Massachusetts DWI DUI OUI Field Sobriety Test Police Training Manual

PRELIMINARY BREATH TESTING

The basic purpose of preliminary breath testing (PUT) is to demonstrate the association of alcohol with the observable evidence of the suspect’s impairment. The suspect’s impairment is established through sensory evidence: what the officer sees, hears and smells. The PUT provides the evidence that alcohol is the chemical basis of that impairment by yielding an on-the-spot indication of the suspect’s blood alcohol concentration (BAC). The PUT provides direct indication of the BAC level. It does not indicate the level of the suspect’s impairment. Impairment varies widely among individuals with the same BAC level.

Preliminary breath testing, like psychophysical testing, is a stage in the prearrest screening of a DWI suspect. Usually the suspect is not yet under arrest when requested to submit to the preliminary breath test. The DWI incident remains at the investigative stage; the accusatory stage has not yet begun. The PBT result is only one of many factors the officer considers in determining whether the suspect should be arrested for DWI. It should never be the sole basis for a DWI arrest. The PUT result is an important factor because it provides direct indication of alcohol impairment. All other evidence, from initial observation of the vehicle in operation through formal psychophysical testing, indicates alcohol impairment.

ADVANTAGES OF PBT

A PBT offers several important advantages for DWI detection. It may:

• corroborate other evidence by demonstrating that the suspicion of alcohol impairment is consistent with the officer’s observations of the suspect’s mental and physical impairment.

• confirm the officer’s own judgment and help gain confidence in evaluating alcohol impairment accurately, based on observations and psychophysical tests. (Many officers experienced in DWl enforcement find that they rely less and less on the PBT as their confidence in their own powers of detection increases.)

• disclose the possibility of medical complications or impairment due to drugs other than alcohol. (The PBT can confirm or deny that alcohol is the cause of the observed impairment. For example, observed psychophysical impairment coupled with a PBT result showing a very low BAC indicates an immediate need to investigate the possibility that the suspect has ingested a drug other than alcohol or suffers from a medical problem.)

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