Over 100 tonnes of coal passed from the hopper and through the apron-chain feeder beneath.

It then filled the primary sizer discharge chute. The coal then poured into and inundated the sizer station access walkway and work area.

The Queensland mines inspectorate found the dump hopper, apron feeder, and discharge chute were not emptied before the sizer was removed.

With that ROM facility configuration – the hopper feeding to the chain feeder then to the sizer – the material could not be locked out or a physical barrier placed between the chain feeder discharge and the sizer.

Normally the coal would choke off at the supply end of the chain feeder with the operation of the chain feeder flights controlling the flow of raw material from the hopper into the sizer.

“In this instance, high moisture levels made the coal more fluid and the chain feeder couldn’t effectively control it, resulting in the uncontrolled inrush of material,” the inspectorate said.

It has recommended that to prevent the material becoming too fluid, dust suppression water sprays be isolated and they should be checked for leaks.

Also, work processes and procedures must account for the hazard of an unplanned in rush of material, the mines inspectorate said.