Measuring the accuracy of breath test devices

Law enforcement officers in North Carolina and across the United States often use roadside breath test devices as a way of measuring a driver’s blood alcohol content level. It is not uncommon for officers to ask drivers’ pulled over on suspicion of drunk driving to submit to a breath test. Those found driving with a BAC level over the legal limit of 0.08 may be arrested and potentially convicted of a DUI. Yet, studies show that the accuracy of breath test devices may be compromised and the inflated results may lead to a wrongful DUI arrest.

Researchers from the State University of New York at Potsdam reported that breath test device readings can vary by as much as 15% when compared to the results obtained from an actual blood test. This means that one in every four people who use the device will show inflated results.

There are several environmental and internal factors that can affect breath test device readings. Breath test devices detect the presence of ethanol alcohol in an exhaled breath sample. Yet, there are other substances that have similar methyl structures and can be confused for alcohol. Factors that can alter breath test device readings include the following:

  • Pollution and dirt in the air
  • The relative humidity and temperature of the air
  • Residual blood, food, drink or vomit in a person’s mouth
  • Cigarette smoke, exhaust fumes and gasoline fumes
  • Electrical interference from officers’ radios and cell phones

Another issue that can affect readings involves the calibration of the machine. If the breath test device is not calibrated properly or the officer is unsure of how to correctly use the device, the results may be inflated.

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