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How Accurate are Breathalyzers?


If you get pulled over under suspicion of driving under the influence of alcohol, a police officer may use a breathalyzer in order to determine your blood alcohol content (BAC) level. It’s important to understand that its reading is based on how much alcohol is contained in a portion of exhaled air, as opposed to how much alcohol is in the blood.

In order to calculate the BAC from that exhaled air, the BAC in the air is typically multiplied by the “partition coefficient” or “partition ratio,” which is the number 2,100. The number is used since the lung air exhaled by an “average” individual often contains 1/2100th the amount of alcohol of an equal blood volume. However, the value calculated can be drastically changed based on particular factors, such as time, body temperature, as well as the rate of respiration, making these calculations possible inaccurate.

The following are other factors which can potentially cause errors:

  • Human Error – Police officers are required to be trained and experienced in administering breathalyzer tests. They must understand the proper conditions and protocols in order to determine an accurate reading.
  • Calibration – Like any other machine which produces measurements, breathalyzers must be periodically calibrated and their batteries must be replaced every so often to maintain accuracy.
  • Alcohol-Containing Substances – False positives can occur due to substances which contain alcohol. This includes toothpaste, mouthwash, breath fresheners, toothache medicines, and even vomit.
  • Consistency – Breath tests need to be taken multiple times in order to produce an accurate result.
  • Environment – False results can occur within the presence of potent chemicals, including varnish, paint fumes, adhesives, and plastics.

If you have been arrested for a OWI, our Milwaukee criminal defense lawyer at the Law Offices of Christopher J. Cherella can thoroughly investigate your case and determine if the breathalyzer test results are inaccurate. We have what it takes to successfully challenge breathalyzers and obtain the outcome you desire.

Contact our Milwaukee criminal attorney at the Law Offices of Christopher J. Cherella and schedule your complimentary consultation today.

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