THE FIRE HAZARD OF COAL DUST
Two Serious Accidents Result from ignition of Dust Cloud—Miners Burned—Remedies Suggested to Prevent Such Occurrences
THE Bureau of Mines for a number of years has conducted experiments at its experimental mine near Bruceton, Pa., on the explosibility of coal dust, with particular reference to dust explosions in coal mines, and the knowledge so gained may well be applied to the handling of coal dust at industrial plants and elsewhere. Powdered coal is coming into use more and more as a fuel, and the dangets incident to its use should be recognized and guarded against, as a number of accidents have occurred in recent years due to ignorance of this danger or to carelessness. Within the past three years two very serious accidents, under almost identical circumstances, have occurred on the surface at two different coal mines in Southeastern Iowa, due in each case to the sudden ignition of a cloud of fine coal dust.
The first accident resulted in the burning of six men, three of them fatally; the second burned eleven; three men died as a result of their burns. The mines in the Southeastern part of Iowa, where these two disasters occurred, are operating in a thin coal bed averaging about three feet in thickness, and are worked on the long-wall advancing system similar to that of Northern Illinois.
The miners in this section arc paid on a screened coal basis; in other words, receive no pay for the fine coal. As a result they use forks in loading the coal into the mine cars, and naturally a considerable quantity of coal is left along the roadways. Subsequently this fine coal, together with the roof rock that is taken down to give sufficient height on the roadways, is loaded into cars and dumped in piles on the surface. This roof rock is a black, oily shale, and the combination of fine coal and oil shale gives ample combustible material to thoroughly burn the rock as it is dumped. These rock piles, or dirt piles, as they are called, take fire spontaneously and continue to burn as long as fresh material is dumped on them.
This rock, after having burned itself out, makes an excellent material for road building and also for railway track ballast. Because of this latter fact the railroads serving these mines were in each instance loading out the burned material from the side of the rock pile with a steam shovel. Having cleaned up all the loose material along the side of the pile next to the track, leaving a nearly perpendicular face, shots were placed in the straight face to bring down additional material for the shovel. In each case a slide took place following the dynamite shots. These slides brought down with them a large quantity of the recently dumped and as yet unburned fine coal from the top of the dump; this fine coal being light, naturally separated out from the heavier rock material and thus formed a dust cloud.
As some of this fine coal was already burning along the outside of the pile where the air could get to it and all of it heated nearly to the ignition point, it was in just the right condition to flash into flame as soon as it was thrown into the air. The combined force of this slide and the rapid burning of the fine coal threw this burning dust cloud several hundred feet from the foot of the rock pile and across the railway tracks, burning those who were unfortunate enough to be in its path. In the latter accident the steam-shovel crew saw the slide take place and shut themselves in the steam-shovel cab to escape what they thought was a dust cloud, and thus escaped injury. The others who escaped were those who were fortunate enough to have run in a direction at right angles to the path of the flame.
One of the lessons learned from the study of dust explosions in coal mines is to keep the dust thoroughly moistened at a point where ignition is likely to occur. This acts in two ways to prevent a serious inflammation of the dust: First, the water tends to compact and bind the dust and prevent dust clouds from forming, and second, if sufficient water is added, it will cool the flame of any incipient inflammation sufficiently to extinguish it.
With the above lesson in mind, it would he advisable for the railway companies engaged in loading up these old dirt dumps to thoroughly wet down the freshly dumped combustible material at the top of the dump for several days prior to its being disturbed. This could best be done by using fire hose with a pipe five or six feet long for a nozzle, which should be forced down into the material on the top of the dump to make sure that the water reaches into the heated material beneath the surface.