Last month, a Tesla Semi truck crashed into a tree and caught fire on a highway in California, causing the I-80 interstate highway to be closed for nearly 16 hours.
The National Transportation Safety Board (NTSB) stated in a preliminary report on Friday that it took 50000 gallons (approximately 190000 liters) of water to extinguish the fire. In addition, the staff also used airplanes to drop flame retardants in the "nearby area".
This accident occurred at 3:13 am on the I80 highway east of Sacramento on August 19th. The Tesla Semi truck deviated from the road while driving on a bend, collided with traffic markings, and finally hit a tree. The driver was not injured, but as a precautionary measure, he was taken to the hospital.
At that time, the 900 kilowatt hour battery of the car caught fire, reaching a temperature of 1000 degrees Fahrenheit (equivalent to 537 degrees Celsius) and emitting toxic smoke. Firefighters kept pouring water on it to cool it down, trying to cool its battery pack to a controllable target temperature of around 100 degrees Fahrenheit while waiting for the battery to burn out. The highway did not reopen until 7:20 pm (more than 16 hours after the accident occurred).
This accident is currently under investigation by the National Transportation Safety Board of the United States. The NTSB stated that the California Fire Department is working hard to extinguish the fire, cooling the large batteries of the vehicles to prevent them from reigniting and to prevent the fire from spreading beyond the accident site.
In addition, the NTSB report confirms that Tesla's driving assistance systems (known as Autopilot and Full Self Driving in the United States) did not "operate" during Semi collisions and fires.
Tesla often uses this commercial truck to transport newly produced electric vehicle batteries from Gigafactory to its car manufacturing plant in Fremont, California. In this accident, it did not tow a trailer, so it seems that the semi-trailer's own battery is burning.
Given the prolonged road closures, dangerous and hot fires, and toxic smoke, this accident has sparked many discussions within and outside the government. Moreover, this is not the first time Tesla's large batteries have caught fire in California. In 2022, the company's megawatt level energy storage battery caught fire at a local utility company, resulting in the closure of some highways.
Is it so difficult to extinguish an electric vehicle fire?
It is understood that once electric vehicles, including Tesla, catch fire, the lithium battery will continue to burn until all energy is exhausted, making it more difficult to extinguish than regular fires.
Due to the use of lithium-ion batteries in electric vehicles, it is necessary to store as much energy as possible in the smallest possible space. Therefore, when the energy demand is high, a large amount of heat energy will be generated, similar to the principle that mobile phone or laptop batteries will become hot after long-term use. And precisely because the allowable temperature range for safe operation of lithium batteries is narrow, most modern electronic products have many protective measures to prevent battery overheating.
For example, almost all smartphones will shut down directly when overheated. Electric vehicles in motion also have complex cooling systems and multiple fault protection devices. If everything operates according to plan, the battery should not overheat to a dangerous level. However, car accidents and malfunctions are inevitable. If debris on the road or a car accident damages the battery of an electric vehicle, a fire may occur.
Experts point out that the reason why lithium batteries catch fire so severely is mainly due to the feedback loop called "thermal runaway": once the battery overheats, the electrolyte in the battery will catch fire, generating more heat energy to ignite more electrolytes.
According to Tesla Model S's emergency response guidelines, if the battery catches fire, is exposed to high temperatures, or generates high heat or gas, a large amount of water must be used to cool the battery. It may take about 3000 gallons (11356 liters) of water to be directly added to the battery to completely extinguish or cool the battery fire, and it will take 24 hours to extinguish.