Toxic gas emission from transponder
- Safety Flash
- Published on 1 July 2002
- Generated on 16 February 2026
- IMCA SF 05/02
- 2 minute read
One of our Members reported an incident involving lithium chloride batteries in a transponder unit which, having been recovered from depth, released a gaseous white powder through its vent valve. The gas was believed to be toxic.
What happened?
People in the vicinity were immediately told to evacuate the deck area and brought into the accommodation. The air flow in the accommodation was increased to minimise the possibility of the gas entering the ship’s internal facilities. The intakes were well away from the transponder.
Those on board immediately contacted the manufacturer. It was established that the most likely explanation of the whitish substance was a combination of sulphur dichloride and hydrogen chloride, both toxic. This combination is caused when the chemicals contained in lithium/thionyl chloride (LiSOCI) batteries leak and come into contact with water. Their advice was to leave the transponder alone until it had stopped venting before going near it and then to quarantine the unit.
The unit vented for some 10 hours before the relief valve reset. (The transponder was still under around 2 bar internal pressure.) It was removed to a well ventilated area, away from general operations, until specialists from the manufacturer could deal with the unit. It was later dis-assembled under controlled conditions using specialist PPE. The unit was then returned to the manufacturer in specialist packing for analysis.
The white powder contamination on deck was neutralised with sodium bicarbonate (baking soda) and washed by fresh water.
All people using transponders, beacons or similar battery powered underwater units should heed this notice, obtain relevant safety data from the battery supplier/manufacturer, and be aware of precautions they must take, especially if they either observe venting of the unit, or suspect water ingress into the unit.
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