Investigators are looking into whether cigarette smoking caused a fire inside the Lion Rock Tunnel that lasted for nine hours yesterday and led to the closure of its Kowloon-bound carriageway for at least three days.
The fire broke out in a drainage tube below the dual-lane carriageway at about 3.30am. Thirty-five fire engines and more than 140 firefighters were put into action. The blaze was put out at 12.30pm.
The Highways Department said the closure was needed because of the collapse of concrete pieces and exposure of the metal frames along the 60-metre-long ceiling of the underground drainage tube.
The fast lane of the affected carriageway is expected to reopen before the morning rush hour on Monday, but it is unknown when the slow lane will be ready for operation again.
In the meantime, the Sha Tin-bound carriageway of the tunnel was converted to two-way traffic. The MTR Corporation and bus companies have been asked to increase their services during the closure.
The blaze brought a public apology from the Water Supplies Department for causing a road closure and traffic congestion, as its workers were carrying out rehabilitation work on the water mains inside the drainage tube when the fire broke out. Water supplies are not affected.
About 20 workers from a contractor for the department were applying non-flammable protective materials to the outer shell of the water mains, about two metres below the tunnel, when protective materials and asphalt-encased water mains ignited.
One worker said he heard someone shout 'dense smoke', 'fire' and 'run'. He said: 'After I ran out, thick smoke filled the tunnel and I could not see the road inside. My face mask was blackened by smoke.'
He was among workers who climbed out of the tube through manholes. No injuries were reported.
The commander of the Fire Services Department's New Territories East division, Leung Kwok-ming, said firefighters' efforts were hampered by dense smoke, high temperatures and the narrow space in the confined fire scene. 'There was intense heat in the tube, which was filled with thick smoke,' he said. 'Inside it is narrow and wide enough to accommodate one person only.'
The department said there were no suspicious circumstances and the cause was under investigation.
A senior resident engineer with the water department, Roger Leung, describing the incident as 'strange', said workers used non-flammable protective materials and no combustion was required in the work.
He said he did not rule out the possibility that the fire was caused by smoking, but, he said, they were also looking into whether other factors such as a short-circuit caused the blaze. 'Under our guidelines, smoking is prohibited in a confined space.'
Leung said existing asphalt encasing ageing water mains could burst into flames if a spark landed on it.
Chief engineer Yung Kin-yee of the Highways Department said there was no sign of road subsidence even though concrete fell down from the ceiling of the underground tube and metal frames were exposed.