The Truth about DUI Breath Tests

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If you're facing charges of DUI (driving under the influence of alcohol or drugs), you may feel like you have little to no chance of being acquitted. But, as a DUI lawyer can tell you, that's simply not the case. New reports from DUI lawyers around the country show once again that some of the "evidence" commonly accepted in DUI cases may not be as accurate as once believed.

A blog by a Texas DUI lawyer recently drew attention to the issue of officer testimony during a DUI trial. Apparently, part of the National Highway Traffic Safety Administration's Standardized Field Sobriety Testing Manual (SFSTM) includes instructions on how officers should testify in the courtroom.

The SFSTM reportedly reminds officers that they have not been instructed in the internal workings of breath testing machines like the Intoxilyzer 5000, and indeed do not need to understand the machine beyond how to operate it during a DUI arrest.

The manual allegedly also discourages officers from researching the accuracy of breath testers on their own, insisting that adequate research has been conducted and has proven the reliability of the breathalyzer.

But, as one DUI lawyer's blog points out, at the time of most breath tests, only the arresting officer and the DUI suspect are present, meaning that neither person involved has an understanding of the breath machine being used. And the results of that machine's test could play a major role in the suspect's DUI case.

A DUI lawyer from Minnesota points out on his blog that, because of the way breathalyzers calculate BAC (blood alcohol content), a variety of factors not related to alcohol can cause an incorrect reading. Basically, breath machines measure the concentration of alcohol in your breath and use a pre-set formula to estimate how much alcohol is in your blood.

That formula is based on an "average person," but does not reflect the actual breath alcohol to blood alcohol ratio of every person tested.

Plus, because of the type of data breathalyzers rely on, a variety of factors have been shown to cause incorrect readings, including:

  • Hyperventilation and/or differences in deep & shallow breathing;
  • Giving a breath sample lasting longer than 10 seconds;
  • Individual differences in body composition and size;
  • Nearness of breathalyzer to other radio-wave emitting equipment;
  • Presence of certain non-alcoholic chemicals (including some used in carpentry);
  • Certain illnesses; and
  • Temperature of breath.

One DUI lawyer in Connecticut has reportedly even suggested that Intoxilyzer machines over-estimate the BAC of black people, women and those who are shorter than average.

And a California DUI lawyer points out on his blog that the company that produces the Intoxilyzer only offers a one-year warranty for the product. This has raised some eyebrows, since many police forces evidently use their breath-testing machines for as long as ten years each!


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