BEIJING, Dec. 14 (Xinhua) -- Three workers died Monday after a chemical tank blew up in a plant in Beijing, local authorities said.

    The accident took place at about 10:40 a.m. at the Beijing Guangzhongyuan Gas Co. Ltd. in the suburban Fangshan District, a spokesman with the Beijing municipal government said.

    Workers were helping with a technological upgrading process near the tank, which was loaded with carbon black, when the explosion happened.

    A fire ensued, but was soon put out, the spokesman said.

    Police, fire-control and work safety authorities were investigating the cause of the accident, he said.

    The privately-run company mainly produces liquid nitrogen and liquid argon. Carbon black is virtually pure elemental carbon. It is used to manufacture tires, rubber and plastics products, printing inks and coating.