Section 6
Fires, Firefighting & Explosions
1. General information
2. How to use hand held extinguishers
d. High expansion foam
1) Tricket’s Ratio
a) Electric
I. Introduction
Firefighting is probably the most frequent duty rescue teams perform. Fires in underground mines are especially hazardous because they produce smoke, toxic gases and heat, pose explosion hazards, and create oxygen-deficient atmospheres. Fires, firefighting, and explosions, and how they affect mine rescue teams will be explained in this manual.
II. Fires
Most mine fires result from a chemical reaction between a fuel and the oxygen in the air. Materials such as wood, coal, methane, gas, oil, grease, and many plastics burn when ignited in the presence of air. In each instance, three key elements are required at the same time for a fire to occur: fuel, oxygen, and heat (which is usually provided by the ignition source).a. Fire Triangle- The "fire triangle" must have the three elements necessary for fire. On each point of the triangle is one of the necessary elements for fire: fuel, oxygen, or heat. These three elements must be present at the same time in order for fire to occur. Any time one of these elements is removed, the fire goes out. Equally important, if one of the elements is missing from the fire triangle, the fire will not start. Therefore, in order to extinguish a fire, it is necessary to remove one element of the point of the triangle.
Removing one of these elements from the fire triangle is the basis of all firefighting.
There are various methods for fighting a fire:
Another way to extinguish a fire is by stopping the chemical reaction between the fuel and the oxygen, which is the principle by which dry chemical extinguishers operate. The function of dry chemical extinguishers is to chemically inhibit the oxidation of the fuel which stops the f ire.
Note: The method to be used to fight a fire is determined by the materials which are burning and the conditions in the fire area. Therefore, a large part of the job for the mine rescue team is to explore the mine and assess the condition of the fire in order for the command center to know how to fight the fire.b. Classification of Fires- Mine rescue teams must know the types of fires they are fighting in order to know how to extinguish them. The National Fire Protection Association lists four classes of fires: A, B, C, and D.Class A Class A fires involve ordinary combustible materials such as wood, coal, paper, plastics, and cloth. They are best extinguished by cooling them with water, or by blanketing them with certain dry chemicals.
Class A fires leave Ashes.
Class B Class B fires involve flammable or combustible liquids like gasoline, diesel fuels, kerosene, or grease, as examples. These fires can occur when flammable liquids leak out of mechanical equipment or are spilled. The best way to extinguish Class B fires is to exclude air or use special chemicals that affect burning reactions.
Class B fires involve contents which Boil.
Class C Class C fires are electrical fires which typically involve electric motors, trolley wires, battery equipment, battery charging stations, transformers, and circuit breakers. They are best extinguished by nonconducting agents such as carbon dioxide and certain dry chemicals.
If power has been cut off to the burning equipment, the fire can then be treated as either a Class A or Class B fire.
Class C fires involve Current.
Class D Class D fires involve combustible metals such as magnesium, titanium, zirconium, sodium, and potassium. Special techniques and extinguishers were developed to extinguish these fires. Normal extinguishers should not be used on Class D fires since they may make them worse. However, the possibility of Class D fires occurring in coal mines is extremely rare.Ill. Firefighting Equipment
Rescue teams must be able to identify the various types of firefighting equipment available. Mines have several different types of equipment for firefighting which include:
· Dry chemical extinguishers.
· Rock dust.
· Water.
· Foam.a. Dry Chemical Extinguishers
1. General Information- Dry chemical extinguishers put out fires by stopping the chemical reaction between the fuel and oxygen (which produces the flame). These dry chemical agents work to inactivate the intermediate products of the flame reaction which reduces the combustion rate (rate of heat evolution) and extinguishes the fire.Basically there are two sizes of dry chemical extinguishers:
1) Hand-held extinguishers which weigh between 2 and 55 lbs, and
2) Larger wheeled extinguishers, which weigh from 75 to 350 lbs. These extinguishers consist of a large nitrogen cylinder, a dry chemical chamber, and a hose with an operating valve at the nozzle.
Mine rescue teams usually use the multi-purpose dry chemical extinguishers which contain monoammonium phosphate because they are effective on Class A, B, or C fires. Monoammonium extinguishers eliminate the team's having to use separate extinguishers for each class of underground fire encountered.
2. How to Use Hand-Held Extinguishers- Note: Rescue team members must check the label on the side of the extinguisher before attempting to extinguish any fire. Using the wrong type of extinguisher can spread the fire instead of putting it out.a. When extinguishing a fire "PASS"
P Pull the pin
A Aim low
S Squeeze the handle
S Sweep from side to sideb. Types of fire extinguishersMonammonium phosphate
Rated for ABC fires, interrupts the basic chemistry of fire.
Not recommended for D fires. (Red body & pressure gauge)CO2
Rated for BC fires, will only extinguish surface area, heated core may reignite. (Red body & horn, no gauge)Halon
Rated for BC fires, used mainly in electronics, dangerous because Halon displaces oxygen. (Red body and gauge)Pressurized Water
Rated for A fires only, usually a baking soda charge. (Stainless steel body)
The label lists information regarding the distance from which the extinguisher is effective. Most dry chemical extinguishers are effective from 5 to 8 feet from the f ire while larger units have ranges from 5 to 20 feet from the fire.
To operate a hand-held extinguisher: grasp it firmly and approach the fire from the intake side. Hold the nozzle down at a 45-degree angle. Stay low to avoid any roll back from the flames but try to get within 6 to 8 feet of the fire before turning on the extinguisher.
To effectively and quickly extinguish the fire, direct the stream of dry chemical to about 6 inches ahead of the flame edge.
Begin far enough away to let the discharge stream fan out. Use a side-to-side sweeping motion to cover the fire with the dry chemical. Each sweep of the chemical should be slightly wider than the near edge of the fire.
While putting out the closest fire, advance slowly toward it, forcing it back. Always be alert for re-ignition of the fire even if it looks extinguished.
The discharge time of hand-held extinguishers varies from 8 to 60 seconds, depending on the size and type of the fire extinguisher. A 30-pound extinguisher usually lasts from 18 to 25 seconds. Always have control of the extinguisher or other team members could be exposed to the dry chemical stream.
3. Using Hand-Held Extinguishers on an Obstacle Fire- If an obstacle fire occurs with flaming equipment at the center, two people using hand-held extinguishers should try to put it out instead of only one person attempting to do so. It is often impossible for one person to put out this type of fire.
The two firefighters should approach the fire together from the intake airside, holding the extinguisher nozzle down at a 45-degree angle. Both streams of dry chemical should be directed to 6 inches ahead of the flame edge.
The two fire fighters should split up and slowly advance around each side of the obstacle while trying to keep up with each other as much as possible. Each person should cover two-thirds of the f ire area, and use a side-to-side sweeping motion with the extinguisher's stream.
When the fire appears to be extinguished, both fire fighters should remain on alert for awhile in case the fire restarts.
4. How to Use Wheeled Extinguishers- To operate the wheeled extinguisher, open the valve on the nitrogen first. Opening the valve forces the dry chemical through the hose to the nozzle. The person operating the wheeled extinguisher can then control the discharge from the hose by adjusting the nozzle operating valve.
This method for approaching the fire and putting it out is the same as the method used with the hand-held extinguisher: use a sweeping motion and direct the dry-chemical stream to about 6 inches ahead of the flame edge.
b. Rock Dust- Rock dust is a fire-extinguishing material which is readily available in most areas of the mine. Rock dust is used to smother fires by eliminating the oxygen from the fire triangle. Rock dust can be used on Class A, B, and C fires.
Rock dust is best used to fight a fire by shoveling it onto the fire or by throwing it on the fire by hand.Note: Although rock-dusting machines are usually available in the mines, they should not be used when a fire is involved because the machines generate air to disperse the rock dust. The dispersed air from these machines can move over the fire area fanning the fire and increasing its intensity.
c. Water- Water can be used to extinguish Class A fires. Water acts to cool the
fire, removing heat from the fire triangle.
In most mines, the water which is needed to fight underground fires
can be obtained from two sources: waterlines and fire cars.1. Disadvantages of water
2. Waterlines- In highly productive working sections of the mine (mining over 300 tons per shift) that do not have portable firefighting equipment, waterlines are required.
Therefore, to fight a Class A fire, where a waterline is available in the mine, hook up the fire hose to the waterline.
a. Nozzles
b. Hoselines
c. Types of nozzle streams
3. Fire Cars- Fire cars (or water or chemical cars) are available in some mines. These cars may be mounted on tires or flanged wheels, and they can be pushed or pulled to the fire area.
The components of a fire car can vary. Some fire cars have a water tank, a pump, or a hose. Others contain a great selection of firefighting equipment such as water, large chemical extinguishers, hand tools, brattice cloth, and rock dust.4. Fire Cars with Low-Expansion Foam- Some fire cars contain a foam agent which can be hooked onto the water hose along with a special foam nozzle to produce a low expansion foam. The foam works to extinguish the fire by smothering and cooling it simultaneously.
Low-expansion foam is very wet and very heavy and can only be used by a fire fighter who is close enough to the fire to force the foam directly on it. Low-expansion foam does not move down the entry like high expansion foam does.
5. Techniques for Applying Water to Fires- The best way to fight a fire with water is to aim the water stream directly at the burning material.
Use a side-to-side sweeping motion to wet the entire burning surface. Where possible, break apart and soak any deep-seated fires and stand by to extinguish any remaining embers.
There are several different types of water nozzles available for the hose. Some nozzles produce a solid stream of water, some produce a fog spray, while others are adjustable like a garden hose.
Solid-stream nozzles are the best ones to use if it is necessary to project water a long distance to the fire.
d. High-Expansion Foam
1. Description- High-expansion foam is mainly used to contain and control fire by eliminating two points of the fire triangle: oxygen and heat. The great volume of the foam also smothers and cools the fire at the same time.
High-expansion foam is used only in fighting Class A or Class B fires. Since the foam is light and resilient, it can travel a long distance to a fire without breaking down (unlike low expansion foam which is used directly on the fire).
Therefore, this foam is very effective and is used to control stubborn localized fires which cannot be approached at a close range when there is too much heat or smoke, or when the fire is spreading rapidly.
Firefighters can be 500 feet from the fire and in some cases, up to 1500 feet away from the fire when using high-expansion foam.
High-expansion foam is normally used to control a fire. When conditions permit, then fire fighters can be sent in to fight the fire more directly.a. Types of foam
Protein
Fluoroprotein
Aqueous Film Forming Foam (AFFF)
Alcohol Type Concentrates (ATC)
High Expansion Foam
No burn back protection, not film forming
Note: It is recommended that teams do not travel through foam-filled areas because hearing is impaired, vision is blocked, and breathing is difficult. There is the added hazard of slipping and falling in the foam. Some manufacturers recommend that personnel do not wear self-contained breathing apparatus, gas masks, or other breathing apparatus into the foam.
In cases where teams must travel through foam, team members must use a link-line to ensure team members do not get lost in the foam. The team should travel along the track or rib where the best footing is likely to be.
Consequently, before entering a foam-filled area, teams should clear away as much foam as possible. One of the best ways to do that is to use a solid stream of water to knock down the foam and clear the area.
2. Foam Generators
a. Description- Foam generators are portable and come in a variety of sizes which have different foam-producing capabilities. The smaller models can be hand-carried by two people or wheeled into position. Other larger models can be mounted on rubber tires or can be transported on a track-mounted mine car.
There are water-driven models of foam generators or diesel- or electric-powered models. The water-driven models produce foam from a water-detergent mixture which is pushed by the water pressure through nylon netting or screen. As in other models, a blower fan produces the bubbles and pushes them out of the generator.
b. How to Use- There are different methods to use foam to fight a fire as described below.
1) The foam generator is positioned outby the fire and the plastic tubing is attached to the foam outlet. The plastic tubing is designed to unroll as the foam passes through it leading the foam directly to the fire area.
2) Create a confined area where foam can be pumped onto the fire to completely fill or plug the fire area. Build a stopping with an opening in it for the foam generator to fit into the opening outby the fire.
Set up the foam generator at the stopping opening and brace it or fasten it down if possible. After it is set up, the generator can be started and foam can then fill the area. Sometimes plastic tubing is attached to the foam generator to direct the foam to the fire area.
In some situations, a team can use the generator in stages, moving it closer to the fire as the fire is brought under control. Before traveling through a foam-filed area, knock down the foam with water to clear a safe passage.IV. Firefightinga. Before Going Underground- Rescue teams should be aware of two main dangers before going underground:
1) Spreading of the fire and
2) Explosions.
Before going underground, the team should make sure that: 0 The main fan is running;
It is important to monitor the levels of oxygen, carbon monoxide, and any explosive gases.
Ventilation should always be continued through the mine during a fire in order to carry off explosive gases and distillates away from the fire area, and to direct the smoke, heat, and flames away from the team.
Note: Do not make any sudden changes to the mine ventilation. If the main fan is off or destroyed, the command center will have to decide what to do before starting the fan. Remember, everyone should be out of the mine before the fan is started.
Before going underground, the team should know about the following:
1) Know ignition sources such as battery-operated or diesel equipment.
2) Know underground storage areas for explosives, oil and grease, or oxygen or acetylene cylinders in or near the affected area; and
3) Cut off electrical power to the affected area. Arcing from damaged cables can ignite and cause additional fires or explosions. Remember, once the power is cut off, power is lost for any underground auxiliary fan, and to any other electrically powered equipment, such as a pump in the area. Losing the pump can result in major flooding.
While most of the above conditions and information should be available to the team at the briefing, some specific information about what is in or near the affected area, and what equipment was left energized, can only be determined by the exploration teams as they advance.
Note: For safety reasons, before and after firefighting, each team member should have a carboxi-hemoglobin test to determine how much carbon monoxide (CO) is in the bloodstream. A small amount of blood is drawn for this test to detect the presence of CO in the blood. Each team member's on-site CO rate should be compared to the base rate obtained during each person's annual physical examination to determine if dangerous levels of CO are present. If a team member has absorbed too much CO, he or she should not be allowed to reenter the mine until his or her CO level is reduced.
b. Locating Fires and Assessing Conditions- The two main objectives of mine exploration work during a mine fire are:
Once the conditions are known and reported to the command center, the officials there can then decide how the fire should be fought.
The command center has to be given the basic information about the fire: where it is, what is burning, how large it is, and what conditions are near the fire area.
Before the team enters the mine, there may be some information available about the location of the fire. Miners who were working in the area may have reported seeing smoke or flames before evacuating the mine. Their reports would help the team pinpoint the fire and its magnitude.
Detecting carbon monoxide or smoke coming from the main fan or main return are obvious indications that a fire exists.
Having a laboratory analysis of air samples taken from the main fan or return give an accurate analysis of the gases which are present and can indicate what is burning. The amount of carbon monoxide found in the samples can indicate the magnitude of the fire.
Certain information is only obtainable from the rescue teams during mine exploration. The teams can pin point an unlocated fire and assess its magnitude by reporting where and how dense the smoke is, and by feeling the stoppings and doors for heat.
If a team encounters a small fire during exploration, it can be extinguished by hand-held fire extinguishers, rock dust, or with water from a nearby waterline. But dealing with large fires requires more equipment and careful planning.
The team is to gather as much information about the conditions in and around the fire area as possible and report it to the command center in order to keep officials up-to-date on conditions.
During mine exploration during a fire the team should:
Once the command center has this information it will have sufficient facts about the fire and what is needed to extinguish or control it, and whether to fight it directly or seal the mine.
This formula should not be used if the air intake is oxygen deficient.
Tr = CO2 + 0.75 CO - 0.25 H2
0.265 N2 - O2
The gas samples needed for the formula to work are carbon dioxide, carbon monoxide, hydrogen, nitrogen and oxygen.
Once the formula is worked, the answer should tell you if the following is burning:
Tr < 0.4 - Generally indicates no fire because:
Tr = 0.45 - .05 - Methane is burning
Tr = 0.5 - 1.0 - Coal, oil conveyor belting, insulation, or polyurethane foam
Tr = 0.9 – 1.6 Wood
Tr = > 1.7 Error
c. Direct Firefighting
1. General Procedures- To fight a fire directly means that an extinguishing agent is put directly on the fire to put it out. To do so means the firefighters have to get very close to the fire for them to use fire extinguishers, water, rockdust, or foam to put out the fire.Always approach a fire from the Intake side if possible when fighting the fire directly. This approach ensures the smoke and heat are directed away from the fire fighter.
Use wide angle fog for team safety and steady steam for direct contact with fire.
Should the fire back up against the intake air in search of oxygen, put up a "transverse" brattice from rib to rib but leave an open space at the top. Doing so will cause increased airflow at the roof and slows down. the progress of smoke and flame into the air current.
Take caution in putting up the brattice. The brattice should cover about one-half to two-thirds of the area from the floor to the roof or top. Do not run the brattice too high or it will cut off the airflow over the fire which could result in an explosion.
If heat, smoke, and ventilating current allow, water is the best means of fighting a fire, provided it is not an electrical fire. However, there has to be a sufficient water supply, water pressure, and available lengths of hose to reach the fire.
In situations where the team finds it impossible to approach the fire for direct firefighting, foam or water can be pushed over the fire area to slow down the fire sufficiently. This method allows the team to get closer to the fire to fight it more directly.
2. Hazards- During direct firefighting, there are certain hazards to the team. These hazards include electric shock and electrocution, toxic and asphyxiating gases, oxygen deficiency, explosive gases, heat, smoke, and steam.
a. Electric Shock and Electrocution- Electric shock and electrocution are the primary hazards to fire fighters using water, foam, or other conductive agents to fight a fire. It is for this reason that it is strongly recommended that the power to the fire area be cut off regardless of the type of fire. Cutting off the power not only eliminates the electrical hazards, but also eliminates the possible hazards to any electrical components that could be involved.
b. Toxic and Asphyxiating Gases- There are several toxic and asphyxiating gases which fire fighters should be very cautious of and be certain to wear SCBAs in mine atmospheres where these gases may be present:
Note: If the mine fan stops or slows down, the fire team should leave the fire area. If the fan continues to run slowly or remains stopped, teams and underground personnel should leave the mine entirely before the fan is restarted.
The mine fan should never be stopped or reversed while teams are underground. Doing so forces unburned distillates from the fire to travel back over the fire area, increasing the magnitude of the fire.
If any explosive concentration of gas is detected in the return air of the fire, all teams and any other personnel should leave the mine immediately.c. Heat, Smoke, and Steam- Heat, smoke, and steam are other hazards underground rescue teams face. These hazards determine how close a team can get to a fire and how long the team can work. Working in these conditions can be extremely uncomfortable.
Smoke limits visibility and causes disorientation. Walking can be dangerous because it is difficult to judge your position in relation to surroundings. This lack of orientation can cause a member to lose his or her sense of balance and fall and get injured.
Working in hot and steamy atmospheres can cause exhaustion and stress the body's system, particularly when working hard.
Heat can weaken the mine roof in the fire area, especially in mines where head coal is left in place. To protect against a weak roof, always test the roof near the fire area frequently and bar-down any loose material.
Remember, during firefighting, smoke and steam are less dense near the mine floor but are more dense at the mine roof. Keep adequate ventilation over the fire area to carry off smoke, heat, and steam away from the team.
As stated earlier, if the fire begins to back up against the flow of the intake air in search of oxygen, put up a transverse brattice from rib to rib, leaving an open space near the roof. Doing so should slow down the progress of the smoke and flame into the intake air current.
d. Indirect Firefighting-
in some instances, fighting a fire directly is ineffective or not possible because of the presence of certain mine hazards such as high temperatures, bad roof, or explosive gases.
Under these circumstances, it may be necessary to fight the fire from a distance, or fight the fire "indirectly," by sealing the fire or by filling the fire area with foam or water.
The indirect methods work by excluding oxygen from the fire. The foam or flood of water also serves to cool the fire.
a. Planning- The purpose of sealing a mine fire is to contain the fire to a specific area and to exclude oxygen from the fire and eventually smother it. Sealing can also be done to isolate the fire to allow normal mining operations to resume in other areas of the mine.
Sealing mine fires underground is complex with no set rule of procedures to follow. Many factors have to be considered to determine the methods to be used for the eventual success of the sealing operation.b. Temporary Seals- There are two types of seals: temporary and permanent. The temporary seals are put up before permanent seals. Temporary seals are erected in order to seal of f a fire as quickly as possible. Usually permanent seals are then constructed outby the temporary seals to seal off the fire more effectively.
Temporary seals are built to be fairly airtight, and are usually constructed of brattice cloth, concrete blocks, or boards.
Permanent seals are built to be much stronger and more airtight than temporary seals. They are notched into the roof, ribs, and floor to make them sturdy to withstand the force of an explosion, should one occur.
Permanent seals are usually built with concrete blocks and strong mortar. They can be made of poured concrete, wood, or plaster, or pack wall of various kinds as well.
Command center officials decide what types of seals are to be erected based on all of the information they receive pertaining to the mine fire.
The command center must consider all dangerous mine conditions when planning to seal a mine fire. The following six factors are of primary concern.
1) The volatility of the coal seam. High-volatile coal seams burn much faster than low- or medium-volatile coal. Sealing a fire that involves high-volatile coal is often necessary because fighting the fire directly is very difficult.2) The amount of methane liberated by the coal seam. As the amount of methane increases underground, the potential for explosion increases.3) The location of the fire and the area involved. These two elements determine the number of necessary seals and where they should be placed.4) The presence of head coal and the composition of roof strata. Mines which have head coal left in them will have a fire spread more rapidly than those that don't. Certain roof strata is greatly weakened by fire and heat, and may be too hazardous for the rescue team to work under.5) The availability of construction materials and the means of transporting them to the sealing sites. This factor affects the type of temporary or permanent seal to be built. Frequently in emergency situations, temporary seals are built with readily available materials.6) The building sites for the seals. These sites are determined by the location of the fire, how fast the fire is spreading, the ability to control ventilation in the fire area, the gas conditions present, and the volatility of the burning coal seam.
Fires involving high-volatile coal are often sealed more than 1,000 feet away from the fire. Fires involving low-volatile, non-gassy coal may be sealed relatively close to the fire.
One of the reasons why seals should be erected as far as possible from a high-volatile coal fire (1,000 feet or more) is to allow sufficient time for the mine rescue teams to leave the mine before an explosive mixture of gas is likely to form inby the seals.
The command center decides the approximate location for building the seals, what material to use, and in what order the seals must be built if more than one seal is to be erected.
The mine rescue team chooses the exact site within the designated entry or heading for building each of the seals and is to construct them well.
When choosing an exact site for temporary seals, the site should have:
When building a temporary seal, it should always be built far enough into the entry or crosscut to allow enough room and good roof outby it for a permanent seal to be built. If the only site available for sealing has bad roof, it may have to be barred down and supported with posts prior to building the seal.
1. Types of Temporary Seals
a) Brattice Cloth- There are three ways to erect brattice seals:
1) The brattice, canvas, or plastic can be attached to the roof and ribs with spads. The surplus brattice at the bottom is then weighted down with timbers or other available loose material to keep the seal closed.
2) The other two methods require nailing the brattice to a framework of posts and boards that are set in a solid and well-squared location. One style involves cutting and nailing the brattice to the frame work and to the ribs, if possible.
It may be necessary to double or triple the thickness of the materials in order to improve the effectiveness of the seal. To seal the bottom as well as possible, shovel loose coal or other material along the bottom of the seal. Doing so provides a seal which is tight enough for most purposes.
3) If time allows and a tight seal is required, a more substantial brattice cloth seal can be erected. To do so, set posts about 1 foot from each rib, and one or more posts in between. Set the posts firmly on solid ground.
Nail boards across the top, the center, and the bottom of the posts. The boards should extend from rib to rib, and the top and bottom boards should be placed as close to roof and floor as possible.
If the ribs are irregular, short boards extending from the top to the center boards, and from the center to the bottom boards should be nailed along both sides of the frame work. These boards should follow the curvature of the rib.
A piece of brattice cloth, canvas, or plastic should be nailed to the boards. The material should be cut with enough room to cover the opening, allowing for extra material on the sides, top, and bottom. It may be necessary to double or triple the thickness of the material in order to improve the air tightness of the seal.
To close small openings around the edges of the seal, small pieces of boards should be used to push the brattice cloth into all irregularities of the roof, ribs, and floor and nailed into place.
To obtain maximum tightness, it may be necessary to caulk the edges of the seal, and to shovel loose coal or other material against the bottom.
If reasonable care is used, a brattice cloth seal can be constructed which will allow only a slight leakage of air.b) Concrete Block- Concrete block seals can be erected quickly, especially if they are laid dry. To lay them dry, the blocks should be built up on a solid bottom, one layer at a time. The last layer of blocks should be wedged between the top of the seal and the roof.
Caulk the edges of the seal with cement or other suitable caulking material. Then plaster the seal with cement or another suitable sealing material to make the seal as airtight as possible.
c) Wood- Various kinds of boards can be used to construct wood seals. Usually rough boards of various widths and approximately 1-inch thick are used. If a tighter seal is desired, it is better to use tongue-and-groove boards or shiplap boards.
Nail the boards horizontally on a frame work of ribs and center posts. The posts should be wedged inward and hitched in the bottom. If possible, a shallow hitch should be dug in the roof, ribs, and floor, and the boards should be fitted snugly into the hitch as the seal is erected.
The boards can be overlapped at the center of the seal if they are too long to fit properly. Overlapping them will eliminate having to saw the boards, which saves time.
If using shiplap boards, nail them onto the framework, starting from the top and overlapping each board while working toward the bottom. After the boards are nailed to the framework, caulk the edges of the seal with cement or other suitable caulking substance.
If using rough lumber and sufficient brattice cloth is available, cover the entire surface of the seal with a layer of the cloth. If brattice cloth is not available, plaster over the cracks and holes to make the seal airtight.
2. Considerations While Building Temporary Seals
a) Air-Sampling Tubes- When building temporary seals, include provisions in some of the seals for collecting air samples from within the sealed area. Pipes with valves are used for this purpose. These pipes are usually quarter-inch copper tubing because it is light and flexible.
This air-sampling tube can be placed anywhere in the seal, and should extend at least to the second crosscut inby the seal in order to get a good representative sample of the air which is close to the f ire. Depending on the situation, it could vary from 40 to 100 feet. The tube can be suspended from the roof by tying it to timbers or roof bolts.
The number of seals in which air-sampling tubes should be placed depends on the sealed area, the number of seals, and their positions.
b) Ventilation- When building temporary seals, consider ventilation. Be sure there are no abrupt changes in ventilation over the fire area.A steady flow of air must continuously move over the fire to carry off explosive gases, distillates, heat, and smoke away from the fire.
The only way to keep the air flowing over the fire area is to leave one intake airway and one return airway unsealed while the other airways are being sealed.
Then as a final step, the last intake and return can be sealed simultaneously. This method enables the ventilation to continue over the fire area until both seals are completed.
Occasionally two teams are used to simultaneously seal the last intake and return. In such circumstances, the teams should be in constant communication between themselves or with a coordinator in order to synchronize the simultaneous construction.
Usually fires are sealed far enough away from the fire in order to keep the heat and pressure in the sealed area from affecting the seals.
In some cases though, the only site available for sealing a fire is close to the fire area where the heat and smoke are very intense in the returns. As a result, the mine rescue teams will not be able to work in the returns for very long.
In this type of situation, the fire can be systematically sealed to protect the team as much as possible from the heat and smoke in the returns.
When the intake seal is finished, the pressure will be reduced in the returns and the brattice curtain can be dropped immediately by the rescue teams, spadded to the ribs and weighted at the bottom-all within a few minutes. The teams then immediately leave the mine.If, for some reason, the seals do not hold because of the heat and pressure within the sealed area, the fire will have to be resealed further away from the fire.
c) Explosion- If an explosion is likely to occur after the seals have been erected, arrangements should be made to close the last seals after all personnel are out of the mine. This can be done by leaving hinged doors (similar to drop doors) that will close automatically in one or more of the seals; usually it is the last intake seal to be erected.
These doors can be temporarily held open with a counterbalance in the form of a perforated bucket filled with water. The holes in the bucket should be made to allow sufficient time to elapse before the water drains from the bucket. Using this device allows enough time for the personnel in the mine to reach the surface before the door or doors close to complete the seals.
When fires are being sealed in gassy or dusty mines, it is essential to apply a thick coating of rock dust to the ribs, roof, and floor of entries, and to crosscuts for several hundred feet outby the seal, and if possible, inby the seal. In the event of an explosion around the fire, there will be less chance of propagating a coal-dust explosion.
d) Isolation- It is important to isolate the sealed area from the mine in as many ways as possible. All power cables and water or air lines entering the sealed area should be removed or severed from the sealed area. Removing a section of rail from the track and a section from any other conductor leading into the sealed area is advised also.
3. Permanent Seals- A mine cannot be returned to production until the sealed area of the mine has been closed off with permanent seals. After temporary seals are erected, the usual waiting period of 72 hours is recommended before beginning construction on the permanent seals.
a) Types of Permanent Seals- Usually permanent seals are built with solid concrete blocks, although other material may be used. When building seals with
concrete blocks, mortar is used in between them, and the entire front of the seal is plastered over. Urethane foam can be put around the edges to seal any leaks.
Urethane foam is an effective sealant around the perimeter of the seal, but should never be applied more than an inch thick because the potential for spontaneous combustion increases with greater thicknesses.
All permanent seals should be well-hitched in the roof, floor, and ribs to make them as airtight as possible.
The type of permanent seals used for sealing a mine fire depends on:
b) Considerations While Building Permanent Seals
1) Isolation- When erecting permanent seals, the area inby the seals is to be isolated from the rest of the mine. All cables, lines, and track which were removed or severed. For the temporary seal must also be removed or severed for the permanent seal.
2) Air-Sampling Tubes- The permanent seals must have provisions for collecting air samples from within the sealed area.
If air-sampling tubes were installed in the temporary seals, it will only be necessary to extend those tubes and valves to the permanent seals if they do not already reach.
4. Taking Air Samples- After the fire area is sealed, it may be necessary to take air samples of the air behind the seal to assess the quality of the air. The best time to do so is when the sealed area is under positive pressure or "breathing
out.
Pressures within and without sealed areas will vary according to temperature and barometric pressure changes. There are three general descriptions for these differences in pressure:
1) "Breathing in", or a negative pressure in the sealed area;
2) "Breathing out," or a positive pressure in the sealed area; and
3) "Neutral," when there is no difference in pressure in the sealed area.
When collecting an air sample, if the sealed area is breathing out, let the pressure evacuate the air from the sealed area for awhile before getting the sample. By doing this, it assures getting a good representative sample of the air that is in the fire area and not getting the air that is right next to the seal.
If the sealed area is breathing in or neutral, use an aspirator bulb or a small pump to evacuate enough air from the sealed area to assure collecting a good representative sample of the air that is in the fire area.
Sometimes though seals are situated so far away from the fire that the air near the seals has a completely different composition from the air near the fire. In these cases, air samples are usually not collected at the seals because they will be inaccurate. Instead, use a 2-inch borehole from the surface to the fire area to obtain air samples.
5. Sealing the Surface
a) Entire Mine- Although it may be possible to seal a fire in a gassy section of a mine without a subsequent explosion during or shortly after sealing operations, undoubtedly the safest method is to seal the mine openings at the surface. On these occasions, any mine opening to the surface is plugged up and sealed as best as possible.
b) Remote Sealing- Another method of sealing a fire from the surface is to pump sealing material down through the boreholes to the fire area. This method is usually used within a mine which was already sealed on the surface, making it possible to establish effective temporary seals in a distant part of a large mine where a fire raged.
By establishing these temporary seals, it may be possible to reestablish ventilation throughout the rest of the mine without disturbing the fire area during the initial recovery of the mine.
Some of the materials which can be pumped through the borehole to seal the fire area are rock wool or fly ash.
6. Foaming the Fire Area- Foam can be used indirectly on a fire in an attempt to bring the fire under control allowing more direct extinguishing methods to be used.
In these instances, the foam generator is setup some distance from the fire. The foam is then pumped down to the fire to smother and cool it.
Sometimes it is necessary to construct a temporary stopping around the foam generator which will create a confined area where the foam can be pumped.
When conditions permit, the foam generator can then be moved closer to the fire, or the team members can move in to fight the fire directly.7. Flooding the Mine- One additional method for indirect firefighting is to flood the sealed area with water. This method is infrequently used. Rather, it is used as a last resort because flooding the mine makes recovery of the mine very difficult and expensive.
Another application is the use of liquid nitrogen which can be injected through boreholes into the fire area to make the mine atmosphere safe during firefighting activities while permanent seals are being built. Injecting nitrogen in this manner is done to make an inert mine atmosphere to reduce the chance of an explosion and the buildup of methane. It also cools the area.
Nitrogen is often used for spontaneous combustion problems since methane is most explosive from 5 to 15 percent in a 12 percent air mixture. Carbon dioxide can also be used following the same principles and applications as nitrogen.
The company brings in its own technicians, plus union (where applicable), state, and federal experts who jointly decide if nitrogen or carbon dioxide should be used.
V. Explosionsa. Causes and Effects- Explosions are very similar to fires in terms of their cause. Just as there are three elements required to cause a fire (recall the fire triangle), three elements must be present for an explosion to occur. Those elements are:
The fuel for an explosion can be an explosive mixture of gas, or a sufficient concentration of coal dust, or a combination of both of them.
Like a fire, an explosion can only occur if all three elements are present at the same time. To avoid an explosion, the three elements of the fire triangle must be kept away from each other.
The most frequent cause of explosions in coal mines is the ignition of methane gas, coal dust, or a combination of the two.The source of ignition is commonly sparks, an electric arc, an open flame, or the misuse of explosives.
Explosions can cause extensive mine damage. Explosions can blow out roof supports, damage ventilation controls, twist or scatter machinery, and ignite numerous fires. Roof and ribs can be weakened, and fires can be spread.
Once an explosion occurs, there is the chance of more explosions. Further explosions are possible because the ventilation system is damaged from the first explosion. Methane can accumulate and ignite either from existing fires which may have started, or from other sources, such as an arcing or damaged cable.
The coal dust which was stirred up from the first explosion can prompt additional explosions.Coal dust explosions travel at a speed exceeding 3000 ft. per second
b. Before Going Underground- Before going underground to explore a mine where an explosion has occurred or is suspected to have occurred, the rescue team should make sure that:
Rescue teams should be aware of the same types of hazards they prepare for to explore a mine where an explosion occurred as they do to prepare for a mine where they must fight a fire. These preparations are reviewed below.
1. Keep the main fan running to prevent a build up of explosive gases and assure ventilation at least up to where underground controls were damaged or destroyed by the explosion.
Testing for CO and explosive gases in the returns is essential to perm it teams to withdraw from the mine if a dangerous situation develops.
2. Cut off power to the affected area. Arcing from damaged cables can ignite and cause more explosions or fires. Remember that cutting the power will affect any auxiliary ventilation which will affect the operation of any electrically powered equipment, such as the pump. The command center will have to consider these factors.
3. The team must know of any possible ignition sources underground, including any battery-powered or diesel equipment left running. Any fires which develop are also ignition sources for more explosions.
4. Teams should know of any underground storage areas for explosives, oil and grease, or oxygen or acetylene cylinders.
The teams should be given this information during their briefing, but more specific information can be gathered by the teams as they advance through the mine during exploration.c. Exploration: Indications of Explosion and Assessing Conditions- Frequently an explosion is suspected to have occurred in a mine, but officials can't know if that is true until the mine exploration team assesses mine conditions firsthand. What may seem like an explosion may turn out to be a major roof fall or a rock burst or a rock bump.
The first indications that an explosion took place may be from reports from miners in nearby sections who felt a sudden movement of air, noticed smoke or dust in the air, or heard the sound of an explosion. A jump in the pressure recording chart for the main fan would be an indication too.
Rescue teams going into a mine to check for an explosion should look for the following evidence:
· The presence of afterdamp and toxic and explosive gases in the main returns.
· Blown out stoppings and roof supports. Examine damaged stop-. pings carefully. The direction in which a stopping has blown indicates the direction of the force of the explosion. If stoppings are not destroyed, note if blocks have moved, especially when stoppings cross entries near intersections. (The movement of blocks from stoppings in crosscuts is seldom significant.)
The initial role of the rescue team after an explosion is usually to explore and assess conditions. After that is completed, the teams begin to restore ventilation and recover the mine.
In some situations it may be too dangerous for teams to explore and re-ventilate safely. If that is the case, teams are usually instructed to seal the area.