Tests Pave the Way for New Energy Vehicle Fire Safety Standards

Chongqing - "Bang—" a sharp cracking sound shattered the tranquility of the laboratory.

A fire simulation test for new energy vehicles was underway at China Automotive Engineering Research Institute Co Ltd in Chongqing on January 15. The battery cells of a new energy vehicle overheated and became uncontrollable after being stimulated, and thick black smoke quickly enveloped the car, followed by a loud explosion and flames shooting into the sky.

Not far away, Su Xiaojia and her team closely monitored every key data through a network of sensors inside and outside the vehicle: temperature, toxic gas concentration, heat radiation intensity... These data are critical for the safety of millions of car owners.

In recent years, fires in new energy vehicles have occurred from time to time, and consumers often struggle to determine whether a particular model meets fire safety standards. This is largely due to the lack of testing standards and methods.

Since 2023, Su and her team have taken on a task: developing evaluation procedures and standards for the fire safety of electric vehicles through scientific testing methods and evaluation models. This ensures the safety performance of new energy vehicles and provides critical references for both automakers and consumers.

Urgent need to decode the mystery of new energy vehicle fires

"There are still many vehicle models waiting for testing in our laboratory," said Su, who participated in the above tests.

The fire risk of fuel-powered vehicles is relatively clear, mainly caused by external factors such as collisions. However, the batteries in new energy vehicles, after experiencing even minor damage, may gradually accumulate irreversible damage, potentially leading to failure, She added.

 "Compared to fuel-powered vehicles, fires in new energy vehicles are like a puzzle, requiring our tests to consider more real-world scenarios."

Through a large volume of test data comparisons, Su and her team discovered that, for vehicles of the same size, the combustion temperature of electric vehicles can reach over 700°C, even 1000°C, far higher than the over 400°C temperature of fuel-powered vehicles. This presents a severe threat to both passengers inside the car and the surrounding environment.

In Su's view, the unpredictability and destructiveness of new energy vehicle fires have caused significant safety concerns among consumers and posed new challenges for fire rescue efforts. Therefore, it is crucial to conduct an in-depth analysis of the mechanisms and patterns of new energy vehicle fires and to establish a scientific and rigorous evaluation system.

Building a technical framework and establishing safety standards

On January 15, before the fire simulation test of complete vehicles was conducted at CAERI, Su and her team set up nearly 60 sensors inside and outside the vehicle.

Among these, gas sensors were placed in the front and rear of the passenger compartment, at the same height as the driver's seating position, to monitor toxic gas concentrations. Temperature sensors were installed on the seatbacks, floor, and steering wheel to monitor temperature changes in real-time. Heat flow density sensors were placed two meters and four meters outside the vehicle to assess the heat radiation intensity at different distances.

"In addition to quantifying the various impacts of a fire as much as possible, we also mapped out the most common scenarios in daily life," Su said. "For example, underground parking lots, outdoor parking lots, independent garages, multi-story parking buildings, as well as tunnel and charging station scenarios. We build test rigs and evaluation plans based on the characteristics of these scenarios for targeted research."

Over the past year, Su and her team have conducted multiple "fire-burning vehicle" tests, optimizing and upgrading testing plans based on model simulations to reveal the objective laws of system-level scale fire development.

Su and her team led collaborations with well-known domestic universities and software development companies to form an innovation joint venture for power battery simulation software. They are developing power battery simulation software with independent intellectual property rights to address the parameter transfer and solver issues in existing software related to the chemical reaction mechanisms across the entire chain, from battery components to the full vehicle system.

The development and design of different vehicle models vary significantly, posing challenges for the standardization of test results. To address this, Su and her team designed standardized target objects to obtain comparable data across different scenarios, providing reliable support for the development and calibration of simulation models.

From individual battery cells, battery packs, and thermal runaways at the vehicle level to thermal runaways in closed garages and multi-vehicle fire tests in multi-story garages, Su and her team have conducted a series of systematic studies. 

They have identified the evolution patterns of battery failure from minor damage to disaster, accumulated quantitative data and experimental experience on dangerous factors such as explosive splashes, flame temperature distribution, smoke toxicity, and combustible gas accumulation, and gradually formed a vehicle fire safety standard framework covering six dimensions, including safety technology. This framework scientifically scores the fire safety performance of new energy vehicles and provides crucial technical support for improving vehicle fire safety performance and enhancing fire rescue efforts.

Identifying hidden risks and driving industry optimization

Through research, Su and her team have not only summarized many characteristics and patterns of new energy vehicle fires but have also discovered several unexpected safety hazards.

"For example, some vehicle models use hidden or embedded door handles for aesthetic reasons. In an emergency, if the electronic system fails, this design can hinder escape and rescue," said Su.

Many models have high-voltage wires and other electrical wires with perforated wiring due to process limitations. If the sealing of these holes is poorly designed, it can affect the flow of smoke into the vehicle after thermal runaway. If toxic gases quickly enter the passenger compartment, occupants might miss the optimal escape opportunity. She further explained that these discoveries have effectively helped optimize and upgrade vehicle safety designs.

Currently, Su and her team are preparing to test used electric vehicles that have been in service for years to study how vehicle aging affects safety performance. This is of great significance for guiding the full lifecycle safety management of new energy vehicles.

"We also plan to conduct tests in more real-world scenarios, such as recreating different failure modes and collaborating with relevant departments to develop timely and effective firefighting and rescue solutions," said Su.

The team will also establish a more scientific and comprehensive evaluation system to ensure the comparability of test results between different vehicle models, thereby driving the advancement of safety technology across the entire industry, Su added.

(Bai Lin and Zhang Zhi, reporters from Chongqing Daily, contributed the Chinese version of this report.)