Satellites reveal Hong Kong building 'sinking fast' before collapse that killed four

Scientist says technology available now would have prevented To Kwa Wan tragedy that killed four but government has turned it down

PUBLISHED : Tuesday, 01 April, 2014, 11:20am
UPDATED : Wednesday, 02 April, 2014, 4:27pm

A scientist believes lives could have been saved in 2010 - when four people died after a building collapsed in To Kwa Wan - if the Hong Kong government had been using satellite technology showing the five-storey block of flats had been subsiding at a worrying rate before the accident.

Block J of 45 Ma Tau Wai Road was apparently dilapidated, with bent metal support columns, and undergoing maintenance when it crumbled and was reduced to a pile of rubbish within seconds on January 29, 2010. Four people inside the building were crushed to death.

“An in-situ survey driven by the warning could have revealed the possibility of collapse, potentially saving four lives”
Dr Daniele Perissin

However, Dr Daniele Perissin, who served as an assistant professor at the Chinese University of Hong Kong’s Institute of Space and Earth Information Science until last year, says technology exists today that could have spotted early signs of problems at the 53-year-old block of flats.

Surveyors and engineers could have been sent promptly to examine the building had government departments monitored its health more closely, he says. “An in-situ survey driven by the warning could have revealed the possibility of collapse, potentially saving four lives.”

The Italian academic is the author of an advanced software program that can detect tiny movements in the ground to provide early warnings of subsidence.

He says he failed last year to persuade the government to start using the software to monitor its many old buildings and identify high-risk sites. Budget concerns halted the idea, which would have cost more than HK$900,000 per year, he says.

Last year a court ruled that a workman was likely to have caused damage to the building with his repairs to the ground floor. But the evidence did not suggest to what extent it caused the immediate collapse.

The 2011 inquest into the four deaths was told the building was in a "very, very dilapidated state" before the repairman began work on the day of the collapse, and that a surveyor's inspection in November 2009 found that it did not pose an immediate danger.

Coroner Michael Chan Pik-kiu concluded that no one should be held criminally responsible. But he found fault with both the owner and buildings officials.

“Before November 2009, the detected movements were not enough to raise a warning, as it could be interpreted as thermal expansion. However, after that it was clear that the building was affected by a different and stronger process,” Perissin says.

Perissin carried out his study using a radar technique called interferometric synthetic aperture radar, or InSAR. It uses satellite signals to measure deformations in the surface of the earth.

A study of satellite radar images of the site since 2008 showed the building began sinking in early 2009, dropped 4mm between June and November 2009 and fell a further 8mm from November – sinking 2cm in total.

In last year's court ruling, the workman, Chu Wai-wing, 77 - the only person prosecuted over the collapse - was fined HK$10,000 for causing damage to the building with his repairs. But he claimed he was being treated as a scapegoat, and that the Buildings Department should have shared the blame.

The department's report into the Ma Tau Wai Road building collapse bshowed it had received a complaint about cracks, loose plastering and spalled concrete in different parts of the building in November 2009. Two inspections were carried out in November and December but found no imminent structural danger.

After the collapse, the department inspected about 4,000 buildings built 50 years ago or more and found about 1,000 buildings which showed obvious defects. Two had emergency work done.

Since then, “a certain number” of private buildings aged 30 or above are inspected every year for defects.

Dr Greg Wong Chak-yan, former president of the Hong Kong Institution of Engineers, said 2cm of subsidence spotted in the study could be an important sign of defects.

“Such subsidence is normal when there is construction nearby. But if a building sinks and other buildings around it don’t, an inspection is warranted,” he said. “It’s a shame we realised it had sunk after it all happened so many years ago.

“There are thousands of old buildings in Hong Kong, and most of them are perfectly fine, so getting the owners to shell out hundreds of dollars a month for regular inspections on them are very hard.”


  • Traffic in To Kwa Wan was thrown into chaos during rush hour yesterday after a 2m section of Ma Tau Wai Road near the junction with Lok Shan Road caved in. The single northbound lane was closed for almost three hours as repair work was carried out. MTR Corporation, which is building the Sha Tin to Central Link in the area, said it would investigate the cause of the incident. No injuries were reported.