Aquaculture worker injures arm in machine

Lookout! Issue 32, December 2014 – January 2015

A man’s arm became entangled in a vessel’s mussel declumping equipment, resulting in serious harm.
Mussel declumping machine
Maritime New Zealand ©2020
The mussel declumping machine uses a rotating shaft, chains and tines to break up clumps of mussels into singles.

The accident occurred at the end of the day’s second harvest of green-lipped mussels. The man, a highly experienced fisherman and aquaculture worker, was one of five crew on board the 18 metre steel vessel.

The crew began cleaning the harvest equipment while the vessel was still alongside the last mussel line. The man started to clean the debris caught inside the tine area of the declumper - a machine that breaks up clumps of mussels into singles, using a rotating shaft, chains and tines. The machine was normally disabled while it was being cleaned, but on this day it had not been shut down effectively.

‘Isolate before opening’ sign
The ‘isolate before opening’ sign is prominently displayed on the hatch and emergency stop is clearly visible.
Maritime New Zealand ©2020

The man had removed several clumps of seaweed with his right hand. As he reached in to pull debris from the tines, he used his left arm for leverage and inadvertently pushed down on the control lever, which started the tines rotating clockwise through his arm and up his hand. The rotating machine caught his arm, severely injuring it. He screamed out and other crew stopped the machine and reversed the tine to release his arm.

First aid was administered while the vessel steamed to the nearest wharf, where the injured man was treated by ambulance staff and transferred by helicopter to hospital.


  • The company and vessel had thorough operating procedures in place for cleaning down this item of equipment. Despite being trained in these processes, the man chose not to follow them.
  • The man did not check that the main isolating valve had been turned off before opening the declumper, and had no reason to know that the secondary isolating valve shaft had failed.
  • This accident fits the classic “Swiss cheese” model, promoted by UK expert in organisational process James Reason. Under this model, holes that vary in size and position in slices of Swiss cheese represent risks or weaknesses in any system. When slices are stacked side by side, the holes do not usually line up, therefore no hazardous situation exists.
Swiss cheese model
Maritime New Zealand ©2020
The Swiss Cheese model demonstrates that the accident occurred due to various weaknesses in the system.
  • In this case, however, the accident was able to happen because the failure of various systems (barriers) designed to prevent the machine from rotating did align, allowing the hazard to pass through. The Swiss cheese model illustrates why it is vital to have more than one way of preventing an action or event in a safety system.
  • A combination of factors was found to have caused the accident:
    • The main hydraulic isolating valve on the deck was not turned off, as set out in the safe operating plan. Turning off this valve shuts off all oil flow to the equipment and should be done before opening the declumper hatch.
    • The automatic cut-out lever on a secondary isolating valve failed as the hatch was lifted. Normally, a short shaft moves this valve to the off position as the declumper hatch is opened, but the shaft had become disconnected and didn’t turn the valve as it was designed to do – although it had been working correctly earlier.
    • The man’s left elbow activated the rotation control lever while his right arm was inside the equipment, which caused the machine to start rotating, catching and severely injuring his arm.
    • Had the injured man correctly followed the procedure required for that item of machinery, this accident could have been avoided. He had worked on the vessel for six years and was fully trained in all aspects of the operation, with detailed knowledge of its safe operating procedures.
  • Had the man followed the procedures as he was trained to do, the accident would probably not have occurred.
  • In response to this and other accidents involving machinery, MNZ has been periodically undertaking at-sea inspections of mussel vessels, to ensure appropriate guarding is in place and procedures are being followed to prevent serious harm injuries.

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