A conviction for driving under the influence of alcohol can lead to severe short- and long-term consequences. Thus, if you face such a charge, one can understand your desire to challenge its validity. Yet if authorities have a breath test result indicating a blood-alcohol level above the legal limit to use against you, you might dismiss such a challenge as futile.
Yet how accurate is that test? There is a reason why many courts do not allow breath test results as evidence in DUI cases. The reason for this is that some experts estimate that breath testing devices may have a margin of error as high as 50%.
Breath test mechanics
Understanding how these devices can have such a high margin of error requires that you comprehend their mechanics. When you ingest ethanol (the alcohol used in alcoholic beverages), it eventually ends up in your bloodstream where your veins carry it throughout your body. Upon arriving in your lungs, some of it vaporizes from coming into contact with gaseous oxygen. You then expel that vaporized ethanol when you breathe. That vaporization process gradually continues, with the amount of ethanol on your breath remaining in equilibrium with that in your blood.
Your blood-to-breath ratio
Breath testing devices measure the ethanol on your breath and then use that measurement to estimate the level in your blood. To do this, according to the Alcohol Pharmacology Education Partnership, they assume a static blood-to-breath ratio of 2100:1 (the alcohol content in your blood being 2100 times greater than that of your breath). However, in reality, your actual blood-to-breath ratio can range from 1500:1 to 3000:1. Any number of factors might influence this, from your gender to your weight to your genetic makeup.