This paper discusses problems arising when breath alcohol values differ so much from simultaneous blood alcohol concentration (BAC), that conclusions must not be drawn about driving ability. BAC and impairment of driving skills have been shown to be related so closely that statutory drink-drive limits, based on BAC, are accepted worldwide. Although various countries have introduced breath alcohol determination, using specially developed instruments for quantitative evidential testing, breath alcohol level is not precisely correlated with BAC. Breath alcohol measurements can be influenced unintentionally or on purpose. The results of drinking experiments show that hypoventilation can cause maximum deviations up to 32% above normal breath measurements, and hyperventilation can cause deviations 24% below them. Four examples out of many cases are given, where very large discrepancies were found between breath test and BAC measures for drivers actually measured by the police in German and Austrian cities. Though they may be rare, the reasons for such blatant discrepancies in measurements on drivers are not yet clear, and can impair evidence prosecuting drunk drivers. Available methods for measuring breath alcohol cannot solve this problem.
Abstract