Gas leaking from a rubber hose showing signs of rat bites escaped through gaps in a workbench in the lead-up to an explosion that killed three workers, an inquest heard yesterday. A report by government chemist Lau Chau-ming into the blast indicated sparks from a metal-cutting machine may have ignited rising gases. The three victims - welders Wu Hin-fai, 41, Cho Yip-hung, 66, and assistant foreman Siu King-fai, 60 - were among a group of workers carrying out metal cutting and grinding when the explosion ripped through the workshop of construction company Bachy Soletanche Group Ltd, in Fairview Park, Yuen Long, on February 12 last year, the inquest heard. Four others were injured. A report from the Fire Services Department found 'the operation of the machine which generated splashes of red-hot embers was the only source of ignition which triggered the explosion'. However, Mr Lau, giving evidence yesterday, said sparks or heat from any number of sources would have been sufficient to ignite the oxyacetylene gas. He said these sources could have included sparks from a grinding machine, flames from a welding torch or heat. Even a hammer being struck on the work platform would have been able to cause a mechanical spark, but that was unlikely in this case, he said. In his report, Mr Lau said signs of rat bites were present on a 40cm section of exposed rubber gas hose under the work platform. Scratch marks were also found on another hose, the report said. Ho Kin-wai, safety supervisor for the company, said yesterday responsibility for checking for any gas leaks rested with the workers. He said he was not aware of the existence of two pairs of gas hoses underneath the platform. It was standard practice for gas hoses to be placed on the platform, the inquest heard. The inquest continues before Coroner Andrew Chan Hing-wai.