Mine fires are
much more common than most people realize. Most fires in
underground mines are small and quickly put out. Disasters
caused by mine fires are less frequent. Any mine fire
could, however, become a major disaster if not quickly
brought under control.
Everyone who works underground in a mine should have
a basic understanding of what fire is and how fires are
best controlled. Knowledge of fire and the hazards of
mine fires will encourage every underground worker to do
his part to prevent fires. Workers must be trained to
take the appropriate action if they discover a fire. The
health and safety of workers cannot be left to chance.
Considerations upon locating fires
A worker discovering a fire must consider several
possible actions very quickly. Any action taken, or not
taken, will have a big effect on the fire and on the
safety of everyone in the mine.
If you discover a fire in a mine, do you:
- Attempt to put it out? How do you attack the fire
and long should you try?
- Sound an alarm? How?
- Attempt to get out of the mine? By what route?
- How do you notify workers in your area?
- Should you shut off burning electrical motors?
- Should you shut off fans? Close or open
It is much better to make informed decisions on the
basis of understanding the situation than to leave the
well being of the workers and the mine to chance.
Knowing what to do if a fire is discovered is important.
Knowing how to prevent fires is even better.
Each mine must develop specific emergency procedures
for its site. All employees must be well trained in
those emergency procedures and understand how to apply
them. The proper response to alarms should be practiced
at least once a year. All fire equipment must always be
kept in proper working condition.
Summary of general underground emergency
Whoever discovers a fire must take prompt action. The
following is a generic emergency procedure for an
underground mine fire.
Important: Safety must be the top priority at
1. If the fire is large and/or obviously
cannot be quickly controlled:
1. Sound the alarm by the established
2. Warn the workers in your area.
3. Begin evacuation.
2. If an incipient or small fire is
found, then the following actions should be immediately
taken to contain or extinguish it:
Use water and Class A
extinguishers on Class A fires and the smothering
approach for Class B and Class C fires (See
Classes of fires P.73)
The current must always be turned
off in an electrical fire.
Never attempt to put an electrical
fire out with a stream of water.
Approach the fire from the upwind
side and be very careful when using the smothering
type of extinguisher in a confined space.
After a fire extinguisher is used,
it must always be returned for recharging and its
3. If, after a few moments, definite
progress is not made or it becomes clear the fire cannot
be contained, follow #1.
Important: Always remember that
deadly gases are constantly being produced and workers
must not be exposed to these gases or other hazards,
such as explosions, weakening timber and deteriorating
Every fire, no matter how small, must be reported at
once as it may have released deadly gases into the mine
air. Once put out, the fire area must be monitored until
re-ignition is impossible.
Fire or burning is a form of rapid oxidation of a
substance that produces much heat and light energy. The
release of heat energy in a fire may be so rapid as to
cause an explosion (a violent expansion of the gases
Oxidation is the chemical reaction combining oxygen
with another element or compound. This reaction is
almost invariably accompanied by a release of heat
energy (exothermic reaction). The amount of heat energy
released depends on the oxidizing (burning) compounds.
Among the hottest heat energy releases are those
occurring when oxygen combines with carbon, hydrogen, or
a compound of both elements.
If the chemical combination of carbon and oxygen is
complete, carbon dioxide, a colourless gas, is produced.
If hydrogen and oxygen combine, water vapour or steam is
produced. If the chemical combination includes both
carbon and hydrogen and the reaction is complete, then
carbon dioxide and water vapour are produced and the
resulting smoke is white. If the combustion is
incomplete, the products of combustion are carbon
monoxide, carbon dioxide, water vapour, and particles of
free carbon, and the resulting smoke is grey or black.
Heat, as energy, is a measure of molecular motion in
a material. Because molecules are constantly moving, all
matter contains some heat regardless of how low the
temperature. The speed of the molecules increases when
any matter is heated. Anything that sets the molecules
of a substance in motion is producing heat in that
substance. There are five general sources of heat
- solar, and
Chemical heat energy
Chemical heat energy is rapid oxidation or
combustion. Substances capable of oxidizing rapidly are
known as combustibles. The most common of these
substances contain significant amounts of carbon and
Sufficient heat for combustion is normally achieved
when combustible material absorbs heat from an adjacent
substance acting as a source of ignition. Some
combustibles are capable of self-generating temperatures
which increase to a point where ignition can occur. This
is known as spontaneous ignition. While most organic or
carbon-based substances do oxidize and release heat,
this process is usually slow enough to dissipate the
heat before combustion takes place. Spontaneous ignition
occurs when combustion heat is not sufficiently
Electrical heat energy
Electrical energy can produce enough heat to start
fires through arcing, dielectric heating, induction
heating or through heat generated by resistance to the
current flow. This last process may be intentional
heating (e.g., filaments or heating elements) or
accidental heating (e.g., electrical "shorts" or
Static electricity causes an arcing effect between a
positively and a negatively charged body when frictional
electricity becomes great enough so that a spark is
discharged from body to body. This spark may not be hot
enough or last long enough to ignite ordinary
combustibles. However, it may ignite flammable liquid,
vapour or gases.
Lightning has an action similar to that of static
electricity. It occurs when one cloud arcs to the ground
or to another cloud with an opposite charge. The
magnitude of a lightning charge often generates
sufficient heat to ignite combustible materials. The
high amperage and high voltage potential, although of
short duration, can do much structural damage even
though fire may not occur.
Mechanical heat energy
One source of mechanical heat energy is friction or
the resistance to motion of two bodies rubbing together.
Another source is produced by the compression of gases.
When a gas is compressed, its temperature increases.
This can be demonstrated by pumping compressed air into
a car tire or tube. As the pressure builds, the tube
valve and pump fitting heat up. This can easily be felt
by the hand.
In mines, a more common occurrence of mechanical
heating can be found when the bearings seize or the
brakes lock on a moving vehicle. Small fires from such
sources are quite common.
The energy transmitted from the sun in the form of
electromagnetic radiation is known as solar heat energy.
Typically, solar energy is distributed fairly evenly
over the face of the earth and, in itself, is not really
capable of starting a fire. However, when solar energy
is concentrated on a particular point, as through the
use of a lens, it may ignite combustible materials.
The release of very large quantities
of energy from the nucleus of an atom is known as
nuclear heat energy. Nuclear heat energy can be released
from the atom by two methods. Nuclear fission is the
splitting of the nucleus of an atom. Nuclear fusion is
the fusion of the nuclei of two atoms.
A number of the laws of physics explain the
transmission of heat. One, the Law of Heat Flow, says
heat tends to flow from a hot substance to a cold
substance. The colder of two bodies in contact will
absorb heat until both objects are at the same
Heat can travel by one of three methods:
The following sections describe how this transfer
Conduction: Heat may
be conducted from one body to another by direct contact
of the two bodies or through another heat-conducting
medium. For example, one end of a metal rod will become
heated when the other end is placed in a fire. The
amount of heat that will be transferred and its rate of
travel depend upon the conductivity of the material
through which the heat is passing.
Not all materials have the same heat conductivity.
Aluminum, copper and iron are good conductors, however,
fibrous materials such as felt, cloth and paper are poor
conductors. Liquids and gases are poor conductors of
heat because of the movement of their molecules. Air is
a relatively poor conductor.
Convection is the transfer of heat by the movement of
air or liquid. For example, as air near a steam radiator
becomes heated (by conduction), it expands, becomes
lighter and moves upward. As the heated air moves upward
(convection), cooler air takes its place at the lower
Fire spread by convection moves mostly in an upward
direction because heated air in an area will expand and
rise. However, air currents can carry heat in any
direction. Convection currents are usually the way heat
is transferred from one area to another.
Although often mistakenly thought to be a separate
form of heat transfer, direct flame contact is actually
a form of convective heat transfer. When a substance is
heated to the point where flammable vapours are given
off, these vapours can be ignited, creating a flame.
energy can travel in waves or rays from one area to
another as radiation. Like light, radiant heat travels
in a straight line through air, glass, water and
transparent plastics to heat combustible materials that
are not in direct contact with the heat source. The
quality and quantity of heat radiation depends on the
temperature of the radiating body and the size of the
The ability to absorb radiated heat depends on the
kind of surface the cooler, absorbing body has and the
area of the hotter, radiating surface. If the receiving
surface is black or dark coloured, it will absorb heat
readily. If the surface is light in colour or shiny and
polished, it will reflect much of the heat.
Radiated heat is one of the main ways fires spread.
Immediate attention is required at points where radiated
heat is severe. When fires produce flames of large size
and volume, radiated heat can ignite nearby
The use of water fog and wetting down can help block
heat radiation from large fires. The fog reflects the
heat rays and breaks up the straight line path of heat
Elements of a fire
In reviewing the rapid oxidation process known as
combustion, we note that three factors are necessary for
- a combustible material
- the presence of oxygen or an oxidizing agent,
- enough heat to increase the temperature of the
combustible material to its ignition temperature
Fire burns in two ways
- smoldering (surface), or
- flaming combustion
The smoldering (surface) mode of combustion is
represented by the fire triangle (fuel, heat and
oxygen). The flaming mode of combustion, such as the
burning of logs in the fireplace, is represented by the
fire tetrahedron (fuel, temperature, oxygen and the
uninhibited chemical chain reaction).
These three factors, fuel, oxygen, and heat, have
been incorporated into the simple fire triangle model:
Figure 4-1: The
The fire triangle is used to explain the components
necessary for burning to occur.
Once combustion has begun, with ample fuel and
oxygen, a fire can become self-supporting. As the fuel
burns, it creates more heat. The increase in heat raises
more fuel to its ignition temperature. As the need for
more oxygen arises to support combustion, it is drawn
into the fire zone. The oxygen, in turn, increases the
heat and more fuel becomes involved. Combustion will
continue as long as the factors from the three sides of
the fire triangle are present.
While oxidation is speeding up to the combustion
stage, another process is occurring that helps
combustion. A chemical decomposition process occurs when
a substance is exposed to heat. As chemical
decomposition takes place, the substance emits vapours
and gases that can form flammable mixtures with air at
certain temperatures (pyrolysis).
This chain reaction and interaction continues until
either all the fuel has been consumed, all the oxygen
has been used up or the heat has been dissipated so that
the temperature of the fuel drops below its ignition
temperature. This, in essence, states the fundamental
method of fire extinguishment -
removal of one side of the triangle by:
Cooling: Cooling reduces the temperature of
the fuel to below its ignition temperature.
One of the most common ways to put out fire is by
cooling it with water. The process of extinguishing by
cooling depends on cooling the fuel to a point where it
does not produce sufficient vapour to burn. Solid and
liquid fuels with high flash points can be extinguished
by cooling. Low flash point liquids and flammable gases
cannot be extinguished by cooling with water as vapour
production cannot be reduced sufficiently. Lowering the
temperature is dependent on the application of enough
flow in proper form to establish a negative heat
Smothering: Smothering is used to prevent
oxygen from reaching the fire by:
- displacing the air with an inert gas
- sealing the fire off within an inert blanket of
- smothering the fire in some other way
Extinguishment by oxygen dilution means reducing the
oxygen concentration in the fire area. This can be done
by introducing an inert gas into the fire or separating
the oxygen and the fuel. This method of extinguishment
will not work on self-oxidizing materials or on certain
metals that are oxidized by carbon dioxide or nitrogen
(the two most common extinguishing agents).
Separation: In some cases, a fire is
effectively extinguished by removing the fuel source.
This may be accomplished by stopping the flow of liquid
or gaseous fuel, or by removing solid fuel in the path
of the fire. Another method of fuel removal is to allow
the fire to burn until all fuel is consumed.
In addition to the fire triangle, the fire
tetrahedron is a four-sided figure, similar to a
pyramid, with the four sides representing fuel, heat,
oxygen and uninhibited chemical chain reaction (Figure
The fire tetrahedron
There are many by-products from fire. These can
include carbon monoxide (CO), carbon dioxide (CO2)
and sulphur dioxide (SO2). The
flammable by-products can combine with oxygen and burn,
thus feeding the chemical chain reaction of combustion
and contributing to the chain that expands the fire. The
vapours that are produced in a fire may also be
combustible and contribute to the fire.
The health hazard from exposure to the thermal
decomposition (burning) process depends on the
particular material involved and the decomposition
temperature. These materials could include such things
as tires, conveyor belting, electrical equipment and
cables, styrofoam, brattice. Gases and smoke produced in
fires involving material can be acutely toxic or
severely irritating to the respiratory tract.
Decomposition products may include hydrogen cyanide,
hydrogen chloride, aldehydes, nitrogen oxides, phosgene
and heavy smoke (particulate). Refer to MSDSs to find
information on hazards specific to a material.
About 10 percent of all fire deaths are unexplained
by carbon monoxide poisoning or other clear causes. They
include deaths with signs and symptoms of respiratory
tract irritants. Such irritants prevent proper breathing
(i.e. choking, suffocation) and impede escape, thus
increasing exposure to asphyxiants such as carbon
monoxide and hydrogen cyanide.
Other than for carbon monoxide, it is difficult to
assess the acute health risk of exposure to fire
decomposition products. There is not one degradation
product that can be used as an index for the toxicity of
the smoke. Smoke from fires involving plastic material
should be considered more toxic than smoke produced by
burning wood or fossil fuel.
Extinguishment by chemical flame inhibition
Some extinguishing agents, such as Halon and certain
dry chemicals, interrupt the flame producing chemical
reaction, resulting in rapid extinguishment. This method
of extinguishment is effective only on gas and liquid
fuels as they cannot burn in the smoldering mode of
combustion. If extinguishment of smoldering materials is
desired, cooling will also be necessary.
Fuel may be found in any of the three states of
Only gases burn. Burning liquid or solid fuel
requires its conversion to a gaseous state by heating.
Fuel gases are evolved from:
- pyrolysis for solid fuels and gases, and
- vaporization for liquids
This is the same process as boiling water to
evaporate it, and water in a container evaporating in
sunlight. In both cases, heat causes the liquid to
Generally, the vapourization process of liquid fuels
requires less heat than does the pyrolysis for solid
fuels. This limits the control and extinguishment of
liquid fuel fires because their re-ignition is much more
Gaseous fuels can be the most dangerous because they
are already in the natural state required for ignition.
No pyrolysis or vapourization is needed for combustion.
Gaseous fuel fires are also the most difficult to
Solid fuels: Solid fuels have a
definite shape and size that significantly affects how
efficiently they catch fire. Of primary consideration is
the surface-to-mass ratio, that is, the ratio of the
surface area of the fuel to the mass of the fuel. As
this ratio increases, the fuel particles become smaller
and more finely divided (i.e., sawdust as opposed to
logs), and the ease of ignition increases tremendously.
As the surface area increases, heat transfer and
vapourization of the small particles
is easier and the material heats more rapidly,
thus speeding pyrolysis.
The physical position of a solid fuel is also of
great concern to firefighting personnel. If the solid
fuel is in a vertical position, fire will spread more
rapidly than if the fuel is in a horizontal position.
The speed of fire spread is due to increased heat
transfer through convection as well as conduction and
Liquid fuels: Liquid fuels have physical
properties that increase the hazard to personnel because
they are harder to put out. A liquid, like a gas,
assumes the shape of its container. When a spill occurs,
the liquid will assume the shape of the ground (flat),
flowing and accumulating in low areas.
The density of liquids in relation to water is known
as specific gravity. Water is given a value of one.
Liquids with a specific gravity less than one are
lighter than water, while those with a specific gravity
greater than one are more dense than water. If a liquid
also has a specific gravity of one, it will mix evenly
with water. It is interesting to note that most
flammable liquids have a specific gravity of less than
one. This means that if a firefighter is confronted with
a flammable liquid fire and pours water on it
improperly, the whole fire may just float away, igniting
everything in its path.
of a liquid fuel in water is also an important factor.
Alcohols and other polar solvents dissolve in water. If
large volumes of water are used, alcohols and other
polar solvents may be diluted to the point where they
will not bum. As a rule, hydrocarbon liquids (nonpolar
solvents) will not dissolve in water and will float on
top of water. This is why water alone cannot wash oil
off our hands; the oil does not dissolve in the water.
In addition to the water, soap must be used to dissolve
must be given to which extinguishing agents are
effective on hydrocarbons (insoluble) and which affect
polar solvents (soluble). Today, multipurpose foams are
available that will work on both types of liquid fuels.
or ease with which a liquid gives off vapour, affects
fire control. All liquids give off vapours to some
degree in the form of simple evaporation. Liquids that
give off large quantities of flammable or combustible
vapours are dangerous because they may be easily
is the density of gas or vapour in relation to air.
Vapour density is of concern with volatile liquids and
gaseous fuels. Gases tend to assume the shape of their
container, but have no specific volume. If a vapour is
less dense than air (air has a vapour density of one),
it will rise and tend to dissipate. If a gas or vapour
is more dense than air, it will tend to hug the ground
and travel, as directed, by terrain and wind.
It is important
for all firefighters to know that every hydrocarbon
except the lightest one, methane, has a vapour density
greater than one and will sink and hug the ground,
flowing into low lying areas. Hydrocarbons are very
dangerous for that reason. Common gases such as ethane,
propane and butane are examples of hydrocarbons that are
heavier than air.
Once a fuel has
been converted to a gaseous state, it must mix with an
oxidizer to bum, usually oxygen. The mixture of the fuel
vapour and the oxidizer must be within the flammable
limits for the fuel. That is, there must be enough, but
not too much, fuel vapour for the amount of oxidizer. If
there is too much fuel vapour, the mixture is too rich
to bum. If there is not enough, it is too lean to burn.
limits of how rich or lean a fuel vapour mixture can be
and still bum are recorded in handbooks and are usually
reported for temperatures of 21°C (70°F). These are
referred to as the lower explosive limit (LEL) and the
upper explosive limit (UEL). These limits change
slightly with temperature.
Oxygen is in the air and will support
combustion of any fuel. The air we breathe contains
approximately 21 percent oxygen (20.94 percent). When
oxygen content is reduced to 16.25 percent or lower,
flames are extinguished.
Some fuels (eg., celluloid,
explosives), contain sufficient oxygen in their makeup
to support combustion themselves.
Pure oxygen is an intense supporter of
Important: Oils or greases
sometimes burst into flames or explode in the presence
of compressed oxygen.
Smoke consists of gases and finely
divided solids. It may be combustible and even explosive
under some conditions (e.g., a sudden inrush of air from
opening of a door). During a fire, smoke and gases rise,
therefore air is more breathable closer to the floor.
Of the various gases associated with
fire, you will probably be most concerned with carbon
monoxide (CO), a product of incomplete combustion.
Common usage of polyvinyl chloride (PVC), polyurethanes
and plastics mean precautions may have to be taken for
phosgene and hydrogen cyanide gas as well.
Suitable breathing equipment must be
worn when it becomes necessary to enter heavy
concentrations of poisonous or objectionable gases. The
mine rescue person will constantly assess conditions
based on chemical and physical facts. Such basic
knowledge is very important in fighting mine fires