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Breathalyzers Are Inaccurate. Here Is Why:

Posted by Jason Beahm | Jul 07, 2014 | 0 Comments

In what could have been a landmark DUI case, the United State Supreme Court refused to consider a strong challenge to the reliability of breathalyzer results. The ruling is a blow against defendants who intend to argue that breathalyzers are inaccurate at trial in their in DUI cases. In essence, the United States Supreme Court has denied the ability of DUI defendants to introduce relevant facts at trial.

The case originated in San Diego, where a trial court prevented the defendant, Terry Vangelder, from using an expert to testify that breathalyzers are inaccurate. Mr. Vangelder was subsequently convicted of drunk driving by a California jury. Vangelder appealed, however The California Supreme Court upheld the trial court's decision. Mr. Vangelder then appealed to The United State Supreme Court.

There was hope among the California DUI defense bar that The United State Supreme Court would hear the case. But instead, The United State Supreme Court denied review of Mr. Vangelder's case. Thus, the California Supreme Court's decision remains and the precedent stants. This means that California DUI defendants lack the ability to exercise their right to introduce evidence broadly challenging the accuracy of breathalyzers in DUI cases. Defendants are not allowed to argue that breathalyzers are inaccurate in general, they may only attack the particular breathalyzer machine used in their case.

While the ruling is a disappointment, we have made a point to remind our clients that there are still dozens of ways in which to successfully attack DUI charges in general. Further, DUI defendants still have the ability to question the accuracy of the particular breathalyzer used in their arrest. As it stands, DUI defendants may not introduce evidence that breathalyzers are  inaccurate. (Despite mountains of evidence to the contrary.)

For those that contend that Breathalyzers are in fact reliable: See LaBianca, “The Myth of Breath Test Accuracy What the Studies Have Really Shown,” 5 DWI Journal: Law & Science 11 (November 1990). “For every one degree centigrade change in alveolar air temperature, the conversion ratio, and the percent blood alcohol content changes by 6.5%.”

I also suggest you check  out Jones, “How Breathing Technique Can Influence the Results of Breath Alcohol Analysis,” 22 Med. Sci. Law 275-280 (1982) Breathalyzers are inaccurate for a number of reasons, perhaps most significantly because they treat every person as if they have the same body chemistry, which is complete nonsense. Every single person is different, in a way that can have a significant impact on the results of a breath test.

About the Author

Jason Beahm

Founding Attorney Profile Credentials Associations Bio Jason Beahm is the Founder and President of Beahm Law. Voted “Best of SF” four out of the past five years by SF Weekly Magazine, Attorney Beahm practices in the areas of DUI, criminal defense, and personal injury. He is passionate ...


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