A rotary blast-hole drill rig was trammed from the workshop to the drill site to start work. The driller stabilised the drill rig using the jacks and raised the mast into position. After raising the jacks, he trammed the rig forward about ten metres to drill the first hole in the blast pattern.
When the driller stopped moving the drill rig forward, he heard a loud bang. An object had landed on the drill deck next to the operator’s cabin he was occupying. It was a 41 kg piece of grid mesh from the mast’s walkway that had detached and fallen to the drill deck 18 metres below.
Direct causes
- The fastening mechanisms holding the grid mesh to the drill mast failed.
Contributory causes
- There were worn washers and non-locking type nuts fitted to the six bolts retaining the grid mesh to the walkway structure.
- Inspections were inadequate and did not identify structural defects in the drill rig.