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The worst mining disaster in South Africa〔(【引用サイトリンク】 title=The world's worst coal mining disasters )〕 occurred in the Coalbrook coal mine of Clydesdale Colliery on 21 January 1960〔(【引用サイトリンク】 title=More than 400 miners are killed in an underground collapse at Coalbrook mine )〕 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 were trapped. 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〔(【引用サイトリンク】 title=Coalbrook )〕 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. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Coalbrook mining disaster」の詳細全文を読む スポンサード リンク
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