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giovedì 25 gennaio 2018

What happened
During offshore subsea operations, an air diver reported to the surface that his helmet had flooded. The supervisor instructed the diver to return to the basket. He then asked the diver to clarify what had happened. The diver reported his helmet had flooded and he had to reclose the neck dam lower hinged swing catch (locking collar).
During the incident, the supervisor jumped the standby diver to assist. The standby diver had made contact with the diver and confirmed with the supervisor that the neck dam was in place and the helmet was secured correctly. It was clear that the diver had closed the locking collar assembly resealing the helmet.
Photo indicates the open locking collar assembly in open position, behind diver’s shoulders
What went wrong
Upon investigation of the dive video and audio recordings, it was identified that at some point during diving operations the knurled end of both helmet locking pull pins, used to secure the locking collar assembly (see photo) had caught on top of the R-Vest shoulder harness at the attachment D-ring “where the inspection equipment (CP-UT meter) are secured via a rope lanyard”. This had pulled the locking pins, thus resulting in the locking mechanism coming open. As a result, the locking collar assembly opened and dropped past the diver’s shoulders removing the primary guard that holds the helmet on the diver’s head.
Just before the event the diver is heard to flush the helmet via the free flow. This slight over-pressurisation caused the inner neck dam ring to pop out of the helmet outer neck dam ring. When the free flow was stopped water could flood into the helmet.
What were the causes?
  • The direct cause was found to be:
    • The knurled end of both helmet locking pull pins that secure the hinged locking collar assembly (see above photo) had caught on top of the R-Vest shoulder harness and pulled to open position;
  • The underlying root causes were found to be:
    • The swing hinged locking collar assembly dropped to an open position whilst the diver was working, without him noticing, and passed the top of his shoulders as he leaned forward to conduct tasks
    • Activation of helmet free flow to help demist the visor caused a slight over-pressurisation inside the helmet resulting in the neck dam O-ring popping open. This allowed water to enter the helmet when free flow was turned off;
  • Root causal factors identified were:
    • Design failure of the locking pull pins was not addressed during helmet maintenance which recommended fitting of KM Pull Pin Sleeve Kit part #525-112.
  • Lessons learnt
  • Helmets should have been maintained and modified to address previously identified findings in the IMCA safety flash 20/16 issued in August 2016;
  • Kirby Morgan Dive Systems Inc have addressed the potential issue by developing a Pull Pin Sleeve Kit part #525-112 (see image below). This device helps reduce the possibility of pins been inadvertently operated. They were not fitted to the equipment involved.
Actions taken
  • All helmets returned to workshop for fitting of KM Pull Pin Sleeve Kits;
  • Divers given familiarisation brief of with potential hazard;
  • Dive tenders reminded of the need to follow pre-dive dressing procedures, ensuring the neck dam is locked and secure and recording that this check has taken place;
  • To prevent recurrence, divers and tenders were instructed to be vigilant regarding items that could cause or interfere with the pull pins;
  • The practice of hanging work tools on the upper part of D-ring on recovery harness will be stopped.
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