Failure of bail-out regulator

When the relief valve was dismantled, it was found that two mild steel washers had been fitted to the valve to effectively increase the spring tension to allow for a 20 bar pressure release. Both washers were badly corroded and prevented operation of the relief valve.

In a situation where a regulator fails because the relief valve is inoperable, there is potential for the low pressure (LP) hose to be subjected to full bail-out pressure of 300 bar. New-type LP hoses have a working pressure in excess of 60 bar but, because of safety factors, will have a considerably higher burst pressure. Thus there is potential to have full bailout pressure at the helmet emergency valve without the diver’s knowledge.

When the history of the first stage regulator’s relief valve was investigated, the company involved could not trace when they had been delivered. The manufacturer had no knowledge of such washers ever being fitted to its relief valves, as the normal relief valve setting from the manufacturer was 15 bar. It is understood that that supplier manufactures special relief valve caps to allow for a 20 bar pressure relief, but this was based on different spring settings. The company’s maintenance procedures would prohibit such materials being inserted in the regulator valves and documentary evidence of when this occurred could not be found.

The company involved is concerned that this may not be an isolated case of incorrect supply or maintenance and has instructed all of its diving supervisors to check all first stage regulators at the earliest opportunity to confirm that the relief valves have the correct components fitted, in accordance with suppliers’ specifications. This check was to include both units in use and stored standby units.