BEIJING — The deadly chemical plant blast in East China's Jiangsu province on March 21 has been identified as an extremely severe production safety accident caused by prolonged illegal custody of hazardous chemical waste, according to the State Council investigation group on the case.

Investigations into the explosion that claimed 78 lives and severely injured 76 people attributed the blast to the spontaneous ignition of nitrified waste, which was illegally stored for protracted periods of time in a plant owned by Jiangsu Tianjiayi Chemical Co Ltd.

The investigation group pronounced the company responsible for the accident for its negligence of laws and regulations regarding environmental protection and production safety in dealing with chemical waste.

The group also pointed out misconduct in emergency management, environment protection, industry, market supervision, planning and other departments in Jiangsu Province.

The explosion that happened at about 2:48 pm on March 21 in Xiangshui county in Yancheng city caused a direct economic loss amounting to around 1.99 billion yuan ($284.3 million).