Mong Kok blaze victims died 25 minutes after fire started

The nine victims of the 2011 Mong Kok inferno are believed to have died 25 minutes after the fire broke out, the inquest into their deaths heard.

The Fire Services Department's acting assistant director, Li Leung-ming, told the Coroner's Court yesterday that his investigation team estimated that the residents lost their lives on the main staircase of the nine-storey Fa Yuen Street walk-up building at 4.55am on November 30, 2011.

He said this would have happened when the ignition of combustible gases from burning materials at the ground and mezzanine levels caused an explosion that sent smoke and heat racing up the stairwell of the building on 192-194 Fa Yuen Street.

The fire had first broken out at stall 268 in the market street before quickly spreading to other stalls and the building, which was adjacent to it.

Li said the estimate was based on evidence given by survivor Kung Sin-shing, who said he had seen sparks coming from electrical boxes on the wall at the main entrance. The boxes looked likely to explode, Kung said.

Kung had also heard a loud bang, followed by a complete blackout, when he attempted to run upstairs, Li said.

The investigation report said that the fire in the hawker stalls below caused insulation materials of electrical installations, as well as the combustible false ceiling at the cockloft level, to emit volatile combustible gases.

"Most probably, all the accumulated combustible gases were ignited at the same time by an explosion of the electrical installations or by the fire or embers from the hawker stalls, and thus emitted [the loud bang]," Li said. He said the pressure from the rapid combustion process had pushed the smoke and heat up the main staircase, catching the evacuees who were still climbing the stairs on their way up to the rooftop.

Professor Ho Siu-lau, of Polytechnic University's electrical engineering department, said the blaze was likely to have been caused by short circuits near the electricity boxes at stall 268, where an electrician had used aluminium cables to extend CLP Power's copper cables when he moved the boxes from outside to inside the stall. The aluminium wires had corroded and become loose.

Stall owner Ma Tat-man told the inquest earlier that he did not alert the power supplier to the relocation, and was not sure whether the electrician was certified.

"If aluminium wires come into contact with other cables, all carrying electricity, short circuits will take place," Ho said. "[The electrical fault] will produce a strong electric current that emits heat."

The heat would ignite flammable items and start a fire.

The professor said he could not find out why aluminium, rather than copper, was used for the cables, as Ma was unable to identify the electrician.

The inquest continues today.

Chain of events

4.30am Fire starts

4.33am Resident Ho Yim-ping discovers the fire

4.37am Ho flees her unit

4.40am Fire is first reported

4.44am First fire engine arrives

4.47am Ho gets to the roof and makes the first call for assistance

4.52am Loud bang heard from main entrance; residents overcome by heat and smoke as they try to escape

4.55am The nine victims die on the main staircase of the building