When facing criminal charges for driving under the influence, you may feel as though you must accept the accompanying consequences if law enforcement officials in Montana have the results of a breath test to use as evidence against you (no matter how lucid you may have felt at the time of your arrest).

Many come to us here at the Stevenson Law Office with that assumption. Yet breath test results are not infallible. Indeed, an understanding of how hand-held breath testing devices generate their readings may even lend weight to an argument challenging their validity.

How breath testing devices work

The actual form of alcohol in alcoholic drinks is ethanol. As a water-soluble compound, ethanol can pass through membrane surfaces (like those lining the organs of your gastrointestinal tract) via passive diffusion. Once this happens, the ethanol ends up in your blood, where the veins carry it throughout your body, eventually arriving at your lungs. In the lungs, the ethanol-saturated blood comes in contact with oxygen, which causes some of it to vaporize into a gas which then leaves your body as you breathe.

The blood-to-breath ratio of ethanol in your body remains in equilibrium as your body metabolizes it. Per the Alcohol Pharmacology Education Partnership. breath testing devices assume a static ratio of 2100:1 (the alcohol concentration of your blood being 2100 times greater than that of your breath) when measuring your breath’s alcohol content.

Breath test margin of error

The trouble with this assumption is that in reality, your actual blood-to-breath ratio may vary from 1500:1 and 3000:1 based on various factors (such as your gender or genetic makeup). This likely contributes to some experts estimating that breath testing devices may have a margin of error as high s 50%.

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