Breath testing is the analysis of a sample of air from the lungs to determine the concentration of certain chemical substances in the body. It is used most often to determine the amount of alcohol a person has consumed in cases in which drunken driving is suspected. The technique can also be used to detect other chemical substances in the body and even diagnose some diseases.
Breath testing for alcohol is based on the principle that the concentration of alcohol in a person’s breath is proportional to the amount in the person’s blood. Consumed alcohol becomes more volatile (quick to evaporate) when warmed by the body. Some alcohol passes from the blood into air inside the lungs. The concentration of alcohol in the blood can be determined from air blown into a test device, sometimes called a breathalyzer. The result is usually displayed as a percentage.
A device called an evidential breath tester provides a reliable measure of blood alcohol concentration (BAC) that is accepted by many courts as evidence. Research indicates that a driver may become impaired with a BAC as low as 0.02 percent. This means that there is 0.02 gram of alcohol per 100 milliliters of blood in the person’s body. Most experts agree that any person whose BAC reaches 0.08 percent is too impaired to drive safely.
The minimum BAC necessary to convict a suspected drunken driver varies from country to country and from state to state within the United States. All U.S. states have an alcohol level limit of 0.08 percent or lower.
See also Driving while intoxicated (DWI) .
