In New Hampshire and many other U.S. states, a police officer who stops a driver on suspicion of drunk driving may ask the driver to take a preliminary breath test using a Breathalyzer or similar device. The breath test measures the driver’s blood alcohol concentration, or BAC. A BAC reading of 0.08 percent often results in drunk driving charges, even though an improperly given breath test may state a driver’s BAC is above 0.08 percent even when it is not.
For example, if the driver has any residual alcohol in his or her mouth, the breath test may read this alcohol instead of what is in the driver’s blood, which can cause a falsely high reading. Alcoholic drinks aren’t the only sources of alcohol: some cough syrups, breath sprays, and similar products contain enough alcohol to trick a breath test device into giving a falsely high reading.
Also, certain contaminants will cause an incorrectly high breath test reading, even if they do not contain alcohol. Chemicals like ether, chloroform, acetone, and chemicals in some kinds of cigarette smoke may be read as alcohol by a breath test machine, resulting in a higher BAC result than the driver actually has.