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Restricted air supply to diver

What happened?

During a diver recovery drill, a contracted subsea company encountered significant issues that led to the standby diver momentarily losing his main air supply.  This restriction in the air supply resulted in the diver going on bailout and the drill being aborted. Both divers were safely recovered to the surface.

Subsea camera still of twisted umbilical

What went right

Both divers worked together during the recovery to amend the issues after the incident. When the primary air supply was restricted, Diver 1 was attentive and assisted Diver 2.  Both divers were recovered to the surface safely.

What went wrong

A review of both divers’ videos showed difficulties in recovery, primarily caused by improper umbilical management and communications.

  • Human error: Diver 2 moved his umbilical restriction from the handle of Basket-2 to the handle of Basket-1, leaving just 2m of slack between this connection and the ring on Basket-2 main wire. This led to his umbilical becoming strained between the baskets due to uneven recovery, causing a restriction in his main air supply;
  • Inadequate supervision: The task plan for the drill lacked detailed and specific instructions, leaving gaps. That caused further issues when coupled with the umbilical placement, uneven recovery of the baskets, and communications issues;
  • Communication breakdown: The placement of Diver 2 umbilical between the baskets was not apparent to the Diving Supervisor.  The Diving Supervisor was unaware of the uncoordinated basket movement and there was inadequate communication between the divers and the diving supervisor, exacerbating the situation.

What were the causes of the incident?

  • Improper umbilical management: Prior to the recovery of the divers, Diver 2 moved his umbilical restriction from the handle on Basket-2 to the handle on Basket-1. Leaving Diver 2 with his umbilical connecting between Basket-1 and the ring on Basket-2 wire, causing a strain on his umbilical when Basket-1 raised before Basket-2. This led to a kink in the umbilical resulted in the loss of the main air supply to the diver;
  • Communication issues: There were initial misunderstandings between the divers and the diving supervisor regarding the issues, resulting in delays in levelling the baskets to remove the strain from Diver 2’s umbilical;
  • Coordination problems: When the instruction was given to recover both baskets together, LARS-2 began lifting Basket-2 while Basket-1 was not lifted. This led to Diver 2 umbilical stretching between the two baskets as Basket-2 pulled it.


Our member took the following lessons:

  • Communication: Establish clear communication protocols before the operation and ensure all team members understand their roles and responsibilities. Ensuring that the crew understand their roles prevents misunderstandings and enhances overall coordination during operations;
  • Supervision: Ensure adequate instructions, communications, and supervision during all operations. Particular attention should be paid during the planning, execution, and oversight of regular emergency drills;
  • Umbilical Management: Proper umbilical management during all diving operations is critical.  Poor umbilical management can lead to serious diver incidents and injuries;
  • Continuous Improvement: Besides annual reviews, lessons learned from incident findings should be included in updates to operational procedures, manuals, and guidelines – helping to ensure that good practices are formally implemented and providing guidance to reduce potential risks in future operations.

Actions taken

  • Ensure that lessons learnt is shared with the entire workforce and with IMCA;
  • Reviewed and updated company diving procedures, training and diving manuals to include learnings outlined above.

Members may wish to refer to:

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