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Ambient Conditions Change Baseline 0 on an IR Breath instrument - Disappearing Alcohol

Updated: Sep 13, 2022

Experiment studying the phenomenon of disappearing alcohol

It is easy to replicate this experiment on an Intoxilyzer® 5000. It is more difficult to replicate this experiment on an Intoxilyzer® 8000 because the 8000 has a very weak pump. The phenomenon applies, however, to both instruments because the baseline zero is always floating.


Intoxilyzer® 5000

Wet-bath simulator with 100 target value solution at 34.0 C

Wet-bath simulator with 50 target value solution at 34.0 C

This video displays the function of and relationship between the air blank and ambient fail systems on an IR evidentiary breath instrument such as the Intoxilyzer® 5000C (or 5000 as in this video) and the Intoxilyzer® 8000C (or 8000). In this experiment the room's ambient conditions have been artificially elevated to 50 mg / 100 mls by attaching a second wet-bath simulator (at 50 mg/ 100 mls and 34C) to the breath tube inlet.

Although the 5000 instrument is programmed to flag "Ambient Fail" at 20 mg/100 mls, no such error message is produced. This is because the instrument can only compare an unacceptable ambient situation ( 50 mg/100 mls) against the baseline established when the instrument was first powered on (50 mg / 100 mls.) Note that the instrument is powered up (cold boot) with the 50 mg/100mls simulator output attached to the breath tube.

The instrument erroneously considers the 50 mg /100 mls as 00 mg /100 mls. Any subsequent breath or cal. check readings will be affected by this baseline. The baseline zero, however, shifts up and down relative to each air blank.

Why is this significant to defence counsel?

The real danger of this phenomenon is that calibration checks become not reliable - and in this example the 100 mg /100 mls alcohol standard produces a calibration check of 51 mg / 100 mls. COBRA data from the weeks before and after a particular subject test may be very useful in flagging unusually low cal checks that possibly are being caused by ambient ethanol. Alternatively, another chemical interferent in the room air (e.g. hand cleaners, paint, cleaning fluids) may do the same thing as ambient ethanol. Unreliable cal checks do not cause erroneous subject test results but they do compromise the scientific reliability of the subject tests, and should compromise the Crown's ability to rely on the 320.31(1)(a) presumption of accuracy.


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