Workers who died after inhaling toxic gas did not wear respirators or follow safety protocol, inspector testifies

SINGAPORE: Two workers who died after inhaling toxic gas entered an enclosed passage at PUB’s Choa Chu Kang Waterworks without respirators and without following safety protocol, the coroner’s court heard on Friday (Oct 2).Mr Srinivasan Sivaraman and Mr Izzat Naqiuddin Dowod died in May 2024 after inhaling hydrogen sulphide, a by-product of the water treatment process. A third worker survived the incident. Hydrogen sulphide is a colourless, toxic gas that can be fatal at high concentrations.Mr Muhd Hafidz, an inspector with the Ministry of Manpower’s (MOM) occupational safety and health division, testified in court on Friday that the workers did not ensure that at least one person remained outside the enclosed passage.Unlike other workers who had entered the passage the day before to drain the tank, the three men did not wear respirators, which are designed to filter out toxic gases. His investigations also found that while there was a ventilator in the passage, it was not in operation at the time, he told the court.According to the inspector, an external ventilator should have been set up to purge the air as part of safety protocol. The passage was not ventilated before the workers entered.Mr Sivaraman, a 40-year-old Indian national, was a cleaning operations manager at Supersonic Maintenance Services. Mr Izzat, a 24-year-old Malaysian, worked for Stargroup. Stargroup had been engaged by PUB for "routine" tank cleaning operations at the plant, with Supersonic Maintenance Services as its subcontractor.Stargroup was charged in July over alleged workplace safety lapses related to the incident – for failing to implement reasonably practicable measures to minimise the risk to any person who may be affected by its undertaking at the workplace.Stargroup’s authorised manager for confined space entry permits, Lim Beng Hock, was also charged with failing to exercise all due diligence in relation to the issuance of the permits.Mr Sivaraman and Mr Izzat were part of a team scheduled to clean a tank at PUB's treatment plant.They had to enter the enclosed passage beneath the tank to drain the water in it before they could clean it, said Mr Hafidz.Mr Izzat and another worker went through the gate to open all three hand valves while Mr Sivaraman stood outside nearby, in line with the buddy system required by safety protocol. None of them were wearing respirators and the valves were opened within five minutes without incident, the inspector said.Mr Sivaraman conducted a gas check before the two workers entered the passage, using a personal gas detector that did not sound an alarm, the inspector said.Mr Hafidz testified that with all three valves open, the wastewater was likely to have been flowing out "quite rapidly", which could have accelerated the release of hydrogen sulphide.After opening the valves, the workers returned to cleaning the tank above the passage. At about 10am, a worker from another PUB contractor told Mr Sivaraman that the wastewater was flowing rapidly into the next tank and that he had detected a strong rotten smell, the court heard.Mr Sivaraman instructed an employee to bring someone, go back to the passage and close the valves, the inspector testified.He also confirmed that nothing had been established about any instructions given by Mr Sivaraman about equipment.The third worker and Mr Izzat both entered the enclosed passage without respirators. Mr Izzat was wearing a personal gas detector, the inspector said.The alarm on his personal gas detector, as well as the ones mounted around the passage, were sounding, he added.This indicated a hazardous environment, but they went into the passage nonetheless, Mr Hafidz said.When questioned by State Coroner Adam Nakhoda, the inspector confirmed that the workers should not have both entered the passage – one of them should have remained outside.Citing the third worker’s account of the incident, Mr Hafidz said the worker and Mr Izzat entered the passage and collapsed.Mr Hafidz said investigators could not establish what happened between 10.30am and about 11am, when the three men were discovered.He testified that Mr Sivaraman likely entered the passage later to check on the workers or attempt a rescue, before being overcome by the gas.The three men were found unconscious in the passage. After they were rescued, they were taken to hospital, where Mr Sivaraman and Mr Izzat died.After the incident, PUB blacklisted Stargroup, barring it from tendering for any of its projects for 18 months from August 2024. MOM also issued PUB a stop-work order covering cleaning work on pre-treatment water tanks and entry into confined spaces adjacent to the tanks. The order was lifted on Aug 6, 2024, after PUB satisfied the stipulated conditions.