Advanced Technical Diving

Abstract

Effective exploration of mesophotic coral ecosystems (MCEs) has been limited primarily by available technology. Although research targeting MCEs led to the development of the first electronically controlled, closed-circuit rebreather in the late 1960s to the early 1970s, it wasn’t until the 1990s that the technology was utilized extensively for MCE research. Over the years, diving techniques and technologies have gradually advanced from conventional SCUBA to open-circuit, mixed-gas diving to closed-circuit rebreathers, each progressively increasing diver safety and bottom time at depth. Over the past decade, the application of closed-circuit rebreathers for use in MCE research has increased dramatically, enabling research activities that are impractical or impossible using other technologies. When conducting advanced diving operations to study MCEs, many logistical and practical considerations must be taken into account. Trained and experienced divers and support personnel are required and must have access to appropriate equipment. Contingencies both during dives (e.g., bailout options) and in response to emergencies must be clearly defined and understood. Insights and guidelines for conducting MCE research using rebreathers are recommended based on over three decades of field experience. As scientific diving programs at more institutions continue to establish support for advanced technical diving operations, the application of this approach to MCE research will help scientists conduct work efficiently and safely.

Full text

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© Springer Nature Switzerland AG 2019
Y. Loya et al. (eds.), Mesophotic Coral Ecosystems, Coral Reefs of the World 12,
https://doi.org/10.1007/978-3-319-92735-0_50
Advanced Technical Diving
RichardL.Pyle
Abstract
Effective exploration of mesophotic coral ecosystems
(MCEs) has been limited primarily by available technol-
ogy. Although research targeting MCEs led to the devel-
opment of the rst electronically controlled, closed-circuit
rebreather in the late 1960s to the early 1970s, it wasn’t
until the 1990s that the technology was utilized exten-
sively for MCE research. Over the years, diving tech-
niques and technologies have gradually advanced from
conventional SCUBA to open-circuit, mixed-gas diving
to closed-circuit rebreathers, each progressively increas-
ing diver safety and bottom time at depth. Over the past
decade, the application of closed-circuit rebreathers for
use in MCE research has increased dramatically, enabling
research activities that are impractical or impossible using
other technologies. When conducting advanced diving
operations to study MCEs, many logistical and practical
considerations must be taken into account. Trained and
experienced divers and support personnel are required
and must have access to appropriate equipment.
Contingencies both during dives (e.g., bailout options)
and in response to emergencies must be clearly dened
and understood. Insights and guidelines for conducting
MCE research using rebreathers are recommended based
on over three decades of eld experience. As scientic
diving programs at more institutions continue to establish
support for advanced technical diving operations, the
application of this approach to MCE research will help
scientists conduct work efciently and safely.
Keywords
Mesophotic coral ecosystems · Technical diving · Trimix
· Mixed gas · Rebreather
50.1 Introduction
SCUBA is one of the most important and widely used tools
for research in reef environments (Sale 1991). With minimal
amounts of training and nancial commitment, researchers
can don SCUBA equipment and easily observe marine life
and collect biological specimens with a high degree of selec-
tivity. SCUBA equipment can easily be transported to remote
destinations, and facilities for conducting SCUBA opera-
tions are available worldwide. Moreover, SCUBA allows
researchers direct access to the environment, allowing for
more effective specimen and data collection than other tech-
nologies (Gilmore 2016).
The primary limitation of conventional air SCUBA for
use in scientic research is the maximum depth to which div-
ers can work safely. This depth limit is imposed by the physi-
ological effects of breathing elevated partial pressures of
oxygen and nitrogen, the primary constituents of air. The
American Academy of Underwater Sciences (AAUS), which
sets guidelines for scientic diving policies followed by
many US institutions (and many institutions in other coun-
tries), establishes a maximum working depth of 58m (190 ft)
for diving on air (AAUS 2016). Such limits notwithstanding,
undersea research efforts using conventional SCUBA have
included brief excursions in excess of 61m (200 ft) and in
some cases as deep as 91 m (300 ft) or more (Pyle 1991;
Gilliam and Von Maier 1992; Somers 1993). In general,
however, breathing air at depths greater than about 50 m
(165ft) is considered too dangerous for scientic research.
The depth limitations of conventional air SCUBA result
from the physiological consequences of increased dissolved
partial pressures of oxygen and nitrogen in the diver’s blood.
Specically, breathing elevated concentrations of oxygen
can induce seizures and pulmonary problems (Bean 1945;
Yarbrough etal. 1947; Lambertsen 1978; Clark 1982), and
breathing elevated concentrations of nitrogen causes nitro-
gen narcosis, which may induce symptoms analogous to
alcohol inebriation such as impaired mental abilities, loss of
R. L. Pyle (*)
Bernice P.Bishop Museum, Honolulu, HI, USA
e-mail: deepreef@bishopmuseum.org
50

960
short-term memory, slowed reaction time, and occasionally
euphoria (Bennett 1982, 1990). Additionally, breathing ele-
vated partial pressures of nitrogen for prolonged periods of
time without adequate decompression can lead to decom-
pression illness or the “bends,” which may cause pain in the
joints, nausea, numbness, and paralysis and may result in
death.
To mitigate these problems, mixed-gas diving techniques,
incorporating reduced concentrations of oxygen and replac-
ing nitrogen with helium in the breathing mixture, were rst
developed in the 1920s (Bennett 1982; Gilliam and Taylor
1993). Commercial divers breathing mixtures involving
helium have attained depths in excess of 390m (1280 ft) and
simulated depths of 675m (2215 ft) (Kindwall 1990). A sim-
ulated depth of 701m (2300 ft) was achieved by the French
commercial diving company COMEX, using gas mixtures
involving hydrogen (Lafay etal. 1995). Throughout most of
the twentieth century, the use of mixed-gas diving was
limited to military and commercial diving operations due
primarily to the experimental nature of the techniques.
Additionally, because the volume of breathing gas consumed
by divers increases with depth (e.g., at a depth of 90 m
(295ft), each breath consumes ten times as much gas as at
the surface), most commercial mixed-gas diving operations
utilize surface-supplied, helium-reclaiming breathing sys-
tems. However, these systems are generally too expensive
for scientic researchers (Lang and Smith 2006).
The use of mixed-gas diving techniques for research on
what are now referred to as mesophotic coral ecosystems
(MCEs; 30–150m; Hinderstein etal. 2010) was pioneered
by Walter Starck, who along with John Kanwisher developed
the rst electronically controlled, closed-circuit rebreather,
called the Electrolung (Starck 1973). Rebreathers, which
recirculate the breathing gas while removing exhaled carbon
dioxide and replenishing metabolized oxygen, obviated the
need for expensive surface-supplied gas and associated
logistics and enabled some of the earliest documentation of
MCEs (Tzimoulis 1970; Starck and Starck 1972). Although
this work inspired other researchers to follow suit (Colin
1997; Wicklund 2011; Gilmore 2016), very little progress
was made with respect to advanced diving technologies for
exploration of MCEs until the 1980s.
Starting in the mid-1980s, an increasing number of non-
military, noncommercial divers began incorporating helium
into their breathing mixtures to extend the depth limitations
of SCUBA (Stone 1989a, 1990; Mount and Gilliam 1993).
This collective effort came to be known as “technical diving”
(Menduno 1991a, b) and steadily grew in popularity over the
course of the 1990s and 2000s as formalized training pro-
grams were developed and specialized equipment became
increasingly available. During the early period of technical
diving, the majority of its utilization in scientic research
was focused on archeological, geological, and speleological
projects (Palmer 1990; Somers 1993), with only a few proj-
ects focused on MCEs (Pyle 1991, 1992a). As the popularity
of technical diving began expanding during the late 1980s
and early 1990s, it mostly involved the use of open-circuit,
mixed-gas diving technology, incorporating standard
SCUBA cylinders and regulators containing different gas
mixtures, particularly trimix (mixtures containing oxygen,
helium, and nitrogen), nitrox (nitrogen and oxygen mixtures
enriched with additional oxygen content), and pure oxygen.
An example of an open-circuit trimix conguration designed
specically for exploring MCEs is shown in Fig. 50.1
(Pyle 1992b). The primary difculty in designing such rigs
for deep diving is balancing the necessary quantities of
breathing gas and equipment redundancy in a system that is
also manageable underwater.
The fundamental problem with open-circuit diving is that
expired gas is exhaled and lost in the form of bubbles. The
length of time a cylinder of compressed gas can support a
diver decreases with increasing depth. Thus, a single cylinder
containing the equivalent of 2265L (80 ft3) of compressed
breathing gas would provide an average diver with about 30
breaths at a depth of 90m (295 ft) (Stone 1989b). The same
cylinder lled with 100% oxygen would support the meta-
bolic needs of a diver for about 2 days, regardless of depth
(if none is wasted). The open-circuit system shown in
Fig. 50.1 incorporates four cylinders containing more than
7000L (>250 ft3) of compressed gas yet only allows about
12min of working dive time at a depth of 100m (328 ft) (Pyle
1992b). The implications of such inefcient gas consumption
present signicant logistical and nancial challenges, espe-
cially when conducting eld expeditions to remote locations.
For example, during a 2009 expedition to the Northwestern
Hawaiian Islands involving open-circuit, mixed-gas diving, a
team of divers conducting a total of 111 dives to depths of
51–76m (170–250ft) with bottom times of less than 20min
each consumed over 280,000 L (>10,000 ft3) of helium
(Kosaki et al. 2010). This represents more than 125 L
(>4.5ft3) of helium per minute of bottom time.
To increase bottom time and decrease the amount of
equipment and gas required for diving at depths >50 m
(>165ft), many in the technical diving community, including
MCE researchers, began using closed-circuit rebreathers.
Rebreather technology (Fig.50.2) differs from open-circuit
SCUBA in that exhaled gas is recirculated through a
breathing loop, processed, and returned to the diver.
Exhaled carbon dioxide is removed from the breathing loop
when it is passed through a chemical “scrubbing” agent (e.g.,
Sofnolime® or other alkaline hydroxides), and oxygen is
added to the breathing mixture when needed (as determined
by electronic oxygen sensors). Rebreathers offer several
important advantages over open-circuit systems (Stone
1989b; Hamilton 1990; Bozanic 2002). The rst advantage is
that very little gas is wasted because rebreathers recirculate
R. L. Pyle

961
Fig. 50.1 Schematic of an open-circuit, mixed-gas diving system designed specically for conducting research on MCEs, incorporating four
cylinders and ve regulators. (After Pyle 1992b)
Fig. 50.2 Richard Pyle using an advanced closed-circuit rebreather to conduct research on MCEs at a depth of 110m in Vanuatu. (Photo credit:
J.L.Earle, can be reused under the CC BY license)
50 Advanced Technical Diving

962
the breathing gas. Gas consumption rates depend on the oxy-
gen metabolism rate of the individual diver and are indepen-
dent of depth. Thus, increased gas efciency greatly extends
the depth and time ranges of diving operations and dramati-
cally reduces the cost and logistics of securing sufcient
quantities of helium and oxygen during eld operations.
Parrish and Pyle (2002) directly compared open-circuit
mixed-gas diving and rebreather diving logistics and found
that open-circuit divers required four times as much time to
prepare equipment, consumed 17 times as much gas, and
cost seven times more in total expendables (e.g., breathing
gas and carbon dioxide scrubbing material). The reported
difference in gas consumption between open- and closed-
circuit diving is likely more conservative than actual con-
sumption in eld operations, and the difference increases
substantially as the depth increases.
The second advantage of rebreathers is that the breathing
mixture is dynamic, maintaining a constant oxygen partial
pressure at any depth. This minimizes the non-oxygen frac-
tion of the breathing gas across different depths and thereby
minimizes the time required for decompression for a given
dive prole. Open-circuit divers have been shown to incur up
to 70% more decompression time than divers using closed-
circuit rebreathers with the same dive proles to depths of
58–69m (190–226ft), contributing to an eightfold increase
in overall support time (including time spent decompressing,
as well as preparing and maintaining equipment) for a given
amount of research time with open-circuit diving compared
to closed-circuit diving (Parrish and Pyle 2002).
The third advantage of rebreathers, which can be of par-
ticular importance for undersea biological research, is that
no bubbles are exhaled into the water during normal breath-
ing. This allows for virtually silent operation, enabling close
observation of marine life with minimal disturbance. For
example, the silent operation of rebreathers allowed divers to
observe the behavior of cephalopods and shes (Hanlon
et al. 1982) and for the rst time mating of hammerhead
sharks (Hall 1990). In general, rebreathers have been shown
to enhance the effectiveness, convenience, and safety of
underwater biological research (Collette and Earle 1972;
Pyle etal. 2016b).
Following the pioneering work by Walter Starck and oth-
ers in the early-to-mid 1970s, rebreathers were not widely
used by diving scientists for any application (including MCE
research) for over two decades. This was largely due to a
general lack of commercially produced rebreather systems
outside of the military, a dearth of formal training standards,
a reputation for unreliability, and the relatively high cost and
logistical difculty in obtaining and maintaining rebreathers.
Beginning in the 1990s, rebreathers became increasingly
available from several manufacturers and gradually started to
be used by the scientic diving community for biological
research (e.g., Pyle 1996a, b, c, 1998, 1999a, 2000; Lehnert
and Fischer 1999; Lobel 2001; Parrish and Pyle 2002; Pence
and Pyle 2002). Toward the late 2000s, driven in large part
by broader adoption of policies and standards developed by
a few advanced scientic diving programs and associated
workshops (Hamilton etal. 1999), a new surge of research
on MCEs using rebreather technology began to be published
(e.g., Nemeth etal. 2008; Sherman etal. 2009). In the 7-year
period from 2010 to 2017, there were more than 100 papers
published on MCE research using rebreathers, compared to
only ~30 over the 40-year period from 1970 to 2009. Starting
in 2008–2009, there was a sharp increase in the number of
researchers in different geographic regions using closed-
circuit rebreathers for scientic research. Although a few
published studies conducted by these researchers focused on
the advantages of bubble-free diving (e.g., Tomoleoni etal.
2012; Lindeld etal. 2014; Gray et al. 2016; Lopes 2017),
the vast majority of researchers used rebreathers to investi-
gate MCEs.
As rebreather technology continues to improve (Pyle
2016), and more scientic diving organizations incorporate
them into their programs (Sellers 2016), rebreathers will
continue to increase in importance as a tool for MCE research
(Pyle et al. 2016a). This chapter provides general insights
and guidelines on using advanced technical diving tech-
niques for MCE research, specically concerning diving
safety and standards, logistics, equipment options, and con-
tingency planning, and is largely based on nearly three
decades of experience during eld expeditions to many loca-
tions in the Pacic Ocean. This chapter is meant to comple-
ment existing diving standards, regulations, and training and
not serve as a replacement for such.
50.2 Diving Safety andStandards
As with any SCUBA diving activities, advanced technical
diving involves inherent risks. In an effort to manage these
risks, governments, institutions, and other organizations
have established standards for diving. Because most scien-
tists operate and receive research funding in the context of an
academic or research institution, these institutions are
required to abide by laws established to ensure workplace
safety, which includes diving. For example, in the United
States, the Occupational Safety and Health Administration
(OSHA) establishes rules to ensure the safety of employees,
including diving operations, as does the Health and Safety
Executive (HSE) in the United Kingdom. In some cases, par-
ticularly in Europe (Norro 2016) and Australia, specic laws
pertaining to occupational diving impose restrictions on
what specic diving activities are allowed.
In addition to following OSHA rules and regulations,
many US institutions are members of AAUS, which estab-
lishes standards and practices for scientic diving (AAUS
2016). With nearly 150 member institutions, AAUS facili-
tates the development of institutional diving programs,
R. L. Pyle

963
gathers extensive data on scientic diving activities, and
enables collaborations among member institutions through
diver reciprocity agreements. AAUS standards cover decom-
pression diving, mixed-gas diving, and rebreathers and can
serve as a model for developing institutional support for sci-
entic technical diving worldwide. Similar standards have
been developed for the US National Oceanic and Atmospheric
Administration (NOAA) and the Confédération Mondiale
des Activités Subaquatiques (CMAS; World Underwater
Federation).
Several nongovernmental organizations have been cre-
ated specically to support technical diving and research,
such as the Cambrian Foundation, the Association for Marine
Exploration, Project Baseline, and Ocean Opportunities.
Organizations such as these may serve as effective collabora-
tors for institutions and independent scientists that do not
have access to robust technical diving infrastructure.
Regardless of how an organization develops infrastructure to
support advanced technical diving activities for research, it is
important to understand the legal constraints and potential
liability issues that may exist and balance these concerns
against an overarching priority to ensure adherence to best
practices and maintain adequate levels of safety for all
involved divers.
In addition to following the appropriate diving standards,
all scientic divers participating on any expedition involving
advanced technical diving should have training and experi-
ence commensurate with the role or tasks to be performed.
Newly trained rebreather divers should not attempt to con-
duct advanced diving up to the limit of their training within
an expedition setting. Sufcient experience should be
acquired under more controlled and familiar diving condi-
tions, closer to home, before attempting to exercise those
skills in a remote or otherwise challenging situation. Divers
serving in a support capacity should likewise gain rsthand
experience with specic procedures and protocols during
non-expedition circumstances before a eld expedition. Two
helpful resources on rebreather diving in particular are
Bozanic (2002) and Gurr (2010), as well as training manuals
for the different instruction and certication agencies [e.g.,
BSAC (British Sub-Aqua Club), IANTD (International
Association of Nitrox and Technical Divers), TDI (Technical
Diving International), GUE (Global Underwater Explorers),
NAUI (National Association of Underwater Instructors), and
SSI (Scuba Schools International)].
50.3 Logistics
The logistical circumstances surrounding technical diving
operations may vary enormously. In some cases, logistical
support includes a large research vessel with wet and dry
laboratories, internet and telephone service, air compressors
and gas-mixing equipment, dedicated small boats with
highly trained staff, and a large and well-maintained hyper-
baric chamber (e.g., Kosaki et al. 2010). In other cases,
particularly in remote locations, logistics are constrained to
locally available small boats and basic accommodations or
live-aboard dive vessels not equipped to support technical
diving, which requires the scientists to supply all necessary
equipment to blend gas mixtures, maintain and repair dive
equipment, and process specimens and data.
Many aspects of logistics planning (e.g., ights, special
equipment, permits, packing strategies, contingencies, and
other details) are common to all scientic eldwork in
remote locations and are not particular to research involving
advanced technical diving on MCEs. As with any expedition,
whatever the specic circumstances, it is vital that a com-
plete understanding of available services and resources at the
destination is understood by all expedition participants well
in advance. In terms of planning, particularly for operations
involving technical diving, it is best to assume that any piece
of dive equipment will fail at some point. Critical equipment
items, for which a malfunction represents an inability to con-
duct dive operations (e.g., booster pumps and other gas
blending hardware, gas analyzers, rebreather electronics, and
bailout regulators), should have backups.
Under ideal circumstances, dedicated support personnel
are assigned to manage many aspects of project logistics,
such as gas blending, equipment maintenance and prepara-
tion, specimen handling, and many other tasks. More often,
however, these responsibilities will fall on the scientists
themselves, and although these issues exist for most scien-
tic eld expeditions, they can be particularly acute in the
context of expeditions involving technical diving. In such
cases, it is often most efcient for certain team members to
focus on the specic tasks for which they are most capable
of, or most comfortable with, fullling. For example,
researchers often need to spend hours each day processing
specimens, data, or images (or all three), so it can be helpful
if others take responsibility for general tasks like relling
cylinders, checking the functionality of emergency equip-
ment, and performing maintenance or repairs. Another
important task is to monitor remaining supplies such as oxy-
gen, helium, and carbon dioxide absorbent to ensure that suf-
cient quantities remain to complete the planned dives. In
some situations, it is preferable for all participants to share or
trade off tasks to ensure all maintain adequate prociency.
Regardless of how expedition tasks are shared and
divided, it is generally considered standard practice for indi-
vidual divers to maintain their own personal life-support
equipment and be responsible for conducting all necessary
predive, post-dive, and routine maintenance and procedures.
Expeditions should be planned with no diving for the rst
2 days after arrival on site or the last 2 days before departing.
The rst 2days of any expedition are needed to set up blending
50 Advanced Technical Diving

964
equipment, ll initial bailout cylinders, assemble and test
dive equipment, and arrange and prepare all other equip-
ment. The rst one or two dives of every expedition should
be treated as “work-up” dives to ensure all equipment are
operational. Such dives should be relatively shallow (no
more than 30–40m deep, or 100–130 ft), with no decom-
pression. However, they should be performed as if they were
full-depth technical dives, including relevant bailout equip-
ment and data or specimen collection tools. These dives are
also very useful for practicing emergency procedures, espe-
cially if support divers have not worked in the same environ-
ment with the same deep-diving team previously.
50.3.1 Gas Blending
In some situations, technical dive facilities are already avail-
able locally (either at an institution, dive shop, or on a live-
aboard vessel). However, in many remote locations, team
members must be prepared to blend their own gases. In some
cases, it is possible to arrange for custom gas blends to be
available on-site, in which case relling cylinders is simply a
matter of using a small booster pump to trans-ll gas from
supply cylinders directly to bailout and rebreather cylinders
(Heinerth 1989). However, such services are unlikely to be
available in many locations, and even when they are, mixed-
gas rebreather diving operations often require multiple dif-
ferent blends for different purposes. Therefore, arranging for
all of the required gas mixtures in advance can be problem-
atic. When gas blending facilities are not available on-site,
arrangements for obtaining helium and oxygen and the
blending equipment for different mixtures will need to be
made.
Different regions have different standards and availability
for different grades of gases. Most locations have local hos-
pitals, so medical-grade oxygen is usually available. In some
cases, there is no distinction between different grades of oxy-
gen, so the dive team will need to ensure the purity of the gas
mixture directly through the use of reliable analyzers. In
general, oxygen should be at least 96% pure and ideally
98–99%. Cylinder handling and relling should be done in a
manner consistent with medical-grade oxygen. It is often
helpful to know whether oxygen supplies are generated
locally or shipped in from another source. In most cases, the
majority of impurities in oxygen supplies will consist of
nitrogen, particularly when the oxygen supply is generated
locally. However, it is imperative to ensure that the gas sup-
ply will be safe to breathe under elevated ambient pressures.
Even when oxygen is obtained from a hospital, it must be
analyzed prior to use for blending or diving purposes. During
one early mixed-gas diving expedition, the oxygen provided
by the local hospital contained only 68% oxygen and the
other 32% was unknown (pers. obs.).
Helium is rarely generated locally and thus must be
shipped in from an external source. It is important to deter-
mine the original source of the helium to ensure it is not con-
taminated. It is also important to use a calibrated helium
analyzer on the supply gas before blending to ensure that the
helium content is close to 100%. In some cases, helium sup-
plies may contain up to 10–20% oxygen. Usually, but not
always, this is denoted on the cylinder itself. As long as the
analyzed supply gas reveals that the sum of oxygen and
helium combine to a value close to 100%, such mixtures
should be safe for diving purposes. However, the oxygen
concentration will affect the blending calculations and may
prevent generating mixtures with very low oxygen fractions.
When considering all the factors related to gas supplies, it
is often best to arrange to ship the gas in from a known and
trusted supplier rather than rely on local gas supplies. When
making plans to ship gas to the destination, it is important to
consider what happens to the cylinder after the expedition is
complete. In many cases when purchasing gas, a deposit is
paid for the cylinder itself, which may be lower than the cost
of returning the empty cylinders. If the research site will be
revisited, it may be preferable to purchase the cylinders out-
right and leave them on-site, particularly if a local gas supply
company is willing to exchange the empty cylinders for fresh
ones in lieu of deposits.
Once the helium and oxygen supplies are secured, meth-
ods and equipment for blending must be dened. Selecting
gas mixtures for rebreather diluent and bailout is an impor-
tant part of any expedition. There are many factors to con-
sider when selecting the correct gas mixture to use during
different phases of the dive. Perhaps the most important fac-
tor is how much oxygen to include in the breathing mixture.
It is generally accepted in the technical diving community
that divers should limit the oxygen partial pressure (PO2) in
their breathing mixture to 1.4atm during working portions of
the dive and a maximum of 1.6atm during resting phases of
the dive (e.g., decompression) (Stone 1989a; Pyle 1996b, d,
1998, 2010). For open-circuit diving, these values are used to
determine the fraction of oxygen (FO2) included within each
cylinder intended to be breathed at different depths. For
closed-circuit rebreather diving, these values are considered
when selecting a PO2 “set point” at which the control system
maintains the PO2 of the breathing mixture during the dive.
Due to the dynamic nature of the actual breathing mixture on
a rebreather (which can change in response to sudden depth
changes or unintended addition of gas into the breathing
loop), it is often a common practice to reduce the set point to
1.2–1.3atm to allow some margin for error (Bozanic 2002).
The other main consideration for selecting gas supplies
and breathing mixtures is the amount of nitrogen to include.
For the dives to depths >30m (> 100 ft), helium should be
incorporated into the breathing mixture. Some have argued
that the best mixture to use in terms of safety is “heliox,” a
R. L. Pyle

965
binary mixture containing only helium and oxygen (e.g.,
Stone 1989a). However, during early attempts to use heliox
with rebreathers for exploring MCEs, unusual and previ-
ously unreported symptoms of nervousness, jitters, and
impaired muscular coordination were consistently encoun-
tered at depths >80m (>260 ft) (Pyle 1996d, 2002, 2010).
These symptoms are generally consistent with mild high-
pressure nervous syndrome (HPNS; Bennett 1990), but such
symptoms are generally reported only on dives to much
greater depths. The severity of HPNS is related to the rate of
descent (Bennett 1990), so it is possible that the very rapid
descents typically conducted by mixed-gas divers exploring
MCEs result in subtle manifestations of mild HPNS at much
shallower depths than typically reported. One way to miti-
gate HPNS symptoms is to include a limited amount of nar-
cosis-inducing inert gas (e.g., nitrogen or hydrogen) into the
breathing mixture. Indeed, experience on our expeditions has
been that the addition of a small amount of nitrogen to the
deep-diving mixture (typically in the form of trimix that lim-
its the concentration of nitrogen to what an air-breathing diver
would experience at depths of about 15–30m, or 50–100 ft),
eliminates these HPNS-like symptoms completely for dives
to about 120m (~400 ft) and reduces them substantially for
dives in the range of 120–150m (400–500 ft). In addition to
improving overall diver safety, the incorporation of nitrogen
in the breathing mixtures reduces the total amount of helium
needed to conduct an expedition. It also substantially reduces
the amount of time needed to rell cylinders after each dive
(due to the use of a conventional air SCUBA compressor
instead of a booster pump to achieve the full operating pres-
sure of the cylinder).
Traditional diving practice for open-circuit diving
involves switching from trimix or heliox mixtures during the
deep phase to air or enriched-air nitrox during intermediate
decompression phases of the dive (Mount and Gilliam 1993).
Initially, my protocol for deep rebreather diving for MCE
exploration likewise included the practice of ushing the
breathing loop with air (creating an enriched-air nitrox
breathing mixture) at a depth of about 25m (~80 ft) during
the decompression ascent (Pyle 1996d). However, more
recently the mixed-gas rebreather deep-diving community
has shifted toward eliminating the practice of ushing the
breathing loop with a nitrogen-rich mixture during interme-
diate decompression (Pyle 2002, 2010), and a recent experi-
mental study comparing heliox and trimix decompression
tends to support this (Doolette etal. 2015). Eliminating this
step of deep rebreather diving protocol reduces the complex-
ity of the overall dive operation and reduces the potential for
dangerous errors (e.g., ushing the loop but failing to adjust
the decompression computer accordingly). Additionally,
eliminating the nitrogen gas ush may reduce the risk of
experiencing certain vestibular decompression symptoms
associated with sudden gas changes.
In general, it is best to standardize a nite set of mixtures
that all divers agree to use to simplify relling procedures.
While it is certainly possible to blend complex mixtures in
the eld, it is often preferable to dene trimix mixtures for
both rebreather diluent and bailout that represent a blend of
helium and air (with no extra oxygen added). The perceived
(and dubious) decompression advantage of blending custom
gas mixtures is usually more than offset by the advantage of
maintaining a very simple set of procedures for relling cyl-
inders after each day of diving.
Training courses for gas blending are offered by the major
agencies, and all personnel involved with blending should
have appropriate levels of training. A detailed description of
blending techniques is beyond the scope of this chapter, but
several techniques may be useful in the context of MCE
research expeditions in remote locations.
• For rebreather diluents, select an oxygen fraction that will
yield an oxygen partial pressure considerably less than
the intended set point at the intended maximum depth.
This allows more effective reduction in loop PO2 when
needed.
• The optimal number of supply cylinders to use in a bank
for cascading purposes is three at a time. Fewer will
require more boosting time; more requires additional cyl-
inders and likely results in more unused gas.
• Use a labeling system on the supply cylinders to record
pressures after each lling session, and always ensure that
lling begins with the supply cylinder having the lowest
pressure rst (for both cascading and boosting). This
allows tracking of actual consumption rates, minimizes
confusion, and maximizes efcient use of gas supplies.
• Calculate effective volumes of gas cylinders based on a
minimum pressure of about 17–20 bar (250–300 psi).
Extracting gas from supply cylinders below this pressure,
when topping off rebreather cylinders that are typically
half-full or more at the start of the lling procedure, is not
practical with a portable booster pump because of the
excessive amount of time and booster pump drive gas
needed when boosting against large pressure ratios
between the supply cylinder and the cylinder being lled.
• When rotating out empty supply cylinders with full ones,
maintain the same relative positions of the supply cylin-
ders (e.g., lowest pressure nearest to the output). This
avoids confusion and helps to ensure maximum cascading
efciency.
• When possible, rell a set of cylinders requiring the same
mixtures simultaneously, rather than sequentially. This
ensures more consistent mixtures and typically saves time
and gas by reducing the frequency of purging high-
pressure hoses and exchanging cylinders being lled.
• Rell cylinders in the afternoon or evening after a dive,
rather than in the morning before a dive. In general, it is
50 Advanced Technical Diving

966
better to focus on ensuring proper preparation of life-
support systems prior to diving. Trying to ll cylinders
while preparing for a dive can often lead to rushing and
potentially life-threatening mistakes.
There are many other aspects of proper gas blending and
analysis that are not described here (e.g., proper analysis,
labeling, ensuring adequate mixing within the cylinders,
oxygen handling safety concerns, and managing thermal
issues). Optimizing gas blending in the eld is an art form
and will improve with experience and in response to particu-
lar circumstances. Overall, the daily process of relling cyl-
inders represents a balance between maximizing the
utilization of limited supplies of helium and oxygen and
minimizing the time spent relling cylinders.
50.3.2 Equipment
Although some projects still rely on open-circuit trimix div-
ing equipment and protocols, rebreathers have advanced to
the point where it is becoming increasingly difcult to justify
the cost and logistical complexities of conducting open-
circuit mixed-gas scientic diving operations, especially in
remote locations. A basic blueprint for expeditionary mixed-
gas rebreather diving (Pyle 1996d) was rened and updated
in response to 14 years of subsequent expeditionary work
(Pyle 2010). Although most of the suggestions, assertions,
and methods described in those publications (particularly the
latter) remain valid, specic expeditionary procedures have
been rened in recent years. Many equipment-related factors
must be considered carefully, including specic details con-
cerning the rebreathers used, lighting systems, signaling and
communications strategies, and methods for conducting sci-
entic research without compromising attention to dive
safety.
50.4 Primary Life Support
The most important equipment option to consider is the pri-
mary life-support system. Several different models of
rebreathers are commercially available, and each has its own
set of strengths and weaknesses. All of the major models
have been used successfully for eld expeditions, so deci-
sions about which units to use will depend on a wide variety
of factors determined by institutional and individual diver
preferences and constraints. It is often advantageous for all
dive team members to use the same model and general
rebreather conguration, so that spare parts may be shared,
and each diver has a high degree of familiarity with it.
However, this may not be possible as many divers have their
own preferred rebreather model with which they have the
most experience and training and/or level of comfort.
Familiarity and established comfort level with one’s own
gear vastly exceeds any advantages gained by having all div-
ers use the exact same equipment model or conguration.
While the selection of a specic rebreather model should
in most or all cases be left to individual divers, one disadvan-
tage of including different rebreather models on the same
project is that divers may not be as familiar with different
models of rebreather used by different team members. For
this reason, in cases where different models of rebreathers
are used, it is vital that all dive team members become famil-
iar with the different models being used by all members of
the team. In particular, divers should be aware of all impor-
tant valves, controls, alarms, displays, and harness straps for
each model of rebreather on the project. The same applies in
cases where divers use the same model of rebreather but have
made modications to the standard conguration. It is often
helpful for the entire team to spend a full day familiarizing
themselves with each other’s specic congurations, ideally
in the context of a shallow in-water dive, prior to the start of
any eld effort.
Secondary (bailout) life-support systems are described
below, in the Contingency Planning section.
50.4.1 Lighting
Most research divers investigating MCEs will require at least
some form of lighting, either for exploratory purposes (e.g.,
looking inside small caves or crevices) or photographic pur-
poses. A balance must be struck between ensuring adequate
light and maintaining free hands to manipulate equipment or
specimens. Early attempts to emulate practices incorporated
in other diving environments (such as lights mounted on a
divers arm or head) proved ineffective in the context of con-
ducting research on MCEs, where it is often best to have a
more stable lighting platform that is not constantly moving
with the diver’s head and arms. One particularly effective
lighting technique originally developed by Brian Greene and
extended and perfected by Sonia Rowley is to attach a small
but bright light to an articulating arm mounted on the
rebreather back plate and positioned over one or both shoul-
ders (Fig.50.3). When set up correctly, such lights can be
easily reached and positioned at an appropriate angle to pro-
vide hands-free lighting as needed.
When the primary research task involves capturing images
or video, it is often easier to mount a dedicated light to the
camera system (via an extended articulating arm to minimize
backscatter in video images) for use as a primary light source
for all aspects of the dive. Other options for hands-free light-
ing include attaching a light to a diver’s head or to the back
of a diver’s hand or elsewhere on the equipment. Even in
circumstances when specic lighting needs are not anticipated,
R. L. Pyle

967
it is useful to carry at least one light to use for signaling
purposes or in unexpected situations (e.g., dark holes).
In situations involving cave diving or wreck penetration, the
requirements for adequate lighting are much more involved
and are outside the scope of this chapter.
50.4.2 Signaling Devices
One of the greatest challenges to effective team diving is
maintaining adequate levels of communication both among
dive team members and between the dive team and topside
support. Techniques range from hand gestures, light signals,
and tools as simple as a short metal rod used to bang on a
tank to get the attention of other divers to advanced elec-
tronic underwater communication devices. A common form
of signaling between divers and the topside support is a sur-
face marker buoy attached to a long line on a reel. These
devices are standard equipment for open-water technical
diving operations and are included as part of most training
courses. Various strategies for using these as signaling
devices are discussed in Pyle (1996d, 2010). Regardless of
what signaling and communication equipment is used for
any particular project, the most important thing is to ensure
that all team members have a shared understanding on the
meaning of each of the signals.
50.4.3 Research Equipment
Although a great deal of attention is paid to diving equip-
ment during advanced technical diving operations, ultimately
the reason for doing the dives in the rst place is to conduct
research. The exact nature of the research (e.g., data or speci-
men gathering techniques) will vary with each project. In
general, it is important to develop procedures that maximize
the efciency of data gathering during dives with limited
bottom time in a way that minimizes the degree to which the
data gathering equipment or techniques encumber rebreather
operation or otherwise affect safety.
An effective technique for safe and efcient data gather-
ing is to develop simple routines that can be repeated multi-
ple times during a dive. For example, when collecting
gorgonian specimens from MCEs, Sonia Rowley has imple-
mented an efcient protocol: she identies the target speci-
men, takes a photograph of the gorgonian in situ, collects a
sample and places it in a prenumbered bag, and photographs
the rebreather computer display to document the environ-
mental parameters (Rowley 2014). Such carefully designed
protocols both maximize the efciency of data collection and
ensure the integrity of the collected data.
Due to the limited bottom times associated with deep
technical diving for research, there is a temptation to multi-
task to extract as much information as possible out of each
dive. To some extent this can be effective, but trying to do
too many things on a single dive (e.g., capture video and
images, collect specimens, and conduct quantitative tran-
sects) can often result in none being accomplished effec-
tively. Moreover, as each task often requires its own set of
special equipment, the burden of carrying all that extra
equipment can both hamper performance and jeopardize
diver safety.
50.5 Contingency Planning
The most important and complex aspect of any technical
dive is being prepared for and knowing how to deal with
emergencies. Contingency planning involves secondary
(bailout) life-support equipment and many aspects of acci-
dent management. While these are important for any
advanced technical dive operation, particular care, attention,
and planning are especially needed in remote locations.
Fig. 50.3 Sonia Rowley bagging a specimen during a deep dive, with
her two “antenna” lights mounted behind her. (Photo credit: R.L.Pyle,
can be reused under the CC BY license)
50 Advanced Technical Diving

968
50.5.1 Secondary (Bailout) Life Support
No single bailout strategy applies to all situations. Factors
affecting bailout include the bathymetric prole of the dive
site, geographic location, distance from shore, the nature of
currents and sea conditions, the reliability and type of top-
side support, the individual comfort levels of the individual
divers, the availability and experience level of support divers,
and many other variables. A complete discussion of this
topic would require an entire chapter unto itself, but a few
general considerations are presented here.
Bailout strategies for dives where decompression is com-
pleted while ascending along a vertical reef drop-off
(Fig. 50.4) can be very different from strategies involving
blue-water decompression (Fig.50.5). For example, staging
emergency gas supplies on the reef is an option for the for-
mer, but not the latter (Fig.50.6). One particularly important
aspect of bailout strategy is whether or not divers carry all
bailout gas mixtures on their person throughout all phases of
Fig. 50.4 Richard Pyle leans back and looks up toward the boat during
a decompression dive along a vertical reef drop-off in Pohnpei. (Photo
credit: S.J.Rowley, can be reused under the CC BY license)
Fig. 50.5 Randall Kosaki hangs from a line to a surface marker buoy
along with his bailout gas supplies during a blue-water decompression
in the Northwestern Hawaiian Islands. (Photo credit: R.L.Pyle, can be
reused under the CC BY license)
Fig. 50.6 Unused bailout cylinders gathered on a reef following a deep
decompression dive in Pohnpei. (Photo credit: S.J. Rowley, can be
reused under the CC BY license)
R. L. Pyle

969
the dive, or whether certain mixtures (particularly pure oxy-
gen) should be left staged in shallow water or in the boat for
deployment as needed. The case for carrying all gases at all
times accommodates the scenario where an open-circuit
bailout is required when a diver is separated from the team or
cannot return to staged gas supplies and/or alert topside sup-
port to deploy the needed gas. The case for not carrying oxy-
gen during the deep phase of the dives involves the risk of
accidentally breathing it at depth (with likely fatal outcomes)
and the safety hazard imposed by the encumbrance of carry-
ing an additional cylinder. Although empirical data and
experience overwhelmingly supports not carrying oxygen
during deep phases of the dive, ultimately individual diver
comfort is extremely important for favoring rational deci-
sions in stressful situations, and as such divers who prefer to
carry all bailout gas supplies with them at all times should, in
most cases, be allowed to do so. Another related question is
the applicability of so-called team bailout, wherein a com-
mon set of bailout cylinders are shared by an entire dive
team. NOAA currently does not allow this approach to bail-
out, but it is a common practice in many operations. It has
proven to be an extremely effective technique, especially
when diving along vertical reef drop-offs, which is not an
environment typically associated with NOAA technical div-
ing projects.
There are many strategies for labeling bailout cylinders to
ensure each gas mixture can be unambiguously identied
underwater. In many cases, this involves clearly labeling the
cylinders using large writing indicating the maximum oper-
ating depth (MOD) and/or the oxygen percentage. While
proper labeling is critical, it can also cause confusion if done
inadequately. For example, if numbers alone are used to label
cylinders, the meaning of the number may be ambiguous. A
cylinder labeled only with “70” could mean 70% oxygen
(sometimes used for decompression purposes), 70ft MOD
(as one might label a cylinder containing a 50% nitrox mix-
ture), or 70m (in which case some form of trimix would be
expected). Although this seems obvious, confusion of this
sort has happened on dives before and can lead to potentially
life-threatening situations. One solution that has proven to be
extremely effective is to use a color-coded system for the
nylon straps that are attached to bailout cylinders as a handle
or harness. For example, red straps (= black at depth without
articial lighting) are used on hypoxic trimix cylinders, blue
straps are used for “normoxic” mixtures (air or trimix con-
taining about 20% oxygen), yellow straps are used for
enriched-air nitrox mixtures, and green straps are used for
shallow decompression mixtures (80–100% oxygen). Using
this color-coding system minimizes the potential for confu-
sion both among divers and topside support.
Another piece of equipment that should be standard,
especially in areas where there is risk of being separated
from the topside support or other team members, is a water-
proof radio. The Nautilus Lifeline GPS system, which serves
as both a radio and a GPS and is rated to a depth of 122m
(400 ft), can be crucial in certain emergency situations.
50.5.2 Accident Management
Besides the immediate need for addressing contingencies
during a dive, it is also important to ensure a robust plan for
managing potential accidents is in place. In most respects,
accident management for technical diving operations is the
same as for any eld-based operation (e.g., identifying local
medical facilities and evacuation options). One particular
aspect in need of special attention for advanced technical
diving operations, particularly in remote locations, is the
increased potential for (and severity of) decompression sick-
ness. In all cases, careful research on options for the nearest
recompression facilities, ideally in consultation with the
Divers Alert Network (DAN), should be completed as part of
the early-stage expedition planning process. Simply identi-
fying the existence and location of a recompression facility
is not sufcient; conrmation of its active status, and will-
ingness and capabilities for treating divers, must also be
ascertained. Plans for evacuation to such facilities should be
dened in advance, and it is always a good idea to alert the
facilities of the planned diving operations and consult with
them about how best to initiate an evacuation, if needed. In
some cases, particularly in very remote locations, the option
of in-water recompression (IWR) should be considered. This
procedure has been described and documented both in gen-
eral and in the context of MCE expeditions in particular
(Pyle 1996e, 1999b, 2002; Pyle and Youngblood 1997) and
must be thoroughly understood before considering its use
during diving operations.
Another consideration is the effects of chronic oxygen
exposure during long periods in the eld. In particular, pul-
monary oxygen toxicity may become an issue after several
weeks of diving and should be managed in accordance with
well-established exposure limits that are included as part of
technical dive training programs. Also, the effects of pro-
longed hyperoxic exposures on vision (i.e., hyperoxic myo-
pia) should be considered. Though uncommon, this malady
has been documented during rebreather dive expeditions
(Pyle 2002; John L.Earle and Sonia J.Rowley, pers. comm.).
50.6 Future Directions
Without question, the value of advanced technical diving
practices will increase, and the existing trend toward broader
application will continue. The value of SCUBA for docu-
menting shallow coral reefs has proven to be enormous dur-
ing the past seven decades or so and applies equally to the
50 Advanced Technical Diving

970
application of advanced technical diving in MCE research.
Technical diving for scientic purposes will no doubt con-
tinue to increase in much the same way that conventional
SCUBA did during the 1950s–1970s, when it was limited to
only a few of the most intrepid research divers before it
became commonplace and standardized. The history of tech-
nical diving has reached a point where improvements in
equipment, procedures, and training, as well as broader
adoption by scientic diving programs, are transitioning
from fringe to mainstream. New advancements in rebreather
technology, such as more reliable oxygen monitoring and
carbon dioxide detection, continue to be developed, with
more on the horizon (Pyle 2016). As closed-circuit rebreather
bailout systems continue to be developed and become more
commonly available, a major aspect of dive contingency
planning will become substantially simpler and more effec-
tive. Advances in dive computer technology, particularly in
association with rebreather systems, hold the promise of dra-
matically improving scientic data gathering.
While there certainly will be improvements in alternate
technologies such as submersibles, one-atmosphere diving
suits, remotely operated vehicles (ROVs), and autonomous
underwater vehicles (AUVs) (see Armstrong et al. 2019),
these are not likely to replace the capabilities of a free-swim-
ming diver anytime soon (Gilmore 2016). Much more fruit-
ful is the potential to integrate these different technologies in
the future. Several projects have already integrated both sub-
mersibles and technical divers (Pyle etal. 2016a; Fig.50.7),
and the potential for combining divers with ROVs or AUVs
holds a great deal of promise. Without a doubt, advanced
technical diving can, will, and should play an increasing role
in the broader effort to document MCEs worldwide.
Acknowledgments I am extremely grateful to the many talented and
insightful divers who have trained me, worked and dived with me, and
shared their helpful insights in developing these protocols over the
years. In particular, I thank William C.Stone, Sonia J. Rowley, Mike
Rowley, Randall K. Kosaki, Brian D. Greene, John L. Earle, John
E. Randall, Joseph Dituri, Joshua Copus, Ken Longenecker, Ross
Langston, and Roger A.Pfeffer. Research involving the use of rebreath-
ers that facilitated the development of the protocols described herein
has been supported by NOAA, the Association for Marine Exploration,
Bishop Museum, Poseidon Diving Systems, Seaver Institute, Ocean
Classrooms, and the Systematics Association.
Fig. 50.7 A rebreather diver swims past the University of Hawaiʻi’s Pisces submersible during a coordinated dive off Oʻahu. (Photo credit:
R.K.Whitton, can be reused under the CC BY license)
R. L. Pyle

971
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