A breath alcohol test measures how much alcohol is in the air you breathe out. The device uses that measurement to estimate how much alcohol is in your blood. That number is known as your BAC, or blood alcohol content. According to DOT guidelines, a Department of Transportation driver cannot blow a 0.02 or higher. If the result is in fact a 0.02 a confirmation test must be done after waiting 15 minutes. The results of both tests are printed and given to the employer.