How did the fire at the South Korean battery factory happen? Last week, someone heard a "bang" and 35,000 lithium batteries exploded in less than a minute.

On the morning of June 24th local time, a fire broke out at the battery factory of Korean battery manufacturer ARICELL in Hwaseong City, Gyeonggi Province, South Korea.

Surveillance video revealed the horrific moment when the fire broke out at a South Korean battery factory on the morning of the 24th. From the initial smoke rising to the complete loss of control, the entire process took less than a minute.

10:30:03: The first explosion occurred, and white smoke appeared.

12 seconds after the first explosion: Two employees move items away from the explosion area to prevent the fire from spreading.

25 seconds after the first explosion: The second explosion follows.

28 seconds after the first explosion: The third explosion followed and the fire became more intense.

29 seconds after initial explosion: An employee uses a dry powder fire extinguisher but is unable to put out the flames.

31 seconds after the first explosion: The fourth explosion occurred again and the fire got further out of control.

37 seconds after the first explosion: Multiple batteries exploded one after another and the fire spread rapidly.

42 seconds after the first explosion: Thick smoke mixed with black and white completely obscured the view of the surveillance camera.

Then: 35,000 lithium batteries exploded.

As of June 25, the Gyeonggi Province Fire and Disaster Headquarters confirmed that the disaster had caused 23 deaths, including 17 Chinese citizens; 2 people were seriously injured and 6 people were slightly injured. The exact nationality and number of the victims have yet to be further verified.

According to the statement made by Kim Jin-young, chief of the disaster prevention department of the Korean Fire Agency at a briefing, the fire started on the second floor of Building 3 of the factory, where about 35,000 cylindrical lithium battery cells stored there caught fire explosively.

In an interview with Red Star News, Meng Xiangdong, a Ph.D. from the State Key Laboratory of Fire Science at the University of Science and Technology of China, analyzed: "The first time white smoke appeared, it was probably because a battery had thermal runaway. The smoke generated by the internal reaction of the battery was released through the battery safety valve. Then, due to the heat transferred by the thermal runaway battery, its adjacent battery also experienced thermal runaway, and the smoke was even greater." He explained that thermal runaway usually occurs under conditions of thermal, electrical and mechanical abuse, such as excessively high ambient temperature, overcharging or over-discharging, collision and extrusion, etc.

Meng Xiangdong said that at this time, chemical reactions occur between the materials inside the battery and release heat, while producing gases. These reactions will lead to new side reactions, forming a vicious cycle.

When the battery is in thermal runaway, the surface temperature rises very quickly, up to 1000 degrees Celsius. When the internal flammable gas reaches the pressure limit, the battery's "safety valve" will be opened. Subsequently, the flammable gas is released and catches fire and explodes when it encounters an ignition source or a high-temperature object.

The surveillance video released on June 25 showed rows of batteries densely placed in a white square casing, sparking discussion.

Why is this arrangement adopted? Meng Xiangdong explained: "This is to pursue higher energy density. The number of stacking, cylindrical lithium-ion batteries are integrated into battery modules by connecting them in series and parallel. So the white square we see is actually a complete module, which contains multiple small battery cells."

Meng Xiangdong also pointed out the potential risks of this design: "Once one of the batteries has thermal runaway, due to its dense arrangement, the thermal runaway battery will transfer heat to the surrounding batteries, causing the thermal runaway to propagate within the module, causing the fire to spread rapidly."

He further explained: "Lithium thionyl chloride batteries are disposable batteries, which are different from common rechargeable and rechargeable cyclic batteries. Although they have high energy density, low self-discharge rate and excellent performance, once an accident occurs, their danger exceeds that of the rechargeable and rechargeable cyclic batteries we usually use in a half-charged state."

Luo Yongyun, a researcher at the Korea National Fire Research Institute, analyzed the condition of lithium batteries at the fire scene. He pointed out: "Considering the fire risk of rechargeable and discharge cycle batteries, the Korean industry standard is to charge the batteries to about 50% before leaving the factory. Disposable batteries are fully charged before leaving the factory, which makes them much more dangerous and likely to explode in fires than secondary batteries."

Meng Xiangdong added: "Disposable batteries such as lithium thionyl chloride batteries are not commonly used power batteries for new energy vehicles. They are usually used in electronic equipment in the industrial field, such as smart meters and monitoring equipment. Common mainstream batteries on the market, such as lithium iron phosphate batteries and ternary nickel cobalt manganese batteries, are used in energy storage power stations and electric vehicles respectively."

It can be clearly seen in the on-site pictures that the white smoke released at the beginning of the battery fire turned into dense smoke in a very short time, quickly covering the entire work area. According to Meng Xiangdong's analysis, when the battery safety valve ruptures, the first thing that is ejected is an aerosol composed of electrolyte and combustible gases such as hydrogen, carbon monoxide, and methane.

White smoke is a mixture of electrolyte and combustible gas, which is very easy to burn. The subsequent black smoke may be carbon powder particles produced during the combustion of graphite, the negative electrode material of the battery, and particles produced by the melting of current collectors such as aluminum foil and copper foil.

During this period, some employees tried to put out the fire with a dry powder fire extinguisher, but unfortunately, the fire was not effectively controlled. Meng Xiangdong pointed out that the chemical reaction inside the battery will release a lot of heat, and the cooling effect of the dry powder fire extinguisher is not ideal, "and the close contact between the batteries in this module leads to poor heat dissipation conditions, which makes it easy for heat to accumulate."

Regarding the factors that caused serious casualties, Meng Xiangdong pointed out that the fire and explosion caused by thermal runaway of the battery may be the direct cause. In addition, the harmful gases such as carbon monoxide and hydrogen fluoride produced by the battery are suffocating or irritating, which may also be one of the reasons. More importantly, the battery factory’s safety supervision is not in place. "It failed to detect battery failures in time, troubleshoot safety hazards, and was not equipped with effective safety warning and fire extinguishing measures."

Cai Zhen, a professor at the Department of Fire Safety at Mokwon University in South Korea, revealed that the installation of gas detectors in electric vehicle or lithium battery factories in South Korea is not perfect. In addition, the current laws in South Korea have not yet included metal fires in the fire types in the Fire Protection Act, resulting in the quality of "metal fire" fire extinguishers currently on sale not being guaranteed.

Experts speculate: This may be sending a warning signal

According to Korean media reports, a Chinese man said in tears that he had lost his wife. The man said that his wife worked in a battery factory and he came to the factory because he could not contact her. A colleague who came with him said: "I was working inside the factory and heard a 'bang' sound last week. This is not the first time."

Meng Xiangdong speculated that "the 'bang' sound may be the sound of the gas generated by the internal reaction of the battery breaking through the safety valve." He explained that if the temperature of the battery is too high, an exothermic chemical reaction will occur between its internal materials, and flammable gases such as hydrogen, carbon monoxide and methane will be produced. "Then, as the gas continues to accumulate inside the battery, the internal pressure of the battery gradually increases. When the pressure limit is reached, the battery safety valve ruptures and releases the gas instantly. This instantaneous process often makes a 'bang' sound."

"If you hear a 'bang' but don't see flames or the fire spreading, it may be that under the circumstances at the time, the thermal runaway reaction of the battery did not develop further. So, if we hear this sound at work, it is a warning signal transmitted by the battery, which means that we need to effectively cool down the faulty battery in time, remove the flammable gases released by the battery, and prevent fire." He said.

Meng Xiangdong pointed out that there are many ways to improve the safety and prevention of lithium battery fires. "In daily life, what we can do is to master basic safety knowledge, such as prohibiting electric vehicles from being pushed into the corridor, using regular charging piles to charge, understanding the battery life cycle, replacing batteries in time, preparing small water-based fire extinguishers, and taking safety precautions," he said.