Table of Contents
Mine rescue teams have to know the basics of mine ventilation, and secondly, teams have to know how to build mine ventilation controls. Why? During a mine emergency, after an explosion, fire, flood, or whatever the emergency situation is, rescue teams are needed to enter the mine and assess the damage to the ventilation system and reestablish mine ventilation if necessary.
The initial responsibility the rescue team is to report the status of the ventilation system to the command center as the team advances. It is quite possible that the mine ventilation system was damaged or controls were altered during the emergency. Accurate information on the condition of the ventilation has to be given to the command center.
Note: Never alter the mine ventilation without specific, direct orders from the command center.
The command center must rely on information supplied by the rescue team. If ventilation controls have been changed or damaged, the command center can then direct the rescue team on how to reestablish ventilationin the mine.
Team members should know the following:
What is the purpose of mine ventilation?
What are the various ventilation controls?
What purpose do ventilation controls serve?
How do ventilation controls affect mine exploration and rescue?
What are the various symbols used to record ventilation controls and airflow on a ventilation map?
a. Airflow- Every underground coal mine contains harmful gases, dust, fumes, and smoke. Adequate oxygen must be provided throughout the mine for miners to be able to breathe underground. The basic principle of ventilation is controlling or moving (coursing) air currents.
When a mine is ventilated, air from the surface enters the mine at the main intake shaft(s) and is directed or coursed through the mine by a system of ventilation controls. These controls force the air to move in certain directions and at certain velocities to safely ventilate all mine sections.
All return air from the working sections is then rechanneled to the main return and eventually leaves the mine. In order to get airflow, there has to be a difference in air pressure between the intake and the return airways. Air moves from a high-pressure area to a low-pressure area. In order to accomplish that kind of air movement, mine fans are used.
b. Mine Fans- Mine fans create a difference in air pressure (pressure differential) by changing the air pressure at specified points in the mine. The greater the pressure difference the fan creates, the faster is the flow of air. Using a fan to create the pressure differential is known as mechanical ventilation.
Mine fans create the atmospheric pressure differential within the mine by either blowing air into the mine or exhausting the air from the mine. The exhaust fan pulls stale air out of the return, and by pulling out that air, causes a pressure differential, which then pulls fresh air into the mine.
Blower fans are typically used in mines having little overburden. Many of these mines have surface fractures. By using a blower fan, it allows air to leak through those fractures and away from the mine rather than returning air to the mine. Small mines can use one fan for ventilation, but large mines with vast underground workings use several main fans, with each fan used to ventilate specific sections.
When rescue teams are working in a mine with several main fans, teams must be familiar with each ventilation plan for the separately ventilated areas of the mine.
Note: In an emergency situation, to ensure the rescue teamís safety while underground after the fresh air base is established and exploration Is underway, the main fan (or fans) must be monitored or guarded by an authorized individual to make sure the fan operates continuously or to notify the command center if the ventilation system breaks down.
If the mine fan quits while the team is underground, hazardous conditions can ensue without all rescue team members knowing it, and can further endanger trapped miners. If hazardous conditions ensue from the fan being down, rescue teams will be recalled from the mine.
Additionally, having the fan monitored or guarded ensures that no one alters the operation of the mine fan and changes the ventilation controls without direct orders from the command center.
Ill. Ventilation Maps
a. Purpose- All mine rescue team members, particularly the teamís mapman, should know how to read a mine map showing mine ventilation. The mapman is responsible for marking down information on the map to assess ventilation during exploration. The team mapper should attach a legend of the map symbols used by a particular mine at the bottom of the map or mapboard, as well as the scale to which the map is drawn since these maps can differ from mine to mine.
Rescue teams will be given up-to-date mine ventilation maps after the teamís briefing, and before going underground. Teams should study the map to familiarize themselves with the layout of the area to be explored, and to know what to expect. If previous teams have already explored some areas, the map will indicate what was found and done on prior explorations. Teams will need to know the map symbols as well.
B. Map Symbols- Mine rescue teams need to know map symbols in order to understand the ventilation controls and how they affect the movement of air in the mine. Some of the symbols commonly used on mine mapsare:
Devices for Controlling Ventilation
Permanent Stopping w/door
Overcast or Undercast
Line Curtain/Brattice Cloth
Line Curtain/Brattice Cloth
Direction of Intake Air
Direction of Return Air
IV. Types of Ventilation Controls
Ventilation controls are needed and used underground to properly distribute the air to all mine sections. The ventilation controls can do so by controlling the direction of the airflow as well as the amount of air that travels through the mine.
Each working section must be ventilated with a separate supply of fresh air. Ventilation controls are used to split off fresh air from the main intake and direct it to each section since each working section must be ventilated with its own separate supply of fresh, uncontaminated air.
The various ventilation controls work collectively to direct or "course" the movement of the air through the main intakes to the working section and move out through the returns without Short-circuiting. Short-circuiting occurs when air from the intake goes directly into the return without moving up and ventilating the working face areas inside the mine.
Listed below are the ventilation controls commonly encountered by rescue teams with a brief description of the effects each of these devices has on exploration and rescue.
a. Stoppings- Stoppings are used to close off the crosscuts in order to prevent the air in one entry from moving into the return air of the adjacent entry. Stoppings are either permanent or temporary.
1. Permanent Stoppings are built of concrete blocks or other noncombustible material. They are used in areas of the mine where ventilation is well established. Permanent stoppings are tightly sealed against the mine roof, floor, or ribs to prevent any air leakage.
Sometimes permanent stoppings are designed with a man-door or drop-door in them to allow miners to pass through one crosscut entry to another. These man-doors are not designed for ventilation controls, but if a man-door is propped open, it can affect the airflow and may cause intake air to short-circuit into the return.
2. Temporary Stoppings are used in actively working sections of the mine where ventilation is changed as needed, to direct the airflow until a permanent stopping, which is stronger and more airtight, can be erected.
Temporary stoppings are usually built of canvas, brattice cloth, or plastic. Occasionally they are constructed of wood or metal.
The mine rescue team may have to construct temporary stoppings to advance ventilation during exploration or recovery work. There are specially designed temporary stoppings for use in mine rescue work which are installed quickly and easily, and are very effective.
One of the special temporary stoppings in mine rescue work is an inflatable, rubberized stopping. Another type is a self-sealing stopping commonly referred to as a "parachute stopping." Additionally, urethane foam, which is available in pressurized containers, can be used to seal the edges of temporary stoppings to make them more airtight.
b. Check Curtains or Run-Through Checks- Check curtains (run-through checks) are curtains made of brattice cloth, canvas, or plastic which are hung across a passageway but open to let miners or their machinery go through. Check curtains deflect intake air into the working area. They fasten only at the top and are designed in three styles:
1) a one-piece curtain attached at the top and loose at the sides and bottom;
2) a curtain with a long vertical slit down the center which is attached at the top and sides; and
3) a curtain which has three overlapping flaps of material.
Check curtains are designed to close automatically after someone passes through them, and then they close to direct the air to the working area.
If check curtains get pulled down or do not fully close, air will short circuit and will not reach the working face.
Note: If rescue teams find check curtains that are pulled down or do not close fully, teams are to leave the curtains as they are and report the situation to the command center. Changes in ventilation can only be made by the command center. The command center will then decide on what to do concerning ventilation.c. Line Brattice- Line brattice is brattice cloth or plastic used to course air from the last open crosscut to the working face. Line brattice is extended as the mining progresses to keep the air flowing to the face.
Brattice is hung from the roof to the floor extending from the end of the check curtain to within 10feet of the working face. It can be hung from a rough lumber frame, from timber posts, or from special fasteners. It can also be secured to the roof with spads.
Note: Line brattice is particularly useful for rescue teams to use to sweep out or ventilate a room area of the mine or when it is necessary to split an air current as teams advance ventilation.d. Auxiliary Fans and Tubing- In large mines using continuous mining machines to cut great quantities of coal, large amounts of dust result. Auxiliary ventilation systems are often used to control and direct airflow to or from the face in those mines or where a line brattice does not provide adequate ventilation. These auxiliary systems consist of an auxiliary fan and tubing.
Auxiliary fans blow or exhaust air. The tubing, often suspended from timbers or roof bolts (if approved), carries the air to or away from the working face. Tubing is rigid for exhaust systems, or collapsible for blowing systems.
The auxiliary ventilation system allows the continuous miner to operate without being obstructed by line brattice usually required to ventilate the working face. The tubing can be moved easily to t he working face, making it convenient to extend ventilation to the face as mining advances.
e. Overcasts and Undercasts- Intake and return air often cross paths at intersections within the mine. Because of this, overcasts and undercasts are built to allow the two air currents to cross one another separately, without the intake air short circuiting into the return.
Overcasts are like enclosed bridges built above the normal mine roof level. Undercasts are like tunnels built below the normal mine floor. However, undercasts are seldomly used unless unstable roof is present since they fill with water or debris which would slow down the air current.
Overcasts are frequently used and are built with concrete block walls sealed against the ribs and floor, with some kind of airtight roof made of prestressed concrete, railroad ties, or steel beams. Frequently this kind of overcast is used to allow air to cross over a conveyor belt without mixing the split of air which ventilates the belt.
Sometimes overcasts are made of pipes going from one stopping to another, across an intake airway, allowing the return air to pass over the intake air.
f. Mine Doors- Mine doors are used to control ventilation in heavy-traffic areas such as haulageways. Doors are hung in pairs usually, to form an airlock which prevents a change in ventilation if one of the doors is opened. The doors are designed to direct the air flow from the haulage entry into another entry. Mine doors can also be used to isolate separate splits of air.
They can be opened one at a time to allow equipment and personnel to pass through without disturbing ventilation. These doors should always be opened and closed one at a time to maintain the airlock.
Mine doors can be manual or automatic. If the mine doors are manual, they are hung in such a way that the ventilation air pressure will close them if they are left open accidentally. Miners or other personnel should always close the manual doors after passing through. Other doors can be closed automatically.
Note: Rescue teams should be aware that if the normal flow of air is reversed within the mine, the ventilating air pressure will no longer keep the mine doors closed.g. Regulators- Regulators are used in the mine to control and adjust the volume or quantity of airflow within the mine, in order to ensure proper distribution. Regulators are ventilation devices used to regulate airflow to meet the individual needs of each air split.
The types of mine regulators are listed below:
1) Section regulators are used in returns and are often sliding doors or windows built into the permanent stoppings near the mouth of a section. Opening or closing this door or window adjusts the air flow to a section. If one of these regulator doors has to be opened to allow miners to pass through, it must always be closed in the same position it was found.
2) Regulators can be made from knocking out a few blocks from a permanent stopping. The airflow can be adjusted by removing or replacing the blocks.
3) A check curtain can be used as a regulator when one corner is taken down. The corner opening lowers the airís resistance and lets more air flow.
Airflow can be adjusted by lowering the corner and making a larger opening, or by tacking it back up to make a smaller opening.
4) A check curtain can make another kind of regulator when it is hung so it does not reach the mine floor. Doing this lowers the airís resistance and allows more airflow. This kind of regulator is adjustable also.
5) A pipe overcast can serve as a regulator.
h. Box Checks and Regulators- Conveyor belts are usually in or near intake air passages. Because they are, if a belt were to catch on fire, smoke and carbon monoxide would mix with the intake air. It is for that reason that federal law requires that all underground belts be isolated from the main intake and return air. (Title 30, Code of Federal Regulations, Section: 75.326.) Also, conveyor belts must have their own split of air. That is accomplished by using box checks and belt regulators.
Box checks are temporary or permanent stoppings built at each end of the belt to limit the intake air flowing over the belt. The box checks are built with openings in them to permit the belt to pass through. They are designed to let a little air flow through them into the isolated belt entry which ventilates the belt with its own split of air.
After the belt is ventilated, the air is drawn through a belt regulator into the return airway. The belt regulator regulates the quantity of air flowing along the belt.
V. Assessing Ventilation
a. Reporting Ventilation Conditions- As the team advances through the mine during exploration, all ventilation controls should be checked, particularly those in the affected part of the mine. The position of the regulator doors should be noted on the map by the mapman, and then reported to the command center.
Command center officials must have accurate information from the mine rescue team concerning ventilation controls. Team members have to report up-to-date information to the command center in order for the officials to assess the situation correctly.
Team members should note the type of damage and the extent of damage. If a stopping or other type of structure is blown out from explosives, note the direction in which it appears to have blown. If the stoppings were not destroyed, indicate how the blocks moved.
The most positive indicator of the origin of an explosion is the direction in which the blocks moved in or from the stoppings across entries near intersections.
The movement of blocks from stoppings in crosscuts seldom indicates the origin of an explosion.
Note: Teams should never alter ventilation without direct orders from the command center. The command center considers several factors before it makes any change in ventilation. The command center has to evaluate how alterations will affect ventilation into an unexplored area. If teams must alter ventilation, do not alter the ventilation into unexplored areas.
The wrong alteration in the ventilation could cause changes in the fresh air base, pushing toxic gases or smoke into areas where miners are trapped, and force explosive gases back over fires or hotspots, and cause an explosion, or redirect or feed a fire.
Team members must know how to:
1. Recognize damaged or destroyed ventilation controls;
2. Determine the direction and velocity of ventilation air by using an anemometer or smoke tube; and
3. Measure the cross-sectional area of a mine entry and calculate the volume of air by using the area and velocity.
b. Measuring Flow-
1. Anemometer- Rescue teams will be asked to determine the direction and velocity of airflow in certain mine sections. The quantity of airflow can be calculated from the velocity. Being able to determine the direction and velocity of air flow enables the team to check the ventilation system and whether it is fully functioning or working only in a specific area.
By comparing readings reported by the rescue team with readings recorded from normal operation conditions, the command center can then assess the overall condition of the ventilation system. These readings should be reported to the fresh air base as soon as they are taken.
Anemometers and smoke tubes are the most commonly used instruments for measuring air direction and velocity. The anemometer is used for measuring normal-to-high velocities, while the smoke tube is used to measure slowly moving air and its velocity.
The anemometer is a small device like a windmill or propeller attached to a digital counter that records the revolutions caused by the moving air currant. It is used to measure air velocities of 120 to 10,000 feet per minute. It is used to measure and record the number of revolutions for a set period of time: usually 1 minute.
There are two types of anemometers:
1) A medium-velocity or regular anemometer to measure velocities from 120 to 2,000 feet per minute, and
2) A high-velocity anemometer to measure velocities from 2,000 to 10,000 feet per minute.
How does an anemometer calculate this information? The anemometer measures linear feet of travel and requires a time factor, usually 1 minute, to determine velocity in feet per minute. The area of the airway (where the reading is taken) is computed in square feet. The area is then multiplied by the velocity to obtain the quantity of the air current in cubic feet per minute.
How can rescue teams take these measurements? A standard method to measure the velocity of an airway is to transverse the airway to get an average measurement of the average velocity in the airway. The usual procedure is described below:
1. Stand placing your back against one rib and hold the anemometer in a vertical position out at armís length, positioning the anemometer for the air current to enter the back of it (that is the side without the dials). Keep the free arm against the body.
2. Turn on the anemometer and slowly walk to the opposite rib at a pace to get a 1-minute reading, keeping the anemometer out in front to decrease as much air resistance as possible. The anemometer should be raised and lowered slowly while walking to the opposite rib to get an average velocity of air measured.
3. At the end of 1 minute, shut off the anemometer and read the dials. Correct that reading by using the manufacturerís table of corrections for the various velocity readings. The teams should read the manufacturerís instructions for the correct information on how to operate and read the anemometer.
4. Determine the cross-sectional area of the entry by multiplying the width times the height.
5. Report the velocity and area measurements to the command center. The command center will calculate the quantity of the airflow in cubic feet per minute:
Quantity (cubic feet) = Area (square feet) x Velocity (feet per minute)
Velocity is always measured in feet per minute for mine applications.
Occasionally the high velocities encountered are those flowing in ducts or tubing where measurements by an anemometer are difficult to obtain. For these kinds of measurements, the most practical instrument to use is the pitot tube. The pitot tube can be inserted through a small hole in the duct or tubing. The pitot tube has a-U-tube water gauge or some other differential pressure gauge for determining the velocity pressure inside the tubing.
2. Smoke Tube- The smoke tube is another type of device to measure airflow and is used to show the direction and velocity of slowly moving air (slower than 120feet per minute). It is usually used when airflow is too slow for an anemometer to calculate.
The smoke tube is a device which emits a cloud of smoke which floats with the air current showing the direction and velocity of the air. It consists of an aspirator bulb and a glass tube containing a smoke generating reagent.
To operate the smoke tube, break off both ends of the glass tube and then squeeze the aspirator bulb to force air into the tube. A white cloud of smoke will come out of the tube and travel with the air current. This smoke cloud shows the direction the air is moving (when it cannot be determined otherwise).
Note: If teams are not wearing breathing protection while working with the smoke tube, they should avoid being in contact with the smoke since It is very irritating and can cause choking.
There are two methods to measure air velocity with a smoke tube:
1. Take the reading in the center of the airway. This reading is not an accurate measurement but an approximate and high reading because the center of the airway has the fastest moving air.
2. Determine the air velocity at quarter points. Quarter points are points at approximately the center of each quadrant if the airway were divided into Ďlour "equal" parts. This method is done to determine the average velocity in the airway since it varies at different parts of the airway. The procedure for taking readings at quarter points within the airway is described below:
a) Mark off a distance in a relatively straight and uniform way. Usually 25 feet is all right for this measurement if the smoke cloud holds together and is visible.
b) Station one person with the smoke tube at the upwind point of the measured distance, and station another person at the downwind point with a stopwatch.
c) Release a smoke cloud at each quarter point within the airway. The person with the stopwatch must time each cloud from the moment it is released until it reaches the downwind point. Each measurement is taken separately for each smoke cloud released: the first, second, and so forth.
Note: Smoke-tube readings have to be converted to feet per minute.
For example, 25 feet is the measured distance and it averages 23 seconds for the smoke cloud to reach the downwind point. Determine the decimal equivalent of 23 seconds to find out what fraction of a minute it is:
Quantity = Area (200 ft [for example]) x 65.7 Quantity of airflow = 13,140 ft3/Min
Each velocity measurement in a quadrant should be taken several times to get an accurate average. Discard abnormally high and low measurements, and keep the remainder. A correction will have to be made to the averaged figure because the air travel at the quarter points will average about 10 percent high.
(Note: To make this correction for the 10 percent high reading, either multiply the averaged figure by 0.10 and subtract that number from the averaged figure, or multiply the averaged figure by 0.@.)
If the smoke tube is going to be used repeatedly, keep it tightly stopped with a rubber cap or plug since the reagent is very corrosive and can clog the tube openings.
VI. Building Ventilation Controls
Mine rescue and recovery work often requires building or rebuilding ventilation controls to reestablish ventilation within the mine. The rescue teams have to know how to build ventilation controls properly, including:
Temporary and permanent stoppings; Air locks; and Line brattices.
Some team members are skilled at building ventilation controls while other members are inexperienced. Whatever the case, it will take time to get used to whatever control is being worked on. It is very difficult to work in smoke while trying to work quickly in order to reach survivors as fast as possible.
Note: Teams must never make any alterations or do any construction without the approval of the command center.a. Temporary Stoppings- To install a temporary stopping in a crosscut, the stopping has to be erected approximately 4 to 6 feet into the crosscut to allow enough room for a permanent stopping to be built later.
The ideal site for a temporary stopping is one where there is sound roof and ribs, with the floor free of debris in order to give a good seal around
the stopping. Test the roof and bar down any loose material from the roof.
The stopping is constructed by setting posts at each rib and in between if necessary, depending on the width of the crosscut. Nail boards across the top and bottom of the posts for attaching the brattice or plastic. Loose coal can be shoveled onto the excess cloth at the bottom of the stopping to seal the bottom of the stopping.
These stoppings are used to replace stoppings in crosscuts which were blown out or damaged. Temporary stoppings can be constructed quickly to advance ventilation to trapped miners.
If an explosion occurred, teams may encounter a great deal of debris, damage to stoppings, and hazardous roof and rib conditions. Therefore, teams may find it necessary to improvise and control ventilation as much as possible.
Where stoppings in crosscuts are destroyed or damaged or filled with debris, or have large pieces of equipment or contain mine cars, they can be sealed to advance ventilation.
Where this occurs, teams can hang brattice or plastic from the roof and cut and fit the brattice to fit around the piece of equipment or obstruction, and shovel loose material onto the excess brattice at the bottom and-onto the equipment to effect as tight a seal as possible.
Note: Non-sparking tools, nails, or spads must be used in mine atmospheres above 1 percent methane to reduce the chance of a spark causing an ignition. Non-sparking shovels must be used in and around temporary stoppings in such atmospheres.
Pogo sticks (spring-loaded expandable metal rods similar to a pole lamp) can be used instead of posts to erect temporary stoppings quickly since pogo sticks donít need to be cut and fitted. They can be used along with posts in wide crosscuts to reduce the number of posts which would normally be needed.
Rescue teams, through teamwork and practice with the proper materials, can erect adequate temporary stoppings quickly and efficiently.
b. Permanent Stoppings- Permanent stoppings are usually not constructed until ventilation is restored to the mine, but they should be built as soon as possible to replace any temporary stoppings. Usually these permanent stoppings are constructed outby the fresh air base and can be built by barefaced work crews instead of by the mine rescue teams.
However, there are times when the mine rescue team will be required to build a permanent stopping while under oxygen, such as to seal a fire area. This topic will be discussed in detail in the manual entitled: "Fires, Firefighting, and Explosions."
c. Air Locks- An air lock consists of two stoppings with flaps or doors constructed close together to create a space where team members can pass from one mine atmosphere to another without mixing the atmospheres.
To maintain the air lock, one door of the air lock must be kept closed when the other door is open.
In mine rescue work, the air locks are normally put up to establish a fresh air base enabling teams to move inby into questionable air without contaminating the fresh air base.
Air locks are used too, when a team has to break open a stopping or door when conditions on the other side of that stopping are unknown.
Note: Air locks are required prior to opening any barricade or door in irrespirable atmospheres where survivors may be located. If survivors have barricaded themselves in fresh air, the team could contaminate the air when breaking through the barricade. The air lock will prevent any changes in ventilation.
When erecting an air lock, teams should build the two stoppings as close together as possible while allowing enough room for the team and their equipment to fit in between.
d. Line Brattice- Mine rescue teams may find it necessary to use line brattice to sweep noxious or explosive gases from a face area or to split an air current as they advance ventilation.
Line brattice is constructed by installing posts and nailing boards along the roof and floor for attaching the brattice. Brattice can also be attached to the roof with spads or held up with pogo sticks, if they are available. Spads will hold up the brattice better if they are driven through with soda-bottle caps which act as washers.
If the brattice only needs to hang for a short time, the team can holdup the brattice, extending it to the area to be ventilated. In this instance, the team members should hold up their individual section close to the roof.