Skip to content

Toxic gas emission from transponder

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.

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.

IMCA Safety Flashes summarise key safety matters and incidents, allowing lessons to be more easily learnt for the benefit of all. The effectiveness of the IMCA Safety Flash system depends on Members sharing information and so avoiding repeat incidents. Please consider adding [email protected] to your internal distribution list for safety alerts or manually submitting information on incidents you consider may be relevant. All information is anonymised or sanitised, as appropriate.

IMCA’s store terms and conditions ( apply to all downloads from IMCA’s website, including this document.

IMCA makes every effort to ensure the accuracy and reliability of the data contained in the documents it publishes, but IMCA shall not be liable for any guidance and/or recommendation and/or statement herein contained. The information contained in this document does not fulfil or replace any individual’s or Member's legal, regulatory or other duties or obligations in respect of their operations. Individuals and Members remain solely responsible for the safe, lawful and proper conduct of their operations.