Why mines explode

As a result of this, many mine workers continue to suffer from the long-term after-effects of carbon monoxide poisoning even if they are lucky enough to be rescued alive. Methane gas explosions create carbon monoxide when the density of the gas is high, but if there is not much gas it is more often than not dispersed in the air. However, in coal-dust explosions the story is a very different one. Coal dust, being a solid rather than a gas, does not burn completely, and high-density coal-dust clouds can be formed.

This prevents adequate air circulation, contributing to the production of carbon monoxide. Even if a coal-dust explosion does not spread throughout the length and breadth of the mine, the resulting carbon monoxide gas does in fact spread in this way and all the workers are poisoned.

The Miike mine explosion of was a good example of this. There is very little methane gas in the coal seams of the Miike mine. Thus, the possibility of a gas explosion is relatively low and, even if such an explosion came about, the possibility of its initiating a coal-dust explosion is likewise low.

Therefore, in the case of the Miike mine, it is clear that some factor caused the dispersal of the coal dust throughout the mine and some ignition source produced the explosion. There are two possible locations where the conditions for starting an explosion are ideal; one is at the seam working face, and the other on the mining slope.

The Miike mine owners were very careless in relation to coal-dust prevention procedures during mining operations. In order to prevent coal-dust explosions it is necessary to keep the dust out of the air by continuously sprinkling the area with water. Alternatively, rock dust, which is incombustible, can be mixed with the coal dust to prevent a chain reaction.

However, on the first mining slope, there were absolutely no preventative measures taken in relation to the problem. According to the testimony of mine workers at the Fukuoka Prosecutor's Office, one to two centimetres of coal dust had accumulated even at the location of the switch-box for the high-voltage system in the mine, and the walls were black with dust. The Fukuoka Mine Safety Department required that coal dust be cleaned away once a week, but, in locations where cleaning was difficult because of the height of the walls and ceiling, no such cleaning had taken place.

Thus, the risk of a large dust explosion was inherent in the coal-mining operation, especially when conditions existed that could provide the initial detonation. The Miike coal-mine explosion of 9 November At the bottom of the first mining level, ten of the four-wheeled carts filled with coal were being hauled to the surface.

One of the lower three carts derailed and, because of the tension thereby created, the chain of the third cart broke. At 1, metres from the entrance, eight cars began a free-fall run to the bottom of the mine. They ran free for about metres, increasing their speed by 33 metres per second, the momentum breaking archway support frames in the mine.

Then all of the carts were derailed and turned over. At this point the explosion took place. The rapid air displacement caused by the high-speed carts created air cur rents which caused the settled coal dust to mix with the surrounding air.

It is possible that the friction caused by the carts turning over produced the spark that ignited the coal dust; alternatively, the crashing carts could have damaged the high-voltage cables, and this could have been the ignition point for the explosion.

The compression caused by the explosion moved toward the mine entrance, and, metres from the first explosion, a powerful second explosion was created. It has been estimated that the wind created by this second explosion was probably travelling at a rate of 1, metres per second.

The compression from the second explosion, as it headed toward the bottom of the mine, fortunately did not touch off another explosion, but the carbon monoxide that was created by the two explosions spread throughout the entire mine, creating a disastrous poisoning situation.

At that time the second shift of workers 2 to 10 p. Twenty people were killed by the direct effects of the explosions, but died from acute carbon monoxide poisoning, and suffered the after-effects of poisoning. There is to date no other coal-mine accident in the world that has produced such a large number of casualties. Amazingly, the Mitsui Coal Mine Company management had no knowledge of the coal-dust explosion problem.

Most labourers believed that coal-dust explosions were caused by methane gas explosions and therefore were not open to ignition from other causes. Since the coal mine contained almost no methane gas it was believed that coal-dust explosions there were an impossibility. This explosion was to dislodge that myth very effectively. If management had shown a greater sense of responsibility toward the potential for coal-dust explosions, appropriate methods of avoiding such disasters would have been taken, cutting down the damage done and minimizing the danger to life and health.

Increased numbers of gas-poisoning victims due to a lack of education. The number of deaths and injuries resulting from the explosions was greatly increased by the carbon monoxide problem. In other words, had the carbon monoxide and other poison gases generated by the explosions been isolated in the immediate area, the amount of death and injury could have been kept to a minimum.

However, the mining company did not make any efforts to provide for such eventualities. Moreover, it would seem that the company neglected to educate its workers in relation to the potential for gas poisoning.

Indeed, it provided misinformation by spreading the "myth" that coal-dust explosions were impossible in the Miike mine. If the company was unaware of the relationship between dust explosions and the generation of poison gases, then it can only be said that it was irresponsible in the extreme. In most cases the explosion victims were not injured in a physical manner, and many of the corpses recovered from the mine showed no scars or scratches at all, since they were victims of monoxide poisoning.

Many of those rescued alive showed very severe symptoms of monoxide poisoning. The Mitsui Coal Mining Company was aware of these facts but made no attempts to rescue the workers. It indicated that, because of the breakdown of electricity and telephone communications in the mine after the explosions, conditions inside were unclear, and therefore it was too risky to send in rescue crews.

One must infer from these statements that management was willing for the 1, workers trapped inside the mine to be subjected to the possibility of pervasive monoxide poisoning, with no hope of rescue.

The miners of Miike were angered by the situation, feeling that responsible persons should go immediately into the mine with oxygen tanks.

While management was safe from the problem, there were workers in the mine who were at to metre depths and 8 kilometres from the entrance in tunnels.

These workers did not know about the explosions and were forced to remain below ground without electricity or telephones. Figure 5. The encircled numbers above the line indicate those who died because of the explosions, and those below the line indicate those workers present when the explosions took place. This rock dust serves to inert the coal dust when applied in the proper proportion. When explosions do occur, the dispersed limestone powder absorbs the heat generated from the explosion and will either stop the chain reaction or reduce the intensity of the explosion.

It is critical that this inertization practice of rock dusting be consistent with the mining process. Even a thin layer of additional coal dust deposited on a previously rock dusted area can restore the explosive condition.

Prevention of coal mine explosions requires a suite of control strategies, including sustaining a properly designed ventilation system, adequate sealing of abandoned areas, aggressive and frequent monitoring of methane, reduction of coal dust accumulations, and control of potential ignition sources through electrical safety and the use of permissible equipment.

NIOSH continues to conduct research to address these areas to develop more effective intervention measures and provide the science to guide recommendations for implementation of these measures and related policy decisions. Skip directly to site content. Section Navigation. Facebook Twitter LinkedIn Syndicate.

Friday, December 9, Coal dust explosion blast wave exiting mine portal. Methane, the main component of natural gas, is combustible, and mixtures of about 5 percent to 15 percent in air are explosive.

When air contains approximately 9. This produces water, carbon dioxide and a lot of amount of heat. The heat generated by this process raises the temperature of the air within the mine, which causes it to expand in volume. Since hot air cannot expand easily underground, pressure builds in the mine. If this pressure is high enough, it can cause the air ahead of the combustion zone to compress and cause a shock wave, Luo explained. Ventilation is the most common method to avoid such methane explosions in coal mines.

While much progress has been made in preventing explosion disasters in coal mines, explosions still occur, sometimes producing multiple fatalities. In the years from passage of the landmark Federal Coal Mine Health and Safety Act to , the number of fatalities due to underground coal mine explosions had exhibited a general downward trend. From onward, however, the industry has recorded 59 fatalities and 7 injuries from these occurrences.

And, from to , mine explosions accounted for nearly one-quarter of mining-related deaths. Many of these recent explosions have been due to methane ignitions in abandoned workings that breached the mine seals and extended into the active areas or a deficiency in rock dust related to poor rock dusting practices.

Research strategies include eliminating ignition sources, minimizing methane concentrations and coal dust accumulations, applying proper dispersible rock dust in sufficient quantity at all locations, using supplemental protection such as passive and active barriers to suppress propagating explosions, understanding the science of explosions, properly designing and evaluating the strength of ventilation structures, and properly managing sealed areas.

The NIOSH Mining Program's ongoing intramural research addresses methane and coal dust explosion problems in the coal mining industries. Control technologies proven to be successful then undergo final evaluation at operating mine sites.