prevention and control of spontaneous combustion - Mining and

• It is widely recognised that lower rank coals are more susceptible to spontaneous
combustion than higher rank coals. Any abnormalities in this relationship may be attributed
to the petrographic constituents of coal
• Ash content generally decreases the propensity of coal to spontaneously heat. Certain
constituents of the ash, such as lime, soda and iron compounds, may have an
accelerating effect, while others, such as alumina and silica, produce a retarding effect. It
is clear that some chemicals promote combustion while others inhibit its development. It is
known that oil shale bands adjoining coal seams play an important role in mine fires
• The presence of faults and zones of weaknesses around faults may contribute to the
danger by allowing air leakage into the coal mass
• Partial extraction underground mining methods, in which part of the coal seam is left in the
goaf and in pillars, can contribute to the potential for spontaneous combustion. (This may
have relevance to the mining of old workings, since surface mining will expose areas
where crushed coal has been left for long period)
• Air flow rate is a complex factor because air provides oxygen while it also carries away the
heat produced. There is a critical air quantity that supplies sufficient oxygen to allow the
coal to oxidize but is insufficient to prevent the generated heat from accumulating
• Changing atmospheric conditions because of air moving in and out of coal seams. This is
of particular relevance when old workings are exposed by surface mining.
Spontaneous combustion in South African collieries
Current literature indicates that spontaneous combustion is now rare in underground coal mines
in South Africa. The Witbank and Sasolburg coalfields experience spontaneous combustion
mostly in surface mines in areas previously mined by bord and pillar methods. The only surface
mining operation in the Waterberg coalfield is known to have had serious spontaneous
combustion problems with discards. The mining experience of spontaneous combustion within
these coalfields has not been reported consistently or in detail.
The major coal bearing strata in South Africa are associated with the Karoo Basin and occur
primarily on the southern and eastern flanks of the Kaapvaal Craton. The five recognised coal
seams in the Witbank area are numbered consecutively from 1 – 5, the last being the youngest.
These seams occur within a succession about 70m thick. Seam No. 2 and seam No. 4 have
been extensively mined in the past. Bullock and Bell 8 give a description of the underground
mining methods used and provide a case study of spontaneous combustion affecting a mine. In
the 1960s and 1970s, before the advent of large-scale surface mines, nearly all South African
production came from relatively shallow bord and pillar workings. For many years spontaneous
combustion was a problem, with a few mines, e.g. Springfield Colliery, being particularly prone
to heatings leading to underground fires. A number of case studies were reported in the
8 S. E. T Bullock and F. G. Bell, Some problems associated with past mining at a mine in the Witbank coalfield, South
Africa. Environmental Geology 33 (1) December 1997.
9 V C Barnes, F E Joubert and G P Badenhorst, Precautionary measures to reduce the probability of incipient heatings in
coal mines, their early detection and safety procedures in dealing with colliery fires. Proc. Mine Ventilation Society
Symposium on Colliery Fires and Explosion Hazards, March 1977 pp 5 to 22.
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