A member has reported an incident on a dive support vessel in which there was an explosion and a person suffered 2nd degree burns to his hands. The incident occurred during the changing of an Oâ‚‚ gas quad on a diving support vessel (DSV). The injured person, who was competent and qualified for this work, was wearing full personal protective equipment (PPE) for the task including ear protection. He successfully disconnected and vented the used quad which was at a pressure of around 20bar, closed all relevant valves and removed the Oâ‚‚ regulator. The regulator was subsequently removed from the empty quad and transferred directly onto a fully charged quad at a pressure of 200bar. The regulator was tightened and the whip lines fitted as per requirements. The injured person then proceeded to open all 16 of the individual pillar valves on the individual bottles; then checked to ensure the regulator was wound back, prior to cracking the king valve to allow Oâ‚‚ to flow into the regulator.
At this point an explosion occurred and the injured person was exposed to the blast resulting in serious burns to both hands. Because the injured person was shocked due to the sudden blast, he stepped away from the quad. All the pillar valves for all the bottles were open; this allowed the gas to start venting directly from the failed regulator resulting in a potentially catastrophic situation. The injured person tried to close the king valve, but it was later found that the valve seat was damaged during the blast, and thus the Oâ‚‚ could not be isolated by the king valve. More personnel arrived and helped to close all of the pillar valves bringing the situation under control.
It was later established that the injured person sustained 2nd degree burns to both hands due to the high temperatures created by the blast, despite wearing appropriate hand protection (gloves) on both hands.
Our member’s investigation and conclusion noted the following:
- Due to the nature of the incident and the failure of the regulator, the specific cause of the explosion could not be determined;
- The practice of opening all 16 pillar valves meant that once the regulator failure had occurred, the entire contents of the quad was able to vent in an uncontrolled manner;
- The regulator was later identified as being around 12 years old; this was in excess of the recommended working age for this type of equipment;
- There was evidence of white PTFE thread tape having been used on the regulator threads. This could have been a contributory factor and potential fuel for the explosion/fire;
- The PTFE Thread Tape, used for sealing the threads in this operation, was not appropriate or suitable for this Oâ‚‚ application;
- The pipe work directly after the regulator was a 90 degree elbow joint which is not recommended for gas systems;
- The regulator connection nut flats were found to be damaged (rounded) due to the previous use of incorrect/inappropriate tools;
- The regulator had not been cleaned and inspected to appropriate levels for Oâ‚‚ operations, prior to connection to a fully charged quad;
- The maintenance records for the regulator were not adequately documented;
- Pressure gauges installed within an Oâ‚‚ enriched pressurised system should not be used in these cases:
- The gauge is not Oâ‚‚ compatible;
- The gauge has been damaged (including nuts or threads);
- There is suspicion of tampering;
- The gauges are over 5 years old and have not been serviced;
- The gauge operating range is out with the maximum pressure rating of the regulator or cylinder.
Our member took the following actions:
- Personnel working with Oâ‚‚ to be required to review the appropriate company procedures and also manufacturers’ safety, installation and operations precautions;
- Specialised Oxygen Green PTFE Thread Tape (Thread Seal Tape Â½” x 260 T-27730A (rated @10,000 psi) should be used for Oâ‚‚ operations;
- Thread tape must be kept clear of the end of the fitting by 1.5-2 threads;
- A six monthly test and inspection ‘routine’ for loose Oâ‚‚ regulators has been added to the planned maintenance system;
- All regulators to be replaced after 5 years of service and a clear maintenance log maintained;
- Maintenance of the regulators should be conducted by a suitably trained and qualified person;
- Revision of PPE for this work to ensure operators are fully protected against relevant hazards of the task;
- Dedicated set of ‘Clean and Correct’ sized spanners should be purchased and kept specifically for use on fittings. Adjustable spanners should not be used;
- A designated clean environment should be established for maintenance of the regulators;
- Pre-use regulator checklist should be developed following manufacturers’ guidance notice;
- All Oâ‚‚ pipe work to be reviewed and 90 degree joints removed wherever possible, in particular on the inlet or outlet from a regulator to prevent friction and potential ignition points;
- Only Oâ‚‚ compatible gauges shall be purchased as spares and, wherever possible, the same gauge type/model shall be ordered;
- Pressure gauges should be fitted directly to regulators without restrictive or bend connections.
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