October 29, 2015

DWI Detection and Standardized Field Sobriety Testing Session 7 – Phase Three: Pre-Arrest Screening • Breath sample cooling • Breath sample composition

DWI Detection and Standardized Field Sobriety Testing
Session 7 – Phase Three: Pre-Arrest Screening
Breath sample cooling
Breath sample composition
Possible Factors Affecting
Low PBT
7-30
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 low PBT results.
Breath sample cooling. If the captured breath sample is allowed to cool before it is
analyzed, some of the alcohol vapor in the breath may turn to liquid and precipitate out
of the sample. If that happens, the subsequent analysis of the breath sample will
produce a low BAC result.
Breath sample composition. Breath composition means the mixture of the tidal breath
and alveolar breath. Tidal breath is breath from the upper part of the lungs and the
mouth. Alveolar breath is deep lung breath. Breath testing should be conducted on a
sample of alveolar breath, obtained by having the subject blow into the PBT instrument
until all air is expelled from the lungs.
DWI Detection and Standardized Field Sobriety Testing
Session 7 – Phase Three: Pre-Arrest Screening
Radio frequency interference
Possible Factor Affecting
Either High or Low PBT
7-31
Radio frequency interference (RFI) can produce either high or low test results, or can
prevent a breath test device from producing any result. Care should be exercised when
utilizing a PBT around radio equipment.
Notes:_______________________________________________
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Notes:_______________________________________________
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HS 178 R5/13 22 of 26
DWI Detection and Standardized Field Sobriety Testing
Session 7 – Phase Three: Pre-Arrest Screening
Breath sample cooling
Breath sample composition
Residual mouth alcohol
Breath contaminants
Radio frequency interference
Possible Factors Affecting
Preliminary Breath Tests
7-32
Radio frequency interference (RFI) can produce either high or low test results, or can
prevent a breath test device from producing any result. Care should be exercised when
utilizing a PBT around radio equipment.
Notes:_______________________________________________
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HS 178 R5/13 23 of 26
DWI Detection and Standardized Field Sobriety Testing
Session 7 – Phase Three: Pre-Arrest Screening
The Arrest Decision is Based on
All Evidence Accumulated During
All Three Detection Phases
Initial Observation of
Vehicle Operation
Face to Face
Observation
and
Interview
Psychophysical
Tests
Preliminary
Breath Tests
Observation
of the
Exit
Observation of
the Stop
7-33
G. The Arrest Decision
Your arrest/no arrest decision is the culmination of the DWI detection process. That
decision is based on all of the evidence that has come to light since your attention was
first drawn to the vehicle or individual.
PHASE ONE:
• Initial observation of vehicle in motion
• Observation of the stop.
PHASE TWO:
• Face to face observation and interview
• Observation of the exit.
PHASE THREE:
• SFSTs
• Preliminary breath tests.
Your decision involves a careful review of each of the observations you have made.
Conduct a "mental summary" of the evidence collected during vehicle in motion,
personal contact and pre-arrest screening. If all of the evidence, taken together,
establishes probable cause to believe that a DWI offense has been committed, you
should arrest the subject.
Notes:_______________________________________________
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HS 178 R5/13 24 of 26
Standardized Field Sobriety Test Course
Session 7 – Phase Three: Pre-Arrest Screening
QUESTIONS?
7-38
Test Your Knowledge
INSTRUCTIONS: Complete the following sentences.
1. The two major evidence gathering tasks of Phase Three are:
__________________________________________________________________
__________________________________________________________________
2. The major decision in Phase Three is ____________________________________
3. The entire DWI detection process culminates in ____________________________
4. Divided attention tests require the driver to ______________
5. Among the mental and physical capabilities a person needs to drive safely are
these four:
a. ___________________________________________________________
b. ___________________________________________________________
c. ___________________________________________________________
d. ___________________________________________________________
6. The two stages of the Walk and Turn are:
a. ___________________________________________________________
b. ___________________________________________________________
7. The two stages of the One Leg Stand are:
Notes:_______________________________________________
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HS 178 R5/13 25 of 26
a. ___________________________________________________________
b. ___________________________________________________________
8. The purpose of PBT is ____________________________________________
HS 178 R5/13 26 of 26
Test Your Knowledge (Cont.)
9. Two factors that produce high results on a PBT are:
a. ____________________________________________________________
b. ____________________________________________________________
10. Two factors that produce low results on a PBT are:
a. ____________________________________________________________
b. ____________________________________________________________

HS 178 R5/13 1 of 62Source: DWI Detection and
Standardized Field
Sobriety Testing
March 2013 Edition

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