Hong Kong LED screen fell due to ‘fatigue’ in wire bearing it

A government investigation into why a giant LED screen plummeted on to the stage below during a concert in Hong Kong has found that one of the wires it was suspended from showed signs of ‘fatigue’, had been incorrectly installed and its load had been understated.

The 4m by 4m screen fell during a gig by boy Cantonese boy band Mirror at the Hong Kong Coliseum on 28 July. One of the two dancers injured by the screen is still in hospital and is reportedly paralysed from the neck down.

During the incident, one of the two 5mm wires supporting the screen snapped, causing one side of the panel to plunge downwards. Although the other wire remained intact, the eye bolt connecting it to the screen broke, causing the entire display to fall on to the stage.

The incident is being investigated by a taskforce from the Hong Kong government’s leisure and cultural services department. Material testing expert Eric Lim Chaw-hyon said evidence of metal fatigue – “fatigue striations” – had been confirmed by magnifying images of the wire 5,000 times through an electron microscope. But according to Lim, it would typically take tens of thousands or even millions of uses for a steel wire rope to demonstrate metal fatigue, according to a report in the Hong Kong Free Press.

As damage was also discovered on unused sections of the wire, Lim said he believed it was damaged before being installed on the set. He added that the way in which the cables had been installed would also have contributed to the metal fatigue.

The wires were each held in place by a winch and a ‘rope guard’. A rotating rope guard is typically installed on a winch to make sure a wire stays on its thread. However, Lim said the winch system used had a fixed rope guard, which would squeeze the wire, leading to abrasion and hastening the metal fatigue. He added that the first wire had to go through an extra set of pulleys to reach the winch than the second one, placing more pressure on the already worn cable.

“Putting all these problems together resulted in the cables having metal fatigue in a short period of time,” Lim told a second Hong Kong publication.

The taskforce also discovered that there had been an error in the reported weight of the screen. Another member of the taskforce, Louis Szeto, revealed that the screens weighed about 500kg each, but documents submitted to the leisure and cultural services department by the concert organisers said they weighed in at 500lbs (227kg).

Tests on the wire that snapped have revealed that its rated strength was found to be 20% less than comparable wires on the market. However, Szeto said the two wires should have been able to bear a 500kg load as they could each take 1,100kg before breaking. Although the first snapped, he said the load capacity of the second one alone should have stopped the screen from falling.

The taskforce is expected to conclude its investigation this month.