SINGAPORE — One worker has died after inhaling a poisonous gas while carrying out routine tank cleaning at the PUB Choa Chu Kang Waterworks on May 23. The worker was one of three who had collapsed and were found unconscious at the plant at around 11.15am. All three were taken to hospital, where the worker died. The two surviving workers are in the intensive care unit at Ng Teng Fong General Hospital. In a statement, PUB said early investigations suggest that the workers had inhaled hydrogen sulphide, a gas produced from sludge which is a by-product of the water treatment process.  According to the US' National Institute for Occupational Safety and Health, hydrogen sulphide is a colourless gas that gives off the odour of rotten eggs. Exposure to the gas can cause irritation to the eyes and respiratory system, among other effects, one of which includes falling into a coma. Workers in wastewater treatment industries are labelled as a group at risk by the institute. The PUB said that it has called a safety timeout for similar operations in confined spaces and is reviewing the associated safety measures. Read more