Near miss: Failure of subsea lifting equipment

What happened

A dummy spool connected to two lift bags made a rapid and uncontrolled ascent to the surface. The incident occurred during diving operations on a construction barge. There were no immediate consequences but the event had potential to cause serious injury to personnel and damage to assets.

Divers were carrying out a dummy spool removal activity on the seabed at a depth of 110 fsw. As the last bolt was being removed the spool section broke free and rapidly ascended to the surface. When the bags arrived at the surface they lost some of their volume, resulting in partial deflation, and the load fell back to the seabed, away from the dive site. The load was later safely recovered to the deck of the barge.

What went wrong/causes

Investigation suggested that the immediate cause was the absence of hold-back lines from the spool section to suitable fixed anchoring points.
The lift bags had been inflated without appropriate ‘hold-back rigging’ in place and that there had been a failure to follow company procedures, handover instructions and guidance detailed in IMCA D 016 – Guidance on open parachute type underwater air lift bags.

It was also noted that the dive plan had listed ‘install lift bags complete with hold-back rigging to the DMA’ as a specific activity requiring supervisor verification and sign-off on step completion.

The risk had also been identified in the risk analysis and appropriate mitigations defined. In addition, dedicated dead man anchors (DMAs) had been deployed to the seabed for use as anchoring points.

Lessons learnt

Post incident debriefs and ‘times out for safety’ were held with the dive teams, including details of the incident, review of video footage and sharing key lessons learnt, identifying the following lessons:

• Ensure the dive plan is read, understood and followed;
• Ensure mitigations identified in risk assessments are applied stringently;
• Ensure the diving task is conducted following company working procedures;
• Ensure the diving task and company procedures follow IMCA recommendations on any diving operation;
• Ensure dive supervisors fully understand their ownership and accountability for the activities with which they are tasked.

Members may wish to review the following incidents and guidance:

• Uncontrolled ascent of spool and diver during a lifting bag operation
• Uncontrolled ascent of lift bag
• Guidance on open parachute type underwater air lift bags