What factors influence breath test results?

| Mar 3, 2021 | Firm News

Law enforcement officers in Virginia and across the U.S. often use roadside breath test devices to measure drivers’ blood alcohol content level. Rather than measure your BAC level through a blood sample, these machines use an exhaled breath sample to determine whether you are over the legal limit of 0.08.

Yet, researchers show that the results from hand-held breath test machines are not always accurate. In fact, some results may be inflated, which could lead to a wrongful DWI charge and possible conviction.

The facts

Researchers from the State University of New York at Potsdam found that breath test readings may differ by as much as 15% from actual blood test results. This means that one in four people testing using the machine will have inflated results.

While the device is designed to detect ethanol in an exhaled breath sample, it also picks up other substances that have similar methyl group structures.

The factors

While the device is designed to detect ethanol in an exhaled breath sample, it also picks up other substances that have similar methyl group structures. Factors that influence breath test results include the following:

  • Dirt and pollution in the air
  • Electrical interference from police radios and cellphones
  • Residual vomit, food, drink or blood in the mouth
  • Relative humidity and temperature of the air
  • Amount of physical activity conducted
  • Fumes from cleaners, gasoline and cigarette smoke

In addition, the devices must be calibrated properly to the temperature and environment in which it is being used. The officer operating the device must do so correctly as well. Certain models of breath test devices are extremely sensitive to those factors, and the resulting readings are often unreliable and inaccurate.

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