Report Text: Sequence of events:
During the routine maintenance operation of removing a piston from the main engine, the overhead crane was pulled from its gantry and fell to rest on the engine entablature. No one was injured as a result of this accident, but the potential for injury significant.
Findings of subsequent investigation:
After connecting the piston lifting device to the piston crown at Top Dead Centre (TDC – the top of its stroke) with 4 x M16 bolts, the overhead crane (OHC) hook was attached to the device. An initial length of slack chain was then paid out. The engine was then turned utilising the turning gear to lower the piston to Bottom Dead Centre (BDC – the bottom of its stroke) to access the bolts to slacken, for its removal. At this point the crane operator was on the top of the engine and the turning gear operator beside the crankcase door at its base. The two operators were in close communication, although insufficient attention was paid to the chain tension as the piston was lowered.
Insufficient chain was paid out and the downward stroke of the piston put huge tension onto the chain. The resultant force was adequate to ‘splay’ the crane’s end plates, and detach the wheels that support the cranes ‘trolley’. The OHC trolley then fell to rest on the engine entablature.
Insufficient attention was allocated to the ‘paying’ out of chain as the piston descended. The operator was keeping eye contact with the turning gear operator and not the process he was in control of. It is unclear as to whether the chain hoist stopped paying out chain as events soon accelerated.
Recommendations and follow up actions:
The work card associated with the maintenance task does state the OHC to be attached at TDC. The ship will ascertain whether it is viable to attach the chain at BDC.
From this incident the procedure will be:
The turning gear operator is to be located on the top of the engine adjacent to the crane operator. A suitable initial length of chain is to be paid out before the engine is turned. An observer posted at the crankcase door will signal when the piston has reached BDC.
The chain and crane operator are now in close physical contact. Two pairs of eyes are now on the critical task of monitoring crane chain tension. The turning gear can be stopped immediately should a situation arise. This negates the risk of critical communication delay, from the top to the base of engine
The overhead crane in its gantry.
End plates of gantry splayed out.
The crane mechanism lying on top of the engine.
We are grateful to the ship manager for sharing this report. We have heard from another manager that their procedure is first to put the piston to BDC, remove the securing bolts (using gravity to keep it in place), turn the engine so that the piston is at TDC, attach the piston lifting device and lift the piston from this position using the crane.
CHIRP is not able to advise on the appropriate procedure for all types of engines, but clearly this should be in accordance with the engine manufacturer’s guidance and take into account the various risks, including the risk with the crane highlighted in this report. We would welcome any comments on this subject, and, more generally, reports of hazardous incidents related to marine engineering.