How reliable are bomb-sniffing dogs?

The bomb-sniffing dog that indicated a bag at the Twin Cities airport might contain explosives was back at work on Wednesday. But the false alarm it caused a day earlier proved surveillance systems have a ways to go before they detect only real threats.

Officials at Minneapolis-St. Paul International Airport said the dog and emergency personnel did what they were trained to do. Still, authorities will review procedures to see if changes should be made as the false alarm caused some flight delays and evacuations in parts of Minneapolis-St. Paul International Airport.

The dog was one of six that airport police handle for the federal Transportation Security Administration. They search throughout the airport for anything suspicious.

An aviation security expert on Tuesday speculated the bag had once been used for testing, and still had remaining residue when it was used as a "last bag." That's a piece of luggage meant to signal a plane has been unloaded.

Airport spokesman Patrick Hogan says he's not aware of the pink bag in question having been used for testing.

"We're pretty confident there was something on the bag that the dog was trained to detect. And it did," Hogan said. "But that doesn't necessarily mean it was an explosive. There are a number of chemicals that dogs are trained to detect, and sometimes they can come from everyday use, not just from somebody preparing an explosive."

"We're pretty confident there was something on the bag that the dog was trained to detect. That doesn't necessarily mean it was an explosive."

Whatever the dog detected, it wasn't a real threat. And experts said there likely will be more false alarms at airports across the country until security officials refine their response to possible threats.

"Shortly after [the Sept. 11 terrorist attacks] around the country, there were these incidents one after another for a couple of weeks until people calmed down," said Douglas Laird, a former security chief for Northwest Airlines.

Laird, who runs an aviation security consulting firm in Reno, Nev., said airport security officials nationwide must ensure bomb-sniffing dogs don't become less reliable from working long hours. While he said it isn't likely that's happening now, machines might be a good alternative to the dogs.

"The machine never gets tired," Laird said.

The problem with machines is they are expensive. As a suitcase full of bottles of honey proved Tuesday, they can also cause false alarms. Authorities shut down Meadows Field airport in Bakersfield, Calif., for a time after a machine mistakenly detected TNT in a Milwaukee man's suitcase. It turned out to be five bottles of honey.

It's possible a dog trained to sniff for explosives could have made the same mistake, said Patrick Beltz, a longtime dog trainer and owner of California-based Work Dogs International. Even a well-trained dog might alert its handler about something harmless if it has worked a long time without finding something and being rewarded, he said.

"Sometimes they'll try to cheat," Beltz said of the dogs. "Other times, it can be really just a mistake. If they want to too bad, they might smell something."

The key, Beltz said, is to make sure a handler knows the dog well enough to tell the difference between the dog becoming excited about explosives or something else.

"It could be sausage somebody's carrying to a family. It's a big difference between a dog showing, well, this smells good, versus saying 'Whoa, I think I'm near [explosives],'" Beltz said.

Hogan said the airport police dog handlers are with their animals every day and take them home. But he acknowledged the dogs can make mistakes.

"There's always a chance, but we don't think so," he said. "These dogs train all the time, they're tested all the time, and their response is very, very good."

(MPR hosts Tom Crann and Cathy Wurzer contributed to this report.)

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