Carbon monoxide detected at Heirloom Jewelers forced emergency services to block off Third Avenue between Second Street and Third Street in downtown Havre Friday morning. Havre Fire Chief Mel Paulson said the fire department responded to a report of a gas leak at about 10:15 a.m. and called NorthWestern Energy to the scene when firefighters determined carbon monoxide was in the air. NorthWestern Energy spokesperson Brandy Powers said a company gas serviceman found dangerous levels of carbon monoxide upon arriving at the scene. The serviceman immediately evacuated the building and shut down the power to the surrounding buildings until he could determine the source of the leak. Powers said the leak affected several businesses on Second and Third streets.