UL Research Institutes’ Fire Safety Research Institute burned 18 vehicles under full-scale laboratory conditions and concluded that water remains the appropriate tool for controlling most electric vehicle fires. The findings appear in a new report, “Full-Scale Electric Vehicle Fire Experiments and Recommendations for Fire Incident Response,” released this week by the nonprofit research organization. Nine of the vehicles were free burns conducted without any suppression, establishing a baseline comparison between EVs and internal combustion engine vehicles. The remaining nine EVs were burned to evaluate suppression tactics, including water alone, EV fire blankets, and water with an added suppression agent.
Highlights
- 18 full-scale vehicle burns — nine free burns for baseline fire behavior, nine suppression experiments
- Six-minute delay before suppression began, replicating standard fire response time in North America
- No tested technique halted thermal runaway once it started, and an added agent performed no better than water
- Metals and particulate fluoride were measured in smoke, suppression runoff water, and firefighter turnout gear
How the Experiments Were Set Up
Researchers fully charged every EV before testing and initiated the battery fires with a propane burner. Fires were allowed to grow for six minutes before suppression began. According to the institute, that interval replicates standard fire response time in North America.
The free-burn phase measured burning characteristics without intervention. The suppression phase then applied tactics the fire service already carries.
EV and Gas Vehicle Fires Behaved Similarly
Data from the free-burn experiments showed that EV and ICEV fires were similar in fire growth rate, peak fire size, and fire duration. On average, EVs released more total energy, which researchers attributed to greater vehicle mass rather than to the battery itself.
“Lithium-ion battery-powered devices and EVs are already changing how we move, communicate, and enjoy our leisure time,” said Adam Barowy, principal research engineer for the Fire Safety Research Institute. “This research moves us closer to understanding how batteries change the fire environment and helps equip first responders to adequately address fires involving this new source of fuel. Our findings demonstrate that when it comes to EVs, first responders can effectively manage the hazard with familiar tools and tactics.”
What Worked Against a Burning Battery Pack?
For most EV fire incidents, the report recommends using water to suppress the cabin fire, limit exposures, and control flaming while the battery burns itself out. None of the tested techniques stopped thermal runaway once it had started. Direct battery extinguishment or cooling is precluded by vehicle construction and is not recommended.
| Tactic tested | Effect on flaming | Effect on thermal runaway |
|---|---|---|
| Water only | Suppresses cabin fire, limits exposures, controls flaming | Does not halt propagation |
| Water with added suppression agent | No more effective than water alone | Does not halt propagation |
| EV fire blanket | Effective for controlling vehicle flaming | Does not halt propagation; flammable gases accumulate |
Fire Blankets Carry a Deflagration Risk
Researchers observed that an explosion hazard can occur when flammable gases accumulate underneath a deployed EV fire blanket, or when those gases accumulate in a confined operating environment. If a blanket is used, it should not be repositioned. The report recommends against using fire blankets indoors or in confined spaces because of deflagration risk, and states that blankets should not be considered a replacement for water-based suppression.
Exposure Hazards Persist Through Overhaul
Full personal protective equipment and self-contained breathing apparatus are required throughout the incident, including overhaul, because of persistent toxic exposures and the risk of reignition. Much of the exposure hazard is driven by the passenger compartment fire. Even so, elevated concentrations of metals and particulate fluoride associated with the high-voltage battery fires were found in smoke and in suppression runoff water, and were found to contaminate firefighting turnout gear.
Training Materials and Pending Analysis
The full report covers size-up, exposure hazards, suppression, and overhaul. The team also developed an EV Fire Tactical Decision Aid, a step-by-step tool intended to analyze, develop, and improve fireground decision-making.
The findings and tactical considerations will inform an EV firefighting course in the Fire Safety Academy, scheduled for release later this year. Full air, surface, water, and PPE decontamination results are undergoing peer review or final analysis and will be published over the next year.
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