SAN FRANCISCO — The Federal Aviation Administration is looking into how an unidentified man walked away from a security checkpoint at San Francisco International Airport after explosives residue on his shoes triggered a screening machine's alarm.
Twenty-eight gates at the domestic terminal were closed for two hours early Wednesday while the United Airlines terminal was searched. The man was not found. The terminal was reopened midmorning and passengers were rescreened, said airport spokesman Ron Wilson.
"This individual probably has no idea he was the cause of so much disruption this morning," Wilson said. "He is not a mad bomber or a terrorist."
The explosive material could be anything from fireworks residue to nitroglycerin tablets, airport officials said. The substance "is similar to a plastic explosive but has the same signature in many respects as common fertilizer," Wilson said.
He said the man may have simply walked across a fertilized lawn earlier Wednesday.
The residue was detected after a gauze-like material was wiped across the man's brown loafers, then put through a machine. It triggered an alarm during the random screening. While a guard checked with his supervisor, the man put on his shoes and walked away.
"When they went to stop him, he didn't stop," said Mike McCarron, another airport spokesman. Airport officials say he may have left on one of the two planes that departed after the alarm sounded.
Passengers were forced to stand in front of the terminal building on an unusually cold San Francisco morning, with temperatures in the 30s.
Eva Renninger, who was returning to Santa Barbara from Kauai, Hawaii, said a little inconvenience was worth the extra safety.
"There's no point panicking. I would rather be here than on the plane that blows up," she said while waiting to be rescreened.