DWI Detection and Standardized Field Sobriety Testing Session 7 – Phase Three: Pre-Arrest Screening • Residual mouth alcohol • Breath contaminants Possible Factors Affecting High PBT

DWI Detection and Standardized Field Sobriety Testing

Session 7 – Phase Three: Pre-Arrest Screening

• Residual mouth alcohol

• Breath contaminants

Possible Factors Affecting

High PBT

7-29

There are two common factors that tend to produce high results on a PBT.

Residual mouth alcohol. After a person takes a drink, some of the alcohol will remain in

the mouth. If the person exhales soon after drinking, the breath sample will pick up

some of this left over mouth alcohol. In this case, the breath sample will contain an

additional amount of alcohol and the test result will be higher than the true BAC.

It takes approximately 15 minutes for the residual alcohol to be eliminated from the

mouth.

The only sure way to eliminate this factor is to make sure the subject does not consume

any alcohol for at least 15 to 20 minutes before conducting a breath test. Remember,

too, most mouthwashes, breath sprays, cough syrups, etc., contain alcohol and may

produce residual mouth alcohol. Therefore, do not permit the subject to put anything in

their mouth for at least 15 to 20 minutes prior to testing.

Breath Contaminants. Some types of preliminary breath tests might react to certain

substances other than alcohol. For example, substances such as ether, chloroform,

acetone, acetaldehyde and cigarette smoke may produce a positive reaction on certain

devices. If so, the test would be contaminated and its result would be higher than the

true BAC. Normal characteristics of breath samples, such as halitosis (bad breath), food

odors, etc., do not affect accuracy.

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HS 178 R5/13 21 of 26

Source: DWI Detection and

Standardized Field

Sobriety Testing

March 2013 Edition