The hand-held breath testing device is undoubtedly the near-universal symbol of a drunk driving conviction. Almost everyone in Lincoln likely understands that should they find themselves in the position of blowing into such a device, law enforcement officials plan to use the subsequent measurement to determine their blood-alcohol level.

This prompts the obvious question of why is it that officials would measure one’s breath in order to get an idea of the composition of their blood. Knowing the answer to this question requires that one understand three things:

  • How alcohol gets on one’s breath
  • How a breath testing device measures that alcohol content
  • Why this might contribute to breath testing inaccuracy

Alcohol’s path from blood to breath

The alcohol one ingests permeates the lining of the organs of their gastrointestinal tract and enters their bloodstream, which then carries it throughout their body, including to their lungs. In the lungs, that alcohol comes in contact with oxygen, where some of it vaporizes into a gas. That gas then leaves the body as one breathes. The concentration between the alcohol content of one’s breath and one’s blood remains in equilibrium until it eventually works its way out of their system.

According to the Alcohol Pharmacology Education Partnership, breath testing devices assume that equilibrium ratio to be 2100:1 (with the alcohol concentration of one’s blood being 2100 times greater than that of their breath). However, in reality, a person’s actual BAC can vary between 1500:1 to 3000:1. What is more, with each breath, one’s BAC is actually lowering.

Challenging breath test accuracy

It is the dynamic nature of this process that may contribute to breath test inaccuracy (indeed, the American Motorist Association estimates they may have a margin of error as high as 50%). This may help one challenge the results of a breath test used as evidence against them.