Near miss: Unidentified differential pressure led to diver’s umbilical getting trapped

Two divers were working on underwater clamps either side of the entrance to a gravity fed seawater intake in a culvert.

Culverts contained an automated grating and debris cleaning system, 5m (16.5ft) back from the main opening.

Divers had to go repeatedly back and forth across the opening between the clamps.

This allowed slack to be unintentionally introduced into the divers’ deployed umbilicals.

One of the diver’s umbilical became trapped in the cleaning system, and he was pulled towards the intake.

The second diver cut the umbilical. Both divers ascended to the surface without injury.

This incident had fatality potential.

Project team were unaware of the automated debris removal system, therefore there was no process to ensure the system was isolated.

Diver’s umbilical was drawn into the gravity fed seawater intake by the suction generated.

Dive tender was not moved as the dive progressed across the face of the multiple intakes.

• This meant that excess umbilical was deployed in the water, increasing the potential for snagging.

Risk assessment was not effectively reviewed on site to identify appropriate controls for site-specific hazards.

Ensure critical information related to automated systems on site is passed on and acknowledged by all teams involved.

Physical barriers should be placed across intakes.

All personnel involved should be aware of the dangers of differential pressure and its impact on the divers’ activities.

To minimise the risk of snagging, dive tender should be positioned throughout the diving operations (to ensure the optimum amount of deployed umbilical is in the water column).

Lock out/tag out confirmation of the automated systems should be verified before resuming diving activities.

Review risk assessment to ensure adequate measures are in place for site-specific hazards.

What should you do if you come across something unexpected during diving activities (such as the debris removal system)?

What are the dangers of differential pressure during diving operations? What can cause it?

Why do you think the dive tender was not moved during the task?

• Have you ever had to work in similar conditions? Why?

How can you check adequate risk assessments have been carried out before you start work?