<Li> May 17, 1965: Cambrian Colliery in South Wales, 31 died . </Li> <Li> October 21, 1966: Aberfan disaster was a catastrophic collapse of a colliery spoil - tip that occurred in the Welsh village of Aberfan, killing 116 children and 28 adults . </Li> <Li> November 20, 1968: Farmington Mine Disaster in Farmington, WV. 78 workers died . As a result of the disaster, the U.S. Congress passed the Federal Coal Mine Health and Safety Act of 1969 . </Li> <Li> 1972: Wankie coal mine disaster Wankie, Rhodesia / Zimbabwe, 426 fatalities . </Li>

Why do you think the accidents occur in underground mines