In California, When Can You Claim That the Breathalyzer Got It Wrong?

In California, in a per se DUI case, an expert witness cannot conclude that properly-maintained, approved breath testing devices are generally inaccurate.

In a 2013 California case, the California Supreme Court ruled against a defendant who sought to prove the general unreliability of Breathalyzers.

Terry Vangelder was pulled over by a sergeant with the California Highway Patrol (CHP) while driving more than 125 miles per hour on Highway 163 in San Diego County. During the one-and-a-half miles the Sergeant observed him, Vangelder didn’t swerve or weave outside of his lane, and didn’t exhibit any of the normal clues police look for when assessing whether a driver may be intoxicated.

Vangelder told the Sergeant he was “just screwing around” when he produced his license and registration. The Sergeant noticed Vangelder’s eyes were red and watery, and he detected an odor of alcohol, so he asked whether Vangelder had been drinking.

Vangelder admitted he had consumed two glasses of wine that night. (He would later change his story and admit he had actually consumed three glasses.) At that point the Sergeant called for backup. Officers gave Vangelder field sobriety tests and he performed relatively well, exhibiting only a few signs of impairment. Still, because the officers smelled alcohol and because they claimed his eyes were red and glassy, they asked Vangelder to consent to a portable breath test (PBT), which he did.

Although protocol requires officers observe a suspect continuously for 15 minutes before administering a PBT (so they can be sure the suspect does not ingest or do anything that may cause the BAC to shift), the officers only observed Vangelder for nine or 10 minutes.

As a result of the PBT readings and the officers’ observations, Vangelder was arrested and given the choice whether to submit to a blood, breath, or urine test. He elected to give a breath sample and the officers administered a breath-alcohol test with an Intoximeter EC/IR testing instrument.Two results from the Intoximeter were obtained yielding a blood-alcohol percentage of 0.08.

At trial, Vangelder introduced a highly credentialed expert witness — a professor of medicine at the University of Washington and a National Institute of Health committee member — who testified that breath testing machines are always inaccurate because when you give breath to a breath-test machine, the machine assumes that for every percentage point of alcohol in your blood, a certain number of alcohol molecules will be present in your lungs. When you give breath, and the operator asks you to “keep blowing, keep blowing, keep blowing,” the idea is to get an accurate sample of the breath deep within your lungs. Based on a 2009 California Supreme Court ruling, the trial judge blocked Vangelder's expert testimony about the general inaccuracy of Breathalyzers.

The science behind breathalyzers. A famous chemist, William Henry, discovered in 1803 that volatile compounds (an alcoholic beverage for our purposes) eventually settle such that the gas from the compound is 2,100 times less concentrated in air than in liquid form (alcohol in blood in our case). Many jurisdictions use this 2100:1 “partition ratio” (or K in academic shorthand) as the standard by which they judge everyone.

The problem is that while this may be a good approximate value for the machine to use in most cases, the human body is far from a perfect laboratory to perform chemistry. Some people have partition ratios far enough away from the assumed 2100:1 value that it could change the outcome of their case. More importantly, the same person’s partition ratio may be different from one day to another.

The California Supreme Court agreed with the trial court and concluded that general objections to Brethalyzer reliability are irrelevant, and therefore inadmissible.

Bottom Line: In California, in a per se DUI case, an expert witness cannot conclude that properly-maintained, approved breath testing devices are generally inaccurate. The expert may, however, offer testimony establishing that the particular machine in used in the case was wrong.

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