 7.1, 0.34 bar-msec is a completely safe impulse level for
submerged mammals;
2. The scaled impulse is calculated:
0.34/s1/3 = 0.2
3. The quantity 'A' is calculated:
A = (5 x 25)/52/3 =42.7
A= target depth (m) x detonation depth (m)
(charge weight (kg)2/3
4. Using the curve for A =40 in Figure 7.1, we find that a scaled range of 210
corresponds to a scaled impulse of 0.2. Therefore, the safe distance is given
by :
RS = 210 x 51/3 = 359 m
Provided the charge is detonated at least 359 m from the seals, there should be no
risk of damage.
Figure 7.1.-Curves for calculating lethal range from impulse (From Hill 1978 after
Yelverton et al. 1975).
Ketten (1995) suggested that for submerged terrestrial mammals, lethal injuries
occurred at overpressures > 55 kPa and minimal injury limits coincided with
overpressures of 0.5 to 1 kPa. These values seem very conservative when compared
with Richmond et al. (1973) and Yelverton et al. (1973). For example, Richmond et
al. (1973) found no internal damage in sheep exposed to 612 kPa from a 0.5 lb (225
g) charge of Pentolite at 10 ft (3.0 m) depth on sheep at 1 ft (305 mm) depth, 110
ft (33.5 m) from explosion. In addition, they found no ear damage in dogs with
theirs at 1 ft depths (305 mm), exposed to 1.478 kPa from a 1ob (454 g( charge of
TNT dtonated at 10 ft (3.0 m) depth, 60 ft (18.3 m) from the subjects.
BEHAVIORAL EFFECTS OF UNDERWATER BLASTING ON MARINE MAMMALS
There is little published information on the behavioral effects of underwater
blasting on marine mammals. Todd et al. (1996) found that humpback whales
(Megaptera novaeangliae) showed little behavioral reaction to construction
detonations in terms of decreased residency, overall movement, or general behavior.
However, they found increased entrapment of humpbacks in fishing gear. Exposure to
the construction explosions may have affected the hearing threshold of humpbacks,
thus decreasing their ability to use net-produced acoustic cues to avoid net
collisions. The probability of an entrapment occurring within 2 days or less of an
explosion was 0.38, which was significantly greater than the calculated rate of
0.077 for entrapments occurring outside of a 2-day lag (z test of independent
probabilities, p < 0.0001).
MITIGATION TECHNIQUES TO PROTECT MARINE MAMMALS FROM UNDERWATER EXPLOSIONS
Mitigation techniques described for fish are also applicable to marine mammals (see
Chapter 8). Any attempt to reduce the pressure waveform will reduce the potential
kill zone of marine mammals.
As with sea turtles, the simplest method to protect marine mammals from underwater
explosions is to avoid periods when they are in the blasting zone. Avoidance of
marine mammals can be achieved in two manners. Depending on location, there may be
time periods when they are not in the project area due to their life history
characteristics (e.g. migration patterns). This can be determined by coordination
with the state natural resource agency or National Marine Fisheries Service.
Blasting can be planned during time periods of low marine mammal abundance. If
marine mammals are potentially in the area during blasting, an aerial survey using
a light plane or helicopter can be conducted prior to detonation. If they are
observed in the project area, blasting can be halted until they move out of a pre-
determined blast zone.
An example of the above strategy is in place for explosive removal of oil and gas
structures in state and federal waters of the Gulf of Mexico (Gitschlag 1990). For
at least 48 hr prior to detonation, National Marine Fisheries Service observers
watch for marine from the surface. Helicopter aerial surveys within a mile radius
of the removal site are conducted 30 min prior to and after detonation (Gitschlag
and Herczeg 1994). If marine mammals are observed, detonations are delayed until
they have left the area.
"Seal bombs" and shell crackers have been used to "scare" marine mammals from the
blast zone prior to detonating the large explosion. They have been used in attempts
to prevent harbor seals, sea lions and other mammals from feeding on fish (e.g.,
Mate and Harvey 1987). These pyrotechnic devices expose the animals to sharp noise
pulses of varying intensities. Seal bombs explode a few meters below the surface.
Shell crackers fired from shotguns and several types of smaller pyrotechnics fired
from pistols can explode above, at or below the surface. The general consensus from
experience with these devices on the U.S. west coast is that, when first used, they
startle the animals and often induce them to move away from feeding areas
temporarily. However, the avoidance response wanes when the animals learn that the
noise pulses are not harmful. Thereafter, some seals tolerate quite intense
underwater sound in order to gain access to food (Mate and Harvey 1987).
There is a potential for marine mammal mortality resulting from the use of "seal
bombs" as repelling charges. A similar device killed a human diver when it exploded
approximately 0.3 m from his head (Hirsch and Ommaya 1972). Myrick et al. (1990)
concluded that one Class-C device will cause injury when detonated within 0.5-
0
.6 m
of a dolphin. They estimate a safe standoff distance of 4 m or more, depending on
explosive type and depth.
CHAPTER 8
MITIGATING THE ADVERSE ENVIRONMENTAL EFFECTS
OF UNDERWATER EXPLOSIONS ON FISH
INTRODUCTION
Development of effective mitigation strategies requires two components: a working
knowledge of explosives and their impacts; and information on current mitigation
techniques related to explosives, well grounded in practice theory. However, this
is difficult because information about explosives and mitigative measures is often
not widely accessible (reports, symposium proceedings, obscure scientific
publications). The purpose of this chapter is to review natural resource agency
mitigation policies; compare recommendations to available scientific literature on
underwater explosive effects; and, develop a series of generic mitigation
recommendations which will be useful to both natural resource planners and the
blaster in developing strategies to reduce adverse effects of explosive use in
aquatic ecosystems. This review is based on a recent publication by Keevin (In
press) reviewing state natural resource agency mitigation policies.
A questionnaire was sent to fish and wildlife agency directors in each state to
determine current agency policies on the use of explosives for legitimate purposes
within waters under their jurisdiction (Keevin In press). Natural resource agencies
were asked the following question concerning mitigation requirements within their
state:
"Does your agency require a person/company to apply mitigative techniques
to reduce the potential for mortality to aquatic life during underwater
blasting? If so, what mitigative techniques are required?"
In addition, the Canadian Department of Fisheries and Oceans' draft national
guidelines, "Guidelines for the Use of Explosives in Canadian Fisheries Waters",
were also reviewed since they provide mitigation recommendations for the use of
explosives underwater.
Seventeen mitigation measures sere identified and are summarized in Table 8.1. They
fall into three general categories: 1) review of the explosive design and provide
mitigation recommendations based on that design; 2) evaluation of the potential
impact and mitigative recommendations based on biological considerations; and, 3)
evaluation of potential impact and require physical measures (e.g., bubble
curtains, physical barriers, etc.) to minimize impacts. Each mitigation
recommendation is reviewed based on existing literature and/or the physics of
explosions. Although the mitigation recommendations were developed for fish, they
are applicable to any organisms (e.g., marine mammals, sea turtles, etc.). However,
specific mitigation recommendations are provided for non-fish species within their
respective chapters.
Table 8.1.- Summary of State Natural Resource Agency Responses. (From Keevin (In
press))
AL AK AZ AR CA CO CT DE FL GA
BLASTING DESIGN
Agency Review --Y----------------
Charge Type -- -- -- -- -- -- -- -- -- --
Charge Weight -- Y -- -- Y -- -- -- -- --
Shaped Charges -- -- -- -- -- -- -- -- -- --
Delays --Y----------------
Decking -- -- -- -- -- -- -- -- -- --
Stemming -- -- -- -- -- -- -- -- -- --
BIOLOGICAL CRITERIA
Mortality Models --Y----------------
Observers Y Y -- Y Y -- Y -- -- --
Compensation Y------------------
Sampling -- -- -- -- Y -- -- -- -- --
Seasonal Restrict -- Y -- -- -- -- Y -- -- --
PHYSICAL MITIGATION FEATURES
Repelling Charges --N----------------
Noise -- --Y------------
Bubble Curtain --N----------------
Physical Barriers -- -- -- -- -- -- Y -- -- --
HI ID IL IN IA KS KY LA ME MD
BLASTING DESIGN
Agency Review Y----------------Y
Charge Type Y------------------
Charge Weight Y------------Y--Y
Shaped Charges -- -- -- -- -- -- -- -- -- --
Delays -- -- -- -- -- -- -- -- -- --
Decking -- -- -- -- -- -- -- -- -- --
Stemming -- -- -- -- -- -- -- -- -- Y
BIOLOGICAL CRITERIA
Mortality Models -- -- -- -- -- -- -- -- -- --
Observers Y -- -- Y -- -- -- Y Y Y
Compensation -- -- -- Y -- -- Y Y -- Y
Sampling -- -- -- -- -- -- -- -- -- Y
Seasonal Restrict Y--YY------YYY
PHYSICAL MITIGATION FEATURES
Repelling Charges ----Y--------------
Noise ----Y--------------
Bubble Curtain -- -- -- -- -- -- -- -- -- --
Physical Barriers -- -- --- Y -- -- -- -- -- --
MA MI MN MS MO MT NE NV NH NJ
BLASTING DESIGN
Agency Review Y -- -- Y -- -- -- -- -- --
Charge Type Y------------------
Charge Weight -- -- -- Y -- -- -- -- -- --
Shaped Charges -- -- -- -- -- -- -- -- -- --
Delays Y------------------
Decking -- -- -- -- -- -- -- -- -- --
Stemming -- -- -- -- -- -- -- -- -- --
BIOLOGICAL CRITERIA
Mortality Models -- -- -- -- -- -- -- -- -- --
Observers -- -- -- Y Y -- -- -- -- Y
Compensation -- -- -- -- -- -- -- -- -- --
Sampling Y------------------
Seasonal Restrict -- Y -- -- Y -- -- -- Y Y
PHYSICAL MITIGATION FEATURES
Repelling Charges -- -- -- -- -- -- -- -- -- Y
Noise -- -- -- -- -- -- -- -- -- --
Bubble Curtain -- -- -- -- -- -- -- -- -- Y
Physical Barriers -- -- -- -- -- -- -- -- -- --
NM NY NC ND OH OK OR PA RI SC
BLASTING DESIGN
Agency Review -- -- -- Y -- -- Y Y -- --
Charge Type -- -- -- -- -- -- -- -- -- --
Charge Weight -- -- -- -- -- -- -- -- Y --
Shaped Charges -- -- -- -- -- -- -- -- -- --
Delays -- -- -- -- -- -- Y -- -- --
Decking -- -- -- -- -- -- -- -- -- --
Stemming -- -- -- -- -- -- -- -- -- --
BIOLOGICAL CRITERIA
Mortality Models -- -- -- -- -- -- -- -- -- --
Observers -- -- -- Y Y -- Y -- -- --
Compensation -- -- Y Y Y Y Y Y -- --
Sampling -- -- -- -- -- -- Y -- -- --
Seasonal Restrict -- Y Y -- -- -- Y Y Y --
PHYSICAL MITIGATION FEATURES
Repelling Charges -- -- -- -- -- -- -- -- Y --
Noise -- -- -- -- -- -- -- -- Y --
Bubble Curtain -- -- -- -- -- -- Y -- -- --
Physical Barriers --Y----------------
DEVELOPMENT OF MITIGATIVE STRATEGIES: THE BLASTING DESIGN
A
gency Review of Blasting Design. Eight states responded that the blaster was
required to submit a detailed blasting design for agency review prior to approval.
The Canadian Department of Fisheries and Oceans also requires detailed blasting
design information as a permit requirement.
Review prior to implementation of a project can be very effective in reducing
impacts. The first step in the review process should be to determine if there is a
need for use of explosives. Obviously, the best way to mitigate impacts of