NIOSH: Firefighter Injuries Linked to Thermal Runaway Event
NIOSH’s Fire Fighter Fatality Investigation and Prevention Program (FFFIPP) has published a report on firefighter injuries associated with a lithium-ion battery thermal runaway event in California last year (PDF). The report describes the incident investigation, medical findings, and industrial hygiene assessment. It also discusses risks associated with lithium-ion batteries and offers recommendations to reduce these risks for firefighters responding to electric vehicle and lithium-ion battery incidents.
On the night of April 11, 2025, firefighters at a city fire department in California responded to a collision between an electric car and a tree, the report explains. The vehicle’s lithium-ion battery pack had been damaged, and battery cells were scattered across the road. Damaged lithium-ion batteries can undergo thermal runaway, a reaction that may produce flammable gases, toxic fumes, fire, or explosion, so the incident was upgraded to a moderate HAZMAT response. After the HAZMAT team arrived, firefighters extracted the vehicle’s driver and began cleanup efforts, removing battery cells from the road and placing them in large water-filled drums. When a tow truck arrived to collect the vehicle, some firefighters doffed their personal protective equipment, as they assumed the incident was over. The portion of the battery that remained in the damaged car then entered thermal runaway. It emitted a dense, low-lying plume of white smoke that engulfed five firefighters not wearing PPE.
The firefighters reported a metallic or acrid taste. One immediately began vomiting and was transported to an emergency department. Four others received medical treatment that night or the next morning for symptoms including throat pain and coughing. The firefighter who experienced nausea quickly recovered and returned to work, but the others’ symptoms worsened over the following days, weeks, and months. One developed blistering on the roof of his mouth, which took weeks to heal. All four developed cardiovascular and respiratory symptoms, such as shortness of breath, elevated resting heart rate, and hypertension, followed by behavioral symptoms, such as brain fog and mood changes. When NIOSH began investigating the incident in spring 2026, these four firefighters had still not returned to work due to symptoms that prevented them from performing essential job functions.
Physicians who treated the four most severely affected firefighters attributed their symptoms to the smoke plume exposure. However, no environmental monitoring was conducted during the incident, making it uncertain what chemicals or metals were present. “Importantly, it is not clear from this exposure or from the available literature which component of the smoke plume is primarily or completely responsible for the [firefighters’] respiratory symptoms,” the report states. Prior research by NIOSH indicates the cause may have been hydrogen fluoride, particulate fluoride, nickel, lithium, cobalt, or some combination thereof.
The report issues seven recommendations for reducing risk to firefighters responding to similar incidents. First, fire departments should require firefighters responding to incidents involving damaged vehicles to use self-contained breathing apparatus (SCBA) within established hazard control zones. For incidents involving electric vehicles or lithium-ion batteries, SCBA should be used as long as thermal runaway or off-gassing remains possible. Second, fire departments should identify hazard control zones for electric vehicle and lithium-ion battery incidents using a risk assessment method that incorporates environmental and structural factors. Other recommendations cover training, symptom awareness, isolation of contaminated gear, standard operating procedures for handling damaged lithium-ion batteries, and physical examinations.
For a full discussion of the incident, medical findings, exposure modeling, and recommendations, see the FFFIPP report (PDF).