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How do alcohol breath tests work?

Breath testing is commonly used in Massachusetts and throughout the U.S. by law enforcement agencies in order to identify if drivers are under the influence of alcohol. Under the state’s implied consent law, you could face serious civil penalties if you refuse a breath test. Therefore, it may be of benefit for you to understand how these machines work.

When you drink alcoholic beverages, the alcohol travels to your stomach and small intestines where it is absorbed by oxygenated blood. It is then carried throughout your body, eventually passing in front of the alveoli and transferring to your lungs. Then, as you breathe, it is exhaled.

Most law enforcement agencies use electronic breath analysis machines that are about the size of a walkie talkie. After you blow into a mouthpiece, the device provides a BAC reading. According to FindLaw, while this is less invasive than obtaining a BAC measurement from a blood sample, breath testing is also less accurate.

The current generation of breath analysis devices in use provides BAC measurements using infrared spectroscopic analysis. This analysis method utilizes the principle that light waves are absorbed by captured alcohol vapor. So, when you blow into the mouthpiece, a sample of your breath is captured. The amount of alcohol present in your breath determines the frequency of the waves being absorbed. The data is analyzed by the device’s internal computer and is converted into a BAC measurement.

The information in this post is intended for general purposes only and should not be considered legal advice.

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