Should someone in Texas ask you what comes to mind when thinking of a drunk driving offense, your mind likely immediately conjures up the image of one standing on the side of the road blowing into a hand-held breath testing device. This thought, however, prompts a question: why is breath used to determine your supposed level of intoxication?

The near-universal standard of .08 as the legal limit for intoxication is actually a measurement of your blood-alcohol content. How can you breath offer an indication of the alcohol content of your blood?

Understanding how alcohol gets on your breath

Knowing this may actually provide you with sufficient evidence to challenge any drunk driving charges pending against you. The alcohol you ingest breaks down into its molecular parts during digestion. That alcohol then permeates the lining of the organs of your digestive tract and enters your bloodstream. Eventually, that alcohol-saturated blood reaches your lungs, where some of the alcohol vaporizes upon coming in contact with oxygen. You then expel that gaseous alcohol when you breathe.

The levels of alcohol on your breath and in your blood remain in equilibrium as this process gradually continues. It is that blood-to-breath ratio that indicates your level of intoxication. According to the Alcohol Pharmacology Education Partnership, hand-held breath testing devices assume a blood-to-breath ratio of 2100:1.

Citing breath testing margin of error

The trouble with this assumption is that in reality, your actual blood-to-breath ratio may range from 1500:1 to 3000:1 depending on various biological factors. This wide range of variance no doubt contributes to experts’ arguments that breath tests may have a margin of error as high as 50%. Should your arrest hinge primarily on breath test results, this information might chip away at its validity.