A spokeswoman for the Department said 19 glass panels, measuring 3.8 metres by 1.7 metres, cracked and disintegrated more than a week ago.
The spokeswoman said the panels from the facade above the main entry on Constitution Avenue ”progressively failed” from about midday on February 24.
”The panels had not yet been permanently fixed to the building,” she said.
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”Workers in the vicinity were evacuated before the first panel failed and the area was cordoned off. No one was injured.”
She said an investigation was underway into why the glass panels, each of which cost about $3500, had fallen off the building and how builders would prevent the other panels lining the building falling.