MA Police Training Manual - OUI Stop Field Sobriety Tests
help to establish probable cause for a DWI
arrest. (The role of the PBT in establishing probable cause may be affected by
the evidentiary value of PBT results in your state. Consult your specific PBT
law, your supervisor, or the local prosecutor for clarification, if necessary.)
LIMITATIONS OF PBT
Attorney Note: Preliminary, or Portable Breath test devices (PBT)
are inadmissible in Massachusetts courts
as evidence of intoxication in OUI cases. The police sometimes still use
them in determining whether or not to arrest you, but that fact won't come
out of you fight your case in court. See
PBT. -RJM Preliminary breath testing my have both
evidentiary limitations and accuracy limitations. Evidentiary limitations vary
with specific laws. In some states PBT results are admissible as evidence; in
other states they are not admissible. Where the results are admissible, there
may be differences in the weight or value they are given. Consult your state PUT
law, your supervisor or your local prosecutor, as necessary, for clarification.
PBT instruments have accuracy limitations.
Although all PBT instruments currently used by law enforcement are reasonably
accurate, they are subject to the possibility of error, especially if they are
not used properly. There are factors that can affect the accuracy of preliminary
breath testing devices. Some of these factors tend to produce “high” test
results; others tend to produce “low” results.
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 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 is always best not to permit the suspect 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
conceivably could produce a positive reaction on
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