About 1000 Defence staff were evacuated from the Russell Offices after someone burned their lunch so badly it turned to ash.
An Emergency Services Agency spokeswoman said the overcooked food was unrecognisable by the time firefighters got to it, and it had filled the building with an "acrid smell", setting off a fire alarm and leading to the evacuation.
Crews were called to the scene at 3.13pm Thursday. Firefighters ventilated the building and the hazmat team assessed the area, before allowing staff back inside about 4.30pm.
There was also one pumper, a commander and a breathing apparatus van on the scene, but they have now left.