On August 5 2017 Independent Mining Services employee Daniel Springer was fatally injured while performing maintenance on the outside of an excavator bucket.
The work involved removing an external wear plate of the bucket by cutting it into smaller pieces. While performing a cut, part of the plate unexpectedly sprung up and struck Springer in the head.
The Queensland Mines Inspectorate conducted an investigation over the ensuing nine months, which included the commissioning of an independent metallurgical analysis.
That analysis was carried out by experts at the University of Queensland Materials Performance facility.
The investigation revealed the mine commissioned an engineering company to undertake maintenance on a number of buckets in 2014, which involved modifications being made to the original equipment design.
During these modifications the external wear plate, which was made up of multiple small plates, was replaced with two large plates.
The original manufacturer was not consulted about the modifications.
Commissioner for Mine Safety and Health, Kate du Preez said analysis by UQMP showed indentations in the external wear plate were the major reason for the build-up of stored tension, which caused the plate to violently spring out during maintenance work.
"It was also concluded that having two large wear plates would cause the spring-back to occur with much greater force compared to small thin plates and the spring-back distance would be magnified by the length of the wear plate," she said.
"The investigation found that the mine did not undertake a formal risk assessment prior to making the modifications to the bucket.
"It also found that there was a lack of understanding in the mining industry more broadly regarding the hazards associated with stored energy in steel plates, and how that energy could be introduced."
The inspectorate made a number of recommendations to the Queensland mining industry to ensure this type of accident did not occur in the future.
"Smaller wear plates are to be used on excavator buckets as they are safer because the stored tension and spring-back is less than a design using larger plates," it said.
"The large plates have inherently higher risk and the potential of being a fatal hazard.
"All mines are to ensure that they have a procedure within their safety and health management system that requires an effective risk management process to be carried out on any modification being made to plant and equipment prior to the modification being conducted.
"If a modification to plant and equipment is changing the original equipment manufacturer's design, the mine must consult with the manufacturer and/or an appropriate technical expert prior to the modification being conducted."
The hazard of mechanical spring-back is not limited to excavator buckets.
Since the incident, it has been identified that this hazard may also be present in other equipment types due to indentation.
"It is recommended that a risk assessment takes place before any indented plate sections are cut for removal from any equipment," the inspectorate said.