The worst mining disaster in South Africa occurred in the Coalbrook coal mine of Clydesdale Colliery on 21 January 1960 at around 19:00 when cave in occurred about 180 metres underground. About 1 000 miners were in the mine at the time and 435 died after being trapped the rest escaped from an incline shaft.
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Immediately after the incident, rescue teams arrived from other mines in the region and boreholes were drilled into areas where survivors were expected to be. But when microphones were lowered no signs of life were detected, there were no survivors. After 11 days the rescue was called off.
Causes of the disaster
The production at the mine had increased from 134 230 tons per year (1954) to 2 260 660 tons per year (1958) in response to the newly built Taaibos power station at Kragbron.
The accident was caused by cascading pillar failure (CPF) where a few pillars fail initially and this increases the load on the adjacent pillars causing them to fail. This cascading failure caused pillar collapse over an area covering 324 hectares.
Factors contributing to the collapse were the process of top coaling which raised the height of the tunnels and pillar and panel mining reducing the size of structures holding up the tunnel roof.
Top coaling
Top coaling began as a method of increasing production in areas that had already been mined. In 1932 the tunnels were 2.4 m high, in 1948 some top coaling was done to raise the height to 3.7 m, but the coal yielded was a poor grade and the practice stopped. In 1951 top coaling began once again as a new electricity power station had been built and it was able to use lower grade coal. The roof height was raised to 4.3 m and 5.5 m in places, and by 1957 top coaling was a significant contributor to production.
Some time between 1957 and 1959 experimental secondary mining was done in No.10 section to recover coal from a mined out area of the mine. Top coaling raised the roof height to between 4.3 and 6.1 m
Pillar and panel mining
The tunnels in the mine were between 6.1 and 6.7 metres wide. Pillars and panels of coal were left between the tunnels to keep the mine roof from collapsing.
In this time "dummies" of 4 metres wide and 2 metres deep were mined out of the barriers, and in some cases up to four sides of the pillars too, to yield additional coal.
Response to the Incident
Following the disaster, the South African government established Coal Mines Research Controlling Council(CMRCC) to improve coal mine safety and research pillar strength, supported by the Council for Scientific and Industrial Research (CSIR) and the Chamber of Mines Research Organization (COMRO).
The South African Chamber of Mines obtained rescue equipment to reach men trapped underground in coal mines. Similar equipment was used to rescue trapped Chilean miners in 2010.