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The Science Behind .08 BAC

.08 Blood Alcohol Content is the standard used by the State of California (and all states since 2004) to calculate if someone is under the influence of alcohol, and therefore subject to a DUI arrest and conviction.

How did states arrive at this number? Before we answer that question, let us first look at the physiology of alcohol consumption.

Physiology of Alcohol Consumption:

Alcohol is a very light fluid – it diffuses quickly when consumed into parts of the body that have water content. The more water that is present in that particular part of the body, the more rapidly alcohol is absorbed into it. For example, blood is primarily made of water, so alcohol is absorbed quickly into it. Organs like the brain, however, have much less water, so alcohol is absorbed at a much slower rate.

As alcohol is absorbed through the stomach and small intestines, it gets into the bloodstream through the portal vein. The alcohol then moves to the liver, to the right side of the heart, and into the lungs. From there, it travels to the left side of the heart, is pumped into the general circulatory system, and finally makes its way to the brain, which causes intoxication.

Tests utilized by law enforcement measure whether or not someone is under the influence of alcohol by testing the blood, breath, or urine. These areas – blood, breath, and urine – are all places where alcohol travels in a much higher concentration before it reaches the brain to cause intoxication. However, the brain is where the alcohol must be absorbed to cause intoxication and consequently impairment.

What is the Science Behind .08?

In the 1930s, a Swedish research professor, Erik Matteo Prochet Widmark, published a study that identified the average absorption and elimination rates of alcohol by analyzing the results obtained from 20 men and 10 women. His study was predicated on a mathematical formula based on an average number that could measure the overall body alcohol content, including the brain, by measuring the amount of alcohol in the blood. This number, the Widmark Factor R, is the ratio between the alcohol in the whole body divided by the alcohol in the blood.

There were problems with the methodology of the study – for example, it was based on an average person, not individual; the physiological differences between men and women were not accounted for; the sample was incredibly small; the subjects had empty stomachs; and it measured someone consuming all the alcohol at one time. This methodology had its flaws and therefore the .08 number is inherently problematic.

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