Ho Chi Minh City transportation experts said the explosion that ripped through a downtown road on Monday was likely caused by trapped sewer gas or as they called it a “gas bomb.”
The damaged portion on Hoang Sa Street, under Bui Huu Nghia Bridge across the Thi Nghe Canal in District 1, has been fenced off.
The explosion sent two schisms through the surface of the asphalt, each more than 2 meters long and 3 centimeters wide. No injuries were caused as the street was empty at the time of the explosion.
Le Quyet Thang, director of the unit in charge of traffic infrastructure in the area, said the explosion was caused by a glitch in the combined sewer outflow.
Thang said many combined sewers were installed along the canal as part of an official development assistance-funded environmental hygiene project around the Nhieu Loc – Thi Nghe basin in 2012, and the projects have caused a number of small explosions since.
He said holes had to be drilled into sewer tops to reduce gas pressure.
Combined sewers carry flows of both sanitary waste and rainwater.
The system works well during the dry season when the sewage is diverted further underground to treatment plants before being discharged back into waterways.
But extra rainwater challenges the system's capacity, overloading it to the extent that sewage must be discharged directly into the waterway.
The water pollution threat has made these sorts of systems obsolete and newer cities tend to install separate sewer system.
Ho Long Phi, director of Water and Climate Change Institute at Vietnam National University in Ho Chi Minh City, said the explosion happened during a downpour, so there was a high chance that rising water or garbage blocked a gas exhaust gate and the unreleased gas finally exploded.
Phi said the system needs to be checked carefully.
“There could have been faults in the design or construction,” like a gas exhaust gate built too low, he said.
Pham Sanh, a road and bridge lecturer at the HCMC Transport University, suggested the same thing.
He said the whole sewage system in the area is dozens of kilometers long and the entire thing needs to be checked, instead of just the site of the explosion.
Any garbage stuck in the system needs to be cleared to reduce the risk of further explosions.
“If relevant units fail to check and effectively fix the problem of accumulated methane within the system, it could create virtual underground bombs.”
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