SINGAPORE, May 23 — A worker died and two others are in intensive care after collapsing during a routine tank cleaning at Choa Chu Kang Waterworks on Thursday morning (May 23).

In a statement on Thursday, national water agency PUB said the three men are sub-contractors and were found unconscious at around 11.15am at Singapore’s second-largest waterworks along Nanyang Drive.

“Preliminary investigations indicate that the workers had inhaled hydrogen sulphide, a gas produced from sludge which is a by-product of the water treatment process,” said PUB.

Hydrogen sulphide is a colourless gas that is extremely flammable and highly toxic. It is known for its strong odour of rotten eggs.

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PUB said that all three workers were conveyed unconscious to Ng Teng Fong General Hospital.

One of the workers died in hospital, while the other two are still in intensive care.

“PUB expresses our deepest condolences to the deceased’s family,” it said, adding that it is in touch with their contractors and will render support to the workers’ family members.

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“Safety and health at all our workplaces are of utmost importance to PUB. We will cooperate fully with the investigation,” said PUB.

“As a precaution, PUB has called a safety timeout for similar operations in confined spaces and is reviewing the associated safety measures.”

In response to TODAY’s queries, the Singapore Civil Defence Force (SCDF) said it was alerted to the incident at about 11.25am on Thursday.

“SCDF firefighters and HazMat (Hazardous Material) specialists wearing personal protective equipment, including breathing apparatus sets, entered the premises and identified the presence of a hazardous vapour — hydrogen sulphide,” said SCDF.

Two water jets were used to disperse the vapour.

The three workers were unconscious en route to the hospital and cardiopulmonary resuscitation (CPR) had to be performed on one of them.

SCDF did not state if the worker who died was the same one who received CPR.

No hydrogen sulphide was detected in the premises after the water jets were used for an hour, added SCDF. — TODAY