Outburst (mining)

An outburst is the sudden and violent ejection of coal, gas and rock from a coal face and surrounding strata in an underground coal mine. When outbursts occur, they can be very serious events, possibly even resulting in multiple 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 NSW, Australia in June 1985 involved the ejection of 350 tonnes of coal and rock and over 3000 cubic metres of gas, resulting in one fatality. Another outburst at the nearby South Bulli Colliery in 1991 resulted in three fatalities, and yet another outburst at Westcliff Colliery in January 1994 involved 300 tonnes of coal and rock and resulted in one fatality.

Predisposing factors

Several factors predispose certain coal seams to being outburst-prone. These include:

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" refers to a special set of operating conditions that would be adopted when it was anticipated that an outburst could occur. Under "bomb squad" conditions, the following working methods would apply:

See also

Further reading

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