A welding machine was on at full power when the fatal blaze broke out at the Garley Building, a forensic scientist yesterday told the inquiry. Dr Lau Chau-ming, a senior chemist at the Government Laboratory, said he believed welding work in the building's upper floors was the most likely cause of the fire. 'The welding works provide a continuous supply of falling welding debris,' he said. 'The small size of welding debris means it would be possible for it to drop through gaps to combustible materials such as paper on the second floor lift lobby.' A welding machine found at the scene was set to the maximum 220 amps. Dr Lau conducted an experiment on the 12th floor of the Garley Building on November 30, 10 days after the blaze which killed 40 people, to establish if welding sparks could still be red hot after dropping many storeys. Results showed falling debris from the 12th floor could ignite corrugated paper at the bottom of the lift shaft, and could also be deflected to set alight materials near lift doors on other floors. Dr Lau rejected theories by Dongal Drysdale, a fire expert hired by lift company Ryoden, that the seat of the fire was not on the second floor because of the speed at which it affected lower floors. 'Twenty minutes are sufficient for the fire to spread from the second floor to the first floor lift lobby and develop into a major fire,' said Dr Lau. Inflammable materials like wooden planks and corrugated paper were stacked by hoarding enclosing lifts on the second floor ( where he believed the fire started), said Dr Lau. The heat and flames were forced down as there were no outlets in the enclosed machinery room at the rooftop. The hearing continues.