 Does it feel like we have enough air? Let me check this place with gas. The maintenance ship will fix the permissibility problem. I scattered all the rock dust I could find. The reasons for coal mine explosions are well known and can be separated into these four areas. Ventilation, examinations, ignition sources, rock dusting. Preventing a coal mine explosion requires you and your fellow miners to pay special attention to these four areas. Let's take the four areas, discuss them, and turn them into your four lines of defense against a mine explosion. Hello, my name is Bob Painter. I'd like to talk to you about your four lines of defense to prevent an explosion at the coal mine you work in. During the winter months, as you well know, coal mining becomes a more difficult job. The coal-dry winter air tests your endurance, especially when leaving and entering the mine at man-trip time. We also know the same winter conditions causes changes to the conditions in the mine, and those changes can result in an increased risk of a mine explosion. Let me explain. During the winter months, a natural and more frequent lowering of the barometric pressure occurs. As the barometer drops, methane is liberated more freely from the coal bed and surrounding strata. Methane also can accumulate to dangerous levels more quickly. Your first line of defense against methane accumulations is adequate ventilation directed to the working section and gob areas. Good ventilation requires properly installed and maintained stoppings, curtains, regulators, and keeping airways free of obstructions. To demonstrate this point, let's look at a typical layout of a mine. If you think about it, your mine probably has a section or sections very similar to this. And deep within the inaccessible areas of the mine, such as the interior of the gob, or even at the pillar line, quantities of methane gas represented here by a green symbol may reach explosive concentrations. What part does weather play in all of this? During warmer weather, when the barometric pressure is higher, the concentrations of methane gas are more easily controlled. However, when the weather is cold and the barometric pressure falls, methane can increase within the gob, causing an increased problem with the control of methane. The potential is greater for methane to migrate into the active working areas and come into contact with an ignition source. To prevent the excessive build-up of methane and the possibility of it spreading out into the working areas an effective ventilation system must be established and maintained. Ventilation is the lifeline of underground mining systems that help protect miners from explosion and fires. Shown here are bleeder entries around the perimeter of the gob area. As a part of the ventilation system, bleeder entries normally allow methane in the gob to be directed away from the work areas and to the main return. But, if a critical stopping is damaged or removed, the ventilation is disrupted and the bleeder system is no longer effective. Also, roof falls or other blockage can restrict bleeder air flow, allowing a steady growth in the size of the methane build-up and increasing the possibility of gas contacting an ignition source. If the methane reaches the actual working places and is ignited, the result could be a disastrous explosion. As you know, in coal mining, literally everything is constantly moving and changing. Keen vigilance through examinations is required. Examinations is the line of defense that is the key to assuring the other three lines of defense are in place. Examinations determine that ventilation is adequate and moving in its proper direction. Examinations make sure methane has not accumulated to dangerous levels. And, examinations assures that ignition sources are eliminated or controlled. A number of examinations are required, pre-shifts, on-shifts, 20-minute gas checks, weekly exams for hazardous conditions, weekly electrical exams, and others. The importance here is the examinations have to be conducted and conducted completely. Historically, most mine explosions occurred during the winter months. This chart lists selected coal mine explosions from 1980 to 1995, where five or more miners have died in the explosion. Note that six of the eight occurred during the winter alert period months. In all of these explosions, one or more of the lines of defense had broken down. Methane and coal dust won't explode without help. And ignition sources required. Electrical sources, misuse of explosives, or smoking underground are three sources you can control. By following safety regulations, electrical equipment at the face, ignitions from use of explosives, and smoking are eliminated as sources. A great deal of research has gone into controlling electrical sources. The Bureau of Mines conducted research into ways of making face equipment safe. This research led to what we now have as permissible equipment. Well, the Bureau of Mines introduced the process of permissibility in 1911, and it was a result of open flame ignitions, such as you would get from carbide lamp illumination, black potter blasting. Those kinds of things caused many disasters to occur underground in coal mines. Electrification of coal mines introduced another process by which explosions could occur by virtue of electrical sparks. Permissibility means that you would do things like making the gaps, the openings, fittings so small and very precise, such that an internal gas ignition won't escape the enclosure and ignite the surrounding atmosphere. You never underplay the importance of maintaining these machines in a permissible condition. This has to be done, otherwise the permissibility plate doesn't prevent explosions. It merely tells you this machine was built properly, but you as a mine operator have to make this thing work day in and day out, and it has to be maintained in a permissible condition. You just can't underplay the point, it's extremely important. Your line of defense here requires you to maintain face equipment in permissible condition in order to control these ignition sources. Smoking underground was determined to be the ignition source at three of the most recent fatal coal mine explosions. Safety regulations prohibit the taking of smoking materials underground. The line of defense here is for all of us, miners, operators and inspectors, to assure the elimination of smoking underground as an ignition source. It's really up to each individual to eliminate this ignition source. In the winter, the ventilating air current pulls moisture from the mine, drying out the mine dust including the coal dust. Dry coal dust is a serious concern. Remember, the mine is drying out during the winter months, and coal dust in most mines is highly explosive. Rock dusting is your line of defense to eliminate coal dust as a concern. The explosive properties of coal dust has been thoroughly tested for many years by the United States Bureau of Mines. We talked with researchers who conducted these tests. In addition to methane, an even more dangerous substance is generated when mining coal, and that substance is coal dust, and it is an unavoidable byproduct of the mining operations. Dust is always created during coal cutting, coal handling, and the movement of men and machinery. The larger coal dust particles settle out of suspension very quickly while the fine particles known as float coal are entrained and carried by the ventilating air for long distances. The dust settles on rib, roof, and floor surfaces all along the ventilation path. The danger of an un-neutralized float dust deposit lies in the fact that this surface layer of dust can be preferentially skimmed off the rock dust sub-layer, dispersed in the mine atmosphere, and will explode with a tremendous violence. Brewston Experimental Mine Testing at the Pittsburgh Research Center has shown that float coal dust layers as thick as a tenth of a millimeter or about the equivalent of the thickness of a sheet of paper is capable of propagating flame for over three times the length of the dust deposit. Yes, there's been many large-scale explosions conducted at Brewston Experimental Mine using float coal dust. A dramatic explosion occurred on April Fool's Day, 1969, when we were conducting a series of experiments to evaluate the hazards associated with different thicknesses of float coal dust accumulation. So in that day, we boosted the coal dust thickness layer up to about two sheets of paper, and to our surprise, it took off and started to propagate down the entry. It destroyed all our pressure-sensoring sensing equipment. The microwave exited the portal and broke the windows for seven miles around the grounds, and it was heard 30 miles away. Frequent and liberal applications of rock dust to the mine floor, roof, and ribs is needed to control coal dust. Methane and coal dust are an unavoidable part of coal mining, but both can be controlled. Maintain adequate ventilation and ventilation controls to control methane. Conduct the required examinations and ensure that ventilation is adequate. No methane accumulations have occurred, that ignition sources are controlled or eliminated, and that rock dusting is up to par. Keep your equipment in permissible condition. Use explosives in a permissible manner, and don't tolerate smoking in the mine. Rock dust all the mine surfaces liberally and frequently, especially in the belt and return entry. This winter, maintain the four lines of defense at the mine where you work.