Should Car-Deck Fans Stop in an EV Fire?

Yes — shutting down car-deck ventilation is still the right first move once a fire is confirmed. SOLAS II-2/20.3.1.4 requires the means to do it from outside the space, and the EU LASH FIRE project found that switching fans off remains the best way to reduce fire intensity. The catch with EV cargo is that a sealed deck also holds flammable battery vent gas, so the fan decision is really two decisions: when to stop the air, and when it is safe to let it back in.

The stakes are concrete. A closed vehicle deck on a cargo ship runs at a minimum of 6 air changes per hour while vehicles are aboard, which is a steady supply of oxygen to any fire on it. Get the shutdown late or incomplete and the fixed CO₂ system cannot reach its design concentration. Reopen the space too early and the air rushing back in can ignite what the fire left behind. Both failures are on the casualty record.

What does SOLAS require of the fans in a fire?

It requires that they can be stopped, and the space closed, quickly and from outside. SOLAS II-2/20.3.1.1 sets the running capacity at 10 air changes per hour for special category and closed ro-ro spaces on passenger ships carrying more than 36 passengers, and 6 for cargo ships. Regulation 20.3.1.4.1 then requires arrangements for a rapid shutdown and effective closure of the ventilation system from outside the space in case of fire, taking weather and sea conditions into account. Regulation 20.3.1.3 requires the bridge to be told of any loss of ventilating capacity. The rule assumes the crew will stop the air. It says nothing about battery gas.

Why does stopping the air matter so much?

Because no gaseous agent works in a space that is still being fed air. A CO₂ system is sized to reach an extinguishing concentration in a closed volume. An open damper or a fan left running dilutes that concentration and keeps the fire supplied with oxygen. The NTSB's investigation of the Höegh Xiamen fire in Jacksonville in June 2020 found exactly that: the dampers for decks 7 and 8 were ineffective or not adequately secured, the fire kept its oxygen, and the CO₂ release did not work. The ship and 2,420 used vehicles were a $40 million total loss. The contrast is the Honor fire in 2017, where the crew had the ventilation secured before the CO₂ went in eleven minutes later, and the NTSB credited the timely release with limiting the damage.

What changes when the cargo is electric?

The sealed deck now holds fuel as well as fire. A lithium-ion cell in thermal runaway vents a flammable gas mixture — hydrogen, carbon monoxide and light hydrocarbons — and it keeps venting whether or not there is flame. IUMI's August 2025 update to its EV carriage guidance says the risk can shift from fire to explosion if those gases concentrate in unventilated spaces, and asks owners to give careful consideration to ventilation procedures for the extinguishing system they actually have. Trade coverage of the same paper put the hydrogen fraction of EV fire gas at around 30 percent.

Ventilation alone cannot solve this on a large scale. DNV's 2020 technical reference for battery spaces found that if 4,000 Ah or more of cells fail in one compartment at once, even 100 air changes per hour will not prevent an explosion overpressure of 0.5 bar. That work was on battery rooms, not car decks, but the order of magnitude is instructive. A car deck at 6 air changes per hour is not diluting a multi-pack runaway to safety either way. Keeping the fans on buys little against the gas and feeds the fire.

Is there ever a case for keeping the fans running?

Briefly, and only for a small fire near an exhaust. LASH FIRE's ventilation study (deliverable D11.5, RISE) modelled a 5 MW fire in a closed ro-ro space. It found that running fans at increased capacity early on can clear enough smoke to help a hose team, but only if the fire is close to an exhaust duct and still small. A fire away from the ducts gets its smoke thinned downstream, not enough to fight it by hand. The same study concluded that switching fans off, as current practice does, is still the best option for cutting fire intensity, at the cost of visibility. IUMI's position points the same way for PCTCs: apply the fixed system early and correctly, rather than send crew in first.

When is it safe to reopen the space?

Not until the atmosphere and the boundaries say so. This is where the EV case bites hardest. A space starved of air but full of hot, partly burned products, or unburned battery gas, can ignite violently when air returns. At Höegh Xiamen, nine shore firefighters were injured, five seriously, in an explosion that the NTSB report placed at about the time firefighters opened an exhaust vent. That was a conventional-vehicle fire, which shows the hazard does not need lithium to occur. EV cargo adds a source of fuel gas that keeps coming after the flame is suppressed.

• Stop fans and close dampers first, and confirm the closure physically — a secured-looking damper that isn't is how Höegh Xiamen's CO₂ failed.
• Release the fixed system without waiting for manual confirmation of flame; IUMI is explicit that fixed systems come before hose teams on a PCTC.
• Treat reopening as a planned step with gas and temperature readings, not a response to 'it looks out'. Opening a vent is an ignition decision.
• Write the EV case into the ventilation procedure: who decides, which readings, and which ducts open first and away from people.

What it means for owners and underwriters

The fan stop is the cheapest barrier on the deck and the easiest to get wrong. For owners, the questions are whether the shutdown works from outside the space as SOLAS requires, whether dampers are tested closed rather than assumed closed, and whether the fire plan says anything about reopening after an EV event. For underwriters, a CO₂ system on the schedule is only as good as the ventilation closure behind it. Both depend on the same input: knowing early, and exactly where, that a vehicle is going into runaway, so the air is stopped while the problem is still one car and not one deck.

Sources

• 1. IMO, SOLAS Chapter II-2 Regulation 20 — Protection of vehicle, special category and ro-ro spaces: 20.3.1.1 (10 air changes/hour for passenger ships carrying more than 36 passengers; 6 for cargo ships), 20.3.1.3 (bridge indication of loss of ventilating capacity), 20.3.1.4.1 (rapid shutdown and effective closure from outside the space in case of fire). Consolidated text via imorules.com.
• 2. LASH FIRE (EU Horizon 2020), deliverable D11.5 'Elucidation and guidelines for ro-ro space ventilation in case of fire', A. Karlsson, RISE — CFD study of a 5 MW fire; fans-on aids manual firefighting only near an exhaust duct and at the early stage; fans-off remains best for reducing fire intensity. Reported by Fire Safety Search, 13 October 2024.
• 3. IUMI — 'Navigating EV shipping risks: IUMI updates best practice paper', H. Kühl, 29 August 2025, and the position paper 'Risk mitigation for the safe ocean and short-sea carriage of electric vehicles': fixed systems applied early, correctly and safely first; explosion risk from gas in unventilated spaces; careful consideration of ventilation procedures; EV fires exceeding 1,000°C vs ~600°C for ICE vehicles.
• 4. Maritime Executive — 'IUMI: EV Fires Can Cause Explosions on Ro/Ros', 3 September 2025: EV fire gas containing about 30 percent hydrogen; shutting ventilation before CO₂ can trap flammable gas with air.
• 5. NTSB MAR-21/04 — Fire aboard Roll-on/Roll-off Vehicle Carrier Höegh Xiamen, Jacksonville, 4 June 2020: dampers for decks 7/8 ineffective or not adequately secured, negating the CO₂; CO₂ release delayed by the master; nine firefighters injured; vessel and 2,420 used vehicles a $40 million total loss (NTSB press release, 16 December 2021; SWZ Maritime, 14 September 2022).
• 6. NTSB/MAB-18/07 — Fire on board Vehicle Carrier Honor (2017): ventilation secured at 0328, CO₂ released at 0339; timely CO₂ use and boundary cooling likely prevented spread.
• 7. DNV GL — 'Technical Reference for Li-ion Battery Explosion Risk and Fire Suppression' (2020): failure of 4,000 Ah or more in one compartment is not held below a 0.5 bar explosion even at 100 air changes per hour.