Beyond fire: understanding vent gas risks in maritime batteries
As shipping continues its decarbonisation journey, maritime batteries are gaining traction as a low-emission propulsion solution. But alongside growing interest comes increasing scrutiny of their safety challenges. Amy McLellan updates on the latest considerations of the Marine Electrical Special Interest Group about the safety of maritime batteries
Growing awareness of the fire risks of lithium ion batteries means there’s increased scrutiny of their use to power shipping to a low carbon future. A critical misconception underpins many of these discussions: battery failure is not fundamentally a fire event but rather an exothermic chemical reaction. This distinction matters. Thermal runaway can develop silently, producing extreme heat and hazardous by-products long before any fire is evident.
The vent gases are highly toxic, with some of the components having a similar molecular structure to chemical warfare agents. Exposure to vent gases has caused serious health effects which are very hard to treat. At the same time, these gases introduce a secondary hazard: explosion. In enclosed ship compartments, vented gases can accumulate and ignite, creating a confined vapour cloud explosion (VCE).
The challenge is compounded by battery design. Cells are typically enclosed in robust, IP-rated casings that protect against water ingress but also make external cooling extremely difficult, if not impossible. Unlike conventional fires, there is currently no reliable method to stop a battery failure once it has begun; mitigation is limited to slowing or containing propagation.
Despite these concerns, the overall safety record of marine battery systems remains relatively strong. Of approximately 2,000 battery-powered vessels in operation, around a dozen incidents have been reported, most with only minor impact. Importantly, each incident has contributed to improved understanding and incremental advances in safety and regulation.
Battery chemistry also plays a role in how failures manifest. Nickel Manganese Cobalt (NMC) batteries tend to ignite earlier in the failure process, often producing jet-like flames. In contrast, Lithium Iron Phosphate (LFP) batteries are more likely to vent gases first, delaying ignition but increasing the risk of a vapour cloud explosion. In confined marine environments, this distinction is critical, as delayed ignition can allow flammable gases to accumulate to dangerous levels.
However, technology is only part of the equation. In practice, system integration and crew preparedness have a greater influence on safety outcomes. While battery systems are generally designed to meet similar regulatory standards, installation approaches can vary significantly between vessels. This variability complicates emergency response, particularly when crew training does not fully reflect the non-fire nature of battery failure.
Training is therefore essential, yet often inconsistent. Recognising this gap, international efforts are underway to standardise maritime battery education. Initiatives such as the proposed ISO standard on Electric Ship Maritime Education and Training aim to equip personnel with a clearer understanding of battery behaviour and appropriate response strategies. This proposal has been submitted to IMO for approval.
Regulation itself is evolving but not yet fully aligned with emerging evidence. Existing standards, such as IEC 62619, do not classify gas venting as a failure condition, focusing instead on fire or explosion outcomes. In practice, however, venting without ignition is a key indicator of failure and a major source of risk. This mismatch highlights a broader challenge: regulatory frameworks are struggling to keep pace with rapid advances in battery technology. Class rules are trying to plug these testing gaps but this adds another layer of interpretation and adds to the confusion on what a safe system should be.
Efforts by organisations including IEC and IEEE to develop new standards for maritime electrical installations are an important step forward. The MoU of cooperation between IMarEST and IEEE aims, among others, to officially endorse joint efforts to develop safety and training guidelines in the marine electrical engineering scientific area. There is a lot of work to do in this area to keep regulation up to speed, and IMarEST will be part of this ongoing process, alongside other bodies.
Looking ahead, improving marine battery safety will require three key shifts: a clearer industry-wide understanding of what battery failure actually looks like; regulations that better reflect real-world failure modes; and the development of unified standards tailored to maritime applications. As battery technologies continue to evolve, ensuring that safety frameworks evolve with them will be critical to supporting shipping’s decarbonised future.
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Image: Battery powered ship in Sweden. Credit: Shutterstock
