MINNEAPOLIS (AP) -- Police said they're still confident that trained dogs can sniff out explosives, even after false alarms by five dogs closed a section of Minneapolis-St. Paul International Airport on Wednesday.
Authorities found nothing when they dismantled the automated teller machine and soda machine that the dogs singled out. Airport police Cmdr. Merlin Tolsma said it may never be clear what caused the dogs' reactions.
Security experts debate whether dogs or machines are best at detecting explosives, but Tolsma said he believes ''the dog is the best indicator. Their nose is tremendous.''
St. Paul officer Mark Ficcadenti said his department's trained dogs have been fooled before. In one case, it was by felt-tip markers with a nitrate base in a student's locker.
''The dogs are not infallible,'' he said.
Airport director Steve Wareham said he has wondered whether farmers who use fertilizers and then come to the airport may leave traces that alert the dogs.
Patrick Hogan, spokesman for the Metropolitan Airports Commission, said the agency uses six teams of dogs and handlers, all trained by the Transportation Security Administration. The airport also uses electronic equipment to screen passengers and luggage.
On Wednesday, Hogan said, three dogs were being trained at the Humphrey terminal. Their separate positive reactions made it unlikely that they were responding to a spurious scent, he said.
The St. Paul Police Department's nationally-recognized canine units have 21 police dogs, including five that are cross-trained to detect explosives. All get 12 weeks of basic training, plus another 10 weeks for dogs trained to sniff for explosives. The dogs are recertified each year in their specialty.
''We use our drug dogs non-stop and our bomb dogs more and more,'' said Ficcadenti, St. Paul's head dog trainer. ''I feel really comfortable with our dogs. ... We trust our lives with these dogs.''
He said there are instances where the animals will detect something that is not an explosive.
''It's not real common ... but no one knows what the dog is actually smelling and how it discriminates and cuts through the odors,'' Ficcadenti said. ''There are so many variables involved in detection work.''
Ficcadenti said that the dogs are so highly trained to detect such minute amounts that they would react if someone touched gunpowder and then touched a doorknob. He said it is plausible that residue from gunpowder or fireworks could have been transferred onto the ATM and soda machines.
''The dogs' ability to pick up trace amounts and odors is truly phenomenal,'' he said. ''Dogs alert to odor, not necessarily substance. Why those dogs (reacted to the machines) I can't tell you. But it happens, and it doesn't mean that the dogs are any less credible. ''