About 30 employees at the federal government building on North Archibald Street in Thunder Bay have received the all-clear to return to their offices Friday. The Thunder Bay RCMP office was also closed, but will re-open Friday.  The Thunder Bay RCMP office was also closed, but will re-open Friday. (Jeff Walters/CBC)

Workers became concerned this week when legionella bacteria were found in the building's cooling tower.

A spokesperson for the Public Service Alliance of Canada said the health and safety committee determined late Thursday it would be safe to return to work.

"As a precaution, until … it's sanitized and until we realize what the levels were, and the danger to workers, [we chose to] err on the side of caution and get people out of there,” Judith Monteith-Farrell said.

Monteith-Farrell said about 30 people work in the building, including RCMP officers.

According to the Public Health Agency of Canada, people can fall sick if they inhale steam or mist containing the bacteria that causes Legionnaires' disease — a severe form of pneumonia. No one has been known to pass on the infection to others.

Monteith-Farrell said no one working in the building has shown any serious symptoms.