When a person consumes alcohol, it shows up on someones breath because it gets absorbed from the mouth, throat, stomach and intestines into the bloodstream. Alcohol is not digested upon absorption or chemically changed in the bloodstream. As the blood goes through the lungs, a physiologically predictable amount of the alcohol will moves across the lung membranes and into the lungs themselves.
Once in contact with the air in the lungs, it evaporates and is exhaled. The concentration of the alcohol in the air in the lungs is directly related to the concentration of the alcohol in the blood. Alcohol leaves the body via the breath, because the percent of the total blood alcohol that exists this way is predictable, the alcohol content of the breath can be used to calculate the total blood alcohol content, or BAC. The hand-held breathalyzer uses electrochemical fuel cell technology to identify the elements found in the sample, of course, searching specifically for alcohol. Some devices use an infrared spectrophotometer to scan the sample, identify alcohol and calculate its percentage content. The ratio of breath alcohol to blood alcohol is 2100, so the alcohol content of 2100 milliliters of exhaled air will be the same as for 1 milliliter of blood. The math is simple from there and leads to blood alcohol readings expressed as a percentage of alcohol in the blood.
The partition ratio can vary between 1700 and 2400 depending upon the individual and local environmental conditions, leading to a breath analysis reporting either a higher or lower calculated blood alcohol reading.
In the 1954 Dr. Robert Borkenstein of the Indiana State Police invented the Breathalyzer. It was first developed for police use to test alcohol levels. The breathalyzer contains a system to sample the breath of a suspect and also two glass vials containing the chemical reaction mixture. The breathalyzer also has a system of photocells that a re connected to a meter that measures the color change associated with the chemical reaction. Other devices include a intoxilyzer and a alcosensor. The intoxilyzer detects alcohol by infrared spectroscopy, while the alcosensor detects a chemical reaction of alcohol in a fuel cell.
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