Hole in sewer could have carried gas under building, investigators say
Government investigators have said a rare combination of factors was to blame for the Ngau Tau Kok gas explosion last month, which killed one people and injured eight others, including a police officer.
The factors, identified by a joint investigation team from the police, Fire Services Department, Electrical and Mechanical Services Department and government laboratory, have been included in a paper to be discussed by lawmakers on the economic services panel on Monday.
The team said a rare coincidence of factors might have caused the explosion at Wai King Building on the early afternoon of April 11.
In addition to a hole, 7cm in diameter, in an underground gas pipe some 25 metres from the building, there was also a damaged main sewer, about 75cm from the hole, that crossed underneath the gas pipe. This led the team to believe that the gas could have passed through the damaged sewer to a point close to a utility space under the building's entrance.
The gas then seeped out through an abandoned branch sewer and through the soil into a utilities space under the building and the pump room at the rear.
The team suggested that the explosion occurred when gas in the vacant space was ignited by an electric spark arising from normal pump operations.