A member has reported a lost gas incident that occurred with two of its divers on a third party vessel. They do not normally dive from this vessel and were not involved in the maintenance of the diving system. Part way through a bell run, both divers reported a loss of main gas supply. It also appeared that the bell onboard gas failed to automatically operate through the MARA panel. The main gas supply was quickly reinstated to the divers by the actions of the bellman.
The member’s investigation identified the following sequence of events:
- Gauges in the bell panel had been changed from the manufacturer-supplied type of gauge that measures line pressure relative to the ambient pressure inside the bell to sealed units that measure line pressure relative to atmospheric pressure.
- This change had not followed a management of change process and consequently its significance was not adequately assessed. As a result of this, vessel specific procedures were not updated and thus these contained inaccurate criteria.
- Bell checks on this vessel followed the company’s standard practice of creating vessel-specific bell checks based on the actual requirements of the specific bell, which in turn were based on this vessel’s standard procedures.
- During diving operations it was apparent to the divers that, following the vessel bell check, settings gave an inadequate gas supply pressure. This was adjusted as required by each diving team by increasing the flow pressure in excess of the stated 12 bar (the correct pressure setting being 12 bar above ambient). This adjustment was not communicated to the surface and was therefore not recorded.
- A dive commenced to 100 msw with the bell at 85 msw. This should have required the diver’s supply pressure to be set at 20.5 bar (8.5 + 12) because the sealed gauge did not subtract ambient pressure but it was set at 12 bar as stated in the bell check sheet. At depth, a supply to the divers was achieved by the bell man increasing the supply pressure prior to lockout.
- During the dive the bellman re-adjusted the supply pressure back to 12 bar which was insufficient to adequately supply the divers as it only gave 2 bar of pressure above ambient. The divers lost gas and went on to bailout supply. The emergency onboard gas supply did not operate automatically as this had been set at 10 bar on the gauge as required in the bell checks. It thus did not have sufficient pressure to supply the divers.
- The divers supply was quickly re-instated when the Bellman increased the supply pressure at the panel.
The investigation concluded that the equipment specification change had resulted in the requirement for a significant change to standard operating practices. However, as this had not been subjected to a management of change process, those required changes to operating practices had not been recognised or implemented.
The divers had identified that the gas supply pressure required adjusting from the levels stated in the bell checklist in order to obtain an adequate supply. This went unrecorded and was not communicated to supervisors.
This incident could have had considerably more severe outcomes than were experienced and it is suggested that the following lessons could be learned:
- The importance and value of following management of change procedures, particularly for any change to the original manufacturer’s requirements.
- No equipment should be replaced (unless identical to the original) or modified without a competent person considering all of the implications. A dive system technician, even if very experienced, may not have the competence required for this consideration.
- Bell check procedures should include recording of diver main gas supply pressure and onboard backup, downstream of panel regulators;
- Divers should be reminded of the importance of communicating any changes or alterations to normal operating practice to the diving supervisor.
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