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Measuring the accuracy of breath test devices

Nov 1, 2021 | Firm News

Many law enforcement officers in California use roadside breath test devices to determine whether motorists are driving while drunk. These small hand-held devices enable officers to measure a driver’s blood-alcohol level on the roadside rather than process an actual blood sample.

With so much riding on breath test readings, the results need to be accurate and reliable. Yet, studies from the State University of New York at Potsdam show breath test readings can produce inaccurate results which could lead to a wrongful DUI arrest.

How are BAC levels measured?

When drivers exhale into a tube connected to a roadside breath test device, the machine detects the presence of ethanol alcohol. It then converts this number into a blood alcohol content level. Researchers found that BAC levels obtained from actual blood tests can vary by at least 15% from breath test readings.

What are the factors that influence breath test readings?

In addition to detecting ethanol alcohol, the devices may pick up other substances that have a similar structure. Furthermore, other factors can also cause inflated results. These include the following:

  • Remaining blood, food, vomit or drink in the mouth
  • Pollution or smoke in the air
  • Relative humidity or temperature of the air
  • Electrical interference from cellphones or officers’ radios
  • Fumes from gasoline, cleaners or paint thinners

Not only is it critical that officers calibrate breath test devices properly and regularly. Officers must also use the machines correctly to maximize the accuracy of the results.

If an officer pulls you over and asks you to take a roadside breath test, you should know how the machines work. You should also realize that their results may not be accurate.