Two accidents have recently been reported during a lifting operation on a fixed installation.
The first accident happened during the lifting of a 13 tonne tank. When topping the boom to reach the right location to put the load on the deck, the boom suddenly started falling and the load fell down approximately three metres until it hit the top of two other stored tanks. These tanks were about two metres apart and the falling tank got jammed in between them. Fortunately no-one was hurt. The crane boom descent stopped when the crane operator put the boom operating joystick in neutral position which automatically activated the boom brake.
The second incident occurred half an hour later when it was attempted to lay the boom into its rest. To do this, the crane driver had to slew the crane about 45Â°. During this operation, the boom once again fell uncontrolled. The boom hits its rest so hard that it bent the boom rest. The connection bolts between boom sections 2 and 3 were sheared and the forward part of the boom tipped down from the boom rest in a 90Â° angle. Only the whip wire rope prevented the forward two sections falling into the sea.
The immediate cause of the incident was found to be the collapse of the input gear (sun gear) between the main shaft from the hydraulic motor to the gearbox on the boom winch. All teeth were broken off. The most likely cause for this was the incorrect assembly of the sun gear. A washer had probably come out of position during installation and this has led to rapid wear of the sun wheel gear.
The key lessons identified were:
- to ensure adequate inspection and planned maintenance programmes for critical systems/components by persons adequately trained;
- the importance of clear and correct procedures and descriptions of work to be undertaken; and that these be understood and followed during disassembly and assembly of the gear box;
- the importance of the use of carrying out a safe job analysis before critical jobs and operations.
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