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How does a Breathalyzer work?

Most people living in Vancouver have heard the term "breathalyzer" even if they have never seen or used one. All police departments in the state of Washington use breathalyzers to obtain an estimate of the amount of alcohol in the blood stream of a driver who is suspected of drunk driving.

The legislature has defined intoxication as a blood alcohol content exceeding 0.08%. However, a breathalyzer does not directly measure alcohol in a person's blood stream. Instead, it uses a measurement of alcohol in a person's exhaled breath to provide what may be called a precise estimate of a person's BAC.

The driver is directed to breathe into a tube on the breathalyzer. The breathalyzer captures both inhaled breath and exhaled breath. If a person has been drinking, the breath will contain alcohol that has passed from the blood stream through the alveoli (air sacs) in the lungs and into the person's breath. Scientists have determined the mathematical relationship between the amount of alcohol in a person's breath and the amount of alcohol in the blood stream. The ratio of breath alcohol to blood alcohol is 2,100:1, that is, 2,100 ml of alveolar air will contain the same amount of alcohol as 1 ml of blood.

Some breathalyzers use a chemical reaction to determine the percentage of alcohol in a person's alveolar air. Others use an infrared measurement. In any event, the readings produced by a breathalyzer provide significant evidence of whether a person is drunk or sober. Anyone who is asked by police to take a breathalyzer test may wish to seek legal advice before doing so. Refusing to take a breathalyzer test may result in automatic suspension of the right to drive.

Source: Howstuffworks, "How Breathalyzers Work," Craig Freudenrich, accessed on March 19, 2018

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