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SPHL battery charging – build-up of hydrogen

A member has reported an incident in which there was a build-up of hydrogen gas inside the cockpit of a Self-Propelled Hyperbaric Lifeboat (SPHL), and has submitted information to IMCA for use in a safety flash.

The following points were noted:

  • Many designs of battery charging ventilation systems consist of a forced air system from battery compartments/boxes in order to comply with Prevention of explosions during battery charging in relation to diving systems;
  • The member’s SPHL had a ventilation system consisting of a fan on one battery box that pushed air through a further two battery boxes via vent pipes to a discharge pipe overboard. This was complemented by an alarm system if the fan failed;
  • It was discovered that there was no flow in the ventilation system;
  • It was shown in this case that if the vent pipes are blocked or have a restricted flow then the fan alarm will not register;
  • In this particular incident, the original equipment manufacturer indicated that faulty battery lid seals have also been recorded as a potential problem (causing venting through the lid and into the cockpit instead of the vent pipe).

For designs of HLB battery charging systems that consist of a forced ventilation system, our member recommended the following actions:

  • Check that fan(s) are operational and unobstructed;
  • Check vent pipe openings on the inside of any battery boxes are clear of obstructions;
  • Check vent pipes between boxes are free from damage (not kinked);
  • Check battery lid seals are intact and lid catches are fully engaged;
  • Check there is a flow through the actual system (easiest method is to put a polythene bag over the final discharge vent pipe);
  • Modify planned maintenance systems to require a weekly check of the air flow of the ventilation system;
  • If the final discharge point is on the outboard side of the SPHL, then check the flow by disconnecting the vent pipe from the hull penetration inside the cockpit, using a polythene bag or similar over the pipe.

Members may wish to refer to the UK Health and Safety Executive (HSE) industry guidance Using electric storage batteries safely which can be found at

Safety Event

Published: 22 November 2016
Download: IMCA SF 31/16

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