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What is the science behind breathalyzer tests?

Most of us have a good understanding of the various tools that law enforcement in Maryland has at its disposal to combat drunk driving. For instance, we know that officials rely on sobriety checkpoints and enhanced patrols to try to catch people in the act, and use both field sobriety tests and, of course, breathalyzer tests to verify their suspicions about impaired driving.

What people might not have a good idea about, however, is the science behind the breathalyzer test. Specifically, while they might understand that if it measures a .08 or above that they can be placed under arrest for driving under the influence, they might not comprehend just how it arrives at those figures.

In today's post, the first in a series, we'll take a look at the science behind breathalyzer tests.

What exactly do the numbers on the breathalyzer test stand for?

The numbers provided by a breathalyzer test are actually measurements of a person's blood alcohol concentration, which is also referred to as BAC or blood alcohol content.

In general, when a person consumes alcohol -- be it wine, beer or hard liquor -- it's absorbed into the bloodstream thorough the stomach and intestinal walls, and travels directly to the brain. Accordingly, a breathalyzer test measures the concentration of alcohol found in a certain volume of blood.

By way of illustration, if a breathalyzer test measures a person's BAC as .08, a blood sample would theoretically show that their blood was comprised of .08 percent alcohol.

How can a test designed for breath accurately measure a person's blood?    

As explained above, when alcohol is absorbed into the bloodstream, it travels to the brain, passing through the lungs along the way. When it passes through the lungs, a measurable portion of the alcohol is absorbed by the lining of the lungs and passed into tiny air sacs called alveoli.

What a breathalyzer test does is measure the alcohol concentration found in the alveolar air exhaled by a test subject, which, in theory, should be the same as that found in their blood.  

We'll continue this conversation in a future post. In the meantime, if you have been arrested on suspicion of DUI, consider speaking with an experienced legal professional as soon as possible. Together, you can discuss your options, including challenging the accuracy of the breathalyzer test.

Source: Esurance, "Blood alcohol concentration and breathalyzers: How it works," Jessica Guerin, Accessed Nov. 13, 2014 

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