Police officers' detection of breath odors from alcohol ingestion.

Police officers frequently use the presence or absence of an alcohol breath odor for decisions on proceeding further into sobriety testing. Epidemiological studies report many false negative errors. The current study employed 20 experienced officers as observers to detect an alcohol odor from 14 subjects who were at blood alcohol concentrations (BACs) ranging from zero to 0.130 g/dl. Over a 4 h period, each officer had 24 opportunities to place his nose at the terminal end of a 6 in. tube through which subjects blew. Subjects were hidden behind screens with a slit for the tube to prevent any but odor cues. Under these optimum conditions, odor was detected only two-thirds of the time for BACs below 0.08 and 85% of the time for BACs at or above 0.08%. After food consumption, correct detections declined further. Officers were unable to recognize whether the alcohol beverage was beer, wine, bourbon or vodka. Odor strength estimates were unrelated to BAC levels. Estimates of BAC level failed to rise above random guesses. These results demonstrate that even under optimum laboratory conditions, breath odor detection is unreliable, which may account for the low detection rate found in roadside realistic conditions.