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A breakdown of breath testing device mechanics

| Nov 20, 2020 | DUI

Past posts on this blog detailed the pathway that alcohol takes in working its way to your breath after consumption. Given the fluidity of the process, you might rightly question how can any measurement attempting to quantify it have a strong degree of validity.

Such is the question posed to us here at Daniels & Rothman, P.C. by many potential clients. Yet the general assumption is that breath test results serve as concrete proof of your intoxication. Challenging this notion requires that you understand how these devices generate their measurements. 

Your blood-to-breath ratio

As previously ingested alcohol escapes from your body through your breath, the ratio of the gaseous alcohol in your lungs remains in equilibrium with its concentration in your blood. That statistic measuring that equilibrium is your blood-to-breath ratio. Information shared by the Alcohol Pharmacology Education Partnership shows that in order to generate a measurement of your blood-alcohol content from your breath, breath testing devices assume a ratio of 2100:1 (that being that the concentration of alcohol in your blood is 2100 times greater than that on your breath). 

The problem with this assumption is that studies have shown that a person’s blood-to-breath ratio following the consumption of alcohol can range anywhere from 1500:1 to 3000:1. Multiple factors may contribute to this wide variance, such as: 

  • Age 
  • Gender 
  • Body composition 
  • Genetics 

Breath testing device margin of error

Indeed, this variance may give credence to the claims that breath testing devices inherently have too wide a margin of error for authorities to rely on them as evidence. The National Motorists Association reports that margin may actually be as high as 50%. 

You can find more information on challenging drunk driving charges throughout our site. 

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