CRIMINAL DEFENSE • DISCIPLINARY INVESTIGATIONS & HEARINGS

Exploring the reliability of breath tests

Posted January 30, 2015

The reliability of breath tests can be important to many individuals accused of drunk driving and facing drunk driving charges. The DWI charges an accused individual may face following a traffic stop may be based on a breath test administered by a police officer. Because of the significant role breath tests play in assigning criminal charges, such as DWI charges, it is important to fully understand the reliability of breath tests.

Breath tests such as Breathalyzer tests and Intoxilyzer tests, among other brand names of breath tests, do not measure blood alcohol content (BAC) directly which can be a problem. Breath tests are an indirect estimation of blood alcohol content because only a blood test will measure blood alcohol content. In general, larger breath test machines provide more reliable results than hand-held breath tests machines commonly used by authorities. Some states do not permit hand-held test results to be used as evidence in court and at least one state only allows blood tests because of concerns related to the reliability of breath tests when it comes to measuring BAC.

One of the most significant problems with breath tests that may lead to unreliable results is that they identify ethyl alcohol as the same as other similar molecular compounds commonly found in the human mouth. The more ethyl alcohol the breath test measures, the higher the BAC test result will be. Of the over 100 compounds found in the human breath at any time, 70 or 80 percent contain the molecular structure that may be incorrectly identified as ethyl alcohol.

Additionally, research has shown that dieters, diabetics and even those that have recently consumed a large amount of bread can have an increased BAC reading following a breath test due to the measurement of molecular structures similar to those that cause intoxication that are incorrectly measured by the breath test. A variety of environmental factors can also impact a BAC reading from a breath test. According to research, breath tests actually vary 15 percent from actual BAC levels and it has been suggested than in any situation when reliability is important, such as legal situations, breath tests should not be relied upon.

Because drunk driving charges may sometimes rest on breath test results, it is important to understand the nature and reliability of breath tests. It is also important to understand consequences when faced with a breath test or drunk driving charges and the options that may be available to the accused individual in either case.

Source: State University of New York, “Breath Analyzer Accuracy,” accessed on Jan. 29, 2015

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