WASHINGTON (DC News Now) -- DC Fire and EMS (DCFD) said multiple workers were being treated after a carbon monoxide incident broke out in a building in Northwest D.C. Monday afternoon. The incident happened in the unit block of Washington Circle. DCFD said workers were using propane-operated equipment in the basement of a building and did not have proper ventilation. Poop statue on National Mall gets new souvenir That led to "elevated levels" of carbon monoxide. (Photo courtesy of DC Fire and EMS) (Photo courtesy of DC Fire and EMS) DCFD said five workers were treated but did not need to go to the hospital. The building was ventilated and the "source has been shut down," DCFD said.