How Do Alcohol Breath Analyzers Work?
The primary method of determining how much alcohol a person has had to drink is to use an alcohol breath analyzer. The most popular alcohol breath analyzer is the Breathalyzer.
Alcohol Breath Analyzers work, because the concentration of alcohol in the lungs is directly proportional to the concentration of alcohol in the blood. It is the alcohol in the blood that causes drunkenness, but due to the direct correlation between the blood alcohol concentration in the lungs and blood alcohol concentration, a measure of blood alcohol concentration in the lungs is an accurate measure of the body's blood alcohol level.
Alcohol that is ingested shows up in the breath because it gets absorbed (primarily) from stomach and intestines into the bloodstream. Alcohol does not get digested upon absorption and arrives in the bloodstream chemically unchanged. As the blood flows through the lungs, some of the alcohol permeates the lung membranes and into the lungs. When the alcohol reaches the air in the lungs, it evaporates and is exhaled. This percentage of alcohol in the content that passes through the membrane is proportional (in a ratio of between 2400:1 to 1700:1 depending on environmental conditions, but with an average of 2100:1) to the percentage of alcohol in the blood.
The ratio of alcohol content in the blood to alcohol content in the breath is called the partition ratio. A partion ratio of 2100:1 is based on a normal body temperature (37°C/98.6°F). Higher body temperatures will give higher blood alcohol content measurements. This can be significant if (for some reason) one drinks when they have a flu or other sickness - an body temperature increase of 1°C/1.8°F results in a 7% higher value in the result.
For a more detailed overview of how blood alcohol analyzers work, please see the page Blood Alcohol Measurement.