A mining fabrication firm has been fined $500,000 after a boilermaker lost an eye and suffered multiple skull fractures in a workplace accident.

The employee was struck by a falling 500kg steel plate as he worked on a hook-up assembly for an excavator bucket at G&G Mining Fabrications Hazelmere workshop in Perths east.

WorkSafe WA said the worker suffered serious head and facial injuries including multiple skull fractures and the loss of an eye in the August 2021 emergency.

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This was an incident that caused horrific injuries to the boilermaker, WorkSafe Commissioner Sally North said.

G & G Mining pleaded guilty to causing harm to a worker through its failure to provide a safe work environment and was fined half-a-million dollars in Midland Magistrates Court this week.

It was also ordered to pay more than $6500 in costs.

An overhead crane had been used to move the lug plate into place before tack welds were made to hold it while it was aligned.

The crane was then shifted onto another job in the workshop, leaving the plate restrained by the temporary welds and turnbuckles that had also been welded on.

The worker was injured when an assistant was instructed to cut the turnbuckles and the tack welds failed.

After the incident, the company developed a procedure specifically for this task and included that an overhead crane must remain connected to the lug plate until an adequate weld is in place, North said.

Being hit by falling metal objects is one of the highest risks for injuries and fatalities in the manufacturing sector and I encourage leaders working in this sector to consult workers and review their controls in relation to preventing objects from falling.