Patrick J. Silva Professional Law Corporation
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Myth #4:

Breath test: 2100:1 favors your client State scientists claim that the 2100:1 blood-breath partition ratio favors defendants because the true mean is closer to 2300:1. Breath alcohol analysis is by far the most commonly employed form of chemical testing in traffic law enforcement. Hence the true blood : breath ratio for alcohol, originally used to calibrate alcohol analyzers to indicate the supposedly corresponding blood alcohol concentration, has been a subject of much scientific investigation and debate for about 50 years. It is evident from considerations of quantitative human biology that a single ratio or conversion factor will not apply to all persons (Mason and Dubowski, 1974, 1976). Kurt M. Dubowski, Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects, 10 J. Stud. Alcohol Suppl. 98, 102 (1985). Nevertheless, for half of that period, there was general acceptance of 2100 : 1 as the partition ratio of alcohol between blood and alveolar breath, as a population mean (Borkenstein et al. 1972; Harger et at., 1950; National Safety Council, 1953). Quantitative evidential breath alcohol analyzers are still currently factory-calibrated in grams of alcohol per 210 L of breath. Some official guidelines incorporate this calibration (National Highway Traffic Safety Administration, 1984), thus in effect retaining a 2100:1 blood alcohol : breath concentration ratio for those jurisdictions statutorily requiring the reporting of evidentiary alcohol concentrations in terms of blood. Id. at 101-102. Later studies on larger subject groups, with more sophisticated chemical analyses of blood and breath for alcohol and more extensive data treatment, indicated that the mean alcohol partition factor between blood and breath is very close to 2300:1 (Dubowski, 1975; Dubowski and O’Neill, 1979; Jones, 1976; Jones et al., 1975). However, significant variations from this population mean exist during active alcohol absorption and in some individuals even in the postabsorptive phase. The typical biological variability of human alcohol pharmacokinetic parameters is well illustrated by the data from studies of Dubowski and O’Neill (1979). These are summarized in Table 3, for the ratio of alcohol concentrations in whole blood and end-expiratory breath in healthy adult men in the fully postabsorptive phase. Id. at 102. These experimentally determined ratios have a Gaussian distribution. Hence a postabsorptive blood alcohol : breath alcohol concentration ratio range of 1797 : 1 to 2763 : 1 can be estimated for 95% and 1555 : 1 to 3005 : 1 for 99.7% of such a population. Id. at 102. Transposing Dr. Dubowski's figures onto a normal or Gaussian [2] distribution chart makes it easier to conceptualize his findings. While 2300:1 is slightly greater than the mean of 2280:1, 2100:1 or higher accounts for less than 79.95% of the total population. Thus over 20% of persons tested in this study would have a false high reading at 2100:1. In order to achieve a confidence level of 99.7%, the partition ratio of 1555:1 would have to be used.