Incident Report - Army Bay, New Zealand
In May 2018, a crew from Smith Cranes’ Auckland branch were undertaking a job at the Army Bay sewer outfall project.
Smith Cranes was engaged to dismantle a steel structure at the bottom of a 45m mine shaft. The crane operator had successfully winched two workers down the shaft in a man cage, then had lowered the man cage a second time to deliver tools to the team at the bottom of the shaft. While the workers were dismantling the structure at the bottom of the shaft, the crane operator was engaged to remove a steel beam, which required him to reconfigure the crane by removing some chains. The workers at the bottom of the shaft took less time than the operator anticipated, and they notified him they were ready to be extracted from the shaft. The operator then proceeded to lower the man cage to collect the workers and tools without reinstalling the chains. This meant the man cage stopped 10m short of the shaft flooring, as the winch ran out of line. The operator had run the winch drum to the end, causing the drum to trip and automatically begin ascending back out of the mine shaft. This meant the operator’s controls had effectively reversed, causing him confusion as the up control resulted in the winch descending, and the down control resulted in it ascending.
The operator then ascended the man cage to the top of the shaft and proceeded to reinstall the chains to enable the man cage to reach the shaft flooring. He contacted the workshop to discuss the error with the controls, suspecting a breakdown in the machine’s hydraulics. By this time, the workers had been waiting at the bottom of the shaft for well over an hour and were becoming distressed. The operator was also experiencing panic in response to the workers’ distress and confusion in dealing with the reversed controls. He managed to lower the man cage to the shaft flooring, so the workers could board the man cage and ascend out of the shaft. However, the rope started jumping on the drum during the ascent, bunching up on one side so that when the motion of winching stopped, the lays of rope then dropped into a smaller circumference creating the slack in the line and giving a freefall effect. This obviously caused extreme distress to the workers in the man cage. They were ultimately winched up using the emergency davit arm connected to their harnesses.
A comprehensive incident investigation was undertaken immediately following the incident, including engagement of a third-party incident investigator. The key findings of the incident revealed a major contributing factor being the failure to carry out comprehensive lift planning prior to commencing the job, including assessment of the shaft depth and the crane’s reach. Furthermore, changes to the site environment and lift sequence resulted in an unanticipated change of crane configuration, which, compounded with the stress of the situation, caused the operator to make critical errors of judgement. In the panic caused by the workers feeling they were trapped in a deep shaft, the operator did not step back and Take 5 to thoroughly assess the situation and make a calculated rectification plan. Unfortunately, the operator failed to recognise why the levers went into reverse.
No workers were injured in this incident, but critical lessons were learned and shared across the organisation. As a result, several actions were undertaken internally, and lessons learned to ensure there are no re-occurrences of this nature:
The ropes were removed and inspected for damage and replaced where necessary.
The auxiliary hook was removed and wound back to drum and the drum disconnected.
The Rooster and auxiliary anti two-block were removed.
The main hook was removed, and a two-part line installed.
A critical emphasis placed on the importance of comprehensive lift planning.
A reminder of the importance of remaining calm and taking the opportunity to step back and Take 5 when necessary.