The collapse of a ventilation duct in a Nex mall cinema was most likely due to waterlogged insulation material whose weight had overloaded the duct's supporting brackets, according to the Building and Construction Authority's (BCA) preliminary findings.
The Aug 30 incident, which occurred in a Shaw Theatres cinema hall, left two moviegoers injured.
Investigations are ongoing and are expected to be completed by end-October, said the Ministry of National Development (MND) in a written reply on Monday to a parliamentary question from Mr Melvin Yong (Radin Mas).
BCA had found that "a significant amount of water had accumulated in the layer of acoustic material surrounding the air-conditioning and mechanical ventilation (ACMV) duct".
The added weight had most likely caused the brackets holding the duct to give way.
The acoustic material surrounding the duct serves to regulate the surface temperature around the duct to prevent water from forming due to condensation, and to insulate the noise caused by air travelling through the duct.
BCA has alerted other cinema operators to inspect their ACMV ducts and carry out maintenance and repair works where necessary, MND added.
BCA will also assess what further measures need to be taken to prevent a recurrence of such incidents, after it has completed its investigation.
Associate Professor Daniel Wong of the National University of Singapore's School of Design and Environment said the water accumulation could come from a leaking water pipe, a waterproofing defect allowing the ingress of water, or prolonged condensation due to temperature changes.
He noted that these occurrences are common in poorly maintained or abandoned buildings.
Prof Wong stressed that to prevent such failures, scheduled inspections and regular maintenance must be carried out.
When contacted, a spokesman from Nex said it is providing assistance to its tenant, Shaw Theatres, to carry out rectification works.
The mall, which is owned and managed by Gold Ridge, said it will "continue to collaborate with the regulatory bodies to ensure that this is resolved as soon as possible and preventive measures are put in place".
Nex declined to say if it is checking other ACMV ducts in the building for similar issues.
Building owners are responsible by law for the maintenance of their buildings, including interior fixtures.
Shaw Theatres said it conducted inspections at its six cineplexes, following the incident as a precautionary measure, and all were found to be safe.
Golden Village (GV) cinemas said that it conducted a round of inspection and maintenance checks with BCA officers, after recommendations from the authority. This was on top of its scheduled maintenance and inspections.
A GV spokesman added that the cinemas' air-conditioning ducts are designed to be positioned away from the seating zones.
