Hundreds of workers vacated a government building in Ottawa after a small amount of hydrogen fluoride gas spilled. (CBC)

Two people were taken to hospital Tuesday in Ottawa, and a Natural Resources Canada building was evacuated, after small leak of hydrogen fluoride gas in a lab.

A malfunctioning lab device caused the leak around 11 a.m. ET in a seventh-floor laboratory at an office of the Geological Survey of Canada at 601 Booth St.

Thirty-five firefighters, including two hazardous-materials teams, were dispatched to the scene. The building's 300 employees were already leaving the building when crews arrived, fire department spokesperson Marc Messier said.

Two people working in the lab at the time of the spill, a 31-year-old man and a 28-year-old woman, were taken to hospital as a precautionary measure, paramedics said. The woman had been treated at the scene for airway irritation.

Hydrogen fluoride gas is both toxic and highly reactive. It is used to dissolve rocks and other ore samples for analysis.

The fire department sent eight units, including two haz-mat teams, because the gas is highly toxic. (Sandra Abma/CBC)

"The trouble with fluorine is that when it's exposed to oxygen and it's exposed to outer elements such as humidity it changes states," Messier said. "Once we heard that they had an incident in a lab involving a chemical, we basically pulled back and basically made sure everybody's been taken out, make sure that the ventilation system and everything's been done in order to keep this product confined to the lab."

The hazardous materials teams checked the building and confirmed that its safety systems and ventilation equipment had functioned properly, allowing staff to re-enter as of 2 p.m.

"It triggered the emergency response that usually would take place," Geneviève Béchard of the Geological Survey of Canada said. "The two people who were present were obviously shook up."

Booth Street between Norman Street and McCann Street was closed to motorists and pedestrians for two hours, but police later reopened the road.