SINGAPORE - Found floating and unconscious in a waste water pit at their workplace last year, the two labourers died days later.
Chines nationals Zhai Hailei, 26, and Yang Zhonghua, 37, were employees of Nam Heng Leather Dyeing when the tragedy occurred on Dec 26.
During the coroner's inquiry into their deaths yesterday, a Ministry of Manpower (MOM) investigating officer told the court there were four factors that could have led to the tragedy.
Mr Mark Eugene Han said that the men had been standing on planks that were not fully secured; the pit or sump was not fully covered; there was the presence of hydrogen sulphide - a harmful gas - in the area; and Mr Yang had been bending over to retrieve a waste residue basket.
Hydrogen sulphide is the by-product of the leather tanning process.
Responding to queries by State Counsel Paul Wong, Mr Han said that before falling in, Mr Yang had to bend over to retrieve a waste residue basket that was over the sump.
Due to this position, Mr Yang could have lost his balance and fallen into the sump, which was then filled with 2.5m of waste water.
When lawyer Wong Shi Yun, who represents Nam Heng, asked Mr Han what was the key factor, he replied: "The sump was not fully covered up."
Mr Yang had been tasked to retrieve and clean the basket at around 8.30am that day. He entered the sump area about 20 minutes later and was never seen again.
Mr Zhai, who was instructed to conduct a search, entered the area at around 8.55am and he too disappeared.
Their colleagues later found them floating in the waste water and pulled them out.
The authorities were notified and an ambulance rushed them to Changi General Hospital where they died nine days later.
Ms Soo Sze Mun from MOM's occupational safety and healthy division also testified yesterday.
The occupational hygiene specialist told State Coroner Marvin Bay that she tested the air around the pit at around 5pm that day and found that it contained 9.2 parts per million (ppm) of hydrogen sulphide.
Ms Soo said that the gas, which smells like rotten eggs, can cause eye irritation at 5ppm and can knock a person out at 700ppm.
The level of hydrogen sulphide there was higher than 9.2ppm when the incident took place, she said.
However, she could not tell the court how much of the gas was present around the pit that morning as the men had fallen in in about eight hours before she conducted her tests.
"Any disturbance could dilute the gas level," she said.
Ms Soo added that the men could have become dizzy after inhaling the gas, which would have increased their chances of falling into the sump.
The case has been adjourned to Aug 19.
This article was first published on July 11, 2014.
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