After this morning's minor explosions in London, trained dogs helped police search for bombs in the city's subway system. How do dogs learn to smell bombs?
Classical conditioning techniques using food rewards and toys. In the United States, the Bureau of Alcohol, Tobacco, Firearms and Explosives, Customs and Border Protection, and private dog trainers teach bomb-sniffing dogs. The preferred starting age is between 8 months and 22 months, and the Labrador retriever is a favored breed due to its lack of aggression in high-intensity situations.
The training programs derive many of their techniques from narcotics detection. During the ATF's 10-week program, a dog is exposed to an explosive up to 120 times a day, in amounts ranging from 1,000 pounds to 1 gram. In early phases of training, the dog is told to sit each time he finds the odor—that becomes the signal he uses to alert his handler when a bomb is present. The dog is fed only when in the presence of the explosive. Using a food reward instead of praise and play prevents an exclusive bond between dog and handler, which might prevent the dog from working well with others.
One upper-level training scenario uses a rotating wheel with slots for four containers. Some of the containers are empty; others hold explosives, a distracting object such as food, or an explosive combined with a distracting odor. By using the training wheel, the dog learns to ignore food in favor of explosives.
Some agencies avoid mixing food with work and infuse dog toys with explosive odors instead. The dogs learn to root out hidden explosives by simply playing fetch. This approach requires dogs that have a strong natural inclination for play. It also cements a canine-trainer bond, restricting the dog to working with only one handler.
The dog must learn to recognize thousands of active ingredients that might be used in an explosive. Trainers expose the canine to signature compounds that are found in many different types of explosives. In this way, a dog can be trained to detect all manner of bombs by memorizing a dozen or so smells. According to the Army's military working-dog training manual, canines are trained using dynamite, TOVEX, TNT, C-4 plastic explosives, detonating cord, and potassium chlorate, among other explosives.
Some bomb components are more odoriferous than others. C-4 has an incredibly strong scent; it's followed in decreasing order of smelliness by dynamite, TOVEX, detonating cord, and TNT.
Explainer thanks Mike Bullock of Bullock Canine Service, Anthony Jerone of the Academy of Canine Education, and Jason Purgason of Tarheel Canine Training.