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State v. Hanks3/2/2001
On Appeal from District Court of Vermont, Unit No. 3, Caledonia Circuit September Term, 2000 Walter M. Morris, Jr., J.
Defendant appeals his jury conviction on a charge of driving while under the influence of intoxicating liquor (DWI), in violation of 23 V.S.A. § 1201(a)(2). He argues that the district court erred by limiting his cross-examination of the state chemist so that he was prevented from challenging the State's reliance on a permissive inference that his breath test result indicated he was intoxicated. We conclude that the trial court abused its discretion by refusing to allow defense counsel to cross-examine the state chemist concerning the potential variability among different persons at different times in the conversion rate between their breath-alcohol (BrAC) and blood-alcohol (BAC) concentration. Because we cannot be sure that the error was harmless, we reverse the conviction.
Defendant was stopped and arrested for DWI in the early morning hours of September 30, 1998. Approximately one hour and twenty minutes after the stop, defendant submitted a breath sample that indicated a concentration of .109 grams of alcohol per 210 liters of breath. Defendant was charged with driving "under the influence of intoxicating liquor," in violation of 23 V.S.A. § 1201(a)(2), rather than driving with an alcohol concentration of .08 or more, in violation of § 1201(a)(1). Nevertheless, the State indicated that it intended to introduce defendant's breath test result to take advantage of the permissive inference that defendant was intoxicated at the time of the alleged offense. See 23 V.S.A. § 1204(2) ("If the person's alcohol concentration at [the time of operation] was 0.08 or more, it shall be a permissive inference that the person was under the influence of intoxicating liquor in violation of section 1201(a)(2)"); id. § 1204(3) ("If the person's alcohol concentration at any time within two hours of the alleged offense was 0.10 or more, it shall be a permissive inference that the person was under the influence of intoxicating liquor in violation of section 1201(a)(2)").
A jury trial was scheduled for September 28, 1999. The day before trial, the State filed a motion in limine asking the court to limit defense counsel's cross-examination of the State's expert witness, a Department of Health chemist who was expected to explain the results of defendant's breath sample. The State asked the court "to exclude any examination based on variations as a general matter in the human population in the so-called 'partition ratio.'"
The "partition ratio" refers to the conversion rate between a person's BrAC and BAC. Alcohol in the breath does not cause intoxication. Rather, it is the impact of alcohol on the central nervous system, particularly the brain, that causes the physiological and psychological changes associated with impairment. Alcohol reaches the central nervous system through the blood. When used to establish blood-alcohol levels, breath-testing devices such as the Datamaster machine use a mathematical constant to approximate the percentage of alcohol in the blood based on the amount of alcohol present in a breath sample. Like other breath-testing machines, Datamaster uses a conversion rate of 2100:1 as an assumed blood-breath ratio, which represents the relationship between the number of alcohol molecules in the bloodstream to the number present in the breath when both substances are tested simultaneously. Thus, a 2100:1 conversion factor assumes that for each molecule of alcohol in a given volume of breath, there are 2100 molecules of alcohol in the same volume of blood.
It is generally recognized, as confirmed by the proffered testimony of the state chemis
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