An attempt to keep a flat's polished floor free of blemishes led to an explosion which killed an interior decorator, an inquest heard yesterday. Wong Kwok-shing, 45, died in a blast caused by the ignition of varnish fumes in an Ap Lei Chau flat on September 24 last year. All windows and doors in the flat were closed - a common practice in the decorating industry to prevent circulating air from making surfaces of varnished floors uneven, the Coroner's Court heard. Returning a verdict of accidental death, Coroner Paul Kelly said flammable vapours had been concentrated in the flat, resulting in the blast. Wong, along with his brother Wong Siu-ping, 55, went to the 13th-floor flat in South Horizons on September 24 to monitor the progress of decoration work. A smell in the apartment prompted Wong Siu-ping to open a window in the master bedroom. He then heard an explosion and ran out to find his brother lying injured in the bathroom. The worker suffered 80 per cent burns and died from complications at Queen Mary Hospital on October 20. Government chemist Leung Ka-on said the blast could have been caused either by a switch being activated or by a cigarette lighter. He said there were no scorch marks on the flat's switches. Police found a cigarette butt after the accident. But Wong Siu-ping denied he or his brother had smoked in the apartment, although the pair had been smokers for more than 20 years. An occupational safety officer with the Labour Department, Ng Ho-wang, said the department had introduced strict safety measures to control explosive vapours after the incident. He also recommended the decoration industry use scientific instruments which gauged the levels of explosive vapours.