Highwood, IL- By Susan Kuczka, Chicago Tribune – Firefighters took 10 employees of a north suburban insurance agency to hospitals Wednesday after a furnace malfunction filled their office with carbon monoxide fumes, authorities said.

Only one employee had to be hospitalized for treatment of possible carbon monoxide poisoning, authorities said.

“We were lucky,” said Anna Maria Viti-Welch, president of Guy Viti Insurance who was among the employees evacuated from the one-story building in Highwood.

Highwood Fire Chief Tom Lovejoy said high winds and dense air may have contributed to the furnace malfunction, which allowed carbon monoxide to escape into the building.

The wind gusts, apparently pushed dense air down the building’s chimney, allowing the flue to open, he said.

Vita-Welch said she heard a carbon monoxide detector alarm go off in the basement around noon, prompting her to call the Fire Department.

After firefighters evacuated the building and sent the employees by ambulance to four hospitals, a repair crew fixed the furnace.

The insurance agency reopened a few hours later, after Fire Department officials determined it was safe, Lovejoy said.

When firefighters arrived, carbon monoxide levels in the building measured 100 parts per billion, which Lovejoy said was “well over the danger limit.”

“We’re going to keep watching it closely,” Lovejoy said.