A dozen people responsible for an explosion that claimed 24 lives a year ago at a chemical company in Zhangjiakou, Hebei province, were convicted at a local court on Monday.

All 12 were convicted of causing a serious accident through dereliction of duty and violating safety management regulations in the plant's production processes, which led to hazardous chemicals exploding, according to a first-instance judgment by Zhangjiakou's Qiaodong District People's Court.

Based on their duties at the company, responses after the accident and attitudes during confession, 11 of the convicted were sentenced to three to five years in prison, while one did not receive criminal punishment.

On Nov 28 last year, leaking vinyl chloride gas at Hebei Shenghua Chemical Industry Co exploded at around 12:40 am when it came into contact with a high temperature furnace, according to a report by the Hebei Department of Emergency Management released in February.

The highly flammable gas leaked from a chemical storage facility owned by the company, a subsidiary of the China National Chemical Corp.

The blast triggered a chain of explosions and waves of flames that engulfed 38 trucks and 12 other smaller vehicles around the plant, killing 24 people, injuring 21 and causing more than 41.5 million yuan ($6.1 million) in damages, the report said.

The company was fined 9.49 million yuan for failing to meet safety production regulations and obstructing the investigation. After the incident, the company failed to report the situation according to guidelines, concealed the truth and misled the inquiry, the report said.

The indirect cause of the incident was a combination of sloppy management, insufficient attention to and investment in safety production, poor maintenance and mishandling of the emergency, the report concluded.

The court did not release information about the people who were sentenced on Monday, but the report said 12 people, including the company's chairman, general manager, production supervisor, workshop director and operator, were investigated.

Zhang Zhihao contributed to this story.