What is Residual Mouth Alcohol?

Residual mouth alcohol is the alcohol that remains in the mouth after drinking alcohol, using mouthwash, or using breath spray with alcohol.  Residual mouth alcohol can contaminate an alcohol test result by causing a higher test result.  If an employee uses mouthwash or breath spray that contains alcohol immediately prior to an alcohol test it may affect the result.  The alcohol testing device will read the residual alcohol in the mouth rather than the alcohol coming from the lungs.  

Mouth alcohol dissipates within 15 minutes or less.  Typically mouth alcohol is reduced by 75% within the first two minutes, and 50% for every two minutes after.

The DOT alcohol test protocol requires a 15 minute waiting period after a screening test result of .020 or greater, followed by a confirmation test at the end of the 15 minute waiting period.  The reason for this wait is to allow any alcohol that might have been in the employee’s mouth prior to the screening test to dissipate. 

If the confirmation test detects alcohol after the 15 minute wait, you can be certain that the alcohol came from the employee’s lungs, and not from the residual mouth alcohol.  If the positive screening test result was due only to residual mouth alcohol, the breath alcohol test performed after the 15 minute wait will be zero.