Flight operations in the Washington DC area resumed on Friday (local time) after a temporary ground stop due to reports of a strong chemical odor at a major air traffic control facility.Transport Secretary Sean Duffy confirmed the development in a post on Twitter, saying “the ground stop is over and operations have resumed.”He said emergency teams examined the site and found no threat to workers. “Fauquier County and Prince William County firefighters have confirmed there is no threat to air traffic controllers,” Duffy said.According to Duffy, “The temporary ground stop affected Ronald Reagan Washington National Airport (DCA), Washington Dulles International Airport (IAD), Baltimore-Washington International Airport (BWI) and Richmond International Airport (RIC).”The problem began when employees at the Potomac Tracon facility reported a strong chemical odor inside the building. The center manages airspace for much of the Washington area. CNN reported that Ronald Reagan Washington National Airport was hardest hit, with more than 136 cancellations and nearly 300 delays.Emergency responders and a hazardous materials team later traced the problem to a circuit board that had overheated. The component has been replaced.Officials said flights were gradually returning to normal schedules. However, the Associated Press reported that flight schedules in the Washington DC area were expected to remain unstable throughout the weekend.