The mechanics of breath testing devices

On Behalf of | Sep 5, 2020 | dui/dwi

Were most people in New York to describe their thoughts when asked about drunk driving arrest, they would likely describe a scene on the side of the road where one breathes into a handheld breath testing device. That such devices are the near-universal symbol for a DUI should not come as a surprise; indeed, the most common number associated with driving under the influence is .08 (the legal limit for blood-alcohol content adopted by nearly every state, whose measurement such devices generate).

Yet previous posts on this blog detailed the potential shortcomings of handheld breath testing devices. In fact, according to information shared by the American Motorists Association, breath testing devices may have a margin of error as high as 50%. With so much weight given to their measurements, how can this possible?

Assuming a set blood-breath ratio

To understand this, one must comprehend how breath testing devices generate their measurements. When one breathes into such a device, the device itself measures the ethanol alcohol content on their breath. This is the form of alcohol ingested when drinking (which, upon digesting, enters into the bloodstream). The device uses a set blood-breath ratio to come up with its measurement. The Alcohol Pharmacology Education Partnership reports that ratio to be 2100:1 (for every one milliliter of alcohol on one’s breath, their is 2100 times that amount in their blood).

Challenging the set ratio

The trouble is that in reality, a person’s alcohol blood-breath ratio can range between 1500:1 to 3000:1. Factors that influence it include:

  • Age
  • Gender
  • Genetics
  • The time between ingestion and the actual measurement

With such a varying range of actual levels of intoxication, it is little wonder that breath test results are so often challenged during criminal proceedings.