Page 154 - Synthetic Fuels Handbook

140 CHAPTER FIVE

The latter results when flammable gases (such as methane) trapped in the coal are released
during mining operations and accidentally are ignited.
Provision of adequate ventilation is, amongst other aspects an essential safety feature of
underground coal mining. In some mines, the average weight of air passing daily through
the coal mines may be many times the total daily weight of coal produced. Not all of this
air is required to enable miners to work in comfort. Most of it is required to dilute the
harmful gases, frequently termed damps (German dampf, vapor), produced during mining
operations.
The gas, which occurs naturally in the coal seams, is methane (CH , firedamp) that is a
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highly flammable gas and forms explosive mixtures with air (5–14 volume percent methane).
The explosion can then cause the combustion of the ensuing coal dust thereby increasing
the extent of the hazard. In order to render the gas harmless, it is necessary to circulate
large volumes of air to maintain the proportion of methane below the critical levels. Long
boreholes may be drilled in the strata ahead of the working face and the methane drawn out
of the workings and piped to the surface (methane drainage).
Carbon monoxide (CO, whitedamp) is a particularly harmful gas; as little as 1 percent
in the air inhaled can cause death. It is often found after explosions and occurs in the gases
evolved by explosives.
Carbon dioxide (CO , blackdamp, chokedamp, or stythe) is found chiefly in old work-
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ings or badly ventilated headings.
Hydrogen sulfide (H S, stinkdamp) is one of the first gases to be produced when coal is
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heated out of contact with air. It occasionally occurs in small quantities along with the methane
given off by outbursts and is sometimes present in the fumes resulting from blasting.
Afterdamp is the term applied to the mixture of gases found in a mine after an explosion
or fire. The actual composition varies with the nature and amount of the materials consumed
by the fire or with the extent to which firedamp or coal was involved in the explosion.
The continued inhalation of certain dusts is detrimental to health and may lead to reticu-
lation of the lungs and eventually to fatal disease pneumoconiosis or anthracosis (black
lung disease). Coal and silica dusts are particularly harmful and the methods that have
been adopted to combat the dust hazard include the infusion of water under pressure into
the coal before it is broken down; the spraying of water at all points where dust is likely to
be formed; the installation of dust extraction units at strategic points; and the wearing of
masks by miners operating drilling, cutting, and loading machinery.
The environmental aspects of coal mining are varied and range from aquifer disturbance
in the subsurface to floral and faunal disturbance on the surface. In addition, the transporta-
tion of spoil or tipple to the surface from an underground mine where it is then deposited in
piles or rows offers a new environment hazard. Toxic minerals and substances exposed dur-
ing removal of the overburden include acidic materials, highly alkaline materials, and dilute
concentrations of heavy metals. These materials can have an adverse effect on the indigenous
wildlife by creating a hostile environment (often through poisoning the waterways and, in
some cases, destruction of species. Thus, mine design should include plans to accommodate
potentially harmful substances, which are generated by weathering of spoil piles.
Surface areas exposed during mining, as well as coal and rock waste (which were often
dumped indiscriminately), weathered rapidly, producing abundant sediment and soluble
chemical products such as sulfuric acid and iron sulfates. Nearby streams became clogged
with sediment, iron oxides stained rocks, and acid mine drainage caused marked reduc-
tions in the numbers of plants and animals living in the vicinity. Potentially toxic elements,
leached from the exposed coal and adjacent rocks, were released into the environment.
Since the 1970s, however, stricter environment laws have significantly reduced the environ-
ment damage caused by coal mining.
Once the coal has been extracted it needs to be moved from the mine to the power plant
or other place of use.