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How do breathalyzer tests determine blood alcohol content?

If you’ve been charged with a DUI in Chicago, you may be wondering how the device used to measure your blood alcohol content (BAC) actually works. Breathalyzers are a common method of testing BAC, and accordingly are used by most law enforcement agencies when an intoxicated driver is suspected. It’s useful for you to understand how these devices actually work to ensure your rights are being preserved when involved in a sobriety stop.

As stated by Forbes, breathalyzers utilize rather complex scientific concepts to determine the level of alcohol in one’s body.  As ethanol is consumed, it’s absorbed through the stomach and subsequently makes its way into your blood stream. In cases where you consume large quantities of alcohol, more of it will evaporate and be passed through your blood into your lungs. As you breathe, this alcohol then makes its way from your lungs and is expelled from your mouth.

Some breathalyzers determine the actual amount of alcohol in your body via infrared radiation. The overall goal is to get a reading from the deepest areas of your lungs, which is where alcohol is most concentrated. Breath samples are taken every 37 seconds until a consistent reading is achieved for a period of 3 seconds of blowing.

While some people claim that other substances in your body can trigger a false reading, most devices are advanced enough that similar substances will only cause an error. Some devices can even tell the difference between alcohol that is merely present in the mouth (such as from recently using mouth wash) as compared to that which is issuing from the lungs (which means that it is coming from the blood stream). 

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How do breathalyzer tests determine blood alcohol content? | Jim Ryan & Associates