The explosion that ripped through a barbecue restaurant in Yinchuan, the capital of the Ningxia Hui autonomous region, and left 31 people dead on June 21 was caused by the misuse of liquefied petroleum gas cylinders that were illegally manufactured and distributed, according to an investigation report on the accident.

Dereliction of duty by government bodies and poor management in gas safety also contributed to the deadly explosion, which, in addition to the fatalities, injured seven people and shocked the public, said the report published on Saturday.

Meanwhile, 15 people were placed under investigation for the suspected crime of negligently causing a serious accident, and the arrests of 11 of them have been approved. In addition, 66 public servants have been held accountable by supervision authorities, Xinhua News Agency reported on Saturday.

Furthermore, the Central Commission for Discipline Inspection of the Communist Party of China has also launched probes into Chen Chunping, vice-chairman of Ningxia, and Zhao Xuhui, Party chief of Yinchuan, for dereliction of duty in connection with the accident. It has decided to give Chen a warning and Zhao a severe warning as disciplinary punishments.

The explosion occurred at around 8:40 pm on June 21 at the Fuyang Barbecue Restaurant in Yinchuan's Xingqing district.

According to the investigation headed by the State Council, China's Cabinet, the distributor of the LPG cylinders delivered a cylinder with two valves, which allowed it to be used for both liquid and gaseous fuels. However, according to safety regulations, the restaurant was only qualified to use LPG cylinders with just a valve for gaseous fuel. The misuse was the direct cause of the accident.

The restaurant employees then violated safety management regulations and mistakenly connected the gas regulator to the liquid valve the night before the accident.

When the employees noticed the leak on the day of the accident, they decided to repair it by themselves. But they accidentally opened the valve wider, which caused a large amount of gas to escape. The gas then mixed with air and reached a flammable concentration, and it ignited when it came into contact with a fire in the kitchen, the report said.

The head of the investigation team said that instead of reporting the leak and waiting for professional assistance, the employees tried to fix the problem by themselves four times. "After the third attempt, they called the LPG cylinder provider, who asked them to stop and wait for help, but they didn't listen," the report said.

It added that the staircase to the second floor of the restaurant was the only point of exit for people on the second floor, and the windows on the second floor were all barred. After the staircase was damaged by the explosion, people upstairs were trapped, causing more casualties.

The head of the investigation team added that, when the fire broke out, the manager of the restaurant asked people to call the police but failed to inform the guests at the restaurant, so valuable time for escape was lost.

"It's clear that authorities in Ningxia failed to effectively regulate the production and use of LPG cylinders, which has been required by the Work Safety Committee of the State Council and other authorities since 2020," he said.

In addition, the producer of the LPG cylinders was found to have obtained its license with fake documents. And the distributor of the cylinders hadn't obtained the license to handle LPG products and continued to deliver the wrong cylinders to the restaurant when it knew it was against regulations.