Faulty old sleepers split under pressure causing rails to spreadeagle and throw a crowded commuter train off its tracks during rush hour, injuring eight people, according to the government investigation into last September’s derailment outside Hung Hom station.

These rotten sleepers, riddled with screw holes, caused the accident, the government says.

The official explanation for the crash is “track gauge widening”, whereby the width between the tracks was forced wider by the pressure of the train. Wooden sleepers usually keep the width tight, but the sleepers in the area were rotted and riddled with screw holes, weakening them and causing the rails to widen beyond their ability to support the train, whereupon it derailed.

Most of Hong Kong’s straight rail tracks use concrete or synthetic sleepers. But timber sleepers are still used on corners, as they can easily be hewn into shape to fit and fine-tune positions of baseplates and rails.

But shoddy maintenance saw old sleepers re-screwed into place multiple times, with screw holes very close to each other, giving the sleepers the structural integrity of a third-hand flatpack shelving unit.

The government report estimated there were over 9,800 timber sleepers installed on bends on the East Rail Line, and says MTR has begun a programme of replacement – MTR says it has replaced about 2,627 timber sleepers on the line.

MTR’s own account of the accident reveals a subtly different narrative with no mention at all of rotten wood. The rail giant told of the replacement of two timber sleepers ahead of the accident site with synthetic models: the stiffness of the two new sleepers “created a localised hard spot in the rail support system”,  and it was this localised hard spot which caused damage to sleeper screws and which made the track more susceptible to track gauge widening, it says.

However, the government’s independent report does not mention the “localised hard spot”, the replacement synthetic sleepers, nor broken coach screws: the government places the blame 100% on the East Rail Line’s rotten and damaged wooden infrastructure.

MTR has not responded to questions about the different accounts. Meanwhile the firm has pledged to install real-time monitoring on its trains and to follow the trade’s maintenance and inspection procedures.

During rush hour, the East Rail Line carries 86,000 passengers per hour in each direction between the mainland border and Hung Hom.