More than 700 residents returned home on Monday, after local environmental authorities tested air quality normal in wake of a chemical plant blast that killed two people in Chifeng City, north China's Inner Mongolia Autonomous Region.

An initial investigation showed that a high-pressure storage tank containing silicon tetrachloride exploded.

The blast in the Shengsen Silicon Technology Development Co,. Ltd. also injured another person, and forced the residents living nearby to be evacuated. The injured has been confirmed to be in a stable condition in hospital, according to local authorities.

Sources with the company said that the company is building and installing production equipments capable of producing 3,000 tons of silicon dioxide a year.

Police and work safety officials are still investigating the cause of the accident.