Accuracy and Reliability of Breath Testing Instruments

The AS IV and the FST  approved screening devices (ASDs) are handheld alcohol screening devices used at the roadside to detect impaired drivers. Immediate roadside prohibitions (IRPs) can be issued to drivers with ASD test results in the FAIL or WARN ranges. The Intox EC/IR II is a larger evidentiary instrument used in a police office to measure a blood alcohol concentration for a more serious impaired driving criminal code offence. All three of these alcohol testing devices have the same accuracy of plus or minus 10 mg% of BAC when they are operating within the manufacturer’s specifications. However, the devices may or may not be operating within those specifications – meaning the test result might be accurate or it might not. Reliability describes the likelihood of the result being accurate.

While portable and evidentiary instruments may be equivalent in accuracy, they are not equivalent in reliability. An Intox test result is more reliable than an ASD test result because there are more safeguards in both the test procedure and built into the instrument. For instance, the Intox can detect the presence of mouth alcohol and then stop the breath test sequence, but the small handheld devices cannot do this. The Intox procedure requires a 15 minute observation period before each breath test so that potential mouth alcohol contamination of the breath sample is eliminated; the ASD test procedure does not require this. The Intox procedure requires an alcohol standard test at the time of each breath test to ensure the breath test is accurate; again, the handheld ASD procedure does not require this. The Intox device is a highly automated instrument that minimizes operator errors and, at the end of the test sequence, a printed report is produced – verifying the proper procedure was followed by the operator; in contrast, the ASDs have no printed verifications or reports.

Omitting the observation period or the alcohol standard test in an evidentiary Intox breath test would be a serious procedural error, jeopardizing the likelihood the breath test result would be used as evidence in a criminal impaired driving trial.

ASD test results have been acknowledged by the Supreme Court of Canada as less reliable than evidentiary breath tests. But, while it is correct to say that ASD tests are less reliable, it is incorrect to say ASD tests are unreliable – generally ASD tests are reliable. However, the circumstances of the test and the operation of the device should be closely examined to have confidence that any particular ASD test is both accurate and reliable. This is what a Forensic Alcohol Expert is able to do.