Getting pulled over by law enforcement may give you a knot in your stomach, especially if the officer pulls out a breath test device. Law officers often use roadside breath test devices to determine whether you are driving with a blood alcohol content level that is over the legal limit of 0.08. Yet, breath test devices measure blood alcohol content levels indirectly, and do not always yield accurate and reliable results. Rather than measure the concentration of alcohol in the blood, breath test devices determine the amount of ethanol alcohol in your exhaled breath sample and then converts it to a BAC level.

It is during this conversion process that problems may arise. According to research performed at the State University of New York at Potsdam, breath test readings may vary by more than 15% when compared to BAC level results from actual blood tests. This means that one in four people who take the test run the risk of getting inflated results that could cause a wrongful DUI arrest.

Why do the results vary by such a large amount? Instead of just measuring alcohol levels in the breath samples, the machine picks up other substances that have similar methyl groups. Other factors can alter the readings as well. These include the following:

  • Residual blood, food, drink or vomit in the mouth
  • Dirt, smoke and pollution in the air
  • Cigarette smoke and fumes from cleaners or gasoline
  • Electrical interference from cell phones or officer radios
  • Relative humidity and temperature of the air

Furthermore, some officers may not use the breath test machine correctly, which could lead to errors as well. It is critical that you understand how the machines work and what to do if you are pulled over and asked to submit to a roadside breath test.

This information is intended to educate and should not be taken as legal advice.