Workplace safety authorities have ascertained the gas blowout that occurred in southwest China's Yunnan Province last Thursday was nontoxic with only methane.

By press time Monday, all the 4,000-odd evacuees have returned home, noted officials with the Production Safety Bureau of Qilin District in Qujing City, where a gas well No. 2 of Sinopec's Yunnan branch exploded at 2:50 AM Thursday. Local police helped residents in villages within vicinity to evacuate within two hours.

No casualty was reported in the accident and the well has resumed operation by Monday. Environmental workers say they found no toxic gas in the blowout, nor did it contaminate the drinking water.

But management of Sinopec's Yunnan branch say that they are making rigid rules to protect its workers against similar risks.

The blowout was caused by miscalculation of the stratum pressure, experts say. "There's a gap of pressure between the hydraulic pressure gauge of the drilling rig and the stratum when the drilling approached the gas layer," said Tang Jiagui, an official in charge of oil prospecting in Yunnan, Guizhou and Guangxi region in southwestern and south China.

China's worst gas blowout, which took place on Dec. 23, 2003 in Kaixian County in southwestern Chongqing municipality, killed 243 people and injured more than 4,000 others.

(Xinhua News Agency December 6, 2004)