Safety Risks in Electric Vehicle Crashes
by Dave Brown
EV vehicles are everywhere now.
While technology can make up for the limitations of humans, we still need humans to make up for the limitations of technology. This means that even with all their technology, electric (EV) vehicles will still be involved in crashes.
You are the first responder at the scene of a serious vehicle crash and you suspect one of the damaged vehicles is a hybrid or full electric vehicle. There may be people still inside and bystanders milling about. What is the first thing you do?
Answer: Chock the wheels!
Unlike internal combustion engines, there are few signs that an electric vehicle is still “running.” If the battery pack is still energized and the ignition system is still on, one touch of an accelerator pedal may cause it to move without warning.
There are multiple risks inherent with vehicles equipped with high-voltage lithium-ion battery packs, as found on most hybrid and virtually all plug-in electric vehicles. We checked with a few experts to give a quick summary on suggestions for first responders on the scene of a serious wreck.
As always, the science is constantly evolving, and this advice may change as greater standardization increases across the electric vehicle industry.
Firstly, the high-voltage lithium-ion (Li-ion) batteries in hybrid, plug-in hybrid and battery electric vehicles do pose a danger to first responders in crashes where the vehicle may be damaged or in cases where an electric vehicle is disabled. Batteries are contained in a water resistant and fire resistant box. If that box becomes opened or compromised in a crash, there is risk of electrocution if the battery pack or any of the high-voltage cables or connectors have also been compromised. There is also a risk of thermal runaway if the battery pack catches fire, as lithium-ion battery cells do not need oxygen from the atmosphere to continue to burn.
Look for indications the vehicle may contain a high-voltage battery pack. Labels, brand names and even the lack of tail pipes might be an indication. Do not use the lack of sound as an indicator that the vehicle is off. Look instead for lights on the dash or instrument panel that may indicate the ignition is still on and the powertrain is still energized.
Note make and model of the vehicle if possible. Firefighters will need to identify the make, model and year of the vehicle if possible to help select an appropriate Emergency Response Guide as published by the vehicle manufacturers and the National Fire Protection Association.
Police officers and firefighters should always approach the vehicle at a 45-degree angle and expect that the vehicle may start moving without warning at any time until it is immobilized.
The first responders on the scene should find a means to chock the wheels to prevent it from moving before trying to extricate any passengers or disabling the high-voltage battery pack. Once the wheels are prevented from moving, access the passenger compartment if it can be done safely, set the parking brake, place the vehicle in Park and look for any “ready” indicator lights. If any lights are visible, push the ignition button to OFF. Once occupants are safely extracted, remove any key fobs and keep the fobs at least ten meters away. If occupants are conscious, tell them to not use any vehicle apps on their smartphones.
- Watch, Smell, Listen
Watch for lights on the dash or instrument panel that indicate the powertrain is still energized. Look for any damaged high-voltage components or cables. (High-voltage cables and connectors will be colored orange.) If any orange cables or connectors are visibly cut or broken, move away from the vehicle and keep bystanders away due to a possible electrocution hazard. Listen for the sounds of bubbling that may indicate the high-voltage battery pack case may be compromised. If you smell toxic chemicals, move everyone away and do not allow anyone to approach unless equipped with full PPE.
In a serious crash, the vehicle may need to be completely disabled, which means isolating the battery pack completely from the chassis. Depending on the design, the battery pack is usually disconnected by pushing the ignition OFF. On some makes, it is automatically disconnected in a crash where the air bags are deployed. Most hybrid and electric vehicles are also equipped with special firefighter cable cut points, where a low-voltage cable can be cut, thus disconnecting the high-voltage battery pack from the vehicle. These are often marked as “First Responder Cut Loop.”
Cutting or disconnecting the 12-volt battery also disconnects the high-voltage battery pack and isolates it from the chassis. Firefighters should not cut or attempt to disconnect any orange-colored cables or connectors. Orange is the universal designator across the industry for high-voltage components. Unless stated otherwise in the manufacturer’s Emergency Response Guide, the cut should be done at the negative cable of the 12-volt battery to prevent a possible spark if the positive cable is cut while the tool is making contact with a metal part of the vehicle.
If the vehicle is still mostly intact, hybrid and electric vehicles are designed to be safe even when fully submerged in water. Once the high- voltage system is isolated from the chassis, it will pose little danger of shock or energizing surrounding water.
Attempt to turn the ignition off but do not attempt any other measures while it is still submerged. Do not touch, cut or disconnect any orange high-voltage cables. If the ignition cannot be turned off, first responders should wait until the vehicle is recovered and full drained before attempting other methods of disabling it such as removing the 12-volt negative battery cable or cutting the First Responder Cut Loop.
Bubbling and hissing may be signs the high-voltage batteries are discharging. Toxic fumes or potentially explosive hydrogen gases may be emitted until the battery pack is fully discharged.
Once a previously submerged vehicle is recovered and stable, the wheels should first be chocked and the vehicle placed into Park. When safe, the vehicle should be moved to a secure and non-flammable area where it can be monitored for smoke or fire for a minimum of 12 hours.
Firefighters should extinguish hybrid and electric vehicle fires using proper vehicle firefighting practices in accordance with departmental training and standards. In serious crashes, there may be non-electric vehicles involved, with a variety of possible flammable fluids and materials. Firefighters should wear all Personal Protective Equipment and Self-Contained Breathing Apparatus as required for vehicle fires.
If the battery pack is not compromised, a standard attack using typical vehicle fire extinguishing agents is appropriate. If a vehicle is connected to a charging station, treat the scene as an energized electrical fire. Once the vehicle is immobilized, shut down the electrical current supplying the charging station before applying water to a fire. Do not attempt to cut or disconnect any charging cables and do not cut or disconnect any high-voltage cables on the vehicle even if the power has been cut to the charging station.
If battery pack becomes compromised and is involved in a fire, a defensive attack with copious amounts of water is often used. High-voltage battery pack cells continue to burn until expended, so the purpose of the water is not to extinguish a burning cell but an attempt to cool adjacent cells. Burning cells also emit quantities of toxic chemicals into the air.
A 2% to 3% solution of an Encapsulator Agent, such as the F-500 EA manufactured by Hazard Control Technologies, has shown promise in controlling and extinguishing lithium-ion battery fires plus reducing the toxicity of gases emitted during thermal runaway situations.
Without an appropriate Encapsulator Agent added to water hoses or contained in an F-500 extinguisher, allowing a cell to burn itself out and control the spread to adjacent cells is about the only course of action should a high-voltage pack catch fire.
The bottom line in most battery fires is that there are few solutions to stopping thermal runaway aside from letting it burn itself out. Without access to the inside of the battery box, attempting to cool adjacent cells from the outside will result in the need for vast quantities of water and will often have little effect on the outcome.
Emergency Response Guides for Alternative Fuel Vehicles
The National Fire Protection Association (NFPA) has compiled a free database of Emergency Response Guides for many makes and models of hybrid and electric vehicles. These can be found at: