How Reliable are ASD tests?

When people find out  I am an alcohol expert, the conversation usually turns to a question of how accurate the roadside ASDs (approved screening devices) are and the risks of getting an Immediate Roadside Prohibition, or IRP, from a faulty machine. They are often surprised to hear that the roadside ASD has the same accuracy as the evidentiary instrument (commonly called a “breathalyzer”) used in police offices. The real issue isn’t accuracy, it’s reliability. Reliability is a measure of how likely a machine is operating properly and giving accurate results. It is a subtle distinction, but an important one especially when comparing the ASD test to the more reliable evidentiary test.

ASDs and evidentiary instruments in British Columbia use fuel cell technology to measure alcohol in breath samples, and both are accurate to plus or minus 10 mg% when they are properly calibrated. But it’s not only the device that matters when it comes to reliability, it’s the entire test procedure too. You see, ASDs were never intended to provide the most reliable breath test possible. Before the 2010 IRP legislation, ASDs were used at the roadside to help police officers quickly screen which drivers should be tested in the office with an evidentiary instrument and which should be released (that’s why “screening” is the middle name of ASD). An ASD test result cannot even be used as evidence in a criminal trial for impaired driving — it can only be used as grounds for an evidentiary breath demand.

So what bad things happened to a driver who received an ASD FAIL in the old days before the IRP legislation? Well, they could get a 24-hour prohibition but no fines, and maybe an evidentiary demand if the officer wanted to go further. But the really bad stuff like a longer prohibition and fines wouldn’t happen unless there was the more reliable evidentiary test followed by a trial and a criminal conviction.  So why did the British Columbia government start applying harsh penalties based on less reliable ASD results? The answer is complex, but suffice to say it had good evidence that administrative penalties could be more effective than criminal laws in reducing the incidence of impaired driving.

The government recognized some of the shortcomings of the ASD test because it rewrote the IRP law so that a second ASD test on a second device would be offered to drivers who got a WARN or FAIL  the first time. By adding a second ASD test, the reliability of the two tests is greater than the reliability of just the one, but the two roadside tests still are not the most reliable way of measuring a Blood Alcohol Concentration. For that you need the test procedure using an evidentiary instrument, or even a blood sample analysis.

There are 3 important procedural safeguards evidentiary test procedures have that ASD test procedures lack. These safeguards ensure breath tests in the police office are the most reliable breath tests possible.

Next time I’ll discuss those 3 safeguards.

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