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Interpreting Breath Graphs

Intoxilyzer 9000 Operator Guide For Law Enforcement

Interpreting Breath Graphs

Interpreting Breath Graphs

Each time an individual provides a breath sample to an Intoxilyzer 9000, the instrument will produce a breath profile graph. The graph is comprised of two different lines. The ‘thinner/lighter’ line is the breath flow. Typically, the flow starts strong and then declines as the subject continues to blow, and the available air in their lungs decreases. The ‘thicker/darker’ line is the alcohol concentration in the breath sample. It is important to understand that the graph is not designed to prove or disprove the presence of mouth alcohol, but rather to assist the operator in determining what may have occurred when the instrument rejects a sample. Below are some examples and brief explanations of the four most common types of graphs:
Line graphs showing two normal breath profiles when the subject has alcohol in their breath sample.

Figure 1

Two normal breath profiles when the subject has alcohol in their breath sample. Notice the ‘thick/dark’ line in samples 1 and 2 as it rises quickly from the baseline and then appears to plateau towards the end of the sample. This is a normal breath sample.
See Figure 1 larger
Graph showing breath profile from a sample with mouth alcohol.

Figure 2

This is a breath profile from a sample with mouth alcohol. The ‘thick/dark’ line rises just like the previous examples but notice the continual decline in concentration the longer the sample is provided. This is indicative of residual mouth alcohol, and in fact, the instrument rejected this sample.
See Figure 2 larger
Breath profile graph showing that the subject stopped and started a total of three times.

Figure 3

This is a breath profile graph that was made by the subject stopping and starting a total of three times. While the ‘thick/dark’ line does drop, this is not mouth alcohol. It is simply a normal graph when a subject does not provide a continuous breath sample. The instrument correctly accepted this sample.
See Figure 3 larger
Graph that looks normal.

Figure 4

This is a graph that looks normal; however, the instrument rejected this sample. This is why one cannot rely on the graphs to prove or disprove the presence of mouth alcohol. There are a variety of reasons why the instrument will reject a sample, even when the breath profile graphs look acceptable. When a sample is rejected, the correct procedure is to follow the on-screen instructions which will instruct the operator to conduct another test, or in other instances, to seek a blood sample.
See Figure 4 larger
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