A member has reported an incident in which a crane winch wire was lost during light subsea lifting work. The winch wire and the load dropped on to the seabed near to working divers.
A small crane, sometimes referred to offshore as a ‘cherry picker’, was being used to deploy a small tool basket to a diver working on a subsea manifold. It had been identified on the previous shift there was insufficient wire on the crane winch drum to reach the seabed; however there was sufficient winch wire to reach the roof of the manifold. The deck crew and dive supervisors had been briefed by the previous shift regarding the short length of wire.
During the operation to deploy the basket the deck crew was instructed to deploy the tool basket to the ‘short mark’ (rope marks fitted to the cherry picker wire). The diver spotted the tool basket and gave an ‘all stop’ signal. However, the tool basket continued to descend towards the seabed followed by the entire length of the winch wire which landed in close proximity to the divers. The divers were uninjured and returned unaided to the bell.
An investigation took place which, in addition to errors in lift planning, suitability of equipment and management of change, revealed the following:
- The divers were working directly under a suspended load;
- There were several ‘short marks’ identified on the winch wire;
- The pilot of the observing remotely operated vehicle (ROV) had not been instructed to watch the descending load;
- The ‘lineout meter’ giving details of how much winch wire had paid out was defective;
- A hydroacoustic position reference (HPR) beacon had not been fitted to the wire in order to confirm the depth.
The company involved implemented a number of control measures following this incident:
- A ‘dropped object cone’ protection procedure was implemented for divers where the diver(s) must be outside a minimum 30 degree dropped object cone for all subsea lifts; if this is not practical then they must at least retire under the bell. Certain loads being deployed and recovered will require the bell to be recovered.
- At least two independent depth reference devices should be in operation when deploying loads subsea. These can be:
- a line out meter
- an HPR transponder
- rope marks
- ROV observation should be regarded as secondary means of reference;
- The crane or ‘cherry picker’ operator should have suitable visual references to allow an accurate understanding of the position of the subsea load and the capabilities of the lifting equipment.
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