Building's raised lobby design allowed deadly gas to accumulate, says expert 'Unusual' corrosion was found in the section of an underground pipe believed to have leaked the gas responsible for a fatal explosion in Ngau Tau Kok on Tuesday. The Hong Kong and China Gas Company made the announcement yesterday as investigations continued into the blast that killed an elderly woman and injured eight other people. Liu Lok-chun died when she fell into a hole in the lift lobby of the Wai King Building that was rocked by the explosion at 2.30pm. A woman, 94, remained in critical condition in Queen Elizabeth Hospital last night, while two other victims - a 65-year-old woman and traffic policeman Lo Chi-cheung, 35 - were stable in United Christian Hospital. Liu's family has demanded to know who was responsible for the accident and why there was no evacuation immediately after the leak was reported. A Towngas spokeswoman said the corroded section of pipe had been in place for just 23 years, far less than the international safety standard of 60 to 70 years. The corroded section, in which a hole 70mm in diameter was found, was sent to the Electrical and Mechanical Services Department for examination. The ductile-iron pipe, which comes from Britain, had been inspected last month and found to be safe. Gas pipes are usually inspected every three years. It was laid in Jordan Valley North Road in 1983, about 30 metres from the front of Wai King Building. The blast happened just two hours after a gas leak was reported at 12.30pm. The supply was turned off just after 1pm. Kowloon Central Fire Services Department acting divisional commander Ma Ning said firefighters had taken every precaution in handling the problem. When they arrived they could not detect any odour of gas, and had only discovered the leak after inspecting four manholes along the road. However, some gas had flowed into a space under the lift-lobby of the Wai King Building and had not been detected. Speaking on a radio programme last night, Frank Chan Fan, assistant director of electrical and mechanical services, said the design of the lobby, with the entrance hall built a few stairs above the ground, had left a space where the leaked gas could accumulate. He said Towngas had agreed to inspect all similar pipes within three weeks. Initial investigation showed that an unknown spark triggered the explosion under the building, and the force of the blast had travelled in three directions. It ripped open a 2-metre deep hole in the floor of the building's lift lobby and tore into the vacant ground-floor shop on Ngau Tau Kok Road, blowing off a metal shutter that hit Sergeant Lo Chi-cheung, 35, who was riding past on his motorcycle. It had also affected a meter room in an alley behind the building, where it knocked down a 23cm-thick wall. A team involving officers from the police, Fire Services and Electrical and Mechanical Services Departments has been set up to investigate the blast. The Towngas supply to the building and nearby Choi Ha Estate was cut off and about 2,300 households were affected. Yesterday morning, the gas supply to Wai King Building had been resumed, with services to Choi Ha Estate expected to be back to normal last night.