By Cui Xiaohuo and Shi Jinfeng (China Daily)
Updated: 2008-03-05 09:00

The explosion of a pump at a sewage plant in Gaobeidian in eastern Beijing on Monday killed four workers and left 10 hospitalized last night.

More than 20 on-site workers were poisoned when a toxic-gas leak ensued the explosion on Monday morning.

An underground pump connected to four sewage tanks was destroyed in the blast, according to the municipal work safety authority.

Twenty-three workers were treated at Beijing's Chaoyang Hospital.

Two died before arrival and another during emergency treatment, said Li Chunsheng, head of the hospital's emergency treatment department.

Deputy plant director Wang Qi, 28, who had led several workers down to rescue others after the explosion, was among the dead.

The fourth man died after he was admitted to the Civil Aviation General Hospital.

"At present, 10 workers are still in hospital for further treatment," Hao Fengtong, a doctor in charge of the occupational diseases and toxicosis department in Chaoyang Hospital, told China Daily over the phone late yesterday.

"Those slightly poisoned could leave hospital in about 10 days," he said.

According to Hao, the pump's sudden rupture under high pressure probably emitted a heavy concentration of sulfureted hydrogen that caused the temporary loss of consciousness. Subsequently, the workers were likely suffocated by large amounts of toxic mud and sewage.

The actual cause of the explosion is still under investigation. Employees were unable to account for what happened.

A similar incident involving sulfureted hydrogen took place at the plant in the 1990s, Hao said, when four workers were injured after someone failed to carry out underground sampling.

The plant is the largest of its kind in Beijing, responsible for 40 percent of the city's sewage treatment.

It added new tunnels in 1999 six years after opening and recycles 1 million tons of water, as well as producing 4,000 cubic meters of effluent, each day.

Officials at Beijing Water Authority and Beijing Drainage Group Co Ltd, its parent company, declined to give more information. Qinghe Sewage Treatment Plant, another plant in northwest Beijing, also refused to comment.

Operations resumed yesterday.