IMCA Safety Flash 14/09


safety alert

Failure of Gas Supply to Diving Bell

A member has reported an incident in which there was a failure of the breathing system in a diving bell. During diving operations at a storage depth of 102 metres, bell checks were being carried out on one of the bells. The bellman did a full function test on the built-in-breathing system (BIBS) of the bell and it was established that the gas supply system had reduced flow to the BIBS at depth. After getting all divers to put on their own individual BIBS in the bell, to test the gas system, it was found that there was reduced and insufficient gas to supply the full dive team in the bell.

The following actions were taken as part of the investigation.

The dive team made similar checks on the BIBS in the second (port side) diving bell and the same problem was discovered. The starboard bell was surfaced and BIBS was then checked at the surface. The BIBS system could supply three divers at the surface, but under pressure the supply to the divers was inadequate.

The dive system was a new build and it was the first time it had been at a depth of 102 metres. The BIBS system had not been fully tested at this depth. The regulators were stripped to check for defects and none were found. A test rig was then set up in the workshop to mimic the BIBS arrangement and the pressure in the diving bell, where the flow was similarly found to be inadequate.

The problem was solved by fitting a higher performance regulator. This was found to give a far better flow rate on surface. The bell was then blown back down to storage depth, all three divers donned BIBS and a full function test was carried out. Good flow was reported from all divers. The same process was repeated with the port side diving bell with good results.

The company involved drew the following lessons from the incident:

♦ A full function test of the breathing system (BIBS and dive hats/band masks) at all maximum working depths should be conducted whenever there is significant change, including the following occasions:

– when a new build saturation system is first put into commission

– if the depth range of the dive system has changed to a deeper depth

– following any changes, any maintenance or any modifications

♦ It can be shown that during set-up for any new dive operations (e.g. at new locations or new depths) a simple purge of the BIBS and dive hats/band masks is not adequate to establish the full functionality of the breathing system.

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