Journal Article Quantifies the Fire Hazards of Lithium-Ion Battery Fires Caused by Thermal Runaway in E-scooters
The peer-reviewed journal article “Quantifying the Fire Hazard from Li-Ion Battery Fires Caused by Thermal Runaway in E-scooters” has been published in Fire Technology. Key findings from this study support the Examining the Fire Safety Hazards of Lithium-Ion Battery Powered e-Mobility Devices in Homes research project led by the Fire Safety Research Institute (FSRI), part of UL Research Institutes, in partnership with the Fire Department of the City of New York. The article was co-authored by FSRI principal research engineer Charles Fleischmann, FSRI research director Craig Weinschenk, FSRI senior research director Daniel Madrzykowski, UL Solutions fire research manager Alexandra Schraiber, and UL Solutions lead engineer Benjamin Gaudet.
Understanding Fire Hazard from Thermal Runaway in Lithium-Ion Batteries
Fatal fires involving lithium-ion batteries have drawn increased attention in recent years, including in New York City where the use of e-mobility devices is common. In 2023, there were 268 reported fires, 150 reported injuries, and 18 fatalities involving such devices in the city. Fire incidents like these are typically the result of the battery suffering thermal runaway. The most common causes of thermal runaway in lithium-ion batteries include physical damage, overheating, or failure of the battery management system which lead to overcharging or over-discharging.
Lithium-ion battery cells function like other rechargeable cells as they are composed of a cathode, an anode, a separator, and an electrolyte blend. They are more popular than other rechargeable batteries due to their higher energy density at a relatively lower cost. However, the materials in a lithium-ion battery’s separator and electrolyte blend are combustible. When these batteries experience thermal runaway, results can include overheating, flaming, and sometimes an explosion.
Quantifying the Hazards of a Lithium-Ion Battery Powered E-scooter Fire in a Residential Building
This journal article summarizes a study conducted by FSRI in partnership with researchers from UL Solutions and FDNY. This study consisted of three series of experiments to characterize thermal runaway of the lithium-ion battery pack of a seated e-scooter:
- The first experiment series involved both overheating and overcharging a standalone battery pack to measure heat release rate and estimate the contribution of the battery pack in a full e-mobility device scenario.
- The second experiment series involved e-scooter freeburn tests by overcharging the lithium-ion battery to measure heat release rate in a laboratory setting.
- The final experiment series examined the heat release rate and environmental impact of thermal runaway for an overcharge lithium-ion battery pack while the e-scooter was positioned in both a closed bedroom and living room of a purpose-built single-family residential structure.
The standalone battery pack experiments examined two known mechanisms of thermal runaway: external overheating and overcharging of the battery cells. These experiments were conducted in a laboratory set below an exhaust hood equipped to measure oxygen, carbon dioxide, and carbon monoxide emissions as well as the mass flow rate. During the overheating scenario tests, thermal runaway was identified approximately 45 minutes after the start of heat application. There was complete propagation of thermal runaway of the battery pack with a peak estimated vertical flame extension of 3–4 feet over a two-minute duration. During the overcharging scenario tests, thermal runaway was identified approximately 65 minutes after the start of overcharge. Complete propagation of thermal runaway was observed for approximately one minute resulting in flaming combustion 6–7 feet above the battery pack. Based on the results of these experiments, researchers determined that the next two phases would utilize intentional overcharging as this scenario represented the more severe of the two failure mechanisms.
During the intentional overcharge e-scooter freeburn experiments, the battery was supplied with 157 Volts directly to the charging cable of the battery pack with the current limited to 10 Amps. The lithium-ion battery transitioned into thermal runaway approximately 1 hour and 50 minutes after the start of overcharge. A large quantity of visible smoke from below the e-scooter seat was the first outward sign of thermal runaway. Ignition occurred thirteen seconds after first visible smoke and included a large fireball engulfing the e-scooter followed immediately by a jet flame approximately 6–7 feet above the battery compartment.
To quantify the fire hazards in a residential building, the final series of experiments were conducted in a purpose-built single-story residential structure with tests involving two scenarios. The first test involved the intentional overcharge of an e-scooter in a closed bedroom, and the second test involved the intentional overcharge of an e-scooter in a living room adjacent to a closed front door.
During the closed bedroom experiment, the time from first signs of smoke from thermal runaway until the battery gas explosion and bedroom windows failed was approximately 20 seconds and flashover occurred within 30 seconds of visible smoke. Flames were visible out the failed window within 40 seconds of visible smoke.
For the living room experiment, the scooter was in a larger volume due the open floor plan and an open bedroom door. This larger volume diluted gas species, dispersed expanding gases from the explosion, and reduced pressure rise. However, within 10 seconds of sustained visible battery gas, the gas ignited resulting in a pressure increase that caused failure of window frames and individual window components in the living room, kitchen and open bedroom.
The Impact of E-scooter Thermal Runaway Fires in a Residential Structure
This study provided two key takeaways on the impact these fire incidents may pose in a residential structure:
- A lithium-ion battery in a seated e-scooter undergoing thermal runaway can take the room of origin to flashover in a number of seconds.
- The time from visible release of battery gas to explosion of the gases can be only a few seconds, making the room of origin immediately fatal to the occupants.
“The lithium-ion battery in a seated e-scooter undergoing thermal runaway may only provide a few seconds from visible smoke to an explosion. In this situation, occupants may not be able to react fast enough to escape the fire.”
—Charles Fleischmann, principal research engineer, FSRI
The fire hazards posed by lithium-ion battery powered e-mobility devices require further investigation, including potential thermal runaway prevention during similar incidents. A future journal article will evaluate the impact of residential automatic fire sprinklers on e-scooter fires.
About Fire Technology
Fire Technology publishes original contributions, both theoretical and empirical, that contribute to the solution of problems in fire safety science and engineering. It is the leading journal in the field, publishing applied research dealing with the full range of actual and potential fire hazards facing humans and the environment. It covers the entire domain of fire safety science and engineering problems relevant in industrial, operational, cultural, and environmental applications, including modeling, testing, detection, suppression, human behavior, wildfires, structures, and risk analysis.
