What is a Purge Fail on an Intoxilyzer 8000C ?
What is a Purge File on an Intoxilyzer 5000C ?
How does this phenomenon affect reliability of a measurement result?
During an air blank the instrument runs the air pump until the indication of BAC remaining in the sample chamber system drops to approximately what the instrument perceives as 000. As you know from other blog entries, zero floats; it is never fixed; it rises and falls dependent upon ambient alcohol/interferent conditions and other external conditions. Below please see an example of a purge fail on an Intoxilyzer 5000, caused by radio frequency interference, which has changed (lowered) zero to about minus 057 relative to the room air. Note , that in this example, the cal. check reads 57-58 (with no simulator or alcohol standard attached) and the purge fail happens because the air blank indicated value can never get below 57. The indication in this example is reading high.
The CFS 8000C Training Aid describes a situation where an 8000C may read low - in circumstances where room air ambient alcohol (or an interferent) is rising. They note in bold text - "Subject tests will not be overestimated by alcohol in the room air". The issue for a defence lawyer in such circumstances is not whether subject test BAC is raised or lowered but rather the resulting unreliability of the control tests. If control test values have been lowered in the context of this phenomenon (i.e. the control tests read as 90 to 110 when they should read 81 to 101 - using 9 mg/100mL zero elevation) using 100 target value alcohol standard, then the control tests have become unreliable. If the cause of this condition is operator error, then the operator error has caused unreliability of the control tests aka cal. checks.
Watch the following example of a purge fail on an Intoxilyzer 8000. The experimenter uses a small bottle of Vodka near the breath tube.
Think about:
Why does the instrument generate an "ambient fail" message"?
Why does the instrument generate a "purge fail" message?
Will a control test (not shown in this video) be reliable immediately following these sequences? Note the screen saying 3:T1 DWIS. DWIS is (D)ry, W(et),(I)nternal,(S)tability. In other words, choose D, W, I, or S to run a cal. check. Would you run a cal. check in these circumstances and expect it to be reliable?
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