A smelly grey water system lead to the evacuation of 500 people from the Australian Taxation Office in Albury on Tuesday afternoon.
Staff reported what they feared to be a gas leak about 3pm to emergency services.
Fire and Rescue NSW Inspector Stewart Alexander said the building was evacuated quickly.
“We found the cause – it was a grey water system which collects water form hand basin,” he said.
“That had been inactive for a little while and when it was reactivated, it released an odour that got into the ventilation system.”
Inspector Alexander said it was a good result for the incident and those who had reported their suspicions had done the right thing.
“If you have the slightest bit of doubt whatsoever, call emergency services,” he said.