Virginia Mining Disaster

The news of the death of at least 25 coal miners in the Upper Big Branch Mine in West Virginia is a reminder in the human costs which are incurred in the provision of fossil fuels. Even though American mines have grown considerably safer over the years, the nature in the work that when there is an explosion in a mine, that there are numerous deaths due to the layout which is most effective for getting the coal out. It also underlines the greater costs that must be met when mining coal from underground operations, instead of the more visible, and criticized surface mining operations. In the United States this really is the largest mining disaster in more than 25 years at a mine that created 1.2 million tons of metallurgical coal last year. Due to the pressures on surface mining operations Massey Power were moving a growing percentage of their production to the underground. Part of the issue in managing the ignition of gas in such an operation is the fact that the mining machine breaks out the coal in fairly small pieces, by rotating a drum laced with picks against the coal face. The fine crushing in the coal can result in the release of methane gas (organic gas) that is discovered and formed using the coal. Levels of the gas are measured, and controlled by sending enough air down the face to dilute the degree of the gas beneath that at which it is at danger of ignition or explosion. However inside the space that the drum is carving out it is not always feasible to get that air flow into the region to ensure that dilution is immediate. In addition if there are layers of rock hard money lenders within the coal, then the pick can rub against these and generate sparks, and heat up the rock towards the point that it becomes hot sufficient to ignite any methane pockets which have been released. Once that ignition begins the extremely fine coal dust that’s also a part of mining (because the above picture shows) means that this may also ignite, intensifying the resulting explosion. That becomes especially deadly, given the geometry of the longwall. Back in the mid-1800’s underground mining was generally carried out by crews of guys and boys, where the coal was first removed by undercutting the coal seam manually with pick, to a depth of about 3 ft. The bulk in the coal was then broken down to this slot and the fragments (ideally about 4-inches in size) had been track dolly shoveled and hand-loaded into pit tubs, to be hauled away. A great day’s function was about 20 tubs. As the miners drove the tunnels (also called entries, headings, drifts, drives and so on) into the coal they left pillars between the tunnels to hold the roof up. However in about 1870, and possibly within the Lancashire coalfield in the UK, they discovered that if they put these entries together, they could create a way of obtaining all of the coal out from that section (or panel). How could they get away with this? Nicely you will find two things that make it feasible. Firstly, whenever you make a hole within the ground, the rock pressure that was applied to the rock (about the exact same pressure because the depth of the hole) has to move somewhere. And it moves just a bit to ensure that the weight in the ground over the hole is carried by the rock on either side. Nevertheless, what happens if this extra load is too high for the rock and it fails? Well if the rock had been just a thin column it would collapse, but if it had been thicker, then the weight would just move further into the coal. Now if we came along and moved the coal that had failed, then the hole would just continue to obtain bigger. But if we leave the coal in place, then the broken coal acts to confine the coal further into the solid. And this microdermabrasion machines confinement gets higher, as the failing pressure continues to move into the wall. The second thing to know is that when a layer of rock breaks the rock lumps when piled together occupy more space than the solid rock. As a rule-of-thumb the bulking is about 60%. So that if we let the roof over the working area break and collapse, following we have taken the coal out, then by the time about twice the seam height of rock has collapsed, it has filled the hole where the coal used to become, and reaches as much as the solid layers of rock above, to hold them in place. The confinement in the rock around each piece permits it to regain some strength, and so collectively the broken rock behind the operating face (called the goaf or waste) will carry the weight of the ground from about twice the seam height, all the method to the surface, and using the other end of the “bridge” as it had been resting on the confined coal ahead of the working face. The mining process is therefore that initial the shearer moves down the coal face, grinding off the coal to a depth of around 2 ft. After it passes, the rams on the roof supports, in turn, are released, to ensure that they drop away from roof get in touch with. The horizontal ram is metal detector retracted and also the assistance moves forward until it contacts the conveyor. It’s then raised, and re-supports the roof. Every support moves forward it turn, to ensure that the miners (which now include ladies) are always under a roof of steel. After the supports are re-established, the horizontal ram extends, pushing the conveyor over into the open space exactly where the coal has just been mined. The exposed roof rock then collapses into the open space behind the back of the supports. Due to the way the roof rock weight distributes, it’s usual to drive entries out to the edge in the panel first, and then mine back towards the primary drive tunnels, rather than mining away from the mains. In part this is to help keep the excess weight from acting on the tunnels the miners travel via. Because of the collapse in the roof as the coal is removed the panels usually start in the back in the section (known as a panel) and mine toward the primary transport tunnel, with coal and people travelling in roadways on tankless water heaters either side in the panel. Over time the ground movement works to the surface, and the surface of the ground will drop, by some significant percent of the height in the coal removed, because the rock within the waste will crush and consolidate. This is called subsidence, and if the mining is carried out badly, then it could cause significant harm to surface buildings. Nevertheless, if carried out properly, it should not. As usual this has been rather a superficial description of a process, but hopefully it gives you more of a sense as to what goes on in a long wall mining operation.