Just was curious after watching some videos but I still dont understand it. How does measuring the exhale calculate alcohol levels in blood. One of the videos I watched is “Chemistry of breathalyzers” by PhD at living. Its way over my head. He mentions that it will measure ethanol and the ratio from exhaling is 2100:1 to in the blood. How do they even figure that out and without knowing the persons body weight and how accurate are they really?
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Blood alcohol content is an indicator of intoxication regardless of bodyweight. Higher bodyweight individuals simply take more alcohol to be in the tissues to equal certain concentrations in blood.
The handheld breath tests use a fuel cell which essentially burns your breathed out alcohol to produce electricity. The amount of electricity the fuel cell generates indicates how much alcohol was in the sample.
The more accurate machines essentially are spectroscopy machines that hit the sample with infrared light and measure how much light was absorbed to tell the alcohol content of the sample. It’s more accurate than the handheld unit because the fuel cell in the handheld unit can degrade and needs calibrated constantly or it can become wildly inaccurate.
That’s why most police departments use the handheld unit to get the probable cause to arrest you for DUI then they use the larger more accurate machines or a blood draw to get your actual blood alcohol content as evidence.
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