A worker died Friday morning , bringing the death toll in a blast at a chemical plant in east China's Jiangsu Province to four, local government said.

The worker, one of the three seriously injured in the accident, died after emergency treatment failed,.

Three workers were killed at the Fanyou Fine Chemical Plant in Jingjiang City when a boiler exploded around 4:40 p.m. Thursday.

Police have detained Gao Guofan, head of the privately-funded plant that produces about 1,000 tonnes of sodium cyanate and potassium cyanate a year.

Immediate water and air quality tests showed the blast did not contaminate the environment.

The municipal government on Friday ordered a thorough work safety inspection across the city.

Investigators are determining the cause of the explosion.

(Xinhua News Agency August 14, 2009)