The Challenge
In recent years, the growing global adoption of electric vehicles (EVs) have led to an increase in EV fires. EV fires often result in greater damage than fires involving Internal Combustion engines, contributing to the spread of "EV-phobia".
Growth of EV Technology and EV Fires
EV sales have increased for the past 8 years, and is expected to continue.
Alongside the increase in EV supply, the number of EV fire cases has also risen. In Korea, 24 cases were reported in 2021, 43 cases in 2022, and 72 cases in 2023, according to the National Fire Department.
Recently, an EV fire occurred in an underground parking lot in Incheon, South Korea. One of the deadliest ever recorded, it resulted in 140 nearby cars being damaged.
Difficulty in extinguishing EV fires
Can largely be explained by two factors.
Thermal Runaway & Battery's Structure
Thermal Runaway
is a rapid cycle of exothermic reactions in lithium-ion batteries.
A thermal runaway is triggered when the vaporization of liquid electrolytes increases the pressure within the battery cell and damages the structure by breaking the separator between the anode and the cathode. Vaporization of liquid electrolytes often happens due to mechanical shock, overcharging, temperature rise, or aging.
Vaporization of electrolytes, caused due to heating and electric imbalance, forms flammable gases. Gas formation increases pressure within the battery pack, potentially creating openings for oxygen to enter and cause explosions.
Some of the vaporized gases such as Hydrogen fluoride are toxic, endangering those near the fire, and attempting to extinguish it.
The graph above illustrates the sharp temperature increase when the separator fails, initiating the thermal runaway.
Battery Structure
Typically located at the bottom of the vehicle, a battery pack of an electric vehicle consists of modules containing individual cells.
Tightly packed battery cells enable heat to spread, causing a chain reaction of thermal runaways to adjacent cells. This means that fuel is continuously provided until all cells burn down.
Current EV fire extinguishment methods are developed for use after the thermal runaway is initiated.
Currently Existing EV Fire Extinguishment Methods
All of the four methods can prevent the fire from spreading. However, if firefighters arrive after the fire is initiated, they cannot end the thermal runaway.