Understanding EV Batteries: Emerging Risk and Response

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As electric vehicle (EV) adoption accelerates globally, fire services and industrial emergency responders must stay ahead of the evolving risks posed by lithium-ion battery technologies. While the statistical likelihood of an EV battery fire remains extremely low, estimated at 1 in 40 million vehicle fires, the consequences when incidents do occur can be catastrophic. The rare nature of these events should not mislead responders into complacency. Like winning the lottery, someone always does and the result, in this case, is not fortune but fire.

Chemistry Behind the Risk

Most modern EVs now use lithium iron phosphate (LFP) battery chemistries, prized for thermal stability and their lower likelihood of entering thermal runaway compared to earlier formulations. However, all lithium-ion batteries remain vulnerable under certain conditions. Dendrite formation (microscopic metallic filaments) that penetrate separators can result from overcharging or excessive charge/discharge rates, leads to internal short circuits.

Battery state of charge plays a critical role in the onset and intensity of thermal runaway. Packs charged to 20–80% are significantly less reactive; above 75%, the likelihood of a catastrophic reaction increases notably. Conversely, batteries at approximately 30% charge are less likely to experience traffic-related thermal events or ignite rapidly, providing a narrow window of relative safety.

Thermal Runaway and Off-Gassing

Once thermal runaway initiates, EV battery packs release a complex and highly hazardous mix of gases including hydrogen, carbon monoxide, carbon dioxide, hydrogen cyanide, methane, and small quantities of hydrogen fluoride. The initial white smoke plume can contain carbon monoxide concentrations exceeding 25,000 ppm far above the Immediately Dangerous to Life or Health (IDLH) threshold of 1,200 ppm.

Of increasing concern is the delayed onset of thermal runaway. Multiple recent incidents both in the U.S. and internationally have  documented batteries reigniting or entering thermal runaway hours after apparent extinguishment. In the past six months alone, several firefighters have experienced major toxic exposures during post-incident overhaul or while relocating damaged battery packs. In many of these cases, crews had removed their SCBA, unaware of the evolving off-gassing hazard, and now remain off duty due to ongoing health complications from toxic vapor inhalation.

This reinforces a critical operational imperative: SCBA must be worn throughout the entire event, from initial suppression to overhaul, and during any handling or relocation of compromised battery components. Toxic gas exposure is not limited to active fire conditions—thermal instability can persist long after visible flames are extinguished.

Despite their classification as Class B fires, lithium-ion battery incidents defy traditional suppression tactics. Dry chemical extinguishers offer limited effectiveness due to the sealed nature of battery housings and the flammable electrolyte. Water remains one of the most viable tools for suppression and cooling, but must be used at high flow rates and with situational awareness regarding explosive vapor production and thermal spread.

Tactical Response: From Diagnosis to Disablement

Effective incident response hinges on three core actions: Identify, Isolate, and Disable. Diagnostic use of water sprays and the deployment of fire blankets are emerging as viable containment strategies, though research is ongoing. Techniques such as angling the vehicle at 45 to 60 degrees may help responders visualize thermal failure zones beneath the chassis.

A minimum of two hose lines flowing at 150+ gallons per minute is typically required to contain propagation, especially in large-format battery systems. Tools like cell block containment and mineral oil immersion are under evaluation, but care must be taken to manage off-gassing in confined environments.

During rescue operations involving crashed EVs, responders must exercise caution when cutting low-voltage lines or battery loops. While disconnecting these systems is intended to mitigate electrical hazards, it may also inadvertently disable onboard cooling systems designed to regulate battery temperature. Disrupting those systems especially in a compromised or stressed batteries can accelerate thermal instability or contribute to delayed-onset thermal runaway.

Lessons Learned: EV Rescue Operations

• Always monitor the EV with a thermal imaging camera (TIC) throughout the duration of the rescue. If multiple TICs are available, deploy one on each side of the vehicle.

• Place a four-gas meter inside the passenger compartment and in the wheel well closest to the extrication point. This provides early indication of toxic gas release or the onset of thermal runaway.

• Coordinate extrication with suppression crews to ensure battery systems are not prematurely disabled.

• Avoid cutting power cables unless absolutely necessary, and ensure thermal monitoring is continuous throughout any disconnection.

Lessons from Research and Real-World Incidents

These operational insights are not theoretical. They are based on real-world incidents and cutting-edge studies conducted by Underwriters Laboratories (UL), which the author had the opportunity to attend. Data from UL has shaped a better understanding of battery behavior under stress, including how charge level, thermal propagation, and gas release vary across chemistries and designs.

Cabin Involvement and Design Concerns

Notably, many EV designs lack significant thermal barriers between battery packs and the passenger compartment. In crash scenarios or high-energy impacts, the cabin can flood like a bathtub, hastening battery involvement. Structural awareness and preplanning remain critical.

The Future: Sodium-Ion Batteries and New Horizons

Battery technology continues to evolve. Sodium-ion batteries touted as a cheaper, safer, and more environmentally sustainable alternative—are on the horizon. Their chemistry, while similar in function, presents a new set of unknowns for fire behavior and toxicity that responders will need to study closely.

Conclusion

The fire service must treat EV incidents not as rare anomalies but as complex chemical emergencies requiring disciplined, informed, and highly adaptable approaches. While the risk is statistically low, the potential impact is high and as history shows us, preparedness is not measured in odds but in outcomes.

About the Author

Ralph Suppa has over 20 years of experience in the fire service, including 15 years on a hazardous materials team. He currently serves as a Captain in a major metropolitan fire department. Ralph is a member of the International Association of Fire Chiefs (IAFC) Hazardous Materials Committee and actively contributes to national-level workgroups focused on Energy Storage Systems (ESS) and lithium-ion battery safety.