Electric vehicles will be a common sight in a few years...
Electric vehicles (EVs) have been around since the mid-19th century. The past decades, technological advancements, government incentives, and increased consumer awareness have led to a rapid expansion of the e-mobility market. With over two million sales reported in 2019, EVs accounted for 2.5 percent of all new car sales. Despite the short-term negative impact of COVID-19 on total car sales, EVs are expected to secure between 20 and 30 percent of the total market share by 2030.
Plugged-in EVs by the road will be a common sight in a few years. Charging points will take up more parking spots in car parks each year. Bus depots will be redesigned to accommodate the rising number of electric buses.
As the presence of EVs increases, many questions arise with respect to fire safety. In response, Elon Musk tweeted:
‘Tesla, like most electric cars, are over 500% less likely to catch fire than combustion engine cars, which carry massive amounts of highly flammable fuels.’
However, since EVs have not been around as long and they only present a small fraction of all cars on roads now, it's not possible to fairly compare the numbers of gasoline fires to electric car battery fires. When a battery fire does occur, however, it is known to be very challenging from a fire extinguishing perspective. Are we prepared for the new fire risks posed by the tens of millions new EVs coming in the next few years?
New fire risks
The lithium-ion battery packs, used to power EVs, pose new fire risks. The main risk is when temperature rise occurs in the cells of a battery pack. Common causes include internal failure causing self-ignition, heavy collision traffic accidents, arson, and nearby fire.
If heated to a critical temperature, chemical reactions occur that heat the battery cells at rapid rate. The heat causes the chemical reaction to go even faster, in a process that’s called thermal runaway. Thermal runaway in a single battery cell can then cause a chain reaction by heating adjacent cells. Large amounts of flammable gases are released in the process. Moreover, pressure is built up by the release of gases in the sealed packs, possibly leading to jet fires and gas cloud explosions. In addition to flammable gases, large volumes of toxic gases are set free such as carbon monoxide and hydrogen cyanide.
New intervention strategies
Extinguishing a battery fire presents an additional challange. Flammable gases are released as long as the battery pack contains energy. Even after extinguishing the fire, the risk of re-ignition remains high for hours, even days. Research by NFPA showed the re-ignition of a battery fire 22 hours after it was believed to be extinguished (determined by thermal imagining).
Moreover, the battery packs are tightly sealed to protect them from outside influences and moisture, making it difficult to reach with water. As a result, large amounts of fire water are required. One study found that 10 000 litres of water were needed to extinguish the fire in a car-sized battery. This implies that large amounts of contaminated water are created that can heavily impact the environment.
Many manufacturers propose a controlled burn out. However, this is not always feasible as it can have an impact on the environment, people’s health, and even the wider economy. Using a water tank may be an alternative to keep the fire under control. In any case, new intervention strategies are necessary as well as a good infrastructure to facilitate these strategies.
New measures for the prevention and control of fire
To decrease the risk of thermal runaway in car batteries, preventive measures are needed in EVs. Measures are also needed in the spaces where EVs are present such as car parks, warehouses, tunnels, and roads.
In EVs, important preventive measures include:
- Compartmentation of the battery packs inside the battery
- Compartmentation of the entire battery from the rest of the vehicle
- Providing a battery and thermal management system to monitor the temperature and voltage inside the battery
- Providing a mechanical crash structure to protect the battery from impact
- Providing short circuit protection and a disconnection system in case of incident
Possible infrastructural measures include:
- Increased (local) fire rating of constructions housing EVs because of their atypical fire development
- Strategic positioning of charging spots to prevent collision and to allow for safe evacuation
- Ventilation and smoke- and heat extraction systems to allow for safe intervention
- Precautions to prevent contaminated fire water from flowing to the local drainage
- Increased accessibility for fire brigades in car parks
- Infrastructural measures that allow to isolate a burning EV outside or to quench it in a water tank
- Interlock with fire detection system to shut-off the power supply upon fire detection
- Sprinkler protection to prevent fire spread from one vehicle to another
Fire safe into a greener future
There is no doubt that the growing amount of EVs will have a positive impact on the wellbeing of our planet. However, the new fire risks of EVs compared to conventional vehicles require thorough evaluation in order to define effective fire safety strategies for car parks, bus depots, loading stations, etc. The main objective remains fire prevention, but strategies to prevent escalation must also be in place to make sure we can cruise fire safe into a greener future!
Fire Risk Engineer at FPC Risk
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