Police officers in Mississippi and across the nation use roadside breath test devices to measure motorists’ blood alcohol content level. If law enforcement ever pulls you over on suspicion of drunk driving, officers may ask you to submit to one of these tests. Yet, while breath test results may show that you are over the legal driving limit of 0.08, the readings may not always be accurate.

In fact, according to the State University of New York at Potsdam, at least one in four people asked to submit to a roadside breath test show readings that are higher than their actual BAC level. This inaccuracy could result in a wrongful DUI charge.

How breath test devices work

When you exhale a breath sample into a handheld breath test device, the machine measures the amount of ethanol alcohol present in the sample. It then takes this amount and converts it into a blood alcohol content level.

Yet research shows that the discrepancy between breath test device readings and the results obtained from actual blood tests may vary by as much as 15%. What causes this discrepancy, and what does this mean for people asked to take the test?

Factors that influence breath test readings

The problem lies in the fact that breath test devices measure more than just ethanol alcohol. It can also pick up substances that have similar molecular makeup, such as methyl structures. Factors that influence breath test readings include the following;

  • Pollution, such as smoke and dirt in the air
  • Cigarette smoke and gasoline fumes
  • Relative humidity and temperature of the air
  • Residual blood, vomit, food or drink in the mouth
  • Interference from law enforcement radios and cell phones

If the acting officer is not using the device properly, or if the machine is not calibrated correctly, it can give erroneous results. It is critical to keep these factors in mind if you take a roadside breath test.

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