During drilling operations on a land-based drilling rig, the thimble within the hard eye of the winch wire momentarily caught (snagged) on the edge of the drill rig chassis. It then released in an uncontrolled manner very close to the driller. The incident occurred when the driller found it necessary to raise the drill mast, resulting in the winch wire being pulled upwards. As the winch wire was pulled up, the thimble caught on the edge of the drill rig chassis. The driller failed to notice that the winch wire had become snagged and continued to raise the mast, thus continuing to increase the tension in the wire until the steel thimble bent, causing the wire and attached hoist plug to release in an uncontrolled manner.
The sudden and uncontrolled release of the winch wire and the attached hoist plug had the potential to cause significant personal injuries had it struck a member of the drill crew.
What were the causes?
- Failure to identify and recognise snagging hazard;
- Incipient complacency in what was seen as a ‘routine’ task.
What lessons were learned?
- Investigate engineering/practical solution: retract the winch wire to a safe position when not in use; where this is not possible, lower the winch wire to a safe location away from all structures and other potential snagging hazards. Keep contained within a trip tray or bucket to prevent a tripping hazard;
- Highlight the importance of managing all lifting operations, including winch operations and awareness of complacency creeping into routine tasks;
- Review procedures and task risk assessments to ensure that the potential for lifting equipment (winch wires) becoming snagged is appropriately considered and mitigated. All control measures should be included;
- Careful check of potential snagging hazards before operation of the winch or the lowering/raising of the drill mast.