Financial Services Association, September 14 (Editor: Huang Junzhi) Last month, a Tesla Semi truck hit a tree and caught fire on a highway in California, USA, causing the I-80 Interstate to be closed for nearly 16 hours.

The US National Transportation Safety Board (NTSB) said in a preliminary report on Friday that it took 0.05 million gallons (about 0.19 million liters) of water to put out the fire at the time. In addition, the staff also used airplanes to drop flame retardants in “nearby areas.”

The accident occurred at 3:13 a.m. on the I80 highway east of Sacramento on August 19. While driving in a corner, the Tesla Semi truck deviated from the road, hit a traffic sign, and finally hit a tree. The driver was not injured, but he was taken to hospital as a precautionary measure.

At the time, the car's 900-kilowatt-hour battery caught fire, reaching a temperature of 1,000 degrees Fahrenheit (equivalent to 537 degrees Celsius), while emitting toxic smoke. Firefighters kept watering 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 motorway was not reopened until 7:20 p.m. (more than 16 hours after the accident).

The accident is currently being investigated by the US National Transportation Safety Board. The NTSB said the California Fire Department worked hard to put out the fire, cool the car's large battery to prevent it from burning again, and prevent the fire from spreading beyond the accident site.

Furthermore, the NTSB report confirmed that Tesla's driver assistance system (known as Autopilot and Full Self-Driving in the US) did not “operate” when the Semi collision and fire occurred.

Tesla often uses this commercial truck to transport newly produced electric vehicle batteries from Gigafactory to an automobile manufacturing plant in Fremont, California. In this accident, it did not pull the trailer, so it appears that the semitrailer's own battery was burning.

The accident sparked many discussions within and outside the government due to the prolonged closure of the road, the fire was dangerous and hot, and toxic smoke. Also, this isn't the first time Tesla's large battery has caught fire in California. In 2022, the company's megawatt energy storage battery caught fire at a local utility company, causing part of the highway to shut down.

Is an electric car fire that hard to put out?

According to information, once electric vehicles, including Tesla, catch fire, since lithium batteries will continue to burn until all energy is exhausted, it is more difficult to put out than a normal fire.

Since lithium-ion batteries used in electric vehicles need to store as much energy as possible in as little space as possible, when energy demand is high, they generate a large amount of heat. The principle is the same as when a cell phone or laptop battery heats up when used for a long time. Precisely because the allowable temperature range for safe operation of lithium batteries is narrow, most modern electronic products have many protective measures to prevent the battery from overheating.

For example, almost all smart phones shut down directly when they overheat. Electric vehicles in motion also have complex cooling systems and multiple fault protection devices. If everything works according to plan, the battery should not overheat to a dangerous extent. However, car accidents and breakdowns are inevitable. If road debris or a car accident damages the battery of an electric vehicle, a fire may occur.

Experts pointed out that the reason why lithium batteries catch fire so seriously is that they create a feedback cycle called “thermal runaway” (thermal runaway): once the battery overheats, the electrolytes in the battery ignite, which in turn generates more heat to ignite more electrolytes.

According to Tesla Model S's emergency response guidelines, if the battery catches fire, is exposed to high temperatures, or produces high heat or gas, a large amount of water must be used to cool the battery. Approximately 3,000 gallons (0.01 million1,356 liters) of water may be added directly to the battery to completely extinguish or cool the battery fire, and it will take 24 hours to extinguish.