SINGAPORE – The two workers who died after inhaling toxic gas at PUB’s Choa Chu Kang Waterworks were not wearing respirator masks, said a Ministry of Manpower (MOM) investigating officer on Oct 2.

Several other safety protocols were also not followed, including the requirement to ventilate the area before entry, said Muhd Hafidz, a senior investigating officer with MOM’s occupational safety and health division.

He was testifying on the first day of a coroner’s inquiry into the deaths of the two workers.

Malaysian Izzat Naqiuddin Dowod, 24, and Indian national Srinivasan Sivaraman, 40, collapsed after inhaling hydrogen sulphide, which is produced by sludge, a by-product of the water treatment process.

Hydrogen sulphide is colourless and can be lethal even at low concentrations.

Izzat and a third worker entered the enclosed passageway of the pulsator tank to turn off a valve controlling the drainage of sludge on the morning of May 23, 2024.

Sivaraman likely entered the gallery shortly after to check on them, said the investigator.

He added that both Izzat and Sivaraman were not wearing respirator masks when they were rescued.

Sivaraman succumbed to his injures on the day of the incident, while Izzat died on May 28.

The third worker survived the incident.

Izzat was employed by Stargroup Est, a cleaning company, while Sivaraman was a cleaning operations manager at Supersonic Maintenance Services.

Hafidz told the court that a cleaning team, including the two deceased, were supposed to carry out cleaning works on the pulsator tanks that day.