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How does the breath test machine work?

Posted by Ed McClees | May 10, 2024

The Intoxilyzer 9000 is the type of breathalyzer used by law enforcement in Texas to calculate the amount of alcohol in a person's breath. It operates on the principle of infrared spectroscopy.

Here is a simplification of how it works:

1.     Breath Sample Collection: when a person blows into the Intoxilyzer 9000, the device collects a sample of their breath.

2.     Infrared Analysis: collected breath sample is then exposed to infrared light. Ethanol (the type of alcohol found in alcoholic beverages) absorbs specific wavelengths of infrared light.

3.     Measurement: the Intoxilyzer 9000 measures the amount of infrared light absorbed by the breath sample. The amount of light absorbed at these specific wavelengths is proportional to the concentration of alcohol in the breath sample.

4.     Calculation: Based on the amount of infrared light absorbed, the Intoxilyzer 9000 calculates the blood alcohol concentration (BAC) of the individual. This measurement is typically expressed as a percentage, indicating the percentage of alcohol in the bloodstream.

5.     Display of Result: The device then displays the calculated BAC on its screen, providing law enforcement officials with information about the amount of alcohol in the person's system.

Of course, the Intoxilyzer 9000 has many documented limitations and problems. Here are some, but by no means all, of the common issues we see associated with the Intoxilyzer 9000:

1.     Calibration and Maintenance: all breathalyzer devices require regular calibration and maintenance to ensure accurate results. If not properly calibrated or maintained, the readings from the device are unreliable.

2.     Interference: Certain substances or environmental factors can interfere with the accuracy of breathalyzer readings. For example, mouthwash, breath fresheners, and other products containing alcohol and other substances can produce false positives. Environmental factors such as temperature and humidity can also affect the device's performance.

3.     Variability in Breath Composition: Breathalyzer devices assume a certain ratio of alcohol in the breath to alcohol in the blood to estimate BAC. However, this ratio varies from person to person and many times will not accurately reflect an individual's true BAC.

Simply put, the Intoxilyzer 9000 is better at detecting the presence of alcohol than it is at calculating a precise BAC. If you have been charged with DWI or any other intoxication related offense, a lawyer experienced in the nuances of breath testing can be invaluable. Ed McClees has this experience and stands ready to help those facing such charges.

About the Author

Ed McClees

Ed is a criminal trial lawyer who is Board Certified in Criminal Law by the Texas Board of Legal Specialization.  He is a former Harris County District Attorney where he served as chief of the Organized Crime Section, prosecuting cases involving complex organized criminal activities, including Fr...

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