Windblast

Windblast is common in longwall coal mines, especially those whose roof strata are competent, and do not cave immediately behind the roof supports as the face advances. This results in the tendency for a large void to be created behind the roof supports in the goaf (or gob) which collapses when the overlying cantilevered strata can no longer support its own weight. When the collapse occurs, the air or gas occupying the void is displaced by rock, resulting in a pressure wave and windblast that propagates along the roadways (tunnels) of the mine. This may be followed by a "suck back" as the air pressure is equalised with the low pressure created higher up in the goaf.

Windblast can also occur in metalliferous, kimberlite or even evaporite mines, particularly in block caving mines, as happened at the Northparkes mine in NSW, Australia on 25 November 1999, killing 4.^[1]

The effects of a windblast are not limited to the physical effects of the overpressure wave. The effects of a windblast include:

• The displacement of asphyxiating, toxic and/or potentially explosive gases such as carbon dioxide, carbon monoxide and methane from a coal mine goaf into the working environment
• The mixing of coal dust with air, creating a potentially explosive mixture
• The overpressure wave can throw objects into people, knock people over (and potentially throw people into stationary objects or even into automated machinery), knock miners' helmets off, pepper the flesh with gravel or small rocks, stop or alter the normal ventilation of the mine and move large items of machinery, in some cases violently.

Broken bones and fatalities are not uncommon outcomes from serious windblast events.^[1][2]