Firefighters were sent to John Street police station following reports of an unidentified substance discovered leaking from a container in an office.
Two appliances from Hove and Roedean, along with a Hazardous Materials Advisor from East Sussex Fire & Rescue Service, were sent to the scene at 2.12pm to assist with a small chemical leak.
Firefighters entered the building wearing breathing apparatus and wearing protective clothing.
People were evacuated from the office while firefighters identified the substance and removed it into the fresh air, pending specialist recovery.
It was chemical in nature and the occupants of the office were advised to open windows to clear any lingering fumes.
It was not necessary to evacuate the entire building.