The worker, who was directly below the wheel, head a cracking sound and was able to scramble out of the way. He was not hurt.

He was part of a six-person crew that included subcontractors and workers from Winder Controls Australia, which had been contracted by South32 to upgrade a drift winder apparatus.

The NSW Resources Regulator is investigating the incident, which happened on October 6 last year, just before 5pm at the Appin East mine. An "information release" said initial investigations showed the pulley wheel had dislodged after rope tension built up.

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"Just before the failure, a member of the work crew was standing on ground level directly below the pulley wheel within a taped off, restricted access area," the release stated.

"The worker was monitoring the rope to ensure it was correctly travelling through the friction winder. After hearing the cracking noise, the worker took immediate evasive action, moving clear of the fall path of the pulley wheel moments before it hit the ground."

The release said the man had been standing in a roped-off restricted area under the pulley wheel "under the assumption that approval had been given to do so", and restricted areas had not been adequately identified.

It said the winder's maximum force had been set above the maximum safe working level, while communication protocols - the use of radios - had not properly considered the environment and could not be heard over loud background noise.

A South32 said the incident was "an uncontrolled fall of equipment from height". "We take this matter extremely seriously and we are continuing to work with the contractor and the NSW Resources Regulator on this matter," he said.

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