Breath Testing Calibration

If you were charged with driving under the influence (DUI), you were probably given a breath test, or breathalyzer, before you were arrested. As the name suggests, this type of test uses your breath to determine whether you are intoxicated by measuring your blood alcohol content (BAC). If the test reveals a BAC above the legal limit of 0.08%, you will be charged with DUI. However, the results of these tests can often be challenged if the device used to measure your BAC did not meet the necessary breath testing calibration standards.

As with any other type of mechanical device, breath testing equipment must be properly maintained in order to work properly. Part of this maintenance includes verifying the device’s accuracy. To ensure precise results, the device must be checked regularly via a process known as calibration—this involves comparing the device’s results to a known standard, and then adjusting the device as needed.


There are two types of methods used to calibrate a breath test device: dry gas and wet bath. During dry gas calibration, the device is tested using a specially blended mixture of alcohol and nitrogen. The device’s results are then compared to the known alcohol content in this solution. For example, if the mixture has an alcohol concentration of 0.08%, the breath testing device will be adjusted so that it provides a 0.08% reading as well.

Like the dry gas calibration method, the wet bath calibration process also tests the device’s accuracy via a precisely blended alcohol solution. In this case, however, the mixture is comprised of water and alcohol, rather than nitrogen and alcohol.

Because the calibration process requires a great deal of training, as well as expensive testing equipment, a certified technician is the only person who is qualified to calibrate any type of breath test device. As a result, if the device used during your breath test was not recently sent off for calibration, it may provide inaccurate results, which means they cannot be used as evidence against you in court.

If you were recently arrested for DUI after failing a breath test, it is important to obtain legal counsel prior to your day in court. An experienced DUI attorney can review the officer’s maintenance logs to determine whether the breath testing device was properly maintained. Check your local listings to find an attorney who specializes in DUI law in your area today.