A day after the Humphrey Terminal at Minneapolis-St. Paul International Airport was evacuated because bomb-sniffing dogs detected something, officials said they still don't know what the dogs smelled.
All they knew was it wasn't a bomb.
"At this point, we don't know what the dogs hit on," said Cmdr. Kevin Herman of the Bloomington Police Department, whose bomb disposal unit responded to the terminal. "There's a possibility that someone could've touched something earlier in the day and left residue that we weren't able to detect."
About 200 passengers and airport workers were ushered out of the terminal Wednesday afternoon after the specially trained dogs alerted their handlers that there were suspicious odors in two machines an automated teller machine in the central part of the terminal and a soft drink vending machine near the baggage claim area on the terminal's south side.
After the terminal was evacuated, airport security officers and specialists from the Bloomington Police Department opened the ATM where it sat and found nothing out of the ordinary. Airport spokesman Pat Hogan said the soft drink machine was taken to another area of the facility and dismantled; it didn't contain an explosive device, either.
"It appears that whatever the dogs were picking up was innocent. It would have to be something related to explosives, either gunpowder or fireworks," Hogan said. "It could've been as simple as one individual using both machines. Perhaps they got cash and got something out of the vending machine."
The dogs are trained to detect five nitrogen-based compounds used in many different explosives and firearms. Some of those items, like various fertilizers, can have innocent, everyday uses.
It isn't unheard of for the dogs to detect compounds at the airport. But because three dogs owned by the Metropolitan Airports Commission and two dogs owned by the Bloomington Police Department detected something and two different locations were involved, authorities became particularly concerned.
Herman said that after the two machines were determined to be safe, they were returned to their owners and will be replaced at the airport.
Passengers waiting to board a Sun Country Airlines flight were evacuated from the terminal and taken to a parking garage about 6:30 p.m. The terminal was reopened shortly after 10 p.m.
Hogan said airport security officers weigh a number of factors in deciding when to evacuate a concourse at the Humphrey Terminal or the Lindbergh Terminal, which handles the majority of the airport's flights.
"If there's any doubt in the minds of police that the public is safe, then they'll close the terminal or a section of the terminal," he said. "And it depends where the suspicious material is at."
Adding to the officers' concern Wednesday was that the machines were in public areas of the terminal, not in the gate areas that passengers have to go through security to reach.
Evacuations are rare, Hogan said.
"Occasionally, we'll run across a suspicious package and call the bomb squad," he said. Hogan couldn't recall the last time an entire terminal was evacuated but said some concourses were evacuated about a year ago.
"There were bomb threats scribbled on a bathroom stall door," he said. Nothing was found in a search of the area, and the concourses were reopened.