Section 7
Mine Recovery
Table of contents
I. Introduction
The main objective of recovery work is to return the mine or the affected area of the mine to normal operations after a mine disaster as soon as conditions permit.
Recovery operations can span from a few days work to restore ventilation to a section, to many months of work, to restore ventilation and rehabilitate the entire mine, depending on the amount of recovery work that will be required. Naturally it will take more time to restore ventilation throughout the mine than it would to restore ventilation in one section.
The role of a rescue team member in recovery work varies as the operation progresses and conditions change.
Until ventilation is restored in the affected area, apparatus crews will be needed to assess conditions, rebuild stoppings, clear debris, and stabilize the roof and ribs where necessary.
Once the ventilation is restored and fresh air is advanced, non-apparatus crews can then resume the rehabilitation and cleanup effort.
II. Assessing Conditions
In order to plan a recovery operation, there must be an assessment of underground conditions initially. Then as the work progresses, rescue teams will make updated reports on the conditions and damages they encounter.
Assessing conditions is necessary for the safety of the rescue teams, and it also determines how much rehabilitation work is needed to recover the affected area.
One of the most important areas the rescue team will check is tie ventilation system and what damage it has sustained. All ventilation controls and auxiliary fans and tubing will need to be examined.
As the team explores and restores ventilation to the sections, gas conditions, as well as roof and rib conditions, will need to be checked thoroughly.
Track, waterlines, power lines, and phone lines must be investigated for any evidence of flooding, flood damage, smoldering debris, or hot spots in a fire area.
Ill. Reestablishing Ventilation After a Fire or Explosion
Restoring ventilation and returning fresh air to a mine area damaged by fire or explosion is the main task of the mine rescue teams in a recovery operation. Once this is accomplished, regular work crews can help with the recovery effort.
If the fire area was sealed, it means unsealing the area, assessing the damage, and repairing and rebuilding the ventilation system.
If the area was not sealed, the job of reestablishing the ventilation is considerably easier. It involves merely assessing the damage and making the necessary repairs to restore normal ventilation.
In an area which has been damaged by an explosion, the task is the same as it is after a mine fire: to assess the damages and to repair the ventilation controls. After an explosion, a great deal of construction work is usually needed to restore ventilation to its proper function.
a. Unsealing a Fire Area- Unsealing a fire area requires careful planning. To open the seals prematurely could cause an explosion or reignite the fire.
Usually a detailed plan is prepared by company officials, with the, advice of federal, state, and union representatives (when applicable) for unsealing a fire area.
Although mine rescue teams do not plan the unsealing operation themselves, it is important for the teams to know what the considerations and options are, as well as the potential problems in unsealing the mine.
1. When to Unseal- Determining the exact time to unseal a fire area is based on the laws of physics and chemistry, plus experience and good judgment.
A fairly accurate analysis and interpretation of the gases present in the sealed area is possible through the proper sampling techniques and with the assistance of a chemist experienced in mine recovery.
Gas conditions and other factors must be evaluated when choosing the safest time to unseal a fire area.
The main factors governing the time for unsealing a fire area are:
1) The extent and intensity of the fire at the time of sealing.
2) The characteristics of the burning material and surrounding strata.
3) The tightness of the seals.
4) The effect of the barometric pressure on the enclosed area.
5) The effect of temperature on the enclosed area.
6) The location of the fire area with regard to ventilation.
7) The gas conditions as indicated by analysis of the air samples taken from behind the seals. Usually the gases analyzed include: oxygen, carbon monoxide, carbon dioxide, methane, hydrogen, and nitrogen.
2. Preconditions for Opening a Sealed Fire Area
No attempt should be made to unseal a fire area until:
1) The oxygen content of the air behind the seal is low enough to make an explosion impossible (no matter what the quality of the combustible gases is behind the seal);
2) Carbon monoxide (the gas which indicates combustion) has diminished or disappeared from the air behind the seal; and
3) The area behind the seals has been given enough time to cool so when air is again introduced during the unsealing operation, it will not rekindle the fire.
Achieving these goals may be difficult and may require a great deal of time.
3. Preparations for Opening a Sealed Fire Area
Opening a sealed fire area requires specific preparations:
1) Adjustments in ventilation should be made so that toxic and explosive gases released from the sealed area are directed into the main returns.
2) Someone should monitor the operation of the main fan to ensure it is operating correctly. If the fan slows or malfunctions, the teams working underground should be withdrawn at once. Gas levels at the main returns should be monitored also.
If the fan is electrically driven, precautions should be made to prevent explosive gases from coming in contact with the fan motor or any other electrical equipment used to operate the fan.
3) Make checks to ensure that all electrical power in the sealed area was cut off before the unsealing process is begun. Power in the return airways near the sealed area should be locked out.
4) In bituminous coal mines, all entries and crosscuts leading to and from the sealed area should be heavily rock dusted, and this should be done for a considerable distance outby the seals to be opened.
5) Withdraw all unnecessary personnel from the mine.
4. Methods of Unsealing Fire Areas
There are two basic methods for unsealing a fire area: progressive ventilation and direct ventilation.
Progressive ventilation is the reventilation of a sealed area in successive blocks by means of air locks. Progressive ventilation is the most common method of unsealing a fire area in coal mines. The advantage of progressive ventilation is that gas conditions can be carefully controlled, and the operation can be stopped at any point if conditions become hazardous. The disadvantage of progressive ventilation is that it is a slow process.
Direct ventilation is the reventilation of the entire sealed area done at once. With direct ventilation, recovery is accomplished quicker than it is with progressive ventilation, but gas conditions are less controlled. Before using direct ventilation, there should be conclusive evidence that the fire was extinguished.
Direct ventilation must be used to recover mines that have been sealed on the surface.
a) Recovery by Progressive Ventilation- Progressive ventilation is the usual method of recovery in these situations:
With progressive ventilation, the sealed area is explored and reventilated in successive blocks by the use of air locks. As long as the conditions remain favorable, the work can continue and the entire area can be recovered.
Rescue teams are reminded that air locks are two stoppings built approximatelylOtol5feetapart. Each stopping should have a door or flap in it permitting teams to enter and exit the sealed area. One opening in the air lock must be kept closed while the other is open to prevent the two atmospheres from mixing.
Note: Air locking operations should never be undertaken until the oxygen content of the air behind the seals has been reduced to at least 2 percent.
During progressive ventilation, a certain amount of air will enter the area behind the seals, which is unavoidable. But as the work continues, oxygen and explosive gas levels must be carefully monitored, and the operation must be stopped if conditions become dangerous.
Recovery done by progressive ventilation is similar to advancing the fresh air base. It is usually a slower operation, however, because of the damage which is normally found in a sealed area.
The first step in progressive ventilation is to build a stopping at one of the seals on the intake side of the fire area to create an air lock.
Air locking operations should always begin on the intake side of the fire.
Once the air lock is completed and conditions allow for entering the sealed area, a team with apparatus can then enter the air lock and break out an opening in the seal.
Teams may have to wait awhile after removing the first few blocks from a seal to permit the pressure to stabilize.
After the seal is opened, an apparatus team, or if necessary, a rotation of teams can enter the sealed area to explore and assess conditions to the point where the next air lock will be built.
The distance between air locks is generally 200 to 500 feet. The distance between them will depend on the conditions encountered as well as the amount of construction work required to prepare an area for reventilation.
During exploration, the teams should note the general conditions, but in particular, teams should take temperature readings and do the necessary tests for oxygen, carbon monoxide, carbon dioxide, and methane. Air samples should be collected when requested, also.
The team should also take measurements for the new air lock which will be built and for any additional stoppings that will be needed in the parallel entries to seal the area.
Additionally, the team will have to prepare the area between the two air locks for reventilation. This job involves repairing ventilation controls and making the necessary changes to direct the air to a return airway.
Before the team leaves the area being prepared for reventilation, a final check must be made for any possible fires.
After the team is out of the area, it can be reventilated. Usually, a seal on the return side is opened first, followed by one of the seals on the intake side.
The return air should be kept below the lowest explosive limit of methane and oxygen. If conditions are good, the rest of the original seals can then be opened.
This process of putting up air locks and working through them to explore and to reventilate an area can be repeated until the entire area is recovered.
As the work progresses, frequent tests should be made to monitor gas conditions and to determine if the gas conditions in the sealed area and at the end returns of the areas are being recovered since the main concern is the possibility of an explosion or the rekindling of the fire.
Once the work progresses close to the core of the fire, it may be decided to load out the heated materials through the air lock before attempting reventilation.
Once all indications show the fire has been extinguished, then the final sealed area can be reventilated. The gases from this area should be removed as quickly as possible.
b) Recovery by Direct Ventilation- The other method for recovering a seed fire area is by direct ventilation.
In direct ventilation, the affected area is recovered and reventilated as a whole rather than by successive blocks. Therefore, recovery is accomplished faster than by progressive ventilation. However, gas conditions are less controlled.
Before using direct ventilation, there must be conclusive evidence that the fire has been extinguished.
The first step, as in progressive ventilation, is to build an air lock at an intake seal. The apparatus crew can then work through the air lock and enter the sealed area.
The apparatus team, or a rotation of teams, have to take temperature readings and test for oxygen, carbon monoxide, carbon dioxide, and methane. They will probably have to collect air samples too.
Once teams complete their tests and observe the area, they are to return to the fresh air base.
If conditions are favorable, then unsealing can start. A seal on the return side should be broken open and the air lock opened to admit air. Then the area can be reventilated.
Any combustible gases in the main return should be kept to the lowest explosive limit, if possible.
Note: When using the direct ventilation method, be certain that all unnecessary personnel are out of the mine before air Is actually directed into the sealed area. The remaining people needed to open the seals should then come out quickly after the seals are opened.
The command center determines when conditions appear safe to return to the mine.
If the sealed area is extensive, it is advisable that the rescue team wear apparatus to reenter. However, the team should check for and sweep out any standing gases from the fire.
When direct ventilation is used to recover mines which were sealed on the surface, the procedure is basically the same except an air lock is not used.
Just as with underground sealing, surface seals, one on the intake and one on the return, should be opened at approximately the same time. When it is decided that it is safe, then the apparatus teams can explore and begin reventilation.
c) Preventing a Buildup of Gases in the Fan House- If the mine is using an exhausting fan, provisions have to be made to prevent the buildup of explosive gases in the fan house.
One technique used is to ventilate the fan house. An auxiliary fan can be set up a short distance from the fan house with tubing extended into the fan house.
Another technique is to control the volume of air being drawn from the mine. This method can be done by using the explosion doors as a regulator.
b. Reventilation After an Explosion- The objective of restoring ventilation after an explosion is to rid the mine of explosive or potentially explosive gas mixtures and restore normal ventilation and normal amounts of oxygen to all mine workings
1. Considerations- There are three areas of concern to rescue team members and they are listed below.
1) The concentrations of explosive mine gases. Are they within, above or below the explosive ranges?
2) The percent of oxygen present in the mine. Is there sufficient oxygen to support life? Is the amount of oxygen low enough to prevent another explosion?
3) Possible sources of ignition. Are they being considered and eliminated? Possible ignition sources are: electrical power, battery-powered equipment, possible fires and hot spots, and sparks from tools and team equipment.
Note: Teams should check the permissibility of whatever they bring into the sealed area and make sure they use non-sparking tools, spads, and shovels.
During reventilation work, an observer should be stationed at the main fan to ensure it is operating correctly and to warn the team in case of any malfunction. Additionally, someone should be at the main returns to monitor the gas levels.
2. Using Progressive Ventilation- Reventilation of the mine after an explosion is usually accomplished by progressive ventilation.
Afresh air base is established and stoppings are built in parallel entries to isolate the affected area. A team wearing apparatus can then enter the affected area through an air lock (the fresh air base) to explore the mine and assess conditions.
This procedure is basically the same as unsealing a fire area by progressive ventilation.
As long as conditions are favorable, teams can enter and build a new air, lock inby the old one, build other needed stoppings in parallel entries, and prepare the area being recovered for reventilation.
Note: The teams should be sure to make the necessary adjustments to direct air from the reventilated area to a return. While exploring and preparing an area for reventilation, teams should be alert for and eliminate any possible sources of ignition.
Once the new air lock is built and gas conditions are checked, normal ventilation can be advanced to that point by taking down the old air lock and opening an airway to the return for air to circulate through the area.
Teams can continue this procedure until the entire area is reventilated.
The conditions the team encounters determines the area reventilated. When damage is slight, a team can reventilate a large area.
If damage is extensive, however, the team may only be able to do two or three blocks at a time, and much work must be done to repair ventilation controls. The reventilation process is slower where travel is hampered, or where roof and rib conditions are hazardous and require timbering and other roof support.
Once the area is reventilated, labor crews working barefaced can normally do any further rehabilitation work needed in that area. This allows the apparatus teams to prepare the next area for reventilation.
3. Dealing with Obstructed Passageways- If entries are obstructed by falls, debris, or equipment, travel through the entries may be difficult during reventilation. In these circumstances, teams should try to bypass those entries and come in behind the obstructions to erect the stoppings.
Sometimes all entries are blocked by falls. Rescue teams have, in some instances, reventilated as close as possible to the area and then used permissible machinery and tools to clear an entry.
While this is being done, line brattice can be used to ventilate the area, in the same manner that a face area would be ventilated during normal production.
Where fails are extensive, access may be gained to the obstructed area by mining through the solid from the closest unobstructed entry.
In the past in these cases, teams have mined to within a few feet of breaking through the solid. At that point an air lock was erected, the power was turned off, and all unnecessary personnel were removed from the mine.
Then a team with apparatus on went through the air lock and hand mined the last few feet.
These two procedures are mentioned to provide two examples of methods of recovery which were successfully used before. Any decision to use these methods would be made by the officials in charge of the operation who must evaluate the risks. benefits, and costs before implementing such a plan.
IV. Clearing and Rehabilitating the Affected Area
a. Roof and Rib Control- Explosions, fires, and other mine disasters frequently result in weakened roof and rib conditions. Rescue teams should carefully assess roof and rib conditions during recovery work. Teams may find extensive timbering and cribbing is needed to stabilize conditions prior to advancing ventilation.
b. Pumping Water- Rescue teams often encounter large accumulations of water during recovery operations which must be pumped out.
There are two ways to accomplish this.
1) The team is to advance fresh air to the area and then pump out the water.
2) If the team needs to clear the area before fresh air is advanced that far, and if gas conditions allow, the team can use nonconducting suction lines with a pump set up in fresh air to pump out the water.
When using this procedure, teams should make careful analysis of the gas conditions in the area being pumped. Water-soluble gases will be pumped out along with the water. If the line loses suction, toxic or explosive gases from the contaminated atmosphere can be drawn out.
Note: When advancing into an area that has been inundated with water,
teams should be very cautious of the roof and rib conditions since roof
Falls are likely to occur in these areas.
c. Clearing Roadways and Track- Roadways and track should be cleared and restored for use as quickly as possible. Once this is done, it will be much easier to bring in the materials which are needed for the recovery and clean-up effort.
d. Loading Out Falls and Hot Debris- Many times the most practical way to deal with the debris found during recovery operations is to load it onto shuttle cars or onto mine cars and haul it from the mine.
This is especially true of heated debris found after unsealing a fire area. In fact, the only practical means of eliminating the possibility of rekindling the fire is to remove the heated material.
The material should be wetted down before and during the loading operation.
When large areas of heated roof rock fall, water lances can be driven into the debris to aid in cooling it. Water lances are pipes about 10 feet long with holes cut along the length of the pipe.
The lance attaches to a regular hose line.
After the rock cools, it can be broken up and loaded out.
e. Restoring Power- Power is usually restored progressively by an electrician as the ventilation is advanced.
Once the power is restored in an area, the rehabilitation work can proceed much more efficiently since there will be power to transport materials, equipment, and workers.
f. Reestablishing the Communications System- As fresh air is advanced, the mine's communication system should be repaired or a substitute system advanced to aid in expediting the recovery operation.