The Allegheny County bomb squad and county fire marshal are at Pittsburgh International Airport because smoke was spotted at a gate in the D concourse Thursday morning.
Smoke has dissipated, but the D concourse is closed and the flights that operate there have been moved to the A concourse.
Delta, American and United flights are affected by the concourse change.
Spokeswoman JoAnn Jenny said the county Airport Authority got an emergency call at 7:30 a.m. about smoke around gate D80.
Firefighters and airport employees traced the source of the smoke to the men's bathroom in a plumbing access panel, where they found a black satchel and saw charring around the panel, Jenny said.