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What Makes Breathalyzers Inaccurate?


The United State Supreme Court recently refused to hear what might have been a landmark DUI case. In doing so, the United States Supreme Court essentially denies the ability of DUI defendants to introduce facts at their trials.  

A San Diego trial court prevented Terry Vangelder from introducing expert testimony that breathalyzers are inherently inaccurate and Mr. Vangelder was convicted of drunk driving. The California Supreme Court upheld the trial court’s decision and Mr. Vangelder’s conviction. Mr. Vangelder, through his attorneys, appealed to the United State Supreme Court.   The United State Supreme Court denied review of Mr. Vangelder’s case leaving the California Supreme Court’s decision intact: defendants cannot broadly challenge the accuracy of breathalyzers in DUI cases will stand.

While DUI defendants may still challenge the accuracy of the particular breathalyzer used in their respective cases, they may not introduce evidence that breathalyzers are generally inaccurate…even though they are.

So why are breathalyzers inaccurate? Let me count the ways…

The breathalyer cannot differentiate between the alcohol in an alcoholic beverage and the alcohol produced after the ingestion of some foods. Common foods which contain yeast or sugar, if caught in the teeth, can produce low levels of alcohol called “mouth alcohol.” If a person suffers from gastroesophageal reflux disease (GERD) or heartburn, the contents of their stomach gets regurgitated (via a burp or mild vomiting of stomach fluid) into the mouth. This too produces low levels of alcohol. Under both circumstances, a breathalyzer can provide an inaccurate elevated breath reading.

Several studies have shown that elevated body temperatures can cause an elevated reading on a breathalyzer. Researchers in one such study entitled “The Myth of Breath Test Accuracy, What the Studies Have Really Shown” concluded that one degree centigrade change in breath temperature can cause a change in blood alcohol content reading by 6.5 percent. Other studies have estimated the change to be as high as 9 percent.

No two people are the same. Breathalyzers however, cannot account for every single person’s differences. Breathalyzers collect air, which contains alcohol, from deep within the lungs. The alcohol gathered from the breath is multiplied by 2,100. This number is called the “partition coefficient” and represents the “average” multiple to calculate the amount of alcohol in that person’s blood.

Certain diets, such as the low-carb diet, can create false breathalyzer readings. When a person goes on the low-carb diet, their body performs “ketosis.” During ketosis, the body burns fat for energy. The molecules generated by process are called ketones. Ketones create isopropyl alcohol. Breathalyzers cannot tell the difference between isopropyl alcohol and ethanol, which is the alcohol consumed when drinking an alcoholic beverage.

Breathalyzers, through repeated use, begin to malfunction. As a result, breathalyzers must be frequently calibrated. This is done using known air with known amounts of alcohol. If a breathalyzer is not calibrated properly or frequently enough, it may produce inaccurate results.

The abovementioned shortcomings of breathalyzers are not speculation, conjecture, or theory. They are facts, scientific facts. With so much at stake for DUI defendants, why the United States Supreme Court and the California Supreme Court refuse to allow facts to be introduced in DUI cases is beyond me.

The post What Makes Breathalyzers Inaccurate? appeared first on Law Offices of Taylor and Taylor - DUI Central.

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