Fault tree analysis and risk mitigation strategies for mine hoists

Mine hoist are an essential part of an underground mine. In addition to extracting the ore from the mine, this machine transports the miners from the surface to the various underground levels of the mine. The two main hazards to which minors in the cage are exposed to are rope severance and loss of control of the hoisting machine. In both cases, the risk is the crashing of the cage at one end of the shaft. Hoisting accident and fatalities are rare but still happen despite the use of safety catches to retain the cage in the event of rope severance. The objective of this article is to improve mine hoist safety and to prevent the crash of a cage (of more generally any conveyance) at the shaft boundaries. Fault Trees (FT) are used to analyze the accidents scenarios of a cage crash in a shaft. Two generic fault trees are presented: one based on rope severance and the other based on loss-of-control of the conveyance. Results of the study indicate that, in the case of a rope severance, most of the root causes are based on secondary failure of the safety catches. In the case of a loss-of-control of the conveyance, most of the root causes are based on command failures that prevent the cage from stopping before reaching the shaft boundaries. This article suggests general mitigation measures and recommends the use of machinery safety standards in order to improve the reliability of hoisting machines.