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Breaking down the basics of a breath test measurement

Posted on July 29, 2020

Previous posts on this blog share a good deal of information about breath testing to determine intoxication. Yet one question that you (along with many of those that come to see us here at the Law Offices of J.B. Katz, P.C.) may have is why would law enforcement officials choose to test your breath to make such a determination.

After all, is it not your blood-alcohol content that indicates whether or not you drove while drunk? Indeed, the number “.08” (the nearly universally accepted legal limit for alcohol in the body) is a BAC measurement. Understanding how a breath testing device comes up with a BAC measurement may actually support your challenge of the breath test results used as evidence against you.

How alcohol gets on your breath

The ethanol alcohol you ingest when drinking permeates the lining of your gastrointestinal organs and is eventually carried to your lungs in the bloodstream. There some of it vaporizes as it comes in contact with oxygen and leaves your body when you breathe. The content of alcohol on your breath must remain in equilibrium with that in your blood. A breath testing device measures the alcohol on your breath and then estimates the content in your blood based on an assumed equilibrium ratio. Per the Alcohol Pharmacology Education Partnership, that ratio is 2100:1 (implying that the content of alcohol in your blood is 2100 times greater than that of your breath).

The problem with the assumed ratio

In reality, your blood-to-breath alcohol ratio can actually range from 1500:1 to 3000:1. This may contribute to the estimations that many experts make that breath testing devices may have a margin of error as high as 50%. You can learn more about this and other potential challenges to DUI charges by continuing to explore our site.