How long does mouth alcohol last?

Mouth alcohol dissipates after 15 minutes.

The DOT alcohol test procedure requires the operator to observe a 15 minute wait after a screening test result of .020 or greater, and to conduct a confirmation test at the end of the 15 minute waiting period.  The reason for this wait is to rule out that the screening test result was due to residual mouth alcohol.

If the confirmation test is positive after the 15 minute wait, one can be certain that the alcohol came from the employee’s lungs, and not from the residual mouth alcohol.  If the screening test was positive only because of residual mouth alcohol the confirmation test result will be zero.  The confirmation test is used as the final result, regardless of the screening test result.