Government inspectors did not foresee engineering firms colluding to deceive authorities over the use of substandard renovation materials at a Hong Kong residential estate devastated in the city’s deadliest fire in decades, a public inquiry has heard.

Andy Ku Siu-ping, a senior maintenance surveyor of the Housing Bureau’s Independent Checking Unit, on Wednesday blamed “systemic defects” for the body’s failure to rectify the use of flammable polyfoam boards and scaffolding mesh during a HK$336 million (US$42.9 million) renovation project at Wang Fuk Court.

He said the unit, which is responsible for overseeing construction works at subsidised housing complexes, had implemented remedial measures following the fire, such as conducting site checks every four months, requiring registered inspectors to file regular inspection reports and using a computerised system to randomly select project works for review.

Ku was the first of three witnesses from the unit to testify before an independent committee in the fourth round of evidential hearings into the disaster.

The fire at the Tai Po estate broke out on November 26 as the site was undergoing works required under the mandatory building inspection scheme, with various potential fire hazards uncovered in the aftermath of the inferno.

The blaze engulfed seven of the Tai Po estate’s eight blocks and raged for around 43 hours, killing 168 people and leaving nearly 5,000 people displaced.