What's the Pollution Tail of an EV Deck Fire?
A long one. A single 100 kWh EV pack can vent 2–20 kg of hydrogen fluoride, and the firewater runoff carries HF, heavy metals and PFAS foam.
A long one — the fire is the short part. A single lithium-ion EV pack in thermal runaway can release 2 to 20 kilograms of hydrogen fluoride, and the water used to fight it runs off laced with HF, fluoride salts, dissolved cathode metals and — until this year — PFAS firefighting foam. At sea that drains over the side; a sunk hull adds its bunkers to the mix. The environmental bill outlives the incident.
What's actually in the smoke and the runoff?
Hydrogen fluoride, phosphorus fluorides, and heavy metals — not just soot.
- Larsson et al. measured 20–200 mg of hydrogen fluoride per Wh of battery capacity in lithium-ion fires — 2–20 kg of HF for a single 100 kWh EV pack — plus phosphoryl fluoride (POF₃) at 15–22 mg/Wh.
- HF is acutely toxic: the IDLH threshold is around 30 ppm and the 10-minute lethal level (AEGL-3) is about 170 ppm.
- The electrolyte salt (LiPF₆) hydrolyses to HF and phosphorus fluorides; the cathode adds cobalt, nickel, manganese and lithium. All of it ends up in the water used to fight the fire.
Where does the water go?
Overboard at sea, into the harbour in port — either way it leaves the ship. Fighting or boundary-cooling an EV deck fire uses large volumes of water, and that water does not stay put. At sea it drains over the side, carrying dissolved fluorides and metals straight into the marine environment. In port it enters harbour water or the dock drainage system. Peer-reviewed analysis of lithium-ion firewater and emissions finds fluorinated contamination — HF, PF₅, POF₃ — at levels that make the runoff a hazardous waste, not merely dirty water.
The PFAS problem was self-inflicted — and is being fixed
Until 2026 the firewater carried its own persistent pollutant: the foam itself. Legacy aqueous film-forming foam (AFFF) contained PFOS and related PFAS — "forever chemicals" that do not break down in the environment. SOLAS Chapter II-2 now prohibits fire-extinguishing media containing PFOS above 10 mg/kg from 1 January 2026, pushing fleets onto fluorine-free foam. That removes one persistent contaminant from the runoff — but it does nothing about the HF, fluoride and heavy metals the battery produces on its own.
The wreck is the long tail
When the fire wins, the pollution does not sink quietly with the cargo — it leaks from it. A car carrier lost to fire takes its bunkers down with it: Morning Midas was reported to be carrying roughly 350 tonnes of gas fuel and about 1,530 tonnes of very-low-sulphur fuel oil when it burned and sank in 2025; larger casualties carry more. Add hundreds of EV packs' worth of electrolyte and cathode metals, and a sunk hull becomes a slow-release source that drives wreck-removal and pollution-liability costs for years — the part of the loss that outlives the headlines.
Why detection is also an environmental control
Because the size of the environmental tail scales with how much battery burns. A fire caught at one venting cell and contained — the Delphine kept its hull and sailed again — involves a fraction of the HF, runoff and metal load of a fire that consumes a deck or sinks a ship. Early detection is not only a cargo- and crew-safety measure; it is the difference between a contained incident with a manageable clean-up and a marine-pollution event with a multi-year liability. The cleanest EV-fire runoff is the one that never leaves the cell.
Sources
- 1. Larsson, F. et al. — "Toxic fluoride gas emissions from lithium-ion battery fires," Scientific Reports 7, 10018 (2017): 20–200 mg HF per Wh of capacity; 2–20 kg HF for a 100 kWh pack; POF₃ at 15–22 mg/Wh.
- 2. Peer-reviewed firewater-runoff and emissions analysis of lithium-ion battery fires (Science of the Total Environment, 2025): fluorinated contamination (HF, PF₅, POF₃) measured in runoff and air.
- 3. IMO SOLAS Chapter II-2, amended by resolution MSC.532(107): prohibition of PFOS in fire-extinguishing media above 10 mg/kg from 1 January 2026.
- 4. HF toxicity thresholds — US EPA AEGL and NIOSH IDLH (HF IDLH ~30 ppm; AEGL-3 10-minute ~170 ppm).
- 5. Morning Midas (June 2025) bunker quantities — casualty reporting; comparative wreck-pollution context, Felicity Ace (2022).
- [VERIFY: Morning Midas bunker figures (~350 t gas fuel, ~1,530 t VLSFO) are from casualty press reporting; confirm against the owner/USCG statement before publication.]
Questions, answered
How toxic is the smoke from an EV battery fire?+
Very. Beyond ordinary combustion products, a lithium-ion pack in thermal runaway releases hydrogen fluoride — 20–200 mg per Wh of capacity, or 2–20 kg for a single 100 kWh EV — plus phosphoryl fluoride (POF₃) and other phosphorus fluorides. HF is acutely dangerous: its IDLH level is around 30 ppm and the 10-minute lethal concentration about 170 ppm, which is why crews are told to treat the vapour cloud as toxic and stay out of it.
What's in the firewater runoff from an EV deck fire?+
Hydrogen fluoride and fluoride salts, phosphorus fluorides (PF₅, POF₃), dissolved cathode metals — cobalt, nickel, manganese, lithium — and, on ships still carrying legacy AFFF, PFAS foam. The water used to fight or boundary-cool the fire carries all of it overboard at sea or into harbour water in port, which is why the runoff is treated as hazardous waste rather than ordinary firewater.
Does the PFOS foam ban fix the pollution problem?+
Only part of it. From 1 January 2026, SOLAS II-2 bans fire-extinguishing media containing PFOS above 10 mg/kg, removing the persistent "forever chemical" foam from the runoff. But the hydrogen fluoride, phosphorus fluorides and heavy metals come from the battery cell itself, not the foam — so cleaner foam reduces one contaminant while the battery's own emissions are unchanged.
How does early detection reduce the environmental impact?+
The environmental tail scales with how much battery mass burns. A fire caught at a single venting cell and contained involves a fraction of the HF, contaminated runoff and metal load of one that consumes a deck or sinks the ship. Detection that flags a cell before visible smoke turns a potential marine-pollution event into a contained incident with a manageable clean-up — an environmental control as much as a safety one.
Continue the thread
What the 2026 PFOS Foam Ban Means for RoRo
From 1 January 2026 SOLAS II-2 bans PFOS firefighting foam above 10 mg/kg. RoRo and car-carrier operators must swap and certify foam by first survey.
Can Water Suppression Worsen an EV Blast?
DNV found sprinklers can make a battery explosion worse by pocketing vent gas — a sharp question for the water-based systems now mandated on vehicle decks.
Who Fights a Mid-Ocean Car-Carrier Fire?
Often no one, for days. The Morning Midas burned for six days before the first tug arrived and twelve before a firefighting tug did — then it sank.