If you ask anyone in Clearwater to describe to you the first image that pops into their head when you say the term “driving under the influence,” they will likely tell you that they envision a person standing on the side of road blowing into a handheld breath measurement device. That the roadside breath test has become the enduring image of the DUI is not surprising as this is the principal foundation on which many drunk driving charges are built. Yet like many, you may wonder how is it that a measurement of your breath is used to determine the alcohol content of your blood.

Understanding how alcohol gets on your breath could potentially provide you with the knowledge needed to challenge a DUI charge. Per the Alcohol Pharmacology Education Partnership, the type of alcohol that you ingest when you drink is ethanol. This a water-soluble compound, meaning that as it dissolves after ingestion, its molecules are able to permeate the lining of the organs in your gastrointestinal tract and enter into your bloodstream. Once there, it is carried by your veins throughout your body, eventually arriving in the lungs (where it may dissolve into the mucous lining of the alveolar sacs. Here, it comes in contact with the oxygen that you breathe in. Some of these ethanol molecules (upon coming in contact with oxygen) dissolve into a gas which is then exhaled as you breathe.

As this process happens, more ethanol is vaporized to maintain an equilibrium with that which is still in your blood. What this means is that with every breath you take, your blood-alcohol content lowers, thus making the idea of getting an accurate BAC reading from your breath akin to hitting a moving target.