For the past 20 years most advanced breath alcohol testing instruments have incorporated a feature called “automatic breath sampling.” When using an instrument with this feature (such as the Alco-Sensor FST, Alco-Sensor IV, and Alco-Sensor VXL) the operator needs only to hold the instrument while the subject blows into the instrument. The instrument figures out if the subject blows properly, “samples” the subject’s breath at the optimum moment, then displays the results. Not only does automatic breath sampling make the test procedure more convenient for the operator, it also increases the accuracy and precision of breath alcohol testing. How does it work?
What’s a Breath Sample?
Let’s start by understanding what a breath “sample” means. In this case the term “sample” has the same meaning as in science, statistics, and polling. Rather than asking the entire population in the country about their opinion in an election, pollsters ask a small number of people – a sample – that is representative of the entire population. In breath alcohol testing, rather than analyzing the entire amount of a person’s exhalation, breath testing instruments analyze only a small sample of the exhalation – typically only about 1 cubic centimeter. The rest of a subject’s breath goes right through the breath tester without being analyzed.
The Ideal Breath Sample
The portion of a person’s breath that is most representative of blood alcohol concentration is at the very end of the exhalation. We call this deep lung breath or alveolar breath. Breath alcohol testing instruments with automatic breath sampling are able to determine when a subject is nearing the end of the exhalation and take the breath sample at the optimum moment.
How Does it Know?
Intoximeter instruments use proprietary breath sensing technology to detect the flow of breath through the instrument. (Note that the breath sensor is not measuring alcohol – it is only sensing that breath is flowing through the instrument.) The breath sensor can tell if a subject is blowing hard, softly, or not at all. It can tell if a subject’s breath wavers (i.e., the subject alternates between blowing hard and softly), and if the breath is briefly interrupted and starts again. The instrument also calculates breath volume based on the breath sensor information. The instrument uses all this information to determine when the subject has approached the end of the exhalation, and then triggers the breath sample at the optimum moment.
Sampling the Breath
The instrument takes a breath sample by creating a brief vacuum with the breath sampling mechanism that pulls a tiny slice of the subject’s breath into the instrument for analysis. The breath sampling mechanism typically makes a slight “click” noise as it operates. The operator may also be able to feel a slight vibration as they hold the instrument. The moment the breath sampling mechanism operates is the only time that the instrument draws breath into the sensor of the instrument for analysis. All of the breath before the click and after the click passes straight through the instrument without being analyzed.
Precision and Accuracy
Breath sampling is a key element of obtaining evidential quality breath alcohol results. Automated breath sampling adds the additional element of ensuring that the breath sample is always taken at the optimum moment during the exhalation. Using an instrument with automated breath sampling provides the maximum in repeatable, accurate breath test results.