Yacht specific: lithium-ion battery fires
Governing: MGN 681 (M) Amendment 1 (December 2025, updated 13 January 2026); REG Yacht Code Part A, Chapter 14.1. Builds on: L1.1, L3.2.
Electric toys and tenders are now common on yachts. MGN 681 notes they are not necessarily a greater fire risk than petrol craft, but the fire is different, and the precautions are too.
How big
MGN 681 gives typical battery sizes:
| Craft | Battery |
|---|---|
| Electric tender | 40-100 kWh |
| Electric jet ski | 20-50 kWh |
| Underwater scooter | 1-3 kWh |
| E-foil | 1-5 kWh |
| E-SUP | 1-5 kWh |
A large electric car battery fire can need around 10,000 litres of water to suppress. A big electric tender holds a similar amount of energy.
Why it is different
- Thermal runaway: once cell heat exceeds what can be dissipated, temperature rises uncontrollably. MGN 681 notes it may start at 60-70°C inside the battery.
- Self-sustaining: Li-ion fires can burn without additional oxygen, so smothering alone fails.
- Off-gassing: before and during runaway the battery releases flammable and toxic gases, including carbon monoxide, hydrogen, and hydrogen fluoride. They may collect low or high.
- Re-ignition: batteries can reignite long after the fire appears out.
Warning signs
MGN 681: hissing, whistling or popping, a possible sweet chemical smell, then black particulate "smoke", then white vapour. Any leak of clear or blue coolant can indicate damage. Seawater intrusion greatly increases risk.
Storage and charging
MGN 681 section 4, in summary:
- Store craft only in spaces meeting REG Yacht Code Chapter 14.1, or an equivalent container.
- Spare batteries over 100 Wh go in a dedicated cabinet; on open deck the cabinet is at least 1.0 m from combustibles and not on an escape route or near embarkation stations or LSA.
- Keep space ambient temperature at or below 45°C, monitored and alarmed.
- Charge only in dedicated spaces or approved stations, by competent crew, with charging stopped automatically on fire or overheat.
- Never charge a damaged battery; stop charging immediately if damage occurs.
- From 1 January 2027, storage and charging boxes on UK vessels must be UK type approved.
Fighting it
- Raise the alarm and keep people away and upwind.
- Isolate the charging supply before attacking.
- Apply large quantities of water or the fixed water-mist system; MGN 681 calls water mist the most effective battery-fire solution.
- Crew in full PPE and SCBA whenever exposed to the smoke; MGN 681 recommends level 2 suits to BS EN 469:2020.
- Use fire blankets or containment bags only with care: gas can build up under them.
- After knock-down, monitor with trained crew until the craft is removed, and quarantine it.
- Decontaminate crew and equipment, because of hydrogen fluoride.
WARNING — Do not carry a heating battery Carrying a hissing battery through the yacht to throw it overboard exposes you to explosion and toxic gas and may spread the fire. Follow the yacht's procedure.
Training
MGN 681 section 9 expects crew to be trained in safe operation, storage and charging, identifying damage, battery-fire response and specialist equipment, with drills at an interval agreed with the Administration and a named person on board responsible for Li-ion safety.
TIP — Your phone counts too Crew and guest devices are small, but MGN 681 warns of the risk where aggregate capacity exceeds 500 Wh. A bunk full of power banks and vapes is a fire load.