Law enforcement officers in Missouri and throughout the United States often use roadside breath tests to determine whether a motorist is driving with a blood alcohol content level that is over the legal limit of 0.08. Those who have a BAC of 0.08 or higher may be arrested and charged with a DUI. However, researchers found that breath test results are often inaccurate and may lead to false arrests.

According to research from the State University of New York at Potsdam, at least one in four people who use a breath test device have inflated BAC results when compared to actual blood tests. In fact, breath test readings and blood tests results may vary by more than 15%.

How do breath test devices work?

When you exhale air into a breath test device, the machine measures the amount of ethanol alcohol in the sample. The device then converts this amount into a blood alcohol content level. Not only do the machines pick up ethanol groups from alcohol, but they also measure other methyl groups that are similar in structure.

What factors contribute to the BAC reading?

In one study, it was found that people who ate certain types of breads generated a 0.05 BAC reading. Furthermore, a participant who spent an hour painting contact cement on plywood and painting a room blew a BAC level of 0.12, 20 minutes after finishing the task.

Other factors that influence breath test results include the following:

  • Vomit, blood food or drink left in the mouth
  • Pollution, dirt and tobacco smoke in the air
  • Electrical interference from law enforcement officer radios and cell phones
  • Physical activity
  • Relative temperature and humidity of the air

It is important to keep these factors in mind if you are asked to take a roadside breath test.

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