Eight sewerage workers were poisoned by marsh gas Tuesday afternoon when they were connecting an underground drainage pipe in northwest China's Ningxia Hui Autonomous Region.

Currently, they are being treated at a local hospital in the regional capital of Yinchuan, and two are described as critical, said Tian Fengnian, director of the Health Bureau of Yinchuan.

One of the workers, who worked for the Ningxia Zhengfeng Construction Co. Ltd., went into a sewer in Yinchuan at about 6:35 PM without taking any precautionary measures, and failed to return, said Zhang Yuesheng, a spokesman for local fire-control authorities.

His colleagues went down one by one, but were overcome and needed to be rescued themselves, Zhang said.

Other company workers on the ground called the police and the local government dispatched fire-control and health authorities to help with the rescue operation, according to Zhang.

Marsh gas is odorless, colorless and flammable, and largely composed of methane. It can build up inside sewers where organic material decays in the absence of air.

The case is still under investigation.

(Xinhua News Agency March 28, 2007)