San Francisco Airport evacuated

Officials shut down 28 gates at San Francisco International Airport today after security guards detected explosives residue on a man's shoes, but the man disappeared into a crowd before guards could question him.

Spokesman Mike McCarron said "when they went to stop him, he didn't stop."

The passenger was described as a white male in his 40s.

Several thousand passengers were cleared from the United Airlines domestic terminal beginning around 7am (local time), McCarron said. All outgoing flights in the area were held.

Lawyer Kathi Pugh of Berkeley was planning to fly to Philadelphia to attend the American Bar Association's annual meeting.

"It just seems like they could figure out a better way to search people again rather than shut down the entire airport," she said by phone from the crowded security area.