FIRE & EXPLOSIONS
Fires and Explosions
Name the common gases found in coal mines following a mine fire or mine explosion?
Carbon monoxide, carbon dioxide, methane, oxygen, nitrogen, hydrogen, and other hydrocarbons.
What is a dangerous mine atmosphere?
A dangerous mine atmosphere is one that is or is likely to become poisonous to breathe, deficient in oxygen, or explosive.
What is the principle combustible gas found in coal mines?
Methane (CH4) is the principle combustible gas found in coal mines.
What is the explosive range of methane-air mixtures?
5 to 15 percent of methane in air is explosive.
To what extent must the oxygen content be reduced before an explosion of methane and air is impossible?
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.
What is the explosive range of carbon monoxide-air mixtures?
12.5 to 74 percent carbon monoxide in air.
What is the explosive range of hydrogen-air mixtures?
4 to 74 percent hydrogen in air.
To what extent must the oxygen content be reduced before an explosion of hydrogen is impossible?
5 percent or less.
Name the inert gases found in coal mines?
Carbon dioxide (CO2) and nitrogen (N2).
State where you would generally find methane, carbon monoxide, and hydrogen sulfide?
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.
What gas or gases support combustion?
How are persons affected by breathing the various gases found in coal mines?
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 16.25 percent.
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 .005 percent. Somewhat higher concentrations may be considered allowable for short periods of exposure. For example, .04 percent can be inhaled for one hour without appreciable effect, but .15 percent is dangerous to life after exposure of one hour, and .4 percent will cause death in less than an hour.
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.
Fighting and Sealing Coal Mine Fires
What are the major causes of fires in coal mines?
Electricity, open flame, ignition of gas, explosives, cutting and welding. smoking and smokers' articles, spontaneous ignitions, friction, and surface fires communicated to underground workings.
What are the usual methods of controlling or extinguishing mine fires?
Direct attack with water, chemicals, rock dust, or sand.
Enclosing fire area with tight seals.
Flooding affected area or the mine.
Flushing enclosed area with silt or other material.
Enclosing fire area with inert barriers.
Inundating with inert gases.
When should you decide to seal a fire area or mine?
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.
What is the objective of sealing?
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.
What are the principle hazards in sealing a mine fire?
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.
Should the intake or return be sealed first, or both together?
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.
What distance should seals be from a fire?
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.
Should temporary seals be erected first?
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.
What materials should be used for temporary seals?
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.
Should work continue in the mine after seals are completed?
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.
What are the main factors to be considered in erecting permanent seals?
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
What does the presence of carbon monoxide in sealed areas indicate?
The presence of carbon monoxide is an indication of an active or recently active fire.
How much oxygen is considered reasonably safe before attempting to unseal a 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.
What are the principle factors that govern the amount of time a fire area must be sealed before being reopened?
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.
How would you determine when it is sate to reopen a sealed fire 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.
What effect, if any, does the presence of carbon dioxide that is produced in the sealed area have on the fire?
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
What are some of the preparations that should be made before unsealing a fire area?
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.
Briefly describe two methods that have been successfully employed for the recovery of a fire area.
There are in general two systems that may be employed:
Recovering the fire area in successive blocks by means of air locks.
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.
Describe the method of recovering a sealed fire area by the use of air looks.
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.
Describe the method of recovering a sealed fire area by direct ventilation.
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.
What are the principal causes of mine explosions?
Ignition of methane or coal dust or both by electric arc open flame including mine fires), misuse of explosives friction, etc.
How can mine explosions be prevented or their effect minimized?
By adequate ventilation properly distributed, directed and controlled; complete rock-dusting of all open areas; use of sufficient water to allay dust from mining machines at working faces, use of permissible explosives together with proper and adequate supervision to see that the above safeguards are instituted. Procedures and Duties at Fires and Explosions
In case of a mine fire or explosion, who should be notified?
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.
What are some factors that must be considered early to assure a well organized operation?
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.
What one factor is most critical to insure the safety of survivors in the mine?
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.
Fire that was started by the explosion.
Electrical arc that may be created by short-circuited batteries, or power wires that have not been de-energized.
In addition to assuring that the fan or fans are operating, what is another important step to be taken in the attempt to save survivors?
Endeavor to communicate with survivors and direct them to the best means of escape from the mine.
What are the main objectives of the rescue and recovery work after a mine explosion?
Men entombed or missing should be located and brought to safety or their bodies recovered as soon as possible.
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.
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.
While fighting a mine fire what type of major accident should the firefighters be most concerned with?
An explosion is the major accident that is likely to occur during firefighting operations.
How should mine firefighters protect against the occurrence of an explosion?
The air returning from the fire should be monitored for explosibility, and ventilation should be controlled closely and maintained over the fire constantly.
Should one man be in charge of the rescue or recovery work?
Yes, generally a representative of the company.
Should there be an advisory committee to the man in charge of the rescue or recovery work?
Yes The committee should be composed of representatives of the State mining agency, Federal mining agency, the miners, and others.
Should there be a plan made for specific phases of firefighting rescue and recovery procedures such as sealing or unsealing mine fires or recovery of miners following an explosion?
Yes The man in charge and the advisory committee should devise a relatively broad plan of operation which should be followed closely.
What are some factors that may be critical to the safe firefighting or explosion recovery activities, and which would not normally be known or readily available to the planners?
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.
How should the work be divided?
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
Should there be a man in charge of the underground work on each shift?
Yes generally a company representative with experience in such work
Should there be an advisory committee to the man in charge on each shift underground?
Yes. A committee should be composed of representatives of the State mining agency, Federal mining agency, and others as appropriate.
Should there be any restriction on the number of people permitted underground?
Yes Only those people necessary to insure the suitable progress and safety of the operation which would include supplymen, backup workers
After entering a mine following an explosion, what examinations should be made?
Examine return airways for smoke or other indications of active fire.
Following an explosion, how is the location of the first fresh-air base determined?
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.
Describe a fresh-air base.
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.
When should the fresh-air base be advanced?
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
Should exploration trips be made ahead of the fresh-air base or in other areas where an irrespirable atmosphere is or may be present?
Yes. Crews wearing self-contained breathing apparatus should make such trips for gathering information, reestablishing ventilation, rescuing workmen, searching for bodies, etc