Suction from a large GRP (glass-reinforced plastic) cover during lifting resulted in a diver’s umbilical being drawn beneath the load. The incident occurred during hook-up of the GRP lift rigging, when unexpected movement of the cover led to suction which drew Diver 1’s umbilical under the corner of the cover. The cover was lifted and the divers’ umbilical was cleared. The soft nature of the seabed prevented damage to the umbilical. There was no interruption to any diver’s services, and no injuries.
The GRP cover was in its “wet store” position – there were no associated subsea assets. The weather was within the operating envelope of the crane in terms of vessel motions (heave, pitch & roll). No alarms were present and the vessel was operating within her activity specific operating guidelines.
What went wrong?
During hook up of the cover, using crane active heave compensation, the vessel experienced heave which resulted in the cover being lifted in an unexpected way. This occurred when standing up the rigging in active heave compensation (AHC) to ensure there were no twists prior to switching modes into auto tension (AT). At that moment the vessel took a disproportionally large heave and consequently partially lifted the GRP cover.
What was the cause?
Our member notes that large GRP covers (this one weighed over 20 tons) are notorious for the suction forces they create when being lifted, yet the diver needs to be close to enable the fine placement over assets.
Although the diver and dive supervisor were not expecting the GRP cover to lift, and good umbilical management had been identified as a requirement in the risk assessment, the potential for this movement of the umbilical to be sucked under the structure had not been identified and the appropriate umbilical management fully recognized.
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