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Reliability: Air Blanks "System Blank Test"

Updated: Sep 13, 2022

Tip 43: A properly functioning approved instrument air blank system (including the instrument itself, the ambient environment around the instrument, and operator procedure) is a condition precedent to the reliability of any system calibration check (control test). This applies whether the system is using alcohol standard in a wet-bath simulator or using dry gas.

Parliament has recognized in section 320.31(1)(a) that a proper air blank, also known as a "system blank test" is a condition precedent to approved instrument accuracy and reliability:

"before each sample was taken, the qualified technician conducted a system blank test the result of which is not more than 10 mg of alcohol in 100 mL of blood"

It is respectfully submitted that section 320.31(1)(a) implies "a properly functioning" air blank system.

This condition precedent is recognized in the Recommended Standards of the Alcohol Test Committee of the Canadian Society of Forensic Science.

The 2018 ATC Recommended Standards provision reads as follows (see "Canadian Society of Forensic Science Alcohol Test Committee Recommended Operational Procedures Effective: 2018 December 18")

2. A system blank test shall be conducted and shall give a reading not greater

than 10 mg/100 mL.

The 2013 ATC Recommended Standards provision reads as follows at page 12:

The 2009 ATC Recommended Standards provision reads as follows at page 15:

What are the conditions precedent to a proper functioning system blank test / air blank?

It is a requirement of the Alcohol Test Committee that the person responsible for set-up of an approved instrument, in a detachment or breath truck, pay attention to environmental conditions, including ventilation. This requirement is included in the 2014 ATC best practices at page 12:

The iair blank process in the operation of an Intoxilyzer 8000C was reviewed by Justice Tuck-Jackson in R. v O., 2014 ONCJ 440, based on evidence she had heard from a CFS scientist, called by both Crown and defence. The following are excerpts from that decision:

[50] The first stage is an air blank test. In this phase, the A.I., with the use of a pump, draws in room or ambient air through the heated breath tube. In so doing, the A.I. is checking to see whether there is any alcohol or other interfering substances present in the room air that could contaminate the testing process. ... The optimal and typical result obtained registers as “000”. In the instant case, the A.I. conducted an air blank test at 04:05:24 on June 8, 2011 at the conclusion of which a result of “000” mg% was generated. In Mr. Palmentier’s expert opinion, that result indicated that the level of alcohol or any interferent that might be present in the surrounding air was 0 to some amount less than or equal to the equivalent of 7 mg of alcohol in 100 mL of blood. If the level of alcohol or any interferent that might be present equals or exceeds the threshold value of the equivalent of 10 mg of alcohol in 100 mL of blood, then an ambient fail message registers. The instrument immediately initiates a second air blank test, following which the testing sequence is interrupted and cancels itself. This represents an example of how the Intoxilyzer 8000C self-regulates.

[51] Assuming that the air blank test result does not exceed the 10 mg per 100 mL threshold value, the A.I. proceeds to the second stage, namely a diagnostics test.

What should I look for in a Normal System Blank test?

Criminal defence lawyers need to be aware of the sounds and video indications of NORMAL system blank tests. The following video depicts normal Intoxilyzer 8000 air blank sequences before and after both internal test procedure (ITP/internal standards) and control tests at a target value of 45 mg/100mls. Dry gas alcohol standard at 45 was used in this example.

It is respectfully submitted that a complete series of successful air blanks with results of "000" (assuming full disclosure of all air blanks as per Justice Tuck-Jackson's decision in R. v. O.) should be a good indicator that the IR approved instrument and its alcohol standard are not being affected by adverse ambient conditions that would affect the reliability of the alcohol standard and the subject tests.

An IR approved instrument has a floating zero for each ITP check, cal. check or subject test. There is no true zero on an IR instrument. Zero floats and depends on where the instrument hardware and software sets zero - all based on reliable air blanks. If air blanks are contaminated by ambient alcohol in the breath room then zero may be set in the wrong location.

bathroom weigh scale
Most scales for weighing humans have a mechanism for the user to reset zero. If zero is set in the wrong place on bathroom scales or in the gym scales, you may be able to fool youself or your partner into thinking you weigh less. If zero is set in the wrong place on an insrument used for a forensic purpose, then the measurement result iis not reliable in establishing guilt. More importantly, from a section 320.31(1)(a) DUI defence perspective, unreliable zero will result in unreliable system calibration checks.

If there is no significant ambient alcohol or ambient interferent in the room air, then the baseline zero on the IR instrument should not be affected. If so, the reliability of calibration checks should not be affected by ambient conditions.

What can go wrong? Possible Problems for further Experimentation, Study, and Cross-examination:

There is a problem, however, if the supervisor of the detachment or the qualified technician is not paying appropriate attention to ambient conditions, by assuring adequate ventilation and avoiding the presence of interferents (e.g. hand cleaners, cleaning fluids, and fingerprinting chemicals) that may not be detected by the instrument's interferent detect system (e.g. limonene or d-limonene on the 5000C and ethyl or di-ethyl ether on the 8000C).

Defence lawyers need to pay particular attention to protocols, described in the CFS Training Aid, for ventilation and re-positioning the subject following an ambient fail. Defence lawyers may wish to challenge any re-positioning the breath tube before any air blank begins.

Pre-emptive re-positionong of the breath tube is bad practice and should be challenged in section 320.31(1)(a) litigation.

Frequent ambient fails in a particular detachment may reflect bad environmental conditions in the detachment.

Pre-emptive re-positioning of the breath tube because ambient fails are frequent in a particular detachment is not mentioned as a recommendation in the CFS 8000C

Training Aid. See page 136 of 238 (2013 version) respecting the Exception Message

"Ambient Fail":

"When: During the air blank." "Why: The instrument has detected an unacceptably high alcohol concentration in the ambient air drawn in during the air blank. The ambient fail message is communicated when the difference between the vapours in the sample chamber at cessation of the air blank (i.e., when the pump stops) is more than 10 mg/100 mL higher than the baseline measurement obtained before the pump was activated. An ambient fail message can occur if the test subject moves too close to the external breath tube during the air blank, or if the mouthpiece is not removed after the subject breath test "Action: Relocate the subject away from the breath tube, remove mouthpiece, ventilate the room, re-commence testing of the subject." "A continuous purge can be initiated through the keyboard menu using the “Esc Esc A” command."

It is respectfully submitted tha pre-emptive re-positioning of the breath tube because ambient fails are frequent in a particular detachment, constitutes deliberate or negligent operator error and should result in non-applicability of any section 320.31(1)(a) presumption of accuracy. Defence lawyers will, of course, need to call an expert on the subject. CFS experts will probably disagree (see R. v. O.). Ultimately, the challenge should be answered through empirical research and expert opinion based on that empirical research. See other blog articles herein for discussion and experiments by the author.

What does the defence need to know?

Disclosed information about successful and not successful air blanks both prior to and and post calibration checks and subject tests is essential to any audit of calibration check or subject test reliability.


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