The worker was using a sledgehammer to remove the excavator drive sprocket. 

The Queensland Mines Inspectorate said a steel shard projectile created by the hammer striking the sprocket penetrated the coal mine worker's leg.

It said site senior executives should confirm the safety and health management system had effective controls in place to prevent the creation of steel shard projectiles.

"Ensure that supervisors are competent in assessing the risks and hazards associated with the work environment under their control," it said.