The workers opened the lid of a sewer on Tran Van Giau Street at around 9 a.m. to remove the trash to make better drainage capabilities. The sewer was 2 m deep and the water level was chest high.
When the workers fell unconscious down the sewer, one colleague reported the matter to authorities.
Binh Chanh District police sent 12 rescuers bringing oxygen tanks and masks. Around 5 minutes later, five unconscious workers were retrieved from the sewer, soaked in wastewater and sludge.
A 38-year-old worker died, while the other four, aged 22-36, were taken to hospital.
Police said they could have been asphyxiated due to methane and hydrogen sulfide.
Previously, Binh Chanh District authorities were informed that the HCMC Urban Drainage Company would dredge the sewage system in the area within July, including the sewers on Tran Van Giau Street.
Deep sewers may have toxic fumes inside them, including methane, carbon monoxide or hydrogen sulfide due to decaying materials in high concentrations. Those who inhale them may be asphyxiated and fall unconscious, even leading to death.