A piece of gap filler that came loose from a tunnel ceiling caused the 11/2-hour disruption on the MTR's West Rail line which affected thousands of rush-hour commuters on Thursday.
Initial findings of an MTR Corporation investigation show a section of filler 90cm long and 4cm wide became entangled in the pantograph of a passing train.
'This caused a short circuit that triggered the safety device of the overhead line's fail-safe system to turn off power supply in that section,' chief of operations engineering David Leung Chuen-choi said.
He said the filler was found on top of the Hung Hom-bound train, which broke down in the tunnel after it left Mei Foo station at about 8am on Thursday. About 900 passengers had to walk 100 metres back through the tunnel to reach a platform.
An MTR spokesman said it was the first such incident in the system.
The flexible filler, made of composite synthetic materials, is used in expansion joints between concrete beams in the tunnel and an adjacent steel duct enclosing utility equipment. Held in place with industrial adhesive, it prevents the two structures from pressing against each other in hot weather and keeps dust out of the equipment duct.
