Massachusetts DWI DUI OUI Field Sobriety Test Police Training Manual

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.

There are two common factors that tend to produce low PBT results.

Cooling of the breath sample. 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.

The composition of the breath sample. 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.

THE ARREST DECISION

Your arrest/no arrest decision is the culmination of the DWI detection process. Your decision is based on all the evidence you have accumulated during each detection phase.

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

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