MINING SAFETY
or ‘firedamp’ mixture, can be removed by adequate ventilation, not forgetting that the low density of methane can cause the formation of roof layering in some circumstances. Although this will introduce oxygen the ventilation must be sufficient to lower the proportion of methane to below its lower explosive limit.
Although the danger of coal dust has
This shot of an underground pillar-and- stall colliery in Illinois shows white walls due to stone-dusting to cover and dilute possible explosive coal dust. Photo: Illinois State
25 INTERNATIONAL MINING ENGINEER
Te fuel and oxygen must also be present in the correct proportions to form an explosive mixture. Prevention can be achieved by removal of any one of these from the source. Removal of oxygen is largely impractical except in extreme circumstances when an area has to be sealed off. Dealing with atmospheric explosions rather than the less likely possibilities of blasting explosives misfires, liquid fuel explosions or battery hydrogen ignition, the fuel in mining usually consists of mainly methane (not exclusively in coal mines) or coal dust. Methane,
This stone dust bag barrier available from Skillpro of Australia is an alternative to the more common shelves of loose dust used to prevent the propagation of a coal dust explosion underground
long been recognised in propagating an explosion probably starting with methane, the possibility for explosions involving only coal dust in atmospheric suspension took a lot longer to be recognised. Even so UK text books in the 1950s referred to this danger. Te increase of mechanisation has led to the creation of more fine coal dust making this fuel an increasing hazard through both explosions and inhalation to miners’ lungs.
Coal dust can be dealt with successfully
by removal by extraction ventilation and air scrubbing, suppression with water mists at source, and/or clearing up accumulations by manual means. Water barriers have also been tested, but are less effective unless a spray on the flame can be assured to dissipate the cooling effect. Although active barriers, triggered by flame or heat detectors to apply water or special chemical fire extinguishers have been tested for effectiveness and practicality, they have not shown to be substantially more effective than passive stone-dust barriers in mining. Sources of ignition resulting in explosions can vary from open flames, through high temperature surfaces to sparks from mechanical action and electrical arcing. Equipment capable of creating a hot enough arc flash must be housed in strong flameproof enclosures to prevent the ignition of any methane in the enclosure from spreading out to the general atmosphere, and to retain any explosion.
Spontaneous combustion Another common and troublesome
source of ignition can be the spontaneous combustion of volatile coals through passage through the mass, usually fractured in some way. Improved ventilation to remove firedamp could actually increase danger without attention to adequate sealing. Side effects can include the generation of poisonous carbon monoxide and even hydrogen from any water applied to such a fire.
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