Understanding vehicle construction is an important aspect of responding to incidents involving electric vehicles (EVs).
In prior years, most automotive manufactures were offering hybrid/EV versions of existing combustion engine vehicles. They would design a high-voltage battery to fit in whatever space was available.
The industry is now designing the vehicle around the high-voltage battery. This optimizes the battery and has pushed most manufacturers to design a battery as the entire underside of the vehicle, which is often referred to as the “Universal Skateboard Design.” The battery structure is intended to be a structural member of the vehicle and required to dissipate crash energy during impacts with minimal penetration into the box itself. This also changes the weight distribution of a vehicle, as these batteries can weigh as much as, if not more than, 1,500 pounds.
Battery structure – the “box”
The battery structure is a watertight, fire-resistant box that can be made out of steel, aluminum or composite materials. Inside the box are smaller battery modules, containing many individual battery cells. The box also contains high-voltage components, wiring and cooling systems.
The box is fire-resistant for two reasons:
- If there is a thermal runaway event inside of the box, manufacturers want the fire to stay in the box to protect the vehicle’s occupants.
- If there is a fire outside of the vehicle, the goal is to keep the battery cells from going into a thermal runaway event.
Fire attack options
When responding to an EV fire, crews will need to know what exactly is on fire.
If the vehicle is on fire and the high-voltage battery is not involved, it is a standard vehicle fire that should extinguish with a few hundred gallons of water. If the high-voltage battery is on fire, things become much more complicated.
There are many stories about fire departments being on scene for 6 to 8 hours using upwards of 40,000 gallons of water. The issue is that firefighters aren’t really equipped to put out the fire. For example, when an 18650 battery cell (about the size of an AA battery) fails, it releases approximately 6 liters of gas at 1,200 degrees F in tenths of a second. The failure is an exothermic chemical reaction that does not require oxygen from the atmosphere. The energy released from that individual cell is transferred to the neighboring cells, which causes them to fail. This reaction continues until one of two things happens. Either there are no more battery cells, or fire crews can cool the surrounding cells enough that they don’t fail.
So, in order to stop a thermal runaway event, firefighters have the impossible task of trying to cool battery cells inside a watertight, flameproof box.
Note: DO NOT pry/cut/remove any part of the battery case to gain access to the fire!
Assuming no exposures are present, the best solution is to allow the high-voltage battery to burn itself out. While this strategy is not ideal, it should only take an hour for the battery to burn itself out. The alternative will be to continually dump water on the vehicle for 6 to 8 hours.
EV extrication
Extrication is an area that is overlooked when considering EV response.
Depending on the severity of the crash, EVs can provide unique challenges to firefighters. The vehicle construction and weight distribution could change standard strategies for stabilization. Typically, the outer edges of the battery structure mate to, or are considered the rocker panel. If undamaged, this is typically a safe location for rescue struts or cribbing. Further, when faced with a vehicle on its side, DO NOT use any holes that may have been caused by the crash, or pierce, puncture, or create any purchase point in the battery case for rescue struts. This could cause an electrocution and/or fire hazard.
Firefighters should lift an EV at the rocker panel. If the high-voltage battery is intact, an airbag lift could be accessible on the bottom of the vehicle. Auto manufacturers have specific design criteria for customers that misuse jacks; however, be certain to complete any lifts over a large surface area.
While extricating a patient, it will be extremely important to have a hoseline charged and staffed with a firefighter in full PPE ready to fight fire, as there is a significant risk of a delayed fire.
While firefighters are performing the extrication, everyone involved needs to be aware of the battery. If it’s smoking, popping, sputtering, or if firefighters have eye, nose, throat irritation, there could be harmful/flammable gasses being released. Crews should pull back to don full SCBA.
Crews should also consider the health/safety of the patient(s). Using a vent fan may be appropriate to blow fresh air into the passenger compartment of the vehicle. Also, firefighters should remove trim to verify what they are cutting before the cut is made. DO NOT cut any high-voltage cabling (bright orange). Manufacturers are often routing high voltage cables in the center of the vehicle away from our typical cut points.
Notes for the tow operator
After the incident, notify your tow operator that they will be removing an EV. All hybrid and electric vehicles should be transported on a flatbed. If there’s damage, or suspected damage, there is a risk of a delayed fire. Ask the tow operator to store the vehicle outside at least 50 feet from a structure. Also request the tow operator contact the dealer/manufacturer. They may have different methods of rendering the vehicle safe.
Get ready – and train
Electric vehicles are increasing in popularity and will have a much larger presence on the roads within the next five years. While EVs will present new and unique challenges to fire departments, there are simple steps to follow to ensure safe and effective operations. Training is key to all of this.
This article, originally published on March 01, 2022, has been updated.
