In mining, a windblast is a sudden rush of air or gas due to the collapse of a void.

Causes

Windblast is common in

longwall Longwall mining is a form of underground coal mining where a long wall of coal is mined in a single slice (typically thick). The section of rock that is being mined, known as the longwall panel, is typically long, but can be up to long and wi ...

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

cantilever A cantilever is a rigid structural element that extends horizontally and is unsupported at one end. Typically it extends from a flat vertical surface such as a wall, to which it must be firmly attached. Like other structural elements, a cantilev ...

ed 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 Kimberlite is an igneous rock and a rare variant of peridotite. It is most commonly known as the main host matrix for diamonds. It is named after the town of Kimberley, Northern Cape, Kimberley in South Africa, where the discovery of an 83.5-Car ...

or even

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

mines, particularly in block caving mines, as happened at the Northparkes mine in

NSW New South Wales (commonly abbreviated as NSW) is a state on the east coast of :Australia. It borders Queensland to the north, Victoria to the south, and South Australia to the west. Its coast borders the Coral and Tasman Seas to the east. T ...

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

on 25 November 1999, killing 4.

Effects of windblast

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

asphyxia Asphyxia or asphyxiation is a condition of deficient supply of oxygen to the body which arises from abnormal breathing. Asphyxia causes generalized hypoxia, which affects all the tissues and organs, some more rapidly than others. There are m ...

ting,

toxic Toxicity is the degree to which a chemical substance or a particular mixture of substances can damage an organism. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a subst ...

and/or potentially explosive gases such as

carbon dioxide Carbon dioxide is a chemical compound with the chemical formula . It is made up of molecules that each have one carbon atom covalent bond, covalently double bonded to two oxygen atoms. It is found in a gas state at room temperature and at norma ...

carbon monoxide Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...

and

methane Methane ( , ) is a chemical compound with the chemical formula (one carbon atom bonded to four hydrogen atoms). It is a group-14 hydride, the simplest alkane, and the main constituent of natural gas. The abundance of methane on Earth makes ...

from a coal mine goaf into the working environment * The mixing of coal dust with air, creating a potentially explosive mixture * The

overpressure Overpressure (or blast overpressure) is the pressure caused by a shock wave over and above normal atmospheric pressure. The shock wave may be caused by sonic boom or by explosion An explosion is a rapid expansion in volume of a given amoun ...

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.

Management of windblast

Windblast prevention

Windblast prevention is centred on not allowing the void to form in the first place. This can be somewhat achieved through careful mine planning. Windblast prevention also relies on monitoring to ensure the void does not form (and stopping production if one does begin to form), and the use of different methods to try to promote caving, such as

hydraulic fracturing Fracking (also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of Formation (geology), formations in bedrock by a pressurized liquid. The process involves the ...

and the use of explosives.

Windblast harm minimisation

Harm minimisation seeks to minimise the damage to persons and machinery if a wind blast does occur. This may involve the following: * The use of PPE (

personal protective equipment Personal protective equipment (PPE) is protective clothing, helmets, goggles, or other garments or equipment designed to protect the wearer's body from injury or infection. The hazards addressed by protective equipment include physical, elect ...

) * Blast-activated cut-off switches on machinery and electrical circuits (for example, in the form of a paddle that is activated by the blast) * The use of overpressure-rated ventilation devices, of sufficient rating that they won't be destroyed by a windblast * In hard-rock mines, harm minimisation may involve physically separating the cave (the void) from the working area by leaving an adequate thickness of muck-pile, and ensuring no other physical linkages exist between the cave and the working areas * Providing dedicated leakage paths from the cave to atmosphere.

Confusion of windblast with outburst

Windblast should not be confused with an outburst, which is the sudden and violent ejection of rock and gas from a coal seam and the surrounding strata.

References

{{reflist Mine safety