The Yellow River and drinking water sources along its banks were not polluted by Monday's explosion at a chemical factory in Lanzhou, capital of northwest China's Gansu Province, a spokesman said yesterday.

The accident took place at 3:32 PM on Monday, killing four workers and injuring 11, after a fire at a waste acid unit in Lanzhou Petroleum and Chemical Industry Company's organic chemical factory, company spokesman Zhao Mingquan said at a press conference.

The factory, a state-owned enterprise mainly producing nitrobenzene, aniline, cyclohexylamine, rubber accelerator and antioxidant, is located next to the Yellow River, the main water source in northern China.

Normally, its waste water is discharged into the river after being processed.

Zhao said the 80 tons of water used to put out the fire did not go into the Yellow River.

"The four dead and the 11 injured are all migrant workers. They were employed by a construction company that was doing work on our factory. The clean-up operations are going smoothly and the injured are in a stable condition in hospital," he added.

Local media said Lanzhou's environment department inspected nearby sections of the Yellow River and the factory's waste disposal system and found the water met environmental standards and there was no pollution caused by the accident.

(China Daily May 31, 2006)