Past posts on this blog touched upon the fact that you can often call the results of breath tests into question. Having a result showing a blood-alcohol content greater than .08 used as evidence against you may insurmountable when challenging the drunk driving charges, yet understanding that you can scrutinize such a test should give you added confidence when doing so.
Successfully mounting such a challenge, however, requires more than just an assertion questioning the reliability of breath tests. Rather, you need to have a comprehension of the mechanics of breath testing devices.
Understanding how alcohol gets on your breath
Knowing this requires that you understand the pathway that alcohol travels from going into your body to leaving it on your breath. The form of alcohol used in alcoholic drinks is ethanol. This is a water-soluble compound, which allows it to permeate membrane surfaces through a process known as passive diffusion. This is how it gets into your bloodstream after you ingest it. Once ethanol is in your blood, the veins carry it throughout your body, eventually arriving in your lungs. In the lungs, it comes in contact with oxygen (causing a portion of it to vaporize into a gas). That gas then leaves your body when you breathe.
Breaking down breath test mechanics
This process of ethanol vaporizing in the lungs continues, with the concentration of ethanol on your breath remaining in equilibrium with that in your lungs. According to the Alcohol Pharmacology Education Partnership, breath testing devices assume that equilibrium to be 2100:1 (the content of alcohol in your blood being 2100 times greater than that on your breath). That assumption drives their measurements. The trouble is that in reality, your alcohol blood-to-breath ratio can range between 1500:1 to 3000:1. This introduces a potentially large margin of error in to breath test results.