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Measuring BAC levels: Are breath test devices accurate?

| Jan 28, 2020 | Firm News |

Law enforcement departments in Ohio and throughout the country use roadside breath tests as a way to determine drivers’ blood alcohol levels. As you exhale into a tube connected to a hand-held device, the machine measures the amount of ethanol alcohol found in the sample.It then converts this number to a blood alcohol content level, all without actually testing your blood. 

The problem lies in the fact that the BAC reading taken from a roadside breath test device is not always equivalent to the BAC level obtained from an actual blood test. Researchers at the State University of New York at Potsdam discovered that the difference in the numbers can vary by more than 15% in some cases. That means one in every four drivers tested would have an inflated BAC level when tested with a roadside breath test. This might lead to wrongful DUI charges and convictions. 

Studies show that breath test devices pick up more than just ethanol alcohol. The machines also pick up substances with similar structures. Other factors can affect breath test readings as well. These include the following: 

  • Electrical interference from police radios and cell phones 
  • Fumes from paint removers, gasoline and cleaning fluids 
  • Residual blood, vomit, food and drink in the mouth 
  • Dirt and moisture in the air 

It is critical that officers calibrate breath test devices to the environment’s humidity and temperature in order for them to give accurate readings. In addition, the officer using the machine must do so properly. 

In one study, a participant applied a gallon of paint to a wall for an hour. The subject was then asked to exhale into a breath test device 20 minutes after completing the task, and had a BAC reading of 0.12. The legal limit is 0.08 in Ohio, which could have led to a wrongful DUI arrest.