THE preliminary investigation into the Tseung Kwan O footbridge collapse in which a driver was crushed to death two weeks ago has found glaring errors in working practices. These reveal: The design of temporary props supporting the bridge was not checked against the construction; The contractors started to move the bridge from one set of props to another set before an independent engineer had assessed whether the props could take the weight; The work was done while the road underneath was kept open. Secretary for Works Kwong Hon-sang said yesterday that procedures might be reviewed following the results of the inquiry. Cheung Kwok-fai, a 45-year-old truck driver, was killed and four construction workers were injured when two 200-tonne concrete beams crashed across Po Ning Road. The initial findings show key steel plates used to strengthen massive steel beams forming the second set of props were missing. These plates should have been welded at right angles to prevent the beams from twisting. 'Fourteen out of the 24 beams did not have stiffeners,' said a source close to the investigation. Without them, the beams buckled under the weight of the concrete sections until they collapsed. He said it was normal for the design of temporary works to be done by the main bridge contractor, in this case Wan Hin & Co. The report by the government engineer, Maunsell Consultants Asia, shows Wan Hin began to move the concrete sections on to the second set of props before they had been certified as safe by an independent checking engineer. 'Falsework [the temporary supports] had to be certified by letter signed by an independent engineer. A checking engineer was due out the day of the collapse, but the contractor acted in advance of certification,' the source said. Maunsell's report is still at a preliminary stage but corroded scaffolding, thought earlier to be a contributing factor, has been ruled out as a cause. Mr Kwong would not speculate on the causes of the collapse until Maunsell's report, and others by the Territory Development Department and Wan Hin, were completed. 'The next step is to take legal advice from the Attorney-General's Chambers to see how much of the reports we can release,' Mr Kwong said. Wan Hin said it was unable to comment about the Maunsell report because it had not received a copy.