DUI Metrology Dictionary

Ambient threshold/ambient fail threshold (in the context of the Intoxilyzer)

The hardware/software sensitivity/setting on a specific Intoxilyzer 8000C at which that instrument will trigger an ambient fail alarm for room air alcohol/interferent rather than self-adjusting the zero setting for ethyl alcohol analysis. The software used in Ontario is alleged to set the ambient threshold/ambient fail threshold at 10 mg/100 mLs on all Intoxilyzer 8000C regardless of software version. The instruments evaluated by the CFS and the RCMP for the ATC, prior to type approval, with earlier software versions, were tested to establish that 10 mg/100mLs was the threshold. The image attached is an excerpt of Table 2 from the revised CFS evaluation of the 8000C. No metrological authority (e.g. Measurement Canada) is responsible in Canada for metrological supervision of police instruments in-the-field respecting sampling of actual instruments to check the ambient software threshold that they are currently using on test subjects. This huge gap creates a crisis in the reliability of evidentiary breath testing in Canada and will likely result in Charter challenges.

Table 2 CFS 8000C Evaluation re ambient fail threshold
Blog articles on System Blank Test, Ambient Fail Threshold, Air Blanks