300 seconds. After a high-speed collision, a battery might be compromised, and there should ideally be a five-minute warning time before a fire breaks out. This is a requirement of national standards. However, whether this crucial five minutes can actually save lives presents several challenges.
On the evening of March 29, a collision involving a Xiaomi SU7 on the G0321 expressway in Chizhou, Anhui, resulted in a fire that claimed three lives. On April 1, Xiaomi stated that the vehicle was in NOA intelligent assisted driving mode prior to the accident, and that the driver had taken control, reducing speed and steering the vehicle before the crash occurred. Later that evening, Xiaomi clarified that the vehicle’s fire was not due to spontaneous combustion, as some reports suggested, but was likely caused by severe damage to the vehicle’s systems after hitting a concrete barrier.
The media has shown images of the burning vehicle, but the official investigation into the cause of the fire has yet to reach a definitive conclusion. This raises questions about whether electric vehicles are more prone to catching fire and whether there is any chance of escape once a fire ignites. With every other car sold in China now being a new energy vehicle, addressing these concerns has become increasingly urgent.
On February 28, the “Defect Analysis Method for Electric Vehicle Fires” was officially published and is now in the full implementation stage. This standard aims to standardize the investigation of fire incidents and defect analysis in electric vehicles. Existing national standards regarding battery thermal runaway predominantly rely on static testing and do not adequately cover high-speed collision scenarios. The new standard proposes using real accident data to refine analysis methods, thereby supporting recall management and safety regulation.
Current standards require that in the event of thermal runaway, the power battery must issue an alarm signal within five minutes before the passenger compartment becomes dangerous. The latest version of the “Safety Requirements for Power Batteries Used in Electric Vehicles” includes stricter standards, mandating that batteries do not ignite or explode after thermal runaway.
Is a five-minute survival standard sufficient? An electric vehicle’s battery typically consists of over a hundred cells. If one cell experiences thermal runaway, it can trigger a domino effect, leading the entire battery pack to catch fire. According to existing regulations (GB/T 31498-2021), the battery pack must not explode or ignite within 30 minutes of an accident, nor should any electrolyte leak into the passenger compartment. However, specific testing conditions apply; for frontal impact tests, the minimum speed is set at 50 km/h, while side impact tests require a speed of 32 km/h.
Under the aforementioned standards, while the battery must signal an alarm within five minutes of thermal runaway, there is no explicit requirement stating that the battery must not ignite or explode. It’s important to note that during an accident, there is no countdown timer to indicate how much time remains before the five minutes are up. “Five minutes is a laboratory standard. Thermal propagation is influenced by many factors, and the conditions during high-speed collisions differ significantly from those in a lab,” a fire safety expert explained, emphasizing that survival cannot depend solely on this time frame.
The current “Safety Requirements” standards allow for the battery to catch fire or explode in the case of thermal runaway, but only if sufficient time is provided for vehicle occupants to evacuate. This five-minute evacuation period has been established through simulation and verification testing. Following the proposal of this requirement, it has also been widely adopted internationally, as explained by Liu Guibin, Secretary-General of the Electric Vehicle Sub-Technical Committee of the National Automotive Standardization Technical Committee.
The “national standard certification” only sets a minimum threshold; safety in the lab does not guarantee safety in all real-world situations. A researcher from a power battery company indicated that in an effort to produce cheaper cars, some manufacturers intentionally use lower-cost, thinner materials, aiming only to meet laboratory standards. This practice can compromise safety in complex situations, yet such risks are often invisible to the average consumer.
Additionally, some companies have noted that as automakers begin to produce their own vehicles, they are increasingly competing with their suppliers. For example, some automakers have transitioned from being clients to competitors, taking technical solutions from one supplier to another without incurring R&D costs, which leads to lower prices and reduced orders for the original supplier. Others send engineering teams to learn from suppliers under the guise of collaboration, only to return with proprietary information to develop in-house solutions. This approach lowers costs but risks losing crucial knowledge about the entire development and production chain, potentially affecting the final stability of products.
When faced with more extreme scenarios, such as high-speed collisions with sharp objects that can puncture the battery pack, the safety standards may no longer be applicable, according to battery researcher Zhu Yulong. Even more critical is whether drivers and passengers have the awareness and physical capability to escape after an accident, and whether external rescuers can promptly extract them to safety.
It is worth mentioning that a new version of the “Safety Requirements” is expected to be officially released in the first half of 2025, replacing the version that has been in effect since January 2021. The draft of the new requirements specifies that batteries experiencing thermal runaway should not ignite or explode, and that an alarm must be issued no later than five minutes after thermal runaway is triggered, with no visible smoke entering the passenger compartment within five minutes of the alarm.
Are electric vehicles more likely to catch fire? The China Fire Department’s WeChat account disclosed over ten incidents of new energy vehicle fires in 2024. A report by the China Securities Journal summarized that in 2024, 2.32 million vehicles were recalled due to “fire risk,” with 380,700 being new energy vehicles, of which 283,000 were related to battery issues.
The electrolyte in batteries is highly volatile and flammable. If a battery is damaged, the electrolyte can leak and ignite upon exposure to high temperatures or sparks; collisions may also lead to short circuits, releasing large amounts of heat in a short time. Excessive temperature can result in thermal runaway and fire. During a collision, the battery pack may be compressed or pierced, causing a rupture of the cell membranes and a direct short circuit. High-voltage systems in electric vehicles (usually between 300V and 800V) can create arcs or localized high temperatures if damaged in a crash, potentially igniting surrounding materials.
Moreover, investigations into several publicized instances of electric vehicle fires after collisions have shown that some battery packs remain largely intact despite severe fire damage. Some automakers have analyzed accidents and speculated that fires were ignited by high-temperature components or sparks from short circuits in the front compartment.
Is there a higher likelihood of electric vehicles catching fire? In March 2024, Ouyang Minggao, an academician from the Chinese Academy of Sciences and a professor at Tsinghua University, stated that the self-ignition rate of new energy vehicles is lower than that of conventional fuel vehicles. He cited data from relevant national agencies, concluding that the fire rate for new energy vehicles in the first quarter of 2023 was lower when adjusted for the number of vehicles in use.
Causes of battery fires can be categorized into external and internal factors. External factors include overcharging, excessive charging power, and significant impact collisions. Internal factors arise from unstable production quality of power batteries, leading to internal short circuits. If a single cell ignites and is not controlled, thermal propagation can cause the entire battery pack to catch fire. This conclusion has sparked controversy, as factors such as vehicle volume, usage conditions, and fire cause have not been considered. For instance, the data refers to self-ignition incidents rather than fire probabilities due to collisions.
Nonetheless, industry experts believe that the safety of electric vehicles is gradually improving. Sun Fengchun, an academician of the Chinese Academy of Engineering, revealed in 2020 that the fire probability for new energy vehicles in China was 0.049% in 2019, decreasing to 0.026% in 2020, while the fire accident rate for traditional fuel vehicles ranged from 0.1% to 0.2%.
This improvement stems from two main factors. Firstly, power battery manufacturers have implemented a range of technical upgrades, while the industry has undergone significant consolidation, with smaller companies exiting the market and leading to higher market concentration. Secondly, automakers are intentionally enhancing their safety measures by adopting newer materials and manufacturing technologies, such as integrating die-casting technology to encapsulate battery packs in the vehicle’s core space, thus avoiding risks of thermal runaway from collisions or scrapes.
Liu Guibin reported that as of February 2024, 78% of the 36 automotive and battery companies surveyed have the technical capability to prevent battery ignition and explosion, meaning that even if a cell experiences thermal runaway, it would not lead to a fire or explosion in the battery pack due to thermal propagation.
How can one respond to a fire in an electric vehicle? The rescue of electric vehicles after a fire has long posed challenges to all parties involved. “For electric vehicles of the same size, the temperature during a fire is higher, and lithium batteries are more difficult to extinguish,” a rescue system expert explained. Dry powder extinguishers are recommended for initial suppression; if necessary, water may be used to cool the battery pack and prevent reignition. However, fires in electric vehicles have a chance of reigniting and releasing toxic gases, and residual voltage can complicate the situation. The best approach is to use specialized firefighting equipment, though this comes with higher costs and operational requirements, primarily utilized in high-risk or safety-critical environments.
“Fires in new energy vehicles do not mean there is no chance of survival,” the firefighting expert added. “Using a dry powder extinguisher early can suppress the initial smoldering of lithium batteries, buying valuable time for escape and subsequent rescue.” At a domestic airport, it was observed that all battery-operated vehicles, whether shuttle buses or engineering vehicles, prominently display the type of battery used and the required extinguishing equipment on their bodies.
This article aims to address the safety challenges currently faced by the automotive industry, without delving into specific incidents, as investigations are subject to official conclusions.
