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Emergency Lithium battery failed catastrophically in a diving bell

What happened?

During regular planned maintenance, a 24V DC emergency Lithium battery pack in a diving bell activated and failed catastrophically causing an explosion and small fire.  There were no injuries;  the bell was unoccupied at the time.  The incident occurred when a check valve on each of the Bell Emergency Battery Pack Pods was changed out for a more widely available type.

Crucially, the original valves were only threaded on one side with a male thread whereas the replacement type had the same male thread at each end.  A second thread on the new valve was not required as it does not connect to anything. This identical second thread introduced the potential for the new valves to be fitted in the wrong orientation.

After launch, the starboard bell status alarm for the 24V DC emergency battery pack activated. Initial visual inspection indicated no obvious fault. Upon recovery to the bell hanger the battery pack failed catastrophically, a loud noise was heard, and smoke and flames were emitted from the battery pack.

The battery pack pod had flooded through an incorrectly fitted check valve, causing the failure of the pod and subsequent fire.

Findings

  • There had been no Management of Change (MoC) process conducted and there had been no technical consideration of any new potential risks;
  • Valves with identical connection points can easily be fitted in the wrong orientation;
  • The crew were unaware of the immediate required action to extinguish the resulting fire.

Actions

  • Review of similar Emergency Battery Pack pods to review the check valves fitted to ensure they cannot be fitted incorrectly. Check valves with male/male threads to be removed;
  • Ensure that a thorough and appropriately technical Management of Change (MoC) process is carried out when changing out dive related components and equipment;
  • Personnel involved should ensure that they have a thorough understanding of the most appropriate immediate actions in the event of a Lithium type battery fire.

Safety Event

Published: 25 August 2020
Download: IMCA SF 25/20

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