There are numerous things that can result in a false PBT result. Residual mouth alcohol and breath contaminants can cause a preliminary breath test result to be higher than actual blood alcohol content. It takes approximately 15 minutes for residual alcohol to be eliminated from the mouth. Therefore, the officer is supposed to ensure that the subject has not consumed any alcohol for 15 minutes prior to using the PBT. An officer rarely does this. Other substances can skew the results high on a PBT. These include chloroform, acetone, and cigarette smoke.