The rock broke a 10m containment barrier windrow and hit and significantly damaged a lighting plant after falling for 40m.
Dumping above any active working area was poor practice and should not be permitted, NSW Mine Safety warned.
“Work activities should be planned and coordinated to manage risks caused by the work activities of different work groups on each other,” it said.
“It is essential that work instructions are effectively communicated and are understood by all people that may impact, or be impacted by, others. As a minimum, the controls should include more rigorous inspection regimes, increased supervision and improved barriers.
“Mines should review inspection plans and ensure workers and statutory officials are trained in hazard identification and rectification.”