The Variability Between Breath Readings and Blood Tests: Why It Matters in DUI Defence
Breath-alcohol testing is a cornerstone of impaired driving enforcement, widely used in Canada to determine whether drivers are over the legal blood-alcohol concentration (BAC) limit. However, new scientific findings shed light on a significant problem with this method of testing: the variability of the blood/breath ratio (BBR), which directly impacts the accuracy of breath-alcohol test results. This variability raises important questions about how reliable breathalyzer readings truly are, and has serious implications for those facing impaired driving charges.
At the heart of the issue is the BBR, the proportionality factor used to convert a breath-alcohol concentration (BrAC) into an estimated BAC. The standard BBR, used in all breath-alcohol testing devices in Canada, is assumed to be 2100:1. This means that 2100 mL of breath is considered equivalent to the alcohol content of 1 mL of blood. However, as discussed in a recent article by Dominick A. Labianca, The Variability of the Blood/Breath Ratio and Its Impact on the Results of Breath-Alcohol Analyses (2023), this ratio is far from fixed and can vary significantly between individuals.
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