Portable Breath Test Devices Can Produce Falsely High Tests
According to the National Highway Transportation Safety Administration (Student Manual HS178 R2/06), a Portable Breath Test Device may produce an artificially high reading. The government document is clear: “PBT instruments have accuracy limitations.” (VII-8). The NHTSA manual goes on to set forth “two common factors that tend to produce high results on a PBT. The PBT is often seen in Underage Consumption cases and in Boating Under the Influence (BUI) cases as they provide probable cause for an arrest.
Residual mouth alcohol. After a person takes a drink, some of the alcohol will remain in the mouth tissues. 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 evaporate from the mouth.
The only sure way to eliminate this factor is to make sure the suspect does not take any alcohol for at least 15 to 20 minutes before conducting a breath test. Remember, too, that most mouthwashes, breath sprays, cough syrups, etc., contain alcohol and will produce residual mouth alcohol. Therefore, it 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 conceivably could 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, food odors, etc., do not affect accuracy.
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