Mine Rescue and Recovery Operations Following Coal Mine Fires and Explosions Question and Answer

Methane (CH4) is the principle combustible gas found in coal mines.

5 to 15 percent of methane in air is explosive.

For a mixture of strictly methane and air, the oxygen content must be 12 percent or less. It is, however, significant to note that there is a combination of combustible gases following explosions and during fires, so the maximum allowable oxygen will vary according to variations in the combustible and inert gases.

12.5 to 74 percent carbon monoxide in air.

4 to 74 percent hydrogen in air.

5 percent or less.

Carbon dioxide (CO₂) and nitrogen (N₂).

Methane may be found anywhere, but is most likely to be encountered. in virgin coal, roof cavities, high places, abandoned workings, and places that are improperly ventilated. Carbon monoxide may be found in small quantities after blasting and will be found after an explosion or in the return from a mine fire. Hydrogen sulfide may be found in old pipelines, stagnant water, fire areas and occasionally in active workings, usually associated with broken bottom.

Only oxygen.

1. Deficiency of oxygen in the air being breathed deprives the body of the oxygen required for normal life support. Noticeable symptoms such as faster and deeper breathing, dizziness, rapid heart beat, and headache occur when the air contains as little as 15 percent oxygen. Unconsciousness may occur when the air contains 9 percent oxygen: and life is greatly endangered when the air contains 7 percent oxygen. A flame safety lamp will no longer burn when the oxygen content is below 016.25 percent.
   
2. Carbon monoxide breathed in air reduces the capacity of the blood to carry sufficient oxygen, which deprives the brain and body tissues of the oxygen they require for normal functioning. The generally accepted maximum allowable concentration for an 8-hour exposure with normal oxygen is 0.005 percent. Somewhat higher concentrations may be considered allowable for short periods of exposure. For example, 0.04 percent can be inhaled for one hour without appreciable effect, but 0.15 percent is dangerous to life after exposure of one hour, and .4 percent will cause death in less than an hour.
   
3. Hydrogen sulfide in very small amounts will cause irritation of the eyes and respiratory passages, including the lungs; concentrations as low as .07 percent will cause rapid unconsciousness, cessation of respiration, and death.

When it is no longer reasonably safe or feasible to fight the fire directly because of a build up of combustible gases, bad roof due to heat, insufficient firefighting materials, too large an area engulfed by fire, etc.

The object is to control and extinguish the fire by cutting off the oxygen supply so as to reduce the oxygen below that which will support a flame or combustion; also to minimize or eliminate the possibility of an explosion.

When coal burns, explosive and asphyxiating gases are liberated or produced and the heat from fire causes roof falls. Therefore, the installation of seals, the roof falling, or other firefighting activity may cause an explosive mixture of gases to reach the fire causing an explosion. In addition, there is a potential for workmen to be overcome by asphyxiating gases because of the need to work in the return airways and because of roof falls changing the pattern of ventilation. It is important that the air returning from the fire area be monitored for explosibility.

No fixed rule should be established for sealing, but the procedure must be governed by the conditions surrounding each fire. It is, however, preferable to erect both intake and return seals simultaneously. It may even be advisable to devise a method of having doors in the seals closed after all workmen have returned to the surface.

Conditions govern this. As the objective in sealing is to cut off the air so that oxygen will be consumed to the point that there is not enough oxygen to support combustion, the smaller the area sealed, the quicker this will be accomplished. Roof conditions, amount of combustible gases being given off, the intensity of the fire, and the number of seals required are the principle factors to be considered when selecting seal locations.

Not necessarily. Circumstances surrounding each fire will determine whether or not temporary seals should be erected. Factors to be considered when making this determination are the availability of permanent sealing material, the rate of rise of combustible gases, the rapidity of the spread of the fire, the accessibility of the seal locations, etc.

The most common and practical materials are those normally used within the mine such as brattice cloth, brattice boards, plastic material, and other sealing materials. Whatever the materials used, the edges should be sealed with urethane foam or other material to make them as air tight as possible.

Emphatically, no! The main hazard after sealing a mine fire is the possibility of an explosion within the sealed area. All men should be removed as quickly as possible after completion of work on the seals. Normally, no one should enter the mine when it is known that there is an explosive atmosphere within the sealed area. Samples to determine whether or not the atmosphere is explosive should be collected through boreholes from the surface whenever possible. Otherwise, the first trip into the mine after sealing should be for the purpose of collecting samples from the sealed area. The number of people making this trip should be limited to as few as necessary and how soon the trip should be made after seals are completed will depend to a large extent upon the size of the sealed area, the amount of combustible gases in the area when the seals were constructed, and the normal methane liberation in the area.

They should be as air tight as possible and strong enough to resist slight concussions by being constructed of brick, tile cement blocks laid in cement mortar and notched into the floor ribs, and roof. Selected seals should be provided with a door that can be used for exploration or ventilation during recovery work. Selected seals, particularly those at high and low elevation points, should be equipped with sampling pipes or tubing with valves that extend through the seals at least into or beyond the first intersection. A thermocouple should also be placed at or near the fire area with connection to the outer side of one of the seals. Unsealing Fire Areas in Coal Mines

The presence of carbon monoxide is an indication of an active or recently active fire.

The amount of oxygen under these circumstances is critical because of the possibility of explosion when unsealing a fire area. Ideally, the oxygen content should be such that the atmosphere in the sealed area is not explosive and cannot become explosive when air is added. Where this is not possible, the procedure for recovery should insure that men are not in the mine when an explosive mixture exists in the sealed area unless the area has been examined and there is no fire.

Some principle factors are: Tightness of seals and enclosed area: influence of barometric pressure on enclosed area: character of burning material and overlying strata: extent and intensity of fire: location of seals with respect to mine ventilation: the extent of the area under seal: composition of gases in the sealed area.

When the temperature reaches normal and there is no carbon monoxide in the sealed area it can be assumed that there is no longer active fire. There must be a sufficient period of time allowed for the area under seal to cool after the fire is extinguished before recovery operations begin. In addition the atmosphere in the sealed area and procedure for recovery should be such that an explosive mixture will not be present in the sealed area while men are in the mine unless the entire area has been examined and no fire exists.

The amount of carbon dioxide present under these circumstances would have very little effect on the fire but is a factor to be considered in determining whether or not the atmosphere is or may become explosive. Carbon dioxide may be introduced into a sealed area to help control the fire and help create an inert atmosphere

A complete and detailed plan should be prepared and agreed to by various interested parties. Necessary adjustments should be made in the ventilation to assure that an ample quantity of air will be available and that the air that passes by or through the sealed area is conducted in such a manner that it will not pass over power wires or any other potential ignition source and shall be directed by the shortest means to the surface. The area adjacent to the seals should be heavily rock dusted. The tools and supplies that will be needed should be placed at convenient locations.

1. Recovering the fire area in successive blocks by means of air locks.
   
2. Reventilation of the fire area after there is conclusive evidence that the fire has been extinguished or that the atmosphere is not explosive and will not become explosive with the addition of air.

The purpose of air locking is to recover portions of the sealed fire area or the entire area in a manner that will prevent increasing the oxygen content in unexplored areas to avoid an explosive atmosphere or rekindling or intensifying the fire when a suitable air lock has been erected, a proper organization and proper and adequate equipment and material provided and all other necessary arrangements are completed, an oxygen breathing apparatus crew, fully equipped for the work at hand and supported by a fully equipped reserve crew should enter the air lock through a man door and remove the seal. After the seal has been removed, an oxygen breathing apparatus crew, with another crew in reserve, should advance and explore to the point where the next air lock is to be erected. General conditions should be observed by the exploring crew, temperature readings taken, an air sample collected to check previous analysis, measurements made for material required to construct the inby seals of the next air lock, then return to the fresh-air base. An apparatus crew or crews, with a reserve crew at the fresh-air base, should then construct a temporary seal with a door in it at the place previously selected for the next air lock, erect necessary temporary seals in crosscuts or other openings on the intake side and on the parallel entry or entries on the return side opposite the point selected for the air lock to insure resealing of the inby area, and examine any unexplored parts of the isolated area for possible fires. All crews should then be withdrawn from inside the air locks. Next, a seal on the return side should be opened by an apparatus crew: the air-lock doors on the intake side should be opened and air admitted to reventilate the area inside the air locks. Stoppings should be erected in open crosscuts on the return side to advance fresh air to the last crosscut which should be left open to provide a return. The quantity of air should be so regulated that the return will be kept below the lowest explosive limit. After the newly explored area has been reventilated, fresh-air men should erect a tightly constructed stopping with a door in it a suitable distance outby the one previously built to form the next air lock. Advances as described above should be made by successive blocks until the entire area is recovered As the work progresses, frequent analyses should be made to determine the composition o] the atmosphere within the sealed area The oxygen should be kept under control and within safe limits at all times. It is imperative that the oxygen be kept as low as possible at all times by limiting the infiltration of air to the sealed area as the work progresses.

When a decision has been made to recover a sealed area by direct ventilation, an air lock should preferably be constructed near the intake seal. A rescue crew fully equipped for the work at hand breaks the seal, enters. Observes conditions, takes temperature readings and air samples, and returns to the fresh air base. The observations and examination of the affected region have shown that conditions are favorable, the return seal should be broken by an apparatus crew, then the air lock opened to admit air. While the area is being ventilated, the combustible gases in the main return should, if feasible, be kept below the explosive limit. If this method of recovering a fire area is employed, it is advisable that all men be out of the mine before the air is actually directed into the sealed area, unless it has been determined that the atmosphere in the sealed area is not explosive and cannot become explosive by adding air. Some automatic arrangement should be employed which would give sufficient time for all persons to reach the surface before the fire gases were actually moved A reasonable period should be given for the fire gases to be removed and frequent determinations should be made of the return from the mine, and the time for any person to enter should be governed by the quality of the return air if the workings under seal are of an extensive nature it will probably be advisable for crews equipped with oxygen breathing apparatus to re-enter the mine and clear out pockets of standing fire gases that may be present.

Notify as soon as possible: higher company officials. State mining agency. Federal mining agency, representative of mine workers, safety department engineering department, and maintenance department. Also, adjoining mines should be notified for possible assistance or to alert them if they are connected underground with the affected mine.

Rope off and have police guard all roads leading to the mine. Establish a base of operation with ample room and communications. Establish special check procedures for acquiring necessary supplies.

The mine ventilation. The fan or fans should be examined and repaired as necessary, then attended or other action taken to assure continued operation.

A major factor to be concerned with during recovery following an explosion is the possibility of another explosion. List the methane ignition sources which are most likely to be encountered in the affected areas that have not been explored and ventilated.

1. Fire that was started by the explosion.
   
2. Electrical arc that may be created by short-circuited batteries, or power wires that have not been de-energized.

Endeavor to communicate with survivors and direct them to the best means of escape from the mine.

1. Men entombed or missing should be located and brought to safety or their bodies recovered as soon as possible.
   
2. Incipient or active fires should be located and extinguished or sealed off before an air current — possibly laden with explosive gas — is turned upon such a fire. If fire exists, unrestricted restoration of ventilation may fan it to greater intensity and make extinguishing it more difficult; or an explosion may occur killing some or all of the men still alive in the mine.
   
3. Normal ventilation should be restored to all parts of the mine and all noxious gases swept out after the danger of fire has been found nonexistent or under control.

An explosion is the major accident that is likely to occur during firefighting operations.

The air returning from the fire should be monitored for explosibility, and ventilation should be controlled closely and maintained over the fire constantly.

Yes, generally a representative of the company.

Yes. The committee should be composed of representatives of the State mining agency, Federal mining agency, the miners, and others.

Yes. The man in charge and the advisory committee should devise a relatively broad plan of operation which should be followed closely.

Location of all energized power wires or equipment: location of all battery equipment or equipment on which batteries are installed; location of diesel equipment; location of explosives or oil storage areas; location of pressurized containers such as acetylene or oxygen cylinders and the location and description of any other equipment or supplies that may influence the planning.

Preferably. in four six-hour shifts per day and the change of shift should take place underground at the fresh-air base or other work site so that work will be continuous

Yes. Generally a company representative with experience in such work

Yes. A committee should be composed of representatives of the State mining agency, Federal mining agency, and others as appropriate.

Yes. Only those people necessary to insure the suitable progress and safety of the operation which would include supplymen, backup workers

Examine return airways for smoke or other indications of active fire.

Exploration is continued in intake air to the point where normal ventilation controls have been destroyed and ventilation is short circuited. At this point, the first fresh-air base should be established.

The place to which fresh air has been conducted and at which stoppings (seals) or other ventilation controls, including an air lock have been installed in a manner that will prevent reventilation of any area that has not been explored and examined.

Only when an area inby the present fresh-air base has been examined and stoppings installed to permit the explored area to be reventilated without disturbing the inby area that has not been explored

Yes. Crews wearing self-contained breathing apparatus should make such trips for gathering information, reestablishing ventilation, rescuing workmen, searching for bodies, etc.

The object of the excursion; the type of communication used; conditions (such as height) of travelway, etc. will govern the distance to be traveled; always keeping in mind the time limitation of the apparatus.

Such exploration trips should not be taken under the following conditions:

1. In dense smoke, except with life line attached to each member and then only for very short trips to save life, turn valves, or to open or close doors essential to the operation.
   
2. When an explosion is probable.
   
3. In dangerously high temperature with high humidity.
   
4. With apparatus not adequately charged or in unsafe condition.
   
5. When the reserve crew has less members than the advance crew.

Workmen wearing breathing apparatus should install temporary stoppings with plastic material, pogo sticks, inflatable stoppings, etc. Such stoppings should be replaced as soon as possible with more substantial stoppings such as cement block, wood-framed plastic sealed with rigid foam, or other more permanent type structure.

Every effort should be made to reach and extinguish all fires discovered. If this is not possible, the crew should return to the fresh-air base and report the condition.

Yes. So that men and material can be provided without delay and that instruction and information can be relayed promptly between the person in charge underground and the person in charge on the surface.

Yes. So that he can follow progress, make plans. and relay information accurately

Yes. Normally one spokesman should be selected to relay factual information accurately.

1. Provide up-to-date maps of the mine showing normal ventilation and ventilation controls (stoppings, overcasts, etc.).
   
2. Keep map current by recording progress changes in ventilation and other pertinent information such as location of bodies, equipment, etc.

1. Disconnect and lock out a electric power entering the mine or affected portions when authorized to do so, and lock out all other de-energized circuits.
   
2. Notify the electric company that under no circumstances should the electric power be cut off without notifying the mine.
   
3. If it is a shaft or slope mine examine and service necessary hoists and elevators.

Make arrangements for rescue teams including facilities and maintenance of equipment, food and lodging. Arrange for medical or first-aid treatment for injured persons or handling of bodies, if necessary.

Crews with breathing apparatus crews to build stoppings and crews to transport and handle supplies.

What attributes should a person have before being selected as a mine rescue team member? 

The person selected should be a cool competent person who has demonstrated in his past work a willingness to be a good team member. The person should also possess extensive knowledge of mining and should be mentally sound and physically fit.

They should be trained and retrained in accordance with Federal or State requirements for qualification.

At least five and preferably six men should compose a rescue team with the same number fully equipped at the fresh-air base. A crew of less than five may make short excursions for special purposes when a similar number of apparatus men are in reserve at the fresh-air base.

In addition to the standard equipment such as electric cap lamps and self-rescuers they should be equipped with approved self contained breathing apparatus that have been properly tested and inspected under the supervision of a competent person. They should have all the pertinent background information a copy of the latest map of the mine workings and at least an approved and tested methane detector, carbon monoxide detector and oxygen detector.

Make sure that all apparatus are operating properly and check to see that all material necessary for the exploration is on hand and working. The captain should consult with the man in charge relative to the purpose of the trip and extent of travel also be sure that a backup rescue team with all necessary equipment is in readiness at the fresh-air base.