Saskatchewan Mine Emergency
Response Program
Mine Rescue Manual
Chapter Four - Mine Fires

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.

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? How?
• Should you shut off fans? Close or open ventilation doors?

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 fire procedure

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 all times.

1. If the fire is large and/or obviously cannot be quickly controlled:

1. Sound the alarm by the established means.

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 use reported.

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 ground.

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 produced).

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 energy:

• chemical
• electrical
• mechanical
• solar, and
• nuclear

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 hydrogen.

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 dissipated.

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 overloading).

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.

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 temperature.

Heat can travel by one of three methods:

1. conduction

2. convection

3. radiation

The following sections describe how this transfer takes place.

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: 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 levels.

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.

Radiation: Heat 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 radiating surface.

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 combustibles.

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 radiation.

In reviewing the rapid oxidation process known as combustion, we note that three factors are necessary for a fire:

• a combustible material
• the presence of oxygen or an oxidizing agent, and
• 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 fire triangle

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 balance.

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 foam
• 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 4-2).

Figure 4-2: 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.

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 matter:

• solid
• liquid
• gas

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 vapourize.

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 likely.

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 contain.

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 radiation.

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.

The solubility 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 the oil.

Consideration 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.

The volatility, 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 ignited.

Gases

Vapour density 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.

Fuel-to-air mixture

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.

The flammable 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

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 combustion.

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