Understanding how one’s breath equates to their BAC

On Behalf of | Jan 28, 2022 | DUI

Were one to mention the number “0.08,” most might likely recognize to be the legal limit for a person’s blood-alcohol content (both in Florida and throughout most of the U.S.). The visual representation of this statistic (in most people’s minds) is someone on the side of the road, blowing into a hand-held breath testing device.

Yet this prompts the question that many pose to the team here at the Law Firm of Scott T. Moorey: why would law enforcement officials measure one’s breath to determine the alcohol content of their blood?

How does alcohol get on the breath?

To know the answer to this question, one needs to understand the process that ethanol (the type of alcohol consumed when drinking alcoholic beverages) goes through to get on one’s breath. According to information shared by the Alcohol Pharmacology Education Partnership, ethanol breaks down upon consumption and escaped the gastrointestinal tract through passive diffusion (which allows water-soluble molecules to permeate membrane surfaces, like those lining internal organs).

From there, ethanol enters the bloodstream, where the veins then carry it throughout the body. It eventually reaches the heart, which then pumps it (along with oxygenated blood) into the lungs. Once there, the ethanol comes in contact with gaseous oxygen, which causes a portion of it to vaporize. That vaporized ethanol then leaves the body as one breathes.

Trying to hit a moving target?

This process occurs continuously as the body metabolizes the alcohol (with the concentration of alcohol on one’s breath in comparison to that in their blood lowering with each breath). This equates to one’s BAC essentially lowering with each breath. The fact that one’s BAC is so dynamic may lead to one questioning the validity of hand-held breath test device results (indeed, many courts do not allow them as evidence).