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Do Breathalyzers Measure Alcohol?

Breathalyzers don’t actually measure alcohol.

That’s right.  What they actually detect and measure is any chemical compound that contains the methyl group in its molecular structure.  There are thousands of such compounds — including quite a few which can be found on the human breath. And this machine that determines a person’s guilt or innocence in a DUI case will “see” all of those chemicals as alcohol — and report a falsely high blood-alcohol concentration (BAC).

Most breath machines used in drunk driving cases by law enforcement today employ a technology called infrared spectroscopy. The DUI suspect breathes through a tube connected to the machine and a breath sample is captured in a small “sample chamber” inside the machine. Then beams of infrared energy are shot through the captured breath sample. If there are any compounds containing the methyl group, they will absorb some of this energy; the more of the chemical compound in the breath sample, the more energy is absorbed. The more energy that is absorbed, the less infrared energy that reaches sensors at the other end of the sample chamber. And the less energy that is detected by the sensors, the higher the “blood-alcohol” reading.

Problem: the machine is designed to simply assume that the chemical compound absorbing the energy is alcohol. If a person has any of these other compounds on his breath, called interferents by the engineers, he will get a falsely high blood alcohol concentration test result. And if there are two or three such compounds on his breath, the machine will read a cumulative result: it will add them up and falsely report the total as the blood-alcohol level….very possibly resulting in the DUI conviction of an innocent citizen.

So what kinds of compounds may be on a person’s breath that can cause false breath alcohol readings in a DUI case?

In one study of eight men, 69 different compounds containing the methyl group were discovered. “Trace Composition of Human Respiratory Gas”, 30 Archives of Environmental Health 290. In another study involving 28 subjects, researchers found that the “combined expired air comprises at least 102 various organic compounds of endogenous and exogenous origin”. “Characterization of Human Expired Air”, 15 Journal of Chromatographic Sciences 240. And Canadian scientists have discovered over 200 such compounds. “The Diagnostic Potential of Breath Analysis”, 21(1) Clinical Chemistry 5.

What are these compounds? Are there any on my breath?

Well, for starters, diabetics with low blood sugar can have high levels of acetone — which is “seen” as alcohol by breathalyzers. And scientific studies have found that people on diets can have reduced blood-sugar levels, causing acetone hundreds of times higher than found in normal individuals. Frank and Flores, “The Likelihood of Acetone Interference in Breath Alcohol Measurements”, 3 Alcohol, Drugs and Driving 1. And there are many other so-called “interferents”. See, for example, “Excretion of Low-Molecular Weight Volatile Substances in Human Breath: Focus on Endogenous Ethanol”, 9 Journal of Analytical Toxicology 246.

If you are a smoker, your breath alcohol test result is likely to be higher than expected. The compound acetaldehyde — reported by the breathalyzer as “alcohol” — is produced in the human body as a by-product in metabolizing consumed alcohol, and eventually passes into the lungs and breath. Researchers have discovered that levels of acetaldehyde in the lungs can be 30 times higher in smokers than in non-smokers. Result: higher alcohol level readings on the machine…and a possible criminal conviction for drunk driving.

And then there are the industrial compounds: paint, glue, gasoline, thinners, and other compounds contain the methyl group. No, you don’t have to drink the stuff: simply absorbing it through your skin or inhaling the fumes can result in significant levels of the chemical in your body for hours or even days, depending upon the “half-life” of the compound. So if you’ve painted a room or siphoned some gasoline in the last day or two, don’t breath into a breathalyzer.

Some law enforcement officials say that this is not a problem, claiming that levels of the compound would have to be at toxic levels to raise a breath test result to .08% or higher. These officials are displaying their ignorance of the science involved — specifically, of the partition ratio. This is the ratio of the compound found in the breath to that found in the blood. With ethanol, the ratio is 2100-to-1, which means that, on average, there will be 2100 units of alcohol in the blood for every unit found in the breath.

These officials are using this ratio for all compounds, but every compound has its own ratio. Toluene (found in paint, glue, thinners, cleaning solvents. etc.), for example, has a partition ratio of only 7-to-1; a far greater amount of toluene in the blood will pass into the breath, and so a much smaller amount in the body will have a far greater impact on the breath machine.

So….do breath machines measure alcohol on the breath?  Yes, they can…but not reliably or accurately.

About Lawrence Taylor

Lawrence Taylor
Lawrence Taylor is one of the most respected DUI defense attorneys in the country. With over 43 years experience in DUI defense, he has lectured to attorneys at over 200 seminars in 41 states. An original founder and former Dean of the National College for DUI Defense, Mr. Taylor's book "Drunk Driving Defense" has been the best-selling textbook on the subject for 31 years and is now in its 7th edition. He is today one of only 5 DUI attorneys in California who is Board-certified as a DUI defense specialist. A former Marine and graduate of the University of California at Berkeley (1966) and the UCLA School of Law (1969), Lawrence Eric Taylor served as deputy public defender and deputy district attorney in Los Angeles before entering private practice. He was the trial judge's legal advisor in People vs Charles Manson, was Supreme Court counsel in the Onion Field murder case and was retained by the Attorney General of Montana as an independent Special Prosecutor to conduct a one-year grand jury probe of governmental corruption. Turning to teaching, Mr. Taylor served on the faculty of Gonzaga University School of Law, where he was voted Professor of the Year, was invited to be Visiting Professor at Pepperdine University Law School, and was finally appointed Fulbright Professor of Law at Osaka University in Japan. Mr. Taylor continues to limit the practice of his 5-attorney Southern California law firm to DUI defense exclusively. With offices in Long Beach, Irvine, Beverly Hills, Pasadena, Riverside and Carlsbad, Mr. Taylor and his firm of DUI defense attorneys may be reached through their website at www.duicentral.com or by telephone at (800) 777-3349.

If you would like to contact the author, please visit: http://www.duicentral.com/


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