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How accurate are roadside breath tests?


If you have ever been pulled over on suspicion of drunk driving in California, you may have been asked to take a roadside breath test. Law enforcement officers use these tests to determine whether drivers are driving with a blood alcohol level that is above the legal limit of 0.08%. The problem lies in the fact that breath tests may not give accurate and reliable results.

While the most accurate way to get a blood alcohol level is through a blood test, it is not feasible to do so on the road. Instead, drivers are asked to exhale into a breath test device, which converts the amount of alcohol found in the breath sample to a blood alcohol level. There are other factors, however, that can influence the BAC level and may lead to a wrongful drunk driving arrest.

Studies conducted by the State University of New York at Potsdam found that certain environmental factors can affect breath test results. These include the following:

  • Electrical influence from police radios and cell phones
  • Residual moisture, temperature and relative humidity
  • Tobacco smoke, pollution and dirt in the air

It is critical that the breath test devices are properly calibrated and that law enforcement officers use the devices properly to ensure accurate results.

Other factors that can alter breath test results involve whether you have food, drink or blood in your mouth, your hematocrit levels and whether you have been exposed to fumes from cleaners, paint or gasoline. All of these things may cause your breath test results to read higher than they actually are.

This information is intended to educate and should not be taken as legal advice.

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