Understanding the mechanics of breath testing devices

On Behalf of | Sep 14, 2020 | Owi

Past posts on this blog correctly detailed that it is possible for one to challenge the result of a breath test. Indeed, many criminal courts (both in Wisconsin and throughout the rest of the U.S.) often will not consider such results when preparing evidence to support a charge of operating while intoxicated. In fact, the National Motorists Association reports that breath testing devices may have a margin of error as high as 50%.

Given that the results of such tests often serve as the basis for an OWI case, if one successfully challenges their validity, the case against them may collapse. Mounting a successful challenge requires understanding how breath testing devices generate measurements.

Capturing one’s blood-to-breath ratio

The alcohol that one ingests makes its way through their digestive tract and into the bloodstream, eventually reaching one’s lungs. There it comes in contact with oxygen, which causes a portion of it to vaporize into a gas. That gaseous alcohol then leaves the body with each breath.

The amount of alcohol on one’s breath stays in equilibrium with that in their blood. According to the Alcohol Pharmacology Education Partnership, breath testing devices assume that ratio to be 2100:1 (2100 milliliters of alcohol in the blood compared to one milliliter on the breath).

Challenging the baseline assumption used but breath testing devices

The trouble with this assumption is that in reality, a person’s actual blood-to-breath ratio may actually range from 1500:1 to 3000:1. Various factors may influence this, including:

  • Age
  • Sex
  • One’s genetic makeup
  • The amount of time elapsed between the consumption of alcohol and the breath test measurement

This wide range of variability may account for the wide margin of error referenced earlier. Having this information may lend credence to one’s claim that their blood-alcohol content did not exceed the legal limit at the time of their arrest.

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