How do machines test for alcohol in breath?

James Nesci

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DUI / DWI Attorney

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Posted over 2 years ago. 1 helpful vote

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How do machines test for alcohol in breath?

Although three types of breath-testing estimators are approved for use in Arizona, the police only use one–the Intoxilyzer 8000© made by CMI, Incorporated, in Owensboro, Kentucky. The Intoxilyzer 8000 uses Infrared Spectroscopy to analyze breath to create and estimated breath alcohol content. It does this by first projecting infrared (IR) light through a sample chamber at two IR detectors with only ambient air in the chamber. It measures the amount of IR light that strikes the detectors and sets up a baseline to compare to a subsequent breath sample. Next, a person blows into the machine, filling the sample chamber with breath. The Intoxilyzer projects IR light through the breath sample at the detectors. The IR light excites the molecules in ethyl alcohol, causing the molecular bonds to bend, stretch and rock. This causes less IR light to strike the detectors. A difference in the amount of light which struck the detectors before and during breath samples is measured and a breath alcohol estimate is calculated by way of a secret formula known only to CMI. The key to IR testing is that each organic molecule has a unique IR “fingerprint" which cannot be confused with any other molecule. While this may be true, neither the Intoxilyzer 8000 nor any other IR breath tester measure the entire molecule. Some IR breath testers measure up to five different IR wavelengths. The Intoxilyzer 8000 measures only two. By way of analogy, think of it as a roadmap. Your are told that I-10 passes through Tucson and crosses 18th Street and 22nd Street. Thus, any city through which I-10 crosses streets named 18th Street and 22nd Street is Tucson. At 2,460 miles in length, I-10 is the fourth longest Interstate Highway in the United States. Surely, somewhere along its route it passes through another city, crossing 18th Street and 22nd Street. Using Intoxilyzer IR technology, you would mistake that city for Tucson–and using Intoxilyzer IR technology, it can mistake other molecules for ethyl alcohol. If you have any questions about this, or any other legal issue, please feel free to contact Nesci & St. Louis PLLC at (520)622-1222, or visit us on the web at www.AZDefense.com. Nesci & St. Louis PLLC is a criminal-defense law firm located at 216 North Main Avenue in Tucson and is solely responsible for the content of this newsletter. This newsletter is for informational purposes only and is not intended as legal advice. No attorney-client relationship is established by the use of this information. Laws and rules change rapidly and every effort to ensure the accuracy of this information has been made as of the date of this newsletter. © 2011

Additional Resources

Garriott's Medicolegal Aspects of Alcohol, 5th Edition, Arizona DUI Defense, 3rd Edition

Lawyers and Judges Publishing Co.

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