IMCA draws lessons learned from an incident in which a sheave and clump weight fell during wind turbine installation, nearly injuring workers and damaging equipment.
What happened
A high potential dropped object incident occurred when a sheave weighing 204kg fell 64m to deck, and a clump weight weighing 700kg fell onto equipment causing damage. There were no injuries. The incident occurred during routine installation activities for a wind turbine monopile. A spreader bar with lift tools was disconnected from the main block and tuggers, and preparations for lifting a Transition Piece then began. The deck operations involved tasks for three rigger teams and a forklift operator. The rigger teams unhooked the rigging and connected the clump weight to winch #5. The foreman instructed the crane operator to hoist winch wire #5 into a storage position and to lift up the main block. Shortly after that, a request was made to lower winch wire #1 to the main deck. Thus, three different winches were operating simultaneously.
During the hoisting of the winch wire #5, the clump weight was pulled into the sheave, causing activation of the winch overload alarm. Although the crane operator promptly moved the joystick to the “0” position, it was too late. The clump weight had already been pulled into the sheave causing the sheave to break; both the sheave and the clump weight then dropped to deck. The sheave (204 kg) dropped from 64m and bounced, narrowly missing a forklift truck. Nearby crew found it necessary to take cover. The clump weight (approximately 700 kg) dropped onto the umbilical winch, resulting in a hydraulic oil spill on the main deck.
Both dropped objects could have resulted in a fatality or multiple fatalities.
What went wrong?
The investigation revealed that:
- The Crane Operator was performing simultaneous tasks requiring full concentration;
- Neither the Crane Operator nor the Rigger foreman had eyes on the tugger wire / clump weight;
- The tugger winches had no automatic alarm settings with automatic stops.
Lessons learned
- Doing more than one thing at once – DON’T!
- When performing lifting operations, the banksman should always have eyes on the lift and make sure the area below the lift is clear of people;
- Be aware of the limitations of your equipment and stop the job when it cannot be performed safely.
