Several people were treated for what appeared to be carbon monoxide poisoning at a downtown Bismarck office building Friday afternoon.

Bismarck Fire Battalion Chief Kurt Leben said someone from a hospital emergency room called the fire department after two employees from a construction crew came in after not feeling well at work. The employees appeared to have carbon monoxide poisoning.

The fire department and Metro Ambulance responded to Civic Square, 521 E. Main Ave., and evacuated the building, Leben said.

He said a construction crew had been using gas-powered tools while laying concrete on the building's third floor. The building's windows don't open, Leben said. Several other employees also were checked out and treated for elevated carbon monoxide levels.

Carbon monoxide readings on the third floor and in the elevator shaft were around 300 parts per million, Leben said. He said normal levels would be zero, and anything higher than 50 parts per million is troublesome.

None of the employees appeared to be seriously ill, he said.

- Jenny Michael