A blast hole drill rig mast was being lowered from the vertical to horizontal position. Its top end was about 1 metre from its horizontal resting position when a bearing block capping bolt failed. This caused more bolts to fail and the mast then fell close to its intended horizontal resting place, but causing considerable damage. Nobody was injured.
The mast pivot shaft was being held in position by a bearing block at each end. The removable half of each of the blocks was held in position by two capping bolts.
Read more about the causes of this incident and the recommendations to prevent the hazard in this report compiled by the Queensland Department of Natural Resources and Mines.