Near-miss incident lowering concrete mattress

A member reports a diving near miss incident when a concrete protection mattress was being moved into position.

A concrete flexible protection mattress was being deployed by ship’s crane whilst divers were ready to receive it on the sea bed. The procedure demanded that the mattress should be lowered some 60 m offset horizontally from the divers’ position, stopped 10 m from the seabed awaiting instructions before moving the load towards the divers. Visibility was about three to four metres.

During the lowering operation, crane operators changed over and after it was lowered to the prescribed depth, the diving supervisor gave instructions for the mattress to be shifted horizontally toward the divers’ position.

The divers noticed the mattress when it was about two metres away from them but already in partial contact with the sea bed instead of about 10 m off bottom. Nobody was injured.

On investigation, it was established that during the crane operator shift change, the first operator had failed to zero his meter when the load was at the water surface and the replacement operator had not questioned the validity of the meter reading showing the length of wire deployed, having assumed that it had been zeroed. As a result the load contacted the sea bed when the operator expected it to be more than 10 m up.

The member posted the following reminder in the ship’s cranes and recommended that similar ones be posted beside control panels on all cranes capable of subsea operations in the fleet.

Please remember the following rules when deploying loads to the sea bed:

• Before lifting the load off deck, check with dive/shift supervisor regarding the lateral position and initial depth at which the load is to be deployed;
• Always zero the load or hook at the surface of the water and report when completed to dive/operations control;
• During lowering, inform control of the depth of the load every 10 m until it reaches 10 m above the seabed when lowering is stopped;
• Act only on dive/operations control instructions for further crane movements;
• Change over of crane operators shall not take place during the lowering or lifting of a load.