Lithium-ion batteries have transformed maritime operations—from hybrid propulsion and hotel loads to moving EVs on ro-ro vessels. But when a cell fails, the environment at sea magnifies the hazard. A recent Brookes Bell brief highlights a marked rise in major fire events and the growing attention on lithium-ion cargoes and systems, citing 200 fire incidents at sea in 2023 and multiple high-profile cases that intensified the debate around Li-ion risks.
The challenge is not only heat. During failure, batteries can vent large volumes of toxic and flammable vapour; industry sources referenced by Brookes Bell estimate up to 6,000 litres of vapour per kWh, including hazardous species such as hydrogen fluoride—implying a 100 kWh pack could release around 20 kg of HF under worst-case conditions. In a confined deck or battery room, that is a life-safety and corrosion risk as well as a combustion hazard.
Regulatory gaps and operational realities
While the IMDG Code governs dangerous goods at sea, Brookes Bell notes practical gaps: EVs carried on car carriers are often not classed as dangerous goods, crews may not know how many EVs are on board or where they are stowed, and there is no mandatory state-of-charge limit for sea transport (air cargo is typically capped at 30% SOC). These realities complicate risk assessment and emergency response planning.
Industry bodies and flag authorities are moving. New guidance for vehicle carriers focuses on detection, drencher systems and crew training, with mandatory IMO measures expected to follow in the coming years; the US Coast Guard has also issued safety alerts tied to Li-ion system installation and failure modes on inspected vessels. Together, these emphasise early detection, clear procedures and robust design.
Why conventional detection is not enough onboard
Relying on heat and flame sensors alone is risky with lithium-ion. Firefighting at sea is constrained by access, water supply and re-ignition hazards; Brookes Bell points out that EV battery fires can demand an order of magnitude more water and much longer application times than ICE vehicle fires, while still risking re-ignition. In enclosed ship spaces, defensive “let it burn” strategies used ashore are simply not viable. You need to act earlier on the failure timeline.
The earliest practical indicator inside an enclosure is off-gassing—trace volatile organic compounds (VOCs) and other gases released as electrolyte decomposes during the incipient stages of failure. Laboratory and field literature show vent gas mixtures typically include CO₂, CO, H₂ and VOCs, and that gas sensing can reveal abnormalities before thermal runaway escalates. Detecting those gases buys time to isolate, cool and suppress before flames and high temperatures develop.
Cell Guard: in-enclosure early warning for marine battery systems
Metis Engineering’s Cell Guard is designed to sit inside battery rooms, enclosures or pack plenums, continuously sampling the internal atmosphere and publishing data over CAN for immediate use by the vessel’s monitoring and safety systems.
What it measures
- VOCs – an early, cross-chemistry indicator that electrolyte decomposition has begun
- Humidity & dew point – flags moisture ingress or condensation that can drive faults
- Hydrogen – additional context in hydrogen-rich vent events and enclosed spaces
- Temperature, pressure & shock – environmental context and correlation with impacts
How it helps at sea
- Moves detection left on the timeline by focusing on off-gassing rather than waiting for heat or flames
- Triggers graded responses: electrical unload, module isolation, enhanced cooling and targeted suppression early in the event
- Integrates fast via CAN (with DBC mapping) into existing alarm panels, PLCs or BMS/EMS for logging, remote alerts and automation
- Supports compliance drives by evidencing proactive detection and response capability across ro-ro decks, yacht tender garages, ESS rooms and hybrid-propulsion spaces
Applying early gas detection to Brookes Bell’s risk picture
Brookes Bell recommends stronger detection and crew preparedness to cope with lithium-ion hazards at sea. Mapping Cell Guard into that playbook delivers concrete gains:
- Faster situational awareness
VOC rise triggers early alarms, prompting bridge and ECR to enact playbooks while temperatures are still manageable. - Targeted response instead of blanket deluge
With location-specific gas alarms, crews can prioritise stowage bays or compartments, reducing unnecessary water exposure to electrics and cargo. - Reduced exposure to toxic plumes
Early alarms allow ventilation controls and PPE decisions before HF-bearing vapours spread through decks and accommodation. - Better evidence for post-incident reviews
CAN-logged gas, humidity and temperature traces support root-cause analysis and threshold tuning for future voyages.
Design and deployment tips for shipowners and yards
- Sensor placement: Position sensors near expected vent paths—battery module plenums, pack interfaces, charger cabinets, tender garages and EV stowage zones.
- CAN integration: Reserve high-priority message IDs for safety frames; forward alarms to BNWAS/VDR, fire panels and remote monitoring as needed.
- Thresholds and hysteresis: Use staged set-points (warning/critical) to minimise nuisance while ensuring swift escalation when gas rises are sustained.
- Pair with thermal and CCTV: Combine gas detection with thermal imaging and camera views for verification without immediate human entry.
- Drill the sequence: Exercise the full chain—alarm → isolation → drencher/ventilation → muster/containment—so crews act instinctively under pressure.
Cargo operations and ro-ro specifics
- Pre-sail checks: Verify EV declaration, stowage plans and monitoring coverage. Where declarations are not mandatory, implement voluntary manifests and risk zoning.
- SOC policies: Even though sea transport lacks a mandatory SOC cap, adopt an internal target (e.g., parity with air limits) to reduce stored energy and gas production potential.
- Localised detection: Fit VOC/H₂ sensing in high-risk areas (charging zones, garages, vehicle decks with tight clearances). Pair alarms with dampers/vents to manage plumes quickly.
The bottom line
- Maritime fires are unforgiving. Constrained access, re-ignition risk and toxic plumes make late detection a losing strategy. Brookes Bell’s analysis underscores the need for early warning and modernised procedures.
- Off-gassing appears before flames. Detecting VOCs and related gases gives crews precious minutes to isolate, cool and contain.
- Cell Guard operationalises early action. In-enclosure gas sensing, multi-parameter context and CAN-native integration align with emerging guidance from industry and authorities.
Next step: Strengthen your Safety Management System with in-enclosure early gas detection. Explore how Metis Engineering’s Cell Guard integrates with your vessel’s monitoring and response architecture to reduce risk and downtime across ro-ro decks, ESS rooms and hybrid propulsion spaces.
