The blade battery of a certain company has been a bit troubled this year. It has been burning the car some time ago. I don’t know the specific reason; there are indeed some problems with its whole package integration, but based on the design of lithium iron phosphate cells, these problems have been eliminated. So prominent.

What is analyzed here is a fire accident last year. The fire was caused by the collision and damage to the bottom of the battery pack and the intrusion of water at the same time. It had nothing to do with the battery core itself (not spontaneous combustion).

Accident description

The vehicle was a taxi. Due to continuous heavy rains from October 7 to 8, 2021, the vehicle waded through water twice. After wading through water, it caused a vehicle failure alarm; then it went to the 4S shop for repairs on the 9th. A fire broke out during the process.

At the time of the incident, smoke first appeared at the bottom of the vehicle, close to the rear wheel. About 2 seconds later, fire first appeared at the right front wheel of the vehicle. After about 80 seconds, a jet-like combustion appeared at the right rear wheel of the vehicle. The fire was brought under control due to timely efforts to put out the fire.

PART.02

Accident analysis

From a comprehensive analysis, the cause of this accident is relatively easy to determine. First, the entire vehicle and battery pack were not completely burned, and traces of fire can be visually observed with the naked eye, which is equivalent to the scene being well preserved;

Second, it is supported by backend big data, which can connect the entire process of the incident.

Let’s focus on the physical level analysis first:

The first thing I discovered was that there was an obvious hole in the bottom guard plate of the battery pack (made of composite material, not metal). The diameter of the hole was about 15mm, about 230mm from the rear end of the battery pack, and about 200mm from the right side.

There are slight traces of burning and carbonization near the hole, which can be basically determined to be caused by the thermal runaway flames of the battery pack behind it, and the formation of the entire hole should be caused by the impact or puncture of the battery pack by the road.

Judging from the open flames that burned during the accident, this should be the place where the second flame erupted, so there were burn marks around the bottom guard.

When you open the battery pack, you can find that the front end, where the PDU is located, has its main aluminum bar blown out, indicating that the insulation at this location was destroyed first, and then an external short circuit occurred, and the large current caused the fuse there.