Breathalyzers Discriminate Against Women -Part 3

Breathalyzer machines work by measuring the amount of alcohol in a breath sample. They then multiply that amount by 2100 and report that as the blood alcohol volume. This number is called the partition ratio. It assumes that for every gram of alcohol in a breath sample, there are 2100 grams in that person's blood.

Here's the problem. Studies have shown that the actual ratio of breath alcohol to blood alcohol varies from person to person. It varies from around a low of around 1100:1 up to a high of 3500:1. State v. McCarty 434 N.W.2d 67 (S.D. 1988). This means that the lower a person's actual partition ratio, the higher their blood alcohol reading.

Lets take three people, each with .06% true BAC. One with a partition ratio of 2100:1 will have a breath test of .06%. Another person with a low ratio of 1100:1 will report a result 53.26% lower than their true result. Finally one with a high ratio of 3500:1 will report a result 126% higher than the true result. According to a study, women have higher partition ratios than men and will have higher breath test results. Jones, "Determination of Liquid/Air Partition Coefficients for Dilute Solutions of Ethanol in Water, Whole Blood and Plasma", Analytical Toxicology 193 (July/August 1983)