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The use of light metals and their alloys in underground coal mines

Authors:
  • AECOM Canada

Abstract

Light metals, most commonly aluminum, magnesium and titanium, and alloys containing them, are used in many industrial applications where lightness, hardness, ductility and resistance to corrosion are needed. However, these metals and their alloys can be potential ignition sources in underground coal mines. There have been documented cases in the past where coal mine explosions have been attributed to firedamp/coal dust ignitions involving light metals or their alloys. When light metals and their alloys are brought into contact with oxygen-bearing material, such as iron oxide (rust) in the presence of heat, a "thermite" reaction can then occur. This source of heat can be generated from frictional contact or merely a glancing blow. This paper outlines the hazards associated with light alloys, how to address the hazard and regulatory aspects.
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CANMET Technical Information
Mining & Mineral Sciences Laboratories Fact Sheet - Light Alloys
Underground Coal Mining Safety Research Collaboration Revised February 2006
___________________________________________________________________
Fact Sheet on the Use of Light Metals & Their Alloys in Underground Coal Mines
Background
By 1998, Canada’s underground coal industry had
shrunk to 4 mines in 3 provinces across the country.
By early 2006, this had further reduced to one mine
in Alberta, one mine in BC and one mine in the
planning stages in NS. In September 1998, in order
to facilitate an ongoing safety research focus for the
remaining mines, CANMET established the
Underground Coal Mining Safety Research
Collaboration (UCMSRC) to provide a research
mechanism and technology forum for all industry
stakeholders.
One of the first projects undertaken by UCMSRC
was a review of the safety aspects of the use of light
alloys in underground coal mines. It was concluded
that, as most of the research on this had been done
several decades ago, currently in the industry there
were mixed levels of appreciation and aware ness of
on the potential hazard of light alloys and frictional
ignition of flammable atmospheres. There was also
a perceived lack of information on this hazard. As
improved awareness is perhaps the most effective
safeguard, it was therefore decided to produce a fact
sheet, based on earlier research, to provide factual
information on both the hazard of light metals and
their alloys and provision of precautionary
measures.
Hazards Associated with Light
Metals
Light metals, most commonly aluminum,
magnesium and titanium, and alloys containing
them, are used in many industrial applications
where lightness, hardness a nd ductility and
resistance to corrosion are needed. They are widely
considered to be near incapable of creating a
frictional spark which is hot enough to ignite a
flammable atmosphere. However, there are two
exceptions to this where light metal alloys can be
potential ignition sources in flammable
atmospheres (e.g. methane): (a) thermite reaction,
and (b) in cen dive chips (titaniu m) [1].
Potentially hazardous light alloys are those in which
the total weight of aluminum, magnesium and
titanium together exceeds 15%, and/or in which the
content of magnesium and titanium together
exceeds 6% by weight [2].
Thermite Reaction
Light metals and their alloys have an affinity for
oxygen and when t hey are brought into close
contact with oxygen bearing material, such as iron
oxide (rust) in the presence of moderate heat, then
a chemical reaction occurs, called a thermite
reaction [ 1].
-This thermite reaction can generate
temperatures over 2000/C.
-The heat necess ary to start the thermite reaction
can be generated from frictional contact or
from merely a glancing blow.
-A similar reaction can also be produced if
either a smear of light metal is left on a rusty
surface and is then struck with a glancing blow
or where a rusty metal object strikes a surface
coated with alu minum paint.
-Aluminum foils, widely used for cooking and
wrapping candies and cigarettes will also
produce a thermite reaction if laid over rusty
metal and struck a glancing blow.
-Aluminum pop cans and lunch boxes can also
potentially produce a thermite reaction if they
come into con tact with rusty steel.
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Incendive Chips
Titanium and its alloys can produce highly
incendive burning chips when they are struck or
rubbed on various hard materials. These ‘sparks’
are easily capable of igniting a flammable
atmosphere [1].
Experience with Light Metals &
Their Alloys in U/G Coal Mines
Applications
In the 1940's and 195 0's light metals and their
alloys became widely used in the industry to take
advantage of their lightness and resistance to
corrosion. They were used primarily in roof support
materials, but also in many other items of
equipment and their components.
Incidents
Attention was drawn to the thermite reaction hazard
in the UK in 1950, when a thermite flash caused a
firedamp explosion, when a hand drill with a
magnesium casing fell onto rusty steel. A mine
explosion occurred at Glyncorrwg Mine in Wales in
1954 where 24 died and the ignition source was
attributed to an impact of aluminum on rusty stee l.
Again, an explosion occurred at Hapton Valley
Colliery in the UK in 1962 where 19 died. One
possible cause for this ignition was a thermite
reaction between aluminum wrapping foil and rusty
steel rails [3]. In Canada, in 1973, a thermite flash
ignited a small coal dust explosion which then
started an underground fire with one fatality. This
incident occurred when runaway alum inum rail cars
struck rusty stee l arches in No. 12 Colliery, Cape
Breton D evelopment Corporatio n [4].
Regulatory Issues
Following such fatal accidents around the world,
various regulatory jurisdictions subsequently moved
to address this hazard by formally restricting the use
of light alloys in underground coal m ines. These
include United Kingdom, Germany, Australia,
Alberta, British Columbia, etc. A notable exception
to the severely restricted use of light metals and
their alloys in underground coal mines is the USA.
In Canada there are two jurisdictions (i.e. Federal
and Nova Scotia) which have no formal restrictions,
although industry practice has typically included
restrictions on use of light metals and their alloys.
Other Issues
This disparity in restriction produces two groups of
equipment available for use in Canadian
underground coal mines - those available from the
USA, which often have unprotected light alloy
surfaces, or light alloy components; - and those
which include precautionary mea sures (e.g. to
replace or cover the offending material). These
often make them heavier and more expensive.
There is therefore understandable frustration by
Canadian operators who want to use readily
available purpose-designed US equipment in their
underground coal mines but find in some cases that
they do not meet regulatory light alloy
requirements. Modifying US equipment cos ts
money and delays implementation underground.
Industry’s concern is increased by perceived
anomalies in application of the light metal and alloy
restrictions. For example, in some mines, use of
light alloy lunch boxes, cans and foils is allowed,
despite regulatory restrictions.
The thermite reaction between light alloys and rusty
steel is a well researched hazard. Technical
Literature is available outlining research undertaken
in the United States, United Kingdom , Ge rm any,
Poland, Czechoslovakia, Australia, etc. The
literature implies that their unco ntrolled use still
represents a safety hazard. CANMET, through
UCMSRC, is working with industry stakeholders to
rationalize practice and resolve such ambiguities.
Precautionary Measures
Risk Assessment
There are various industry approaches and
techniques for assessment and management of risk
to employee safety and health in use around the
world. Essentially these methods allow safety
management to achieve risk control. Applying the
principles of ‘practical risk assessment’ requires the
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following to be considered for a given activ ity:
identify the hazard (something with the potential to
harm); determine the hazard effect (level of harm
from the hazard - low, m edium or high); estimate
the risk (the likelihood or probability of hazard
occurrence); estimate the severity or level of risk
(product of hazard effect x probability); formulate
preventive or protective measures to reduce the risk
of the activity (prepare method statements or codes
of practice, including appropriate restrictions and
explanation of reasoning). In the case of light
alloys, when applied on a specific case-by-case
basis, as allowed in some jurisdictions in the
industrialized world, safe use of some light alloys is
possible at an acceptable and reasonable level of
risk [5], [6].
Precautions to Address the
Hazard
The final stages of risk assessment methods involve
preparation of method statements or codes of
practice which incorporate appropriate
precautionary measures. Some of these for
consideration in the use of light metals and their
alloys follow.
Covering or Coating
- Prevent direct contact of the light alloy with rusty
steel by covering or coating light alloy components
with a non-incendiary material to protect them from
impact.
- Keep the coatings completely intact and
undamaged. However, this can be difficult as
coatings often don’t survive.
- Decrease light alloy percentage to safe levels, e.g.
below establish ed guideline levels
- Keep electrical components which are comprised
of light alloys within a flameproof en closure.
Removal or Separation from rust
- In most mines rust coatings on steel are
unavoidable and covering or removing the rust
would be impractica ble.
- Precautions would have to pre vent lig ht alloys
from coming into contact with rust by separating
activity from likelihood of contact, for example, by
keeping them in a non-steel/non -light metal
container.
Removal or Separation from Heat
- The most common source of heat in underground
coal mines would be from frictional contact, diesel
and elec trical equipment (suc h as motors).
- Remove the possibility of heat transfer from either
prolonged contact or frictional impact by restricting
use underground to circumstances where there is no
possibility of such contact, friction or impact. This
is often not very practica l and can be difficult to do.
Removal or Separation from Potentially
Explosive Atmospheres
- Restrict the use of light alloys from underground
areas such as working faces, return airways, wastes,
etc. where there could b e exposure to potentially
flammable atmosph eres .
- Keep light alloy materials out of caving areas and
gobs/goafs/wastes.
- If there is a reasonab le probability of flammable
gas or dust being present at the same time of a
glancing blow be tween light alloy and rusty steel,
then unless there are extensive benefits, the risks
probably out-weigh the benefits of such an
application; however, if there is none then the risk
may be very low or negligible.
Examples of Safe Use
USA
The U.S. mining industry does not prohibit the use
of light alloys; however it does restrict their use in
some cases such as: aluminum alloy fan blades and
external rotating parts shall not contain more than
0.5 and 0.6 percent magn esium res pe ctively,
aluminum and aluminum-alloys cannot be us ed in
blasting materials and no ventilation controls
installed after November 15, 1992, shall be
constructed of aluminum . It defends its position of
not outright prohibition by noting that their large
underground coal industry has never had an
accident where the thermite reaction was an issue.
Regular use is made of mining equipment
containing exposed surfaces of light metals or
alloys. These include heavy equipment movers,
hand-held bolting machines and hydraulic props,
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stone dusting machines, non flame-proof vehicles
(some with exposed light metal gearbox casings).
Australia
Queensland, Australia regulations, as with the US
regulations, allow the use of aluminum alloys with
some restrictions, but in different ways. Industry
spent over A$100,000 looking into the use of light
alloys. It had been recommended that total
prohibition is unjustified based on statistical risk
(viz USA example) and a risk versu s benefit
approach was adopted. For example low risk/high
benefit applications were to be imm ediately
adopted [7].
In 1998/99 trials were successfully carried out of
non-flameproof free-steered diesel vehicles. These
were undertaken by ACIRL and overseen by a
formal stakeholder committee (including potential
users, Unions and Mines Inspectorate) necessary to
break down long-held paradigms such as: use of
uncoated light alloys, emission/temperature controls
and non-flam eproof /non-in trinsically safe electrics
on mobile equipment.
The trials used specially modified Toyota HJ75
4WD’s to include control measures determined by
a 'duty of care' approach and specific risk
assessment studies. They were undertaken at the
BHP Crinum Mine and She ll Moranbah North
Mine, both longwall operations in Q ue en sl an d's
Bowen Basin in Australia. The vehicles are allowed
to be used in specified zones only, essentially intake
air zones, where a combination of training, signage
and engineered electronic barriers are the primary
barriers to preve nt inad vertent entry to hazardous
locations.
By April 1999 eight Tro op-carriers and one utility
vehicle had been used covering over 150,000km.
By 2000, two more vehicles have been delivered to
Shell Moranbah and another six were to be built for
another customer. All the monitoring and control
systems have evolved to a commercial level of
reliability. The vehicle location system has proven
it can prevent inadvertent entry into hazardous
zones, the vehicles have low gas and particulate
emissions, there has been on ly minor panel and trim
damage and operator acceptance has been very
high.
The trials demonstrate a recent application of risk
assessment and the determination of both vehicle
modifications and codes of practice for their use
which together represent an acceptable and
reasona ble level of risk [7], [8].
Special Exemptions/Variances
Use of equipment containing light alloys in
jurisdictions which restrict use of light metals and
alloys, usually r equires modification of the
equipmen t, prior to use. This can include
replacement of the offending components by
acceptable ones, enclosing light components or by
covering exposed light metal or alloy surfaces
(although it is questionable whether such coatings
will survive).
From time to time in the jurisdictions which require
restriction, alternatives to the use of light metals or
alloys are not feasible. In such cases, exemptions or
variances may be issued, which usually include
special conditions for use. For example, a video
camera or geotechnical instrumentation, which have
to be in the care of a responsible person all the time,
cannot be left unattended underground and the use
of which is only allowed after gas testing
demonstrates a non-flamm able atmospher e.
References
[1] Health & Safety Laboratories:Technical
Information Sheet - Frictional Ignitions 2;
HSE, London, UK (1980)
[2] NCB Spec No. 481, CENELEC 1977
[3] Hapton valley report
[4] CBDC No. 12 Colliery accident investigation
report
[5] Practical Risk Assessm ent, W. Rowell, Mining
Technology p184-188,Vol78,no899, July 1996
[6] Risk assessment for Busy Mine Managers BG
Staley, Mining Technology p201-204, Vol 78
No 899, July 1996
[7] Correspondence with Terry O’Beirne, General
Manager of Mining Services, ACIRL Ltd .,
Queensland, Australia
[8] Breaking Down the Barriers, T. O’Beirne et al,
2nd International Underground Coal
Conference, 15-18 June 1999, Sydney, NSW,
eds B.K. Hebblewhite et al, pp 145-148
ResearchGate has not been able to resolve any citations for this publication.
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In the UK significant progress has been made over the last two decades in improving mine safety. Most of this improvement has been achieved through technological advances. For a numbers of years the industry has carried out risk assessments for major installations or particularly complex tasks. In this paper, the author outlines how RJB Mining propose to develop the use of practical risk assessment as part of its overall health and safety management to improve the safety performance of the company.
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This paper has arisen from experience gained by the author between 1990 and 1995, during which time he held the position of Group Head of Safety and Environment with British Coal. In early 1990, British Coal, Nottinghamshire Group (renamed Midlands Group in September 1993), worked closely with Du Pont Safety Management Services, USA, to introduce the modern philosophies of safety management into coal mines. The success of the initiative was considerable and can be attributed in no small way to the commitment of directors and management teams within the Group towards the reduction of accidents and the improvement of the industry's safety culture. A key element in support of the initiative was the introduction of a number of safety skills, designed for use by busy mine managers and engineers, which eventually developed into an Integrated Safety Training Programme focused upon human factors. The paper touches briefly upon the management of safety and then turns to one element of the safety training programme, risk assessment, to explain its introduction and the resulting benefits it had and which the author believes has an important role to play in the safety of the British mining industry of the future.
  • Ncb Spec
NCB Spec No. 481, CENELEC 1977
12 Colliery accident investigation report
  • Cbdc No
CBDC No. 12 Colliery accident investigation report
Mining Technology p184-188,Vol78,no899
  • W Practical Risk Assessment
  • Rowell
Practical Risk Assessment, W. Rowell, Mining Technology p184-188,Vol78,no899, July 1996
Breaking Down the Barriers
  • T O'beirne
Breaking Down the Barriers, T. O'Beirne et al, 2nd International Underground Coal Conference, 15-18 June 1999, Sydney, NSW, eds B.K. Hebblewhite et al, pp 145-148