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. The definitive cause of the explosion, however, would remain inconclusive until the results of a full and detailed investigation into the incident are known, it added. The team will submit a full report to the Coroner's Court on completion of its investigation. Hong Kong Institute of Utility Surveyors first vice-president Damien Ku Chi-chung said the findings did go some way to resolve the mystery of the explosion. But he also warned that the Towngas' promise to replace all 150km of gas pipes that are 20 years old was no long-term solution. Mr Ku urged the creation of a comprehensive database of underground utility facilities which would help emergency services determine the potential path of gas leaks and therefore speed up contingency measures. Kwun Tong District Council member Yip Hing-kwok, who has been helping the residents, said he was disappointed by the failure to apportion blame for the explosion. The residents will hold a meeting on Sunday to discuss compensation. The managing director of Towngas, Chan Wing-kin, said the company has doubled the number of inspections on gas pipes to six times a year since the explosion and would have checked on all single-block old buildings before the end of year.