Violent underground phenomenon
An outburst is the sudden and violent ejection of coal, rock, and gas from a coal face and surrounding strata in an underground coal mine. Outbursts can be a very serious events, possibly even resulting in fatalities.
Effects of outbursts.
Outbursts may range in severity from being barely noticeable, to causing the destruction of an entire mining panel, and throwing pieces of machinery weighing tens of tonnes several metres. An outburst at Tahmoor Colliery, in New South Wales, Australia, in June 1985 ejected 350 tonnes of coal and rock and over 3000 cubic metres of gas, killing one miner. An outburst at the nearby South Bulli Colliery in 1991 killed three miners. An outburst at Westcliff Colliery in January 1994 ejected 300 tonnes of coal and rock and killed one miner.
Predisposing factors.
Several factors predispose certain coal seams to being outburst-prone. These include:
The statistical results show that the primary factor in coal and gas outbursts is crustal stress (P), followed by sturdiness coefficient (f). The coal seam gas content (W) affect affects coal and gas outbursts as the least important factor.
Outburst management.
Outburst management primarily focuses on the prevention of outbursts by pre-draining the gas from coal seams prior to mining. The aim of gas drainage is to lower the gas content of the seam below a certain threshold value, at which time it is considered safe to mine the seam. These threshold values should vary depending on the coal seam and coal measure being mined. Since the introduction of threshold values, not a single fatality due to an outburst has been recorded in Australia.
Gas drainage is achieved by drilling boreholes into the seam in advance of mining. Gas liberated from the seam into the boreholes is transported out of the mine via a pipe range.
Where standard gas drainage techniques are ineffectual, mine operators have a number of options. These may include:
Mining under "bomb squad" or outburst conditions is no longer considered acceptable, since this method still presents a fatal risk to at least one miner. "Bomb squad" is a special set of operating conditions that used to be adopted when it was anticipated that an outburst could occur. Under "bomb squad" conditions, the following working methods would apply:
References.
 ;templatestyles src="Reflist/styles.css" / ;