The U.S. Federal Aviation Administration said it stopped traffic at the three primary Washington-area airports on Friday after air traffic controllers at a Virginia facility had to halt work because of a strong chemical smell.

The FAA said the issue disrupted operations at Potomac Consolidated Terminal RADAR Approach Control, which controls airspace over numerous airports in the Washington region and had forced the agency to stop traffic at Reagan Washington National Airport, Washington Dulles International Airport and Baltimore-Washington International Airport.

Airlines told Reuters the FAA was relocating Potomac controllers to a training facility and some would need to begin diverting planes because of congestion.

Controllers will have reduced radar scopes so more delays are likely once the ground stops are lifted.

About 30% of flights at Reagan were delayed, according to FlightAware, a flight tracking site.

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(Reporting by David Shepardson, Kanishka Singh and Jasper Ward in Washington; editing by Scott Malone and Rosalba O’Brien)