For many people in Texas, the de-facto visualization of a drunk driving charge is a person standing on the side of a road blowing into a hand-held breath testing device. Yet the fact that law enforcement officials measure one’s breath to determine the alcohol content of their blood may prompt some to question how legitimate the process is.
Some might think that the results of a breath test serve as essentially insurmountable evidence of a DWI charge. Yet that is not the case (in fact, many courts do not allow them as evidence). Indeed, according to the National Motorists Association, breath testing devices may have a margin of error as high as 50%. Understanding how this is possible requires that one also comprehend the mechanics of these devices.
How does alcohol get on one’s breath?
The form of alcohol included in alcoholic beverages is ethanol. This a water-soluble compound, which allows it to permeate through the membrane linings of the organs of one’s gastrointestinal tract via passive diffusion. This allows the ethanol to enter into the bloodstream, where it then travels through the body in one’s veins. Ethanol in the blood eventually reaches the lungs, where some of it vaporizes upon coming into contact with oxygen. That gaseous alcohol then leaves the body with each breath.
Breath testing devices assume a static blood-to-breath ratio
The concentration of alcohol on one’s breath remains in equilibrium with that in their blood. Per the Alcohol Pharmacology Education Partnership, breath testing devices assume a static blood-to-breath alcohol concentration ratio of 2100:1. However, in reality, one’s blood-to-breath ratio can range from 1500:1 to 3000:1. That wide range may be what introduces the dramatic margin of error referenced earlier. One might use this information to challenge the validity of breath test results introduced as evidence against them.