Fatality during lifting operations

The incident occurred on a drillship while attempting to land a christmas tree (XT), using one of the vessel cranes, on to the XT trolley (see general view below). It was important to centralise the XT, which weighed 50 tons in air, on to the trolley.

Centralising guides were in place on the trolley but lifting conditions (heavy load, near vertical crane boom position and movements of floating unit) required significant planning and supervision for this operation.

The tree was approximately 0.6 m above the trolley for final positioning when the main hoist hydraulic motor of the crane failed catastrophically. The 50 ton XT fell on to the trolley and as a result a further item known as the ‘tea cosy’, weighing 335 kg, came loose from its pedestal on top of the XT and bounced off the XT on its way down to the deck. A member of the crew supervising the operation was struck by the tea cosy and died instantly.

Following investigation, the main causes of the incident were identified as follows:

• Failure in crane control:
  
  
  • A week before the accident the main hoist hydraulic motor was replaced by an incorrectly sized motor available onboard the vessel. Though both motors look very similar and can be installed in the same position they have very different torque characteristics and are designed for different purposes.
    
    
  • There was no in-depth investigation performed following the first hydraulic motor failure a week before.
    
    
  • The hydraulic motor was changed without reference to the crane manufacturer’s manuals (which were available onboard).
    
    
  • A review of the preventive maintenance system used onboard identified defects in spare traceability, maintenance plans and personnel competency and training.
    
    
• Failures in operational control:
  
  
  • The tea cosy was not fully secured on its pedestal. Under ‘normal’ lifting conditions, full securing of the tea cosy was not considered necessary; the sudden shock due to the free fall of the entire XT had not been identified as a hazard.
    
    
  • Free fall of XT assembly was not considered in the risk assessment.
    
    
  • The victim was standing adjacent to the XT during the final landing; though he was co-ordinating the operation he had not been involved in the pre-job meeting.