In the July 2020 incident the two men were at an underground mine hanging an electrical trailing cable for a jumbo drill in an ore drive, hanging from a vehicle mounted mobile elevating work platform.

Suddenly a hydraulic failure on the tilt cylinder on the boom of the ITC caused the WP to suddenly tilt forward and drop 2m to the ground.

One of the workers was thrown out of the WP and onto the ground but the other stayed, as his boot was caught in the door.

The Department of Mines, Industry Regulation and Safety found the tilt cylinder's anti-dump valve had detached from the cylinder port after its mounting bolts sheared.

That happened when the body of the anti-dump valve clashed with the lifting frame of the ITC, as the boom was being raised to full height, because the anti-dump valve was mounted in the wrong place and had no guard or cover.

DMIRS said the anti-dump valve had been retrofitted to the ITC by a previous owner and was not a standard feature provided by the original equipment manufacturer.

While both men had fall arrest harnesses on, the WP was not up high enough for the fall prevention system to kick in, which would have stopped the WP from hitting the ground.

The incident was the third potentially serious incident involving the use of WP and ITC combinations underground at different mine sites in nearly four years.

In an incident in March 2018 a worker was injured when the WP he was in detached from quick hitch and fell to the ground.

Then in February 2020 another two workers were injured when they were ejected from their WP due to a dog-bone failure.

DMIRS said load-holding cylinders on mobile elevated work platforms need to be fitted with a safety device, such as an anti-dump valve, to prevent the basket moving in the event of a hydraulic line failure.