More than 90 people in east China were taken to hospital while others fled to nearby cities after a poisonous gas leak from a chemical factory, officials said Sunday.

The leak of the toxic gas, cis-butenedioic anhydride, happened at the Qianwei Chemical Factory in Xinyu City of Jiangxi Province at around 5:00 PM on Saturday, China News Service reported yesterday.

The leak was stopped three hours later.

Tests conducted by environmental inspection authorities at 9:00 AM yesterday showed no gas remained in the air. Air quality had reached the national second level, meaning good air quality, China News Service said, citing a Xinyu publicity department official surnamed Liu.

Local residents were admitted to hospital suffering eye and throat discomfort but some had already been discharged by yesterday morning, Liu said.

The toxic gas forced some families to flee their homes to nearby Yichun City and Fenyi County. Liu said they started to return after the problem had been resolved.

A citywide conference was held in Xinyu yesterday to tighten up workplace security.

The Qianwei factory was ordered to conduct a thorough internal inspection to investigate the accident and production won't be allowed to resume until any potential hazards are removed and the results of a final investigation are known.

Pressure

Initial investigations showed that cold water leaked into a rectifying still containing the acid through a cracked pipe. The high temperature - 150-160 degrees Celsius - inside the still triggered a reaction between the water and the acid, resulting in a build-up of pressure which caused the still to burst.

When officials from the municipal government learned of the accident, they rushed to the site and launched remedial measures.

The factory halted production at 11:30 PM.

The Xinyu government notified local residents via text messages and the media that the situation was under control.

Cis-butenedioic anhydride is a weak, irritating acid which can invade the human body through respiratory and digestive systems and the skin, experts say. It is considered to be of low toxicity.

(Shanghai Daily October 11, 2010)