The US Mine Safety and Health Administration report said the truck descended about 18m before stopping abruptly against the opposite embankment in the bottom of the spoil “V.”

The victim was not wearing his seat belt when the accident occurred, which resulted in him receiving fatal injuries.

At the time of the accident, the Spring Creek Mine produced 50,000 tons of coal per day and employed 282 miners. The mine operates seven days a week, using two 12-hour production shifts and two maintenance shifts per day.

The mine extracts coal from the Anderson-Dietz seam using two draglines and two electric shovels for overburden removal. The coal is loaded by a shovel, front end loaders, and a hydraulic excavator into 240t haul trucks. The seam averages about 27m thickness and the overburden varies from 12m to 62m thick.

The root cause of the accident was that the mine operator failed to ensure seat belts were used where there was a danger of overturning mobile equipment, according to MSHA.

“The mine operator modified its new miner and contractor training plans to emphasise the importance of the use of seat belts,” it said.

“The plan further emphasised the potential disciplinary actions for not wearing a seat belt.”

Additionally, the mine operator established a Safety Interaction Program that involves performing spot checks on a continual basis to determine if the miners are wearing their seat belts.

This program also involves having conversations with employees about the use of seat belts and the requirement for wearing seat belts.

The mine operator trained all miners and crews on the training plan revision and new safety interaction program, including the mandatory requirements of seat belt usage at the mine at all times.