Section one (1)

Mine ventilation (1)

Section two (6)

Methane and its control (6)

Section three (17)

Mine fires (17)

Section four (21)

Accident prevention principles (21)

Section five (24)

Hazard Identification (24)

Section six (29)

Accident Investigations (29)

Section seven (34)

Accident Analysis in Mine Industry (34)Section one

Mine ventilation

The two purposes of mine ventilation are: (1) to answer the requirements of the law in regard to supplying a stated quantity of fresh air per minute to each man in the mine, and to dilute render harmless, and sweep away dangerous gases. In coal mines the quantity of fresh air prescribed is generally from 100 to 150cu.ft/min/man in the mine. Some mining regulation specify a maximum limit to the quantity of methane permitted in the return air of coal mines, and some limit the amount of carbon dioxide permissible in the mine air. (2) to make working conditions more comfortable for miners. If conditions of humidity and air temperature are favourable, a decide cooling effect on the men is secured by giving the proper velocity to the an current, and the efficiency of the miners is increased. Dust and fumes from explosives are also removed.

Natural and artificial ventilation

Press differences required to cause air flow, may be produced by natural or mechanical forces. Flow caused by unequal densities or weights of air columns in or near the openings (due mainly to temperature differences) is “natural-draft” flow, and resulting pressure-differences are “natural draft pressure”. The relatively feeble currents forming complete flow-circuits in undivided single openings, also due to equal densities, are separately termed” convection currents ”. Many metal mines and some small coal mines are ventilated by natural draft alone, which also acts in conjunction with fan pressure in mechanically-ventilated mines; Where its importance largely depends on depth of workings and mine resistance.

The effect of natural conditions in creating a circulation of air in a mine is illustrated in Fig 1. It will be assumed that the temperature of the air current at any point in the mine is T1, and the outside temperature is T2. The column of air whose weight tends to produce circulation is H1 for the main shaft, and H2 for the air shaft. H2being composed of two sections, namely H a+H m. The direction in which the air will circulate and the pressure producing circulation may be derived by calculating.The difference between the weights of the two columns is the pressure in pounds per square foot that produces circulation of the air, and the direction of flow will be toward the column of lesser weight as indicated by the arrows in the figure.

In mines where the natural ventilation pressure is inadequate to supply the necessary air, fans are used. However, the effect of natural ventilation on the performance of the fan is important. Owing to the change in temperature from summer to winter conditions, natural ventilation may reverse its direction; in one case it assists the fan, in the other case it opposes it.

V entilation of coal mines is nowadays almost universally effected by use of the fans, of which there are many types. Such fans may either exhaust the air from the upcast shaft or blow or force the air down the downcast shaft. With few exceptions, exhausting fans at the top of the up-cast shaft are used in modern mines.

Fig.1 Natural ventilation

Although many types of fans are used for mine ventilation, they fall into two classes, viz, the centrifugal or wheel-type fan and the axial-flow or propeller type fan.

During recent year the centrifugal fan has found a rival in the axial-flow or propeller-type fan, which is now being used in increasing numbers to such an extent that it is largely replacing the centrifugal fan for mine ventilation.

The action of the axial-flow fan differs from that the centrifugal fan in that the air passes axially alone the fan instead of being discharged from the circumference of the fan by centrifugal force. The fan consists essentially of one or more rotors (some- what similar to aeroplane propellers; in the first axial-flow mine fans that rotors wereactually aeroplane propellers). There rotors carry blades and rotate at a high speed within a circular casing which the air enters at one end and is discharged at the other end. The number of rotors or stages depend upon the pressure to be produced, and mine fans may have anything from one to four stages, with the equivalent number of rotors mounted on the same shaft.

Although apparently simple in construction and operation, this type of fan calls for a high degree of skill in the design and arrangement of the blades. With the axial-flow fan it is possible to vary the performance by increasing its speed, by increasing the number of stages or rotors, and by altering the pitch or inclination of the blades, and these alterations can be made over fairly wide limits without seriously reducing the efficiency at which the fan works.

Underground fans

Fans are used underground mainly for two purpose, viz, as boosters for assisting the main fan, and as auxiliary fans for the ventilation of headings and blind ends.

The use of booster fans underground is confined to cases where the workings have extended to such great distances from the pit-bottom that the surface fan is incapable of circulating the quantity of air necessary for the ventilation of these remote workings and where it would be necessary either to install a larger and additional airways to allow adequate ventilation.

Such fans are usually installed in the return airways, but when electrically driven the driven the driving motor must be supplied with fresh of intake air.

The distribution of mine ventilation

The present-day practice is to split the air near the bottom of the downcast shaft into several intake airways, each of which serves a certain area of the workings or district of the mine. Similarly, separate returns are provided for the several working areas or districts near the upcast pit-bottom.

Splitting the air in this way is essential if the large volumes of air required in modern mines are to be provided, and in addition it offers many advantages, the chief of which are:

1.Each district is supplied with fresh air.2.A much large quantity of air circulates in the mine, due to lower resistance by multiple circuits or roadways.

3.There is less risk of accumulation of gas.

4.In the event of trouble in a district or an explosion, the trouble or damage is more likely to be confined to the particular district in which it occurs and less likely to affect the whole mine.

5.The velocity of the air currents in the intakes, returns and workings is lower, and the ventilating pressure required for a given total quantity of air is reduced, with consequent economy in power consumption.

Left to its own devices, the air would simply pass down the downcast and take the nearest way to the upcast shaft, leaving the rest of the mine unventilated. To prevent this and ensure the proper distribution of the air throughout the mine, various devices are employed.

Stoppings. As the mine workings advace, various connections between the intake and return airways must be sealed, as must also be abandoned roadways in order to prevent air leaking and circulating in areas where it is no longer required. It is required that any road connecting an intake and a return airway which has ceased to be required for the working of the mine shall be effectively sealed forthwith. For this purpose stoppings are constructed to confine the air along the desired course. These stoppings are built from floor to roof and from side to side of the roadways, and are constructed in many ways.

In important position they may be built of masonry or concrete, while at other times they may consist merely of debris packed in the roadway to a sufficient thickness to prevent the passage of air.

Doors. It is frequently necessary to prevent the passage of air along roadways which must, however, be available for persons or materials to pass. In these cases ventilation doors are employed. Not less than two doors are usually inserted, so that one can remain shut at all times to prevent short-circuiting of the air which would happen if a single door was used. In important situations near the pit-bottom and between main intakes and returns, it is customary to erect three or more door, and in

up-to-date mines these are sometimes constructed of steel plates with rubber beading around the edges to reduce leakage to a minimum. In other situations strong wooden doors with door frames built in brickwork surrounds are employed.

Sheets. Near the working faces, where the ventilating pressure is small and the ground is unsettled, sheets are sometimes employed as substitutes for doors to divert the air current. These consist of long brattice cloth or sacking, made windproof and usually fireproof, hung from roof to floor, and nailed to a piece of timber, often a roof bar. They can thus be lifted or pushed out of position for men or tubs to pass. The use of sheets is not recommended in position where it is possible to insert doors, as they are far from leakproof and are easily deranged, when they allow the air to short-circuit and rob the working places of ventilation.

Air crossings. To ensure the supply of air to all parts of the mine, if frequently becomes necessary that an intake airway and a return airway shall cross each other. In such cases an air-tight bridge, called an air crossing, overcast or cross over has to be constructed.

Regulators. In order to obtain the desired distribution of air between the various districts, it is usually necessary to restrict the amount of air flowing into certain districts which offer a low resistance to air flow. This is effected by the use of regulators. It is obvious that without regulators large volumes of air would tend to flow in the splits of low resistance, leaving only small quantities for the remote workings which offer a high resistance.

A regulator usually consists of a small sliding door or adjustable shutter set in an ordinary ventilating door.Section two

Methane and its control

Methane and respirable dust are the two common problems encountered in underground coal mining. They are more severe in modern longwall mining because of high production.

Methane and its drainage

Once the air enters the mine shaft, its composition changes and becomes mine air. most notably, the dust and hazardous gases will increase and dilute the concentration of oxygen. In addition, the air temperature, humidity, and pressure will all change. When those changes occur slightly, the mine air, which is not significantly different from the atmospheric air, is called fresh air. This usually refers to the air before passing through the working faces. After passing through working face or gob it is called the return air.

In general, mine gas refers to all the hazardous gases in mines. The most frequently encountered hazardous in underground coal mines are methane(CH4), carbon dioxide(CO2), carbon monoxide(CO), sulphur dioxide(SO2), hydrogen sulfide(H2S), nitrogen dioxide(NO2) and hydrogen(H2).

Methane or marsh gas, by miners it is termed firedamp or simply “gas”, is the major component of the hazardous gases in underground coal mines. It occupies approximately 80~96% by volume. Thus normally when one speaks of mine gas, one means methane. It is colorless and odorless; its diffusivity is about 1.6 times that of air. Since it has a low specific gravity (0.554), methane is easily accumulated near the roof of the roadway and working faces. Though it is harmless to breathe in small quantities, it is suffocating if its concentration is very high.

The most dangerous problem with methane is the potential of methane explosion. It will be ignited when its concentration is between 5 and 16% ( 9.5% is the most dangerous ) and the air temperature is from 1.200 to 1.3820F ( 650~7500C). Some coal seams and rock strata contain large amounts of methane, and under high pressure, the coal and gas will burst out suddenly and simultaneously. Obviously, certain

appropriate measures must be employed to extract methane from these coal seams in advance.

The amount of methane emission in an underground coal mine can be expressed either by the absolute amount or the relative amount of emission. The absolute amount of emission is the absolute amount of emission per unit time in the whole mine. Its volumetric unit will be ft 3/day (m 3/day) or ft 3/min (m 3/min). However, the relative amount of emission is the average amount of emission per ton coal produced within a certain period of time, ft 3/ton (m 3/ton).

During a normal production period the methane concentration is diluted to below the lowest limit allowed by law mainly adjusting the volume of the ventilated air. The required volume of air in a working face can be determined by k c Q Q gas

air =;

where Q air is the required fresh air volume in ft 3/min (m 3/min). C is the maximum allowable limit of methane concentration in the return air, generally 1~1.5%. The allowable limit of methane concentration varies from country to country. For instance, the limit in China is 1%; Holland 1.5% up to 2% in some area; West Germany 1~1.5%; France 1.5~2% for some faces with monitoring instrument; and in the U.S. 1~2%. K is the nonuniform coefficient of gas emission, generally 1.5.

Following the recent rapid development in longwall machinery, the longwall productivity has improved greatly while the coal produced is much smaller in size. These two events increase the amount of methane emission tremendously and consequently require a much larger volume of ventilated air. For example, in the United States the fresh air required at the longwall face is from 1.800 to 50.000 ft 3/min (510~1.417m 3/min).

Most of the methane produced during coalification and metamorphism escapes to the atmosphere through fissures in the strata. A small part stays in the fissures in the surrounding strata and still another small part remains in the coal. The methane stays in the coal or the fissures in the surrounding strata either in free or adsorbed state. The free methane moves freely in the coal or the fissures and fractures in the strata, whereas the gas molecules in the adsorbed methane tightly adhere to the surface of the

Methane content of seam and surrounding strata is the most important factor controlling the amount of methane to be emitted. If the seam contains a large amount of methane, it will emit more methane during mining. In addition, methane content in the coal seam and the surrounding strata also depends on the seam depth and geological conditions. Generally methane content in creases with seam depth. If the seam is close to the surface, especially if there are outcrops, methane will escape to the atmosphere and consequently methane content will be lower. The seam inclination is also a controlling factor. Since flowing along the bedding planes is much easier than flowing perpendicular to them, the larger the seam inclination, the more the methane escapes. If the surrounding strata are thick and tight in structure, the methane will more likely remain in the strata. Conversely, if the fissures are well developed in the strata, the methane will escape easily.

If the seam being mined has a high methane content, the mining method employed should be those that extract with high recovery and leaves as leaves as little coal in the gob possible. In this respect, longwall mining is the most suitable.

During coal cutting the amount of methane emission increases sharply. However, different methods of coal cutting produce different amounts of methane emission. It depends mainly on the amount of coal cut loose, the size of the newly exposed coalface, and the size of the broken coal, For example, if air picks are used, the amount of methane emission increases 1.1~1.3 times; 1.4~2.0 times for blasting;1.3~1.6 times for shearer cutting; and 2.0~4.0 times for hydraulic jetting. This is why coal seams with high methane content are not suitable for hydraulic mining. In modern longwall faces, the shearer cuts rapidly, resulting in high production. Consequently the amount of methane emission is large. It will be necessary to strengthen ventilation in order to reduce the methane concentration.

If longwall mining with the full-caving method is used, the methane originally stored in the roof strata and adjacent seams will be released and will flow into the normal ventilation networks. This is especially true during the periodic roof weighting when the main roof acts vigorously and caves in large areas. It may also reactivate the static air accumulated in the gob and flow into the face area and the tailentry. If the sealing method is used, the gob must be kept sealed tightly, because in a sealed gob, the methane accumulated may reach as high as 60~70% in the static air. The methane-rich static air should not be allowed to leak into the normal ventilation networks If, on the other hand, the open gob is employed, the gob must be ventilated adequately to reduce the potential of accumulating high concentrations of methane in certain areas.

Methods of Preventing Methane Explosion 1

There are three requirements methane explosion: a minimum concentration of methane and of oxygen and a suitable heat source. The min. concentration, 5％，is the lower explosion limit, and 15% is the upper limit. If below 5%, it forms a bluish stable combustion layer around the flame without initiating explosion. If larger than 5%, there is insufficient amount of oxygen to promote the chemical reactions leading to explosion. When the methane content in fresh air 9.5%, once it encounters a heat source of sufficient temperature, the whole amount of methane and oxygen will participate in the chemical reactions.

It must be noted, however, that as the oxygen content in the air decreases, the lower explosion limit will slowly increase while the upper explosion limit will drop sharply. When the oxygen content is decreased to 12%, the methane-air mixture will not be ignited. If the gob is sealed, there will be considerable accumulation of methane. But it will not be ignited even if there were spontaneous combustion in theremanent coal. This is due to the fact that in the sealed gob, there is insufficient amount of oxygen in the air.

The ignition temperature is the lowest temperature for igniting a methane explosion and generally ranges from 1,202 to 1,292 F(650~700℃). There are many underground heat sources that can ignite a methane explosion. These include any exposed fires, spontaneous coal combustions, electric arcings, high temperature gases from blastings, every hot metal surfaces and sparks due to impact and friction. However, once the methane-oxygen mixture encounters the heat source it requires a minimum reaction time before explosion. Although the reaction time is extremely short(Table),it is very important for mining operations. Therefore, when using permissible explosives, as long as the shot-firing is properly implemented, the methane will not be ignited.

In underground coal mines , methane explosion can occur in any place, however, most of them occur at the working faces where methane emission is the largest. Based on the factors contributing to methane explosion, the most effective methods for preventing methane explosion are to reduce the accumulation of methane and to eliminate high-temperature heat sources.

The areas where methane is likely to accumulate are the gob, working faces at the development entries, gob-side tailentry T-junction, near cutting drums off the shearer, and in the roof fall cavities.

It is very likely that methane accumulates to high concentration in the gob. In the United States the gobs are ventilated to prevent methane accumulation and to reduce the temperature. In most other countries the gobs are tightly sealed that it

completely cuts off any fresh air flowing into the gob or prevents high-concentration methane air flowing out of the gob. In any event, if amount of methane emission is large, some methods of methane drainage directly from the gob to the surface are necessary. The withdrawn methane can be used as a fuel or as a raw material for chemical by-products.

Frequently at the working faces of the development entries. due to insufficient air volume and speed, the methane cannot be effectively diluted and/or swept away. The methane concentration may reach a critical level. Since the specific gravity of methane is very small, it tends to accumulate near the roof line and forms a methane layer, sometimes up to 8~12 in (200~300mm) thick. It can be diluted or swept away by directing air flowing at 1.~3.28ft/ sec(0.5~1m/sec). If necessary, a guide board or pipe, or perforated compressive air pipe may be installed along the roof line to dilute the methane layer.

To increase the air volume and air speed is an effective method for diluting the methane concentration in the entries. But if the methane emission is very heavy, other supplementary measures are necessary. These include; (1) natural drainage-in this method, several entries are driven alternately. The methane will drain itself during the period of alternate stoppage; (2) drain as advance-in this method, holes are drilled on either one or both ribs approximately 49~66ft(15－20m) outby from the face. Each hole is connected to the drainage pipe out; (3) holes are drilled ahead of the face and the methane is drained for a period of time before the face is advanced.

Methods of Preventing Methane Explosion 2

The tailentry corner is the major area where high-concentration methane accumulates. This is due to the facts that, first, it serves as the major exit for the high-concentration methane in the gob, and second, when the fresh air reaches the tailentry T-junction it has to make a 90°turn which results in a turbulent air flow in the tailentry corner. Consequently, the methane accumulated in this area cannot be carried away. Several methods can be employed to eliminate the problems:

1. If the methane emission is heavier, some drainage methods are necessary in the tailentry corner (Fig.2).A steel pipe 150~300ft (46~92m)long is installed long the tailentry. The gob end of the pipe extends through the curtain separating the tailentryfrom the tailentry corner. The methane accumulated in the corner will flow out through the pipe due to air pressure differentials. If the air pressure differential is too small, the drainage efficiency can be increased by installing a high-pressure water pipe or a compressed-air pipe alongside the steel pipe with nozzles at predetermined intervals connecting the two pipes.

Fig 2 Method of draining methane accumulated at the tailentry corner if the methane

emission is medium high

2. When the methane emission is larger than 176~212ft3/min(5-6m3/min), some special measures of methane drainage must be employed.

If the coal seam has a high methane content, methane emission under high production by longwall mining will be very high. In such cases, it would be rather difficult and uneconomical to dilute the methane by increasing ventilation alone. Therefore, methane drainage must be considered. Methane drainage involves drilling boreholes into the solid coal, the roof and sometimes the floor. The methane contained in the coal or rock within a radius of up to 200ft(60m), depending on the permeability, will flow into the boreholes from which the methane is vacuum-pumped, viapipelines, to the surface.

In the United states, the most common method for methane drainage in longwall mining is by surface boreholes. Before the retreat mining begins, one to three surface boreholes, depending on the panel length, are sunk along the centerline of the panel.

Each borehole is sunk to a depth near the roof of the coal seam. The first borehole is usually located approximately 500ft（155m）from the panel setup room.Methane begins to emit from the borehole when the longwall face reaches to a few meters within the borehole. The initial methane flow rate is high but erratic. It becomes stabilized after nearly 60 days. It is not uncommon that using this method the total methane flow reaches 1,000,000ft3/day and the methane emission from the gob is reduced by more than 50%.

Another gob degasification method for advancing longwall panel where methane emission of up to 3,000ft3/ min ( 85m3/min ) per ton of coal is liberated, is shown in Fig.3-in(10-cm) holes are drilled into the roof from the return entry at an angle of 60°for about 90 ft deep and at 75-90 ft ( 23-27m ) intervals. Bottom holes are also drilled at an angle to stay under and ahead of the faceline. All holes are fitted with 4-in (10-cm) pipe and packed. The methane is vacuum-pumped to the surface and released into the atomosphere. This method can also be applied to retreat longwall panels with multiple entries, except that the holes will have to be drilled from the second entry.

3. Water Infusion Water infusion involves drilling in seam horizontal holes into the solid coal ahead of mining. High pressure water from 300 to 1,500 psi is injected into the boreholes. The high-pressure water moves away in a cylindrical water front. As the water moves away from the borehole, the methane is also driven away. In order to prevent water leakage and to increase the infusion zone, hole is generally either grouted or sealed with packers at 5 ft (1.5m) intervals. In general the infusion zone is approximate twice the length of the grouted portion of the hole. Therefore, with proper orientation and spacing of boreholes, the advancing water fronts can be merged to form a complete seal which in effect prevents the methane from being emitted into the coal face. In addition, water infusion tends to wet the coal before it is broken by the cutting machine. This is a very effective way of reducing the respirable dust level.

Fig.2 Gob degasification method for advancing longwall panel Fig.3 A shows a longwall retreating panel using one hole for water infusion. The panel width is 500ft (152m). The infusion hole is 275 ft (84m) long. A plastic pipe 255 ft (78m) long is inserted into the hole, with the outer 225 ft (69m) grouted. This leaves a 50-ft (15-m) open section at the bottom of the hole for water infusion. With this arrangement the infusion zone can cover the whole face width. The infusion holes along the panel length direction should be spaced at less than 400 ft(122m) so that the infusion zones will merge to from a complete seal.

Alternatively, two short holes, one from each side of the panel, can be drilled for water infusion in order to avoid the difficulties associated with long horizontal-hole drilling (Fig.4).

Fig4. Method of water infusion in a longwall panel with one(A) and two(B) The water flow rates for water infusion range from 7 to 20 gal/min (26~76liters/min). The water can be injected either by high volume in a short time period or low volume in a long time period Test results have shown that in the Pittsburgh seam, methane emission in the face area is reduced 79% and 39% when the face advancing direction is perpendicular and parallel, respectively, to the face cleat.

At the longwall face, one of the areas where the methane accumulates is in the neighborhood of the cutting drum. This occurs because the shearer moves at high speed, cutting a large volume of coal. Additionally the coal blocks cut loose from the face are further broken into smaller pieces as they travel rearward along the spiral vanes or scrolls of the cutting drum. As a result, an extremely large volume of methane is emitted from the coal face and the broken coal. The methane concentration is high, sometimes reaching up to 75%. Furthermore, a dead-end corner always forms in front of the leading drum where the air becomes turbulent and methaneaccumulates. As the web width increases, the ventilation of the dead-end corner becomes more difficult, resulting in more methane accumulation. Under this conditions, if the bits cut into some rock partings, the high temperature sparks produced could ignite the methane.

The problem of eliminating methane accumulation near the cutting drum must be considered in conjunction with dust suppression methods. The simplest method for diluting the methane accumulated in this area is increase air volume and air speed. If necessary, a water spray device or a small fan can be installed at the cutting drum. Furthermore, in the longwall faces with a larger volume of methane emission, the web width and haulage speed should be properly reduced so that the methane will be emitted slower and more uniformly from the face. In addition, methane emission can further be reduced by increasing the size of the broken coal.

Another important measure for prevention of methane explosion is the strict control of high temperature heat source. In the United States, the major heat source for the 209 cases of methane fires and explosions that occurred between 1952 and 1961 were the frictional sparks from the electrical machinery and cutting bits. Nowadays, all electrical installations are explosion- proof; that is, transformers and other electrical devices, capable of producing spark arcing, or very hot surfaces are enclosed in an antiexplosion enclosure.

Section three

Mine fires

Three classes of fires encountered in coal mines are:

Class A-fires in which the fuel is coal, rubber, wood or other solid burnable material.

Class b-fires in which the fuel is a liquid, such as gasoline or oil.

Class c-fires which occur in electrical equipment during arcing.

Most coal mine fires result from electrical failures, which cause arcs and class c blazes, which normally last only a short time but are important as the ignition source of other fires. A study of 92 face-equipment fires showed that 50 occurred on cutting machines. For the 92, points of origin were: trailing cable on reel, 33;trailing cable off reel, 22; machine cable, 26; others, 9. Also notable was that 85% of the fires occurred on d-c equipment and only 7% on a-c. Further, a substantial number of fires involved ignition of coal dust or oil accumulations on the machines.

Other sources of fires include open flames, are from bare trolley or other wires to wood crossbars, door beaders, top coal and the like, and spontaneous combustion in gob areas where the materials (coal, broken timber, etc.) are combustible, the heat of combustion is retained because the material is a poor conductor, ventilation is sufficient to provide the necessary oxygen but not sufficient to carry away the heat of oxidation or combustion, and there is enough air to keep the fire burning after it starts.

Fire prevention-methods of preventing mine fires include, in brief, the following:

Use of flame-resistant materials-conveyor belting and hydraulic fluid, as examples.

Good housekeeping-keeping mine openings free of oily rags, wood, rubber sand other combustible materials and storing and handling oil and other flammable materials to prevent leakage and spillage; keeping equipment free of oil, coal dust and other flammable materials.

Good maintenance from both the electrical and mechanical standpoints. No arcsin equipment or cables means no ignitions from this source. And from the mechanical standpoint, even if the hydraulic fluid is of the fire-resistant type, rupture of a hydraulic hose or leakage can leave oil on coal, increasing the liability of ignition, as a result of evaporation of the water forming the emulsion.

Use of properly rated and installed fuses and circuit breakers to quickly cut power off face equipment and cables and thus reduce the intensity and duration of arcs.

Proper installation and guarding of trolley, feeder and other bare wire to prevent arcing to coal and timber.

Firefighting-keeping little fires that do start in spite of the preceding and other precautions is the major objective in firefighting, approaches include:

Fire extinguishers at strategic locations and on equipment.

Fire extinguishing systems of the liquid, dry-chemical or foam type on mobile equipment, shuttle cars, miners and so on.

Installation of fire-suppressing divices-deluge-type water sprays or foam generators automatically activated by temperature rise on unattended underground equipment (pumps as an example), on main and secondary belt drives and at other appropriate locations. In the case of belt conveyors specifically, the act of 1969 required slippage and sequence switches on all underground main and panel belts, and, beginning may 31,1970, automatic fire-warning devices which also activate the fire-suppression system, and providing in addition that the secretary of the interior prescribe a schedule for installing fire-suppression devices in belt haulageways.

Installation of water lines large enough to supply sufficient water, with taps and valves every 300 to 400 ft for connecting fire hoses, plus shut off valves every 1000 ft, since experience has shown that water is the most effective means of coping with fires that are not controlled during their early stages. Federal regulations spells out minimum requirements for a water-supply system and fire hose for use in coal mines.

Acquisition of high expansion foam equipment for use of if the fire is or spreads beyond the effective rage of portable extinguishers and hose lines. If available in sufficient quantity, rock dust can serve as a fire extinguisher when conditions areright.

The last resort in fighting a fire is sealing that portion of the mine or, in severe cases, the entire mine. Flooding of sealed sections with water, where the dip makes it possible, or with nitrogen, has been done in a few instances of such steps, at least 100 days usually is allowed for extinguishment. Usually, after 100 days, an air analysis of 0.0% carbon monoxide, less than 1% oxygen and high concentrations of nitrogen and methane indicate a good possibility of success. Extreme caution must be exercised when removing seals to prevent rekindling of the fire or ignition of an explosive mixture in the sealed atmosphere.

Survival Measures-Carbon monoxide is the major hazard for men after explosion and during and after mine fires. Self-rescuers provide individual protection, and the act of 1969 provides that an approved unit capable of functioning for 1 hr or more be made available to each miner. If not worn on the person because it would hamper the man’s activities and thus constitute a hazard, a unit must be available in a place not cover 25 ft away. In the early days of mining workers on occasion achieved protection by going into a fresh-air place and sealing it off, and some mines provided materials for such sealing at strategic spots. Now, under the act of 1969, the secretary may prescribe that rescue chambers, sealed and ventilated, be built and equipped with first-aid materials, self-contained breathing apparatus and an independent communications system to the surface. A general communication system is mandatory in all coal mines.

Underground coal fires-a looming catastrophe

Coal burning deep underground in China, India and Indonesia is threatening the environment and human life, scientists have warne. These large-scale underground blazes cause the ground temperature to heat up and kill surrounding vegetation, produce greenhouse gases and can even ignite forest fires, a panel of scientists told annual meeting of the American association for the advancement of science in Denver. The resulting release of poisonous elements like arsenic and mercury can also pollute local water sources and soils, they warned.

“Coal fires are a global catastrophe,” said associate professor Glenn Stracher of east Georgia College in Swainsboro, USA. But surprisingly few people know about them.Coal can heat up on its own, and eventually catch fire and burn, if there is a continuous oxygen supply. The heat produced is not caused to disappear and under the right combinations of sunlight and oxygen, can trigger spontaneous catching fire and burning. This can occur underground, in coal stockpiles, abandoned mines or even as coal is transported. Such fires in China consume up to 200 million tones of coal per year, delegates were told. In comparison, the U.S. economy consumes about one billion tones of coal annually, said Stracher, whose analysis of the likely impact of coal fires has been accepted for publication in the international journal of coal ecology. Once underway, coal fires can burn for decades, even centuries. In the process, they release large volumes of greenhouse gases, poisonous fumes and black particles into the atmosphere.

The members of panel discussed the impact these fires may be having on global and regional climate change, and agreed that the underground nature of the fires makes them difficult to protect. One of the members of the panel, assistant professor Paul V an Dijk of the international institute for Geo-information Science and Earth Observation in the Netherlands, has been working with the China government to detect and monitor fires in the northern regions of the country.

Ultimately, the remote sensing and other techniques should allow scientists to estimate how much carbon dioxide these fires are emitting. One suggested method of method of containing the fires was presented by Gary Colaizzi, of the engineering firm Goodson, which has developed a heat-resistant grout ( a thin mortar used to fill cracks and crevices), which is designed to be pumped into the coal fire to cut off the oxygen supply.Section four

Accident prevention principles

Coal mining historically has been a hazardous occupation but, in recent years, tremendous progress has been made in reducing accidental coal mine deaths and injuries.

Accident prevention fundamentals are to no different for coal mining than for any other type of work. The fundamentals apply to all industries. Construction workers may be struck by falling tools and materials, and mines may be trapped by mine fires. Railroad brakemen may lose hands and fingers positioning couples, and miners may lose hands and fingers positioning couplers, many other examples could be cited, but the point is that accidents that happen in coal mines are basically similar to accidents that happen in other industries. Thus, the basic principles for preventing accidents apply in coal mining as they do in any other type of work.

A personal accident is defined as an unexpected happening that interrupts the normal work activity of an employee and usually, although not necessarily, results in an injury. An equipment accident is an unexpected happening that results in damage to equipment and under certain circumstances results in injury to employees.

The supervisor should understand why men act in an unsafe manner and how unsafe conditions are produced, so he will be able to recognize and correct both situations before they lead to an accident. He can learn this in many ways but one major method is from thorough accident？

Accidents are complex. Usually there are several causes, both personal and environmental, that operate in sequence or in combination to result in an accident.

To prevent an accident from happening, the causes of accidents must be determined and eliminate. Accidents are caused! They don’t just happen.

The basic principles of accident prevention are establishing the potential and a actual causes of accidents, and eliminating the causes.

The first principles emphasizes that causes exist before accidents happen.Properly trained supervisors can recognize potential accident causes and eliminates them before accidents happen. In the event an accident has occurred, they are able to determine the actual causes and eliminate them before they cause additional accidents.

Having determined the principles for accident prevention, what is needed to put them to work?

First, the potential and actual causes of accidents must be established.

Potential causes are the unsafe conditions and unsafe practices that have not yet caused an accident. To detect and determine potential unsafe conditions, a mine safety program should include planned safety inspections, which are explained under accident prevention tools.

There could be a tendency for coal mine operators to consider the requirements of the federal Mine safety and health act of 1977 the basis for an adequate inspection program⑹. These regulations, however, are directed principally toward specific types of unsafe conditions and the physical environment. They should therefore not be the only items an inspection program for unsafe conditions, but should supplement the operator’s own inspection program.

To detect and correct unsafe practices that have not yet caused an accident. Supervision could make regular, planned job procedure observations of a specific employee performing a specific job. This planned safety observation is also explained under accident prevention tools.

Actual conditions or actions, which have contributed to an accident, can be determined with the aid of another safety tool, the accident investigation report.

The second principle of accident prevention is to eliminate the cause of accidents.

Where the supervisor has the authority he should eliminate any unsafe conditions and any causes of the unsafe conditions. If he lacks this authority then he should report the unsafe conditions and their causes to his superior together with recommendations for correction.

Unsafe practices are just as important as unsafe conditions. Unsafe practices stem from many sources, all of which must be eliminated if accidents are to be

prevented.

One major cause of unsafe practices is lack of knowledge or skill. Fortunately, it can be eliminated by job safety instruction before a man starts on a new job, by follow-up observations, and by repeated instruction of safe job procedures as explained under accident prevention tools.

Another source of unsafe practices is improper motivation and attitudes. This, too, can be eliminated by repeated emphasis on the gains to be achieved by working safely compared with the pain, suffering, and loss that are incurred in an accident. Changing attitudes requires considerable tact, skill, and patience on the part of the supervisor. His knowledge of the miners, the work situation, and practices in the mine will determine how he will handle the situation.

Any safety program should be audited to determine if it is being implemented as designed⑻. The audit of an accident prevention program should determine if each member of management is carrying out his responsibilities and if each accident prevention tool is properly used.

The audit should be a formal procedure and should be performed, if practicable, by mine supervisors who are not associated with the mine being audited.

The mine may have a well-designed safety program, but supervisors may be only going through the motions, filling in the forms, and presenting the appearance of an active safety program. If so, the accident experience might will be poor. The audit determines the areas in which the program needs to be improved.Section five

Hazard Identification

Hazard identification is a process controlled by management. Y ou must assess the outcome of the hazard identification process and determine if immediate action is necessary or if, in fact, there is an actual hazard involved. When you do not view a reported hazard as an actual hazard, it is critical to the ongoing process to inform the worker that you do not view it as a true hazard and explain why. This will insure the continued cooperation of workers in hazard identification.

It is important to remember that a worker may perceive something as a hazard, when in fact it may not be a true hazard; the risk may not match the ranking that the worker placed on it. Also , even if a hazard exists, you need to prioritize it according to the ones that can be handled quickly, which may take time ,or which will cost money above your budget. If the correction will cause a large capital expense and the risk is real but does not exhibit an extreme danger to life and health, you might need to wait until next year’s budget cycle. An example of this would be when workers complain of a smell and dust created by chemical process. If the dust is not above accepted exposure limits and the smell is not overwhelming, then the company may elect to install a new ventilation system, but not until the next year because of budgetary constraints. The use of PPE until hazards can be removed may be required.

The expected benefits of hazard identification are a decrease in the incidents of injuries, a decrease in lost workdays and absenteeism, a decrease in workers’compensation costs, increased productivity, and better cooperation and communication. The baseline for determining the benefit of the hazard identification can be formulated from existing company data on occupational injuries/illnesses, workers’ compensation, attendance, profit, and production.

Hazard identification includes those items that can assist you with identifying workplace hazards and determining what corrective action is necessary to control them. These items include jobsite safety inspections, accident investigations, safetyand health committees, and project safety meetings. Identification and control of hazards should include periodic site safety inspection programs that involve supervisors and, if you have them, joint labor management committees. Safety inspections should ensure that preventive controls are in place (PPE, guards, maintenance, engineering controls), that action is taken to quickly address hazards, that technical resources such as OSHA, state agencies, professional organizations, and consultants are used, and that safety and health rules are enforced.

Many workplaces have high accident incidence and severity rates because they are hazardous. Hazards are dangerous situations or conditions that can lead to accidents. The more hazards present, the greater the chance that there will be accidents. Unless safety procedures are followed, there will be a direct relationship between the number of hazards in the workplace and the number of accidents that will occur there.

As in most industries, people work together with machines in an environment that causes employees to face hazards, which can lead to injury , disability, or even death. To prevent industrial accidents, the people, machines, and other factors which can cause accidents, including the energies associated with them, must be controlled. This can be done through education and training, good safety engineering, and enforcement.

The core of an effective safety and health program is hazard identification and control. Periodic inspections and procedures for correction and control provide methods of identifying existing or potential hazards in the workplace and eliminating or controlling them. The hazard control system provides a basis for developing safe work procedures and injury and illness prevention training. Hazards occurring or recurring reflect a breakdown in the hazard control system.

The written safety and health program establishes procedures and responsibilities for the identification and correction of workplace hazards. The following activities can be used to identify and control workplace hazards: hazard reporting system, job site inspections, accident investigation, and expert audits.

After all basic steps of the operation of a piece of equipment or job procedure have been listed, we need to examine each job step to identify hazards associated with eachjob step. The purpose is to identify an list the possible hazards in each step of the job. Some hazards are more likely to occur than others, and some are more likely to produce serious injuries than others. Consider all reasonable possibilities when identifying hazards.

1. Accident Types

Struck –against Type of Accidents

Look at the first four basic accident types-struck----against, struck-by, contact-with and contacted-by—in more detail, with the job step walk-round inspection in mind. Can the worker strike against anything while doing the job step? Think of the worker moving and contacting something forcefully and unexpectedly----an object capable of causing injury. Can he or she forcefully contact anything that will cause injury? This forceful contact may be with machinery, timber or bolts, protruding objects to sharp, jagged edges.Identify not only what the worker can strike against, but how the contact can come about. This does not mean that every object around the worker must be listed.

Struck-by Type of Accidents

Can the worker be struck by anything while doing the job step? The phrase “struck by” means that something moves and strikes the worker abruptly with force. Study the work environment for what is moving in the vicinity of the worker, what is about to move, or what will move as a result of what the worker does. Is unexpected movement possible from normally stationary objects? Examples are ladders, tools, containers, and supplies.

Contact-by Contact-with Type of Accidents

The subtle difference between contact-with and contact-by injuries is that in the first, the agent moves to the victim, while in the second, victim moves to the agent. Can the worker be contacted by anything while doing the job step? The contact-by accident is one in which the worker could be contacted by some object or agent. This object or agent is capable of injuring by nonforceful contact. Examples of items capable of causing injury are chemicals, hot solutions, fire, electrical flashes, and steam.Can the worker come in contact with some agent that will injure without forceful contact? Any type of work that involves materials or equipment that may be harmful without forceful contact is a source of contact-with accidents. There are two kinds of work situations which account for most of the contact-with accidents. One situation is working on or near electrically charged equipment, and the other is working with chemicals or handing chemical containers.

Caught-in and Caught-on Type of Accidents

The next three accident types involve “caught” accidents. Can the person be caught in , caught on ,or part between objects? A caught-in accident is one in which the person, or some part of his or her body, is caught in an enclosure or opening of some kind. Can the worker be caught on anything while doing the job step? Most caught on accidents involve worker’s clothing being caught on some projection of a moving object. This moving object pulls the worker into an injury contact. Or , the worker may be caught on a stationary protruding object, causing a fall.

Caught-between Type of Accidents

Can the worker be caught between any objects while doing the job step? Caught-between accidents involve having a part of the body caught between something moving and something stationary, or between two moving objects. Always look for pinch point.

Fall-to-Same-level and Fall-to-Below Types of Accidents

Slip, trip, and fall accident types are some of the most common accidents occurring in the workplace. Can the worker fall while doing a job step? Falls are such frequent accidents that we need to look thoroughly for slip, trip, and fall hazards. Consider whether the worker can fall from something above ground level, or whether the worker can fall to the same level.

Two hazards account for most fall-to-same level accidents: slipping hazards and tripping hazards. The fall-to-below accidents occur in situations where employees work above ground or above floor level, and the results are usually more severe. Overexertion and Exposure Types of Accidents

The next two accident types are overexertion and exposure. Can the worker beinjured by overexertion; that is, can be he or she be injured while lifting, pulling or pushing? Can awkward body positioning while doing a job step cause a sprain or strain? Can the repetitive nature of a task cause injury to the body? An example of this is excessive flexing of the wrist, which can cause carpal tunnel syndrome (which is abnormal pressure on the tendons and nerves in the wrist).

Finally, can exposure to the work environment cause injury to the worker? Environmental conditions such as noise, extreme temperatures, poor air, toxic gases and chemicals, or harmful fumes from work operations should also be listed as hazards.

2. Hazard Reporting System

Hazard identification is a technique used to examine the workplace for hazards with the potential to cause accidents. Hazard identification, as envisioned in this section, is a worker-oriented process. The workers are trained in hazard identification an asked to recognize an report hazards for evaluation and assessment. Management is not as close to the actual work being performed as are those performing the work. Even supervisors can use extra pairs of eyes looking for areas of concern.

Workers have already hazard concerns an have often devised ways to mitigate the hazard, thus preventing injuries and accidents. This type of information is invaluable when removing and reducing workplace hazards.

This approach to hazard identification does not require that someone with special training conduct it. It can usually be accomplished by the use of a short fill-in-the-blank questionnaire. This hazard identification technique works well where management is open and genuinely concerned about the safety and healthy of its workforce. The most time-consuming portion of this process is analyzing the assessment and response regarding potential hazards identified. Empowering workers to identify hazards, make recommendations on abatement of hazards, and then suggest how management can respond to these potential hazards is essential.

Section six

Accident Investigations

Although accident investigation is an after-the-fact approach to hazard identification, it is still an important part of this process. At times hazards exist, which no one seems to recognize until they result in an accident or incident. In complicated accidents it may take an investigation to actually determine what the cause of the accident was. This is especially true in cases where death results and few or no witnesses exist. An accident investigation is a fact-finding process and not a fault-finding process with the purpose of affixing blame. The end of any result of an accident investigation should be to assure that the type of hazard or accident does not exist or occur in the future.

Your company should have a formalized accident investigation procedure, which is followed by everyone. It should be spelled out in writing and end with a written report using as a foundation for your standard company accident investigation form. It may be your workers’compensation form or an equivalent from your insurance carrier.

Accidents and even near misses should be investigated by your company if you are intent on identifying and preventing hazards in your workplace. Thousands of accidents occur throughout the United States every day. The failure of people, equipment, supplies, or surroundings to behave or react as expected causes most of the accidents. Accidents investigations determine how and why these failures occur. By using the information gained through an investigation, a similar or perhaps more disastrous accident may be prevented. Accident investigations should be conducted with accident prevention in mind. Investigations are NOT to place blame.

An accident is any unplanned event that results in personal injury or in property damage. When the personal injury requires little or no treatment, it is minor. If it results in a fatality or in a permanent total, permanent partial or temporary total(lost-time) disability, it is serious. Similarly, property damage may be minor or serious. Investigate all accidents regardless of the extent of injury or damage. Accidents are part of a broad group of events that adversely affect the completion of a task. These events are incidents. For simplicity, the procedures discussed in later sections refer only to accidents. They are, however, also applicable to incidents.

1. Accident Prevention

Accidents are usually complex. An accident may have 10 or more events that can be causes. A detailed analysis of an accident will normally reveal three cause levels: basic, indirect, an direct. At the lowest level, an accident results only when a person or object receives an amount of energy or hazardous material that cannot be absorbed safely. This energy or hazardous material is the DIRECT CAUSE of the accident. The direct cause is usually the result of one or more unsafe acts or unsafe conditions, or both. Unsafe acts and conditions are the indirect causes or symptoms. In turn, indirect causes are usually traceable to poor management policies and decisions, or to personal or environmental factors. These are the basic causes.

In spite of their complexity, most accidents are preventable by eliminating one or more causes. Accident investigations determine not only what happened, but also how and why. The information gained from these investigations can prevent recurrence of similar or perhaps more disastrous accidents. Accident investigators are interested in each event as well as in the sequence of events that led to an accident. The accident type is also important to the investigator. The recurrence of accidents of a particular type or those with common causes shows areas needing special accident prevention emphasis.

2. Investigative procedures

The actual procedures used in a particular investigation depend on the nature and results of the accident. The agency having jurisdiction over the location determines the administrative procedures. In general, responsible officials will appoint an individual to be in charge of the investigation. An accident investigator should use most of the following steps:

Define the scope of the investigation.Select the investigators. Assign specific tasks to each (preferably in writing). Present a preliminary briefing to the investigating team.

Visit and inspect the accident site to get updated information.

Interview each victim and witness. Also interview those who were present before the accident and those who arrived at the site shortly after the accident. Keep accurate records of each interview. Use a tape recorder if desired and if approved. Determine the following:

What was not normal before the accident.

Where the abnormality occurred.

When it was first noted.

How it occurred.

Determine the following:

Why the accident occurred.

A likely sequence of events and probable causes (direct, indirect, basic). Alternative sequences.

Determine the most likely sequence of events and the most probable causes.

Conduct a post-investigation briefing.

Prepare a summary report including the recommended actions to prevent a recurrence. Distribute the report according to applicable instructions.

An investigation is not complete until all data are analyzed and a final report is completed. In practice, the investigative work, data analysis, and report preparation proceed simultaneously over much of the time spent on the investigation.

3. Fact-Finding

Investigator collects evidence from many sources during an investigation, gets information from witnesses and observation as well as by reports, interviews witnesses as soon as possible after an accident, inspects the accident site before any changes occur, takes photographs and makes sketches of the accident scene, records all pertinent data on map, and gets copies of all reports. Documents containing normal operating procedures flow diagrams, maintenance charts or reports of difficulties or abnormalities are particularly useful. Keep complete and accurate notes in a boundnotebook. Record pre-accident conditions, the accident sequence and post-accident conditions. In addition, document the location of victims, witnesses, machinery, energy sources, and hazardous materials.

In some investigations, a particular physical or chemical law, principle, or property may explain a sequence of events. Include laws in the notes taken during the investigation or in the later analysis of data. In addition, gather data during the investigation that may lend itself to analysis by these laws, principles, or properties. An appendix in the final report can include an extended discussion.

4. Interviews

In general, experienced personnel should conduct interviews. If possible, the team assigned to this task should include an individual with a legal background. After interviewing all witness, the team should analyze each witness’ statement. They may wish to re-interview one or more witnesses to confirm or clarify key points. While there may be inconsistencies in witnesses’ statements, investigators should assemble the available testimony into a logical order. Analyze this information along with data from the accident site.

Not all people react in the same manner to a particular stimulus. For example, a witness within close proximity to the accident may have an entirely different story from one who saw it at a distance. Some witness may also change their stories after they have discussed it with others. The reason for the change may be additional clues.

A witness who has had a traumatic experience may not be able to recall the details of the accident. A witness who has a vested interest in the results of the investigation may offer biased testimony. Finally, eyesight, hearing, reaction time, and the general condition of each witness may affect his or her powers of observation. A witness may omit entire sequences because of a failure to observe them or because their importance was not realized.

5.Report of Investigation

As noted earlier, an accident investigation is not complete until a report is prepared and submitted to proper authorities. Special report forms are available is many cases. Other instances may require a more extender report. Such reports areoften very elaborate and may include a cover page, title page, abstract, table of contents, commentary or narrative discussion of probable causes, and a section on conclusions and recommendations

Accident investigation should be an integral part of your written safety and health program. It should be a formal procedure. A successful accident investigation determines not only what happened, but also finds how and why the accident occurred. Investigations are an effort to prevent a similar or perhaps more disastrous sequence of events. You can then use the resulting information and recommendations to prevent future accidents.

Keeping records is also very important to recognizing and reducing hazards. A review of accident and injury records over a period of time can help pinpoint the cause of some accidents. If a certain worker shows up several times on the record as being injured, it may indicate that the person is physically unsuited for the job, is not properly trained, or needs better supervision. If one or two occupations experience a high percentage of the accidents in a workplace, they should be carefully analyzed and countermeasures should be taken to eliminate cause. If there are multiple accidents involving one machine or process, it is possible that work procedures must be changed or that maintenance is needed. Records that show many accidents during a short period time would suggest an environmental problem.

Once the hazards have been identified then the information and sources must be analyzed to determine their origin and the potential to remove or mitigate their effects upon the workplace. Analysis of hazards forces us to take a serious look at them.Section seven

Accident Analysis in Mine Industry

Coal is produced from underground mines in about 50 countries. Underground coal mines range from modern mines using the latest remote-controlled equipment operated by a small, highly skilled workforce benefiting from continuous monitoring of all aspects of workplace conditions, to mines that are dug by hand and where the coal is extracted and transported by hand, often in conditions that are unsafe and unhealthy.

Underground coal mining has historically been one of the highest risk activities as far as the safety and health of workforce are concerned. Fortunately, significant, sustained improvements in coal mining occupational safety and health have been achieved as a result of new technologies, massive capital investment, intensive and continuous training and changes in attitudes to safety and health among those in all stages of the coal chain. Nonetheless, if a safety net, which includes a number of critical checks and balances, is not in place to asses and control the hazards, accidents, ill health and diseases can and do occur. These are discussed as follows.

1.Rock Falls

Underground coal mines frequently suffer from roof falls which have various consequences ranging from fatalities and injuries to downtimes. Underground mining still has one of the highest fatal injury rates of any U.S. industry-more than five times the national average compared to other industries. Between 1996 and 1998, nearly half of all underground fatalities were attributed to roof, rib and face falls. Small pieces of rock falling between bolts injure 500-600 coal miners each year.

Several factors have contribution to occurrences of roof falls in underground coal mines, such as geological and stress conditions, mine layout, mine environment. Among the factors affecting the roof fall hazards in coal mines, stress conditions and mine layout are somewhat controllable by appropriate mine design. However, it is relatively more difficult to control the effect of geological conditions on roof falls,

since the geological conditions are the nature’s uncertainty, and hence they comprise inherent variability in roof fall occurrence. Therefore, in order to deal with the uncertainties associated with the roof falls, risk assessment methods are required for decreasing the consequences and related costs of roof fall hazards.

2.Outburst

Natural phenomena of sudden gas and rock mass outbursts, such as volcano eruption, geysers, huge bursts of water saturated with CO2, out of the reservoirs in former volcano craters have been known for a long time. As mining activities upset the natural balance in the rock mass containing the substances that undergo phase transitions, the outbursts of rock and gas may occur. Their occurrences in mines have been recorded for more than 150 years. Attempts have been made to provide an adequate explanation of these processes. Increasing frequency of outburst occurrence after World War Ⅱcalled for still more extensive research.

Coal and gas outburst problems have been exacerbated significantly over the past decade because of higher productivity and the trend towards recovery of deeper coal seams. However, despite of great efforts, surprisingly little progress has been made towards understanding outburst mechanism. Prediction techniques continue to be unreliable and unexpected outburst incidents are still a major concern for underground coal mining.

In China outbursts occur in a number of coal fields and in a large number of mines. In fact, the largest number of outbursts have been recorded in China. The most important coal fields where outbursts occur are in the provinces of Shanxi (Yangquan); Liaoning (Beipiao); Henan (Jiaozuo), Chongqing (Nantong and Songzao) and Hebei (Kailuan). Coal and gas bursts are differentiated in China into four categories: Coal bursts with no gas;

Gas bursts;

Coal and gas outbursts;

Rock and gas outbursts

3.Mine Fires

Three ingredients are necessary for a fire. These are fuel, oxygen and ignition,referred to as the fire triangle. Coal seams make up a third of the fire triangle with natural deposits of both solid and gaseous fuels. Mine ventilation carries oxygen, the second part of the fire triangle, throughout the mine. Electrical machines, equipment, lights, power stations and circuitry, along with diesel equipment, conveyor belting frictional sources, welding, acetylene cutting and other produces of friction, spark or flame used throughout a mine are ignition sources which add the third ingredient of the fire triangle. To prevent the outbreak of coal mine fires, a number of critical safeguards, checks and balances are necessary.

Fires are significant hazard to the safety and health of mine workers. Fires at underground and surface mines place the lives and livelihood of our nation miners at risk. V entilation streams in underground mines can carry smoke and toxic combustion products throughout the mine, making escape through miles of confined passageways difficult and time consuming. A fire in an underground coal mine is especially hazardous due to the ultimate fuel supply and the presence of flammable methane gas. The greatest mine fire disaster in the US occurred at the Cherry Coal Mine, IL, in November 1909, where 259 miners perishes. During 1990-2001, more than 975 reportable fires temporary closing of several mines. Over 95 of the fires occurred in underground coal mines. The leading causes of mine fires include flame cutting and welding operations, friction, electrical shorts, mobile equipment malfunctions, and welding spontaneous combustion. The prevention, early and reliable detection, control, and suppression of mine fires are critical elements in safeguarding the lives and livelihood of over 230000 mine workers.

4.Explosions

While much progress has been made in preventing explosion disasters in coal mines, explosions still occur, sometimes producing multiple fatalities. Explosions and the resulting fires often kill or trap workers, block avenues of escape, and rapidly generate asphyxiating gases, threatening every worker underground. Explosions in underground mines and surface processing facilities are caused by accumulations of flammable gas and/or combustible dust mixed with air in the presence of an ignition source. Explosions can be prevented by minimizing methane concentrations throughmethane drainage and ventilation, by adding sufficient rock dust to inert the coal dust, and by eliminating ignition sources. Explosion effects can be mitigated by using barriers to suppress propagating explosions.

5.Coal Dusts

The production, transportation and processing of coal generates small particles of coal dust. If uncontrolled and allowed to accumulate, that highly explosive dust can ignite. If it becomes airborne the coal dust can cause violent explosions. Coal dust explosions can create deadly forces, fire and super-heated air which can quickly spread through a mine, killing or injuring several miners. Explosion forces can destroy ventilation and roof controls, block escape routes and trap miners in conditions where oxygen in the mine air is replaced with asphyxiating gases.

The production, transportation and processing of coal generates tiny respirable coal dust particles that become airborne and are invisible to the naked eye. Appropriate instrumentation should be used to quantify the level and size of dust particles present in the air. Coal is made up of a variety of elements. It is mixed with other dusts, most notably crystalline silica, generated from fractured rock in the mine roof, floor or the coal seam which can also become airborne. So coal mine dusts can be a significant health risk. When inhaled by miners, dust can result in diseases of the pulmonary system (lungs), including coalworkers’pneumoconiosis(CWP), progressive massive fibrosis (PMF), silicosis,and chronic obstructive pulmonary disease (COPD). These lung diseases are progressive, disabling and can be fatal.

6.Electricity

The use of electricity and energized equipment in underground coal mines can result in injuries and death from electrical shock or arc burn. Given the confined space of underground mines, which are a dark, and at times a harsh environment, with several pieces of energized equipment and circuitry in close proximity to workers and with self-propelled equipment in motion, the potential of shock or electrocution exists.

Coal mines contain natural deposits of coal, coal mine dust and mine gases that are flammable and explosive. The introduction of electrical and energized equipmentin coal mines creates the potential of igniting mine fires and explosions, which can cause numerous deaths and injuries from single events and devastate the mine.

Electrical accidents are the 4th leading cause of death in mining and are disproportionately fatal compared with most other types of mining accidents. About one-fifth of these deaths result when high-reaching mobile equipment contacts power lines overhead. One-half of all mine electrical injuries and fatalities occur during electrical maintenance work, with the following electrical components most commonly involved: circuit breakers, conductors, batteries, and meters.

7.Inrushes of Water, Gas or Other Material

Inrushes of water, noxious or flammable gas or other material are a serious hazard in coal mining. Mining operations can get too close to old workings or geological abnormalities that contain water, gases or materials that could inundate the mine. One particular hazard is mining next to old workings that were poorly surveyed, not surveyed at all, or not adequately inspected, which contain bodies of water or dangerous mine gases. Old workings filled with water, particularly at elevations higher than the active mine, could quickly flood the mine and drown miners before they could escape if inadvertently cut into. Inrushing mine gases inadvertently encountered can overpower mine ventilation and the oxygen in the air and suffocate miners or, with the right mixture of oxygen, trigger explosions.下载本文