Explosives detection by military working dogs: Olfactory generalization from components to mixtures

The training of scent detection dogs using samples of explosives or their chemical precursors is a well-established and documented practice. However an area of canine odor detection that remains under-studied regards a trained dog's perception of an explosive odor when more than one odorant is combined to produce a mixture. The first objective of our study was to determine whether training adult Labrador Retrievers (n = 20) to detect the scent of chemically pure potassium chlorate (PC) was sufficient to produce generalization to PC-based explosive mixtures that contained a novel component. We found that the majority of dogs (87%) trained with pure PC alone did not correctly signal the presence of one or more of four PC-based explosive mixtures. Our second objective was to determine whether training dogs using the separated components found in the PC-based explosives would subsequently enhance detection. Dogs were then trained using a novel static odor delivery device that safely segregated the PC and non-PC components and presented a merged odor to the dog. A statistically significant improvement in percentage of dogs detecting PC-based mixtures after training with the separated components compared to training with PC alone was seen with Mixture 1 (27–100%, P < 0.0001), Mixture 2 (40–81%, P = 0.0229), Mixture 3 (38–94%, P = 0.0004), and Mixture 4 (69–100%, P < 0.005). The results of this study highlight the potential limitations of dogs trained to detect a single odor to then recognize the odor when mixed with other substances. The odor delivery device developed for this study represents an important and effective training option that may reduce the need for using a final PC explosive mixture in canine training.