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:_______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

Notes:_______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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:_______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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:_______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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:_______________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

_____________________________________________________

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