Open doors turned the Top One Karaoke bar into a deadly trap where toxic gases spread so quickly that victims had no chance to escape, an inquest heard yesterday. Fire-resistant doors are built to withstand flames for at least 30 minutes, but investigations revealed that the Tsim Sha Tsui bar's protective doors would have been wide open at the time of the blaze on January 25 last year. 'If the fire doors had been closed on the second floor, it would have made a lot of difference,' forensics expert Dr Lau Chau-ming told Coroner Ian Thomas. 'It would have stopped the smoke in the stairway from entering unchecked. 'Any smoke that penetrated the doors would have activated the alarm, alerting people inside. 'In normal circumstances, if the door was closed the fire would have been controlled.' Seventeen people died after a dispute between triad members and club bouncers led to the bar being fire-bombed. All victims died on the second floor. There were no deaths on the third floor, where fire doors were closed. If the sprinkler system had been activated it would have further protected victims by reducing the searing heat inside, said Dr Lau, a senior chemist for the government laboratory forensic science division. He found the fire was started by three Molotov cocktails - one thrown at the front entrance leading to the second floor of the building, one at a landing between the first and second floors and one in the first-floor lobby. The blaze raced up the stairway to the open doors on the second floor and on to the cluster of karaoke rooms with such speed that victims were caught unaware. 'The smoke-logged corridors and karaoke rooms became a deadly trap where the 17 victims were incapacitated and eventually killed by the toxic smoke,' Dr Lau said. Temperatures would have soared to about 1,000 degrees Celsius after foam in sofas in the karaoke lobby exploded into flames, releasing toxic hydrogen cyanide gas. The inquest continues.