The leak forced the evacuation of about 100 people earlier in the day after office workers at the building in the area of Homer and Nelson streets started smelling an unknown substance in the air.
Firefighters quickly closed off the building as they tried to figure out what was causing the panic.
“They were having a hard time describing the smell,” said Battalion Chief Steve Chila. “We interviewed eight people, we got eight different responses.”
Five people were taken to St. Paul's hospital for further treatment.
Chila later said investigators might have some idea what the leak was, if not where. “We've put it down to some form of leak in the cooling system, some kind of Freon-based gas. We're not exactly sure where the leak is originating right now.”
Neighbouring buildings were not impacted, but the operation snarled traffic in Yaletown for most of the day.
Officials weren’t sure when people would be allowed back into the building.