Quite often using Alco-Sensor IV DWF Screeners in our office we obtained false positives for alcohol. What happens is that a drinking subject blows, and quickly thereafter a non-drinking subject is tested and the unit provides a reading indicating some amount of alcohol. In other words, the unit is either malfunctioning or it has retained alcohol in the sample chamber.
The problem with this is that the alcohol from the later sample will simply combine with the alcohol from the first sample. And the danger is that a person who has had nothing to drink may be called a liar for denying consumption, and a person who is on the edge may go over the legal limit because of alcohol from a previous subject.
Consider for a moment the margin of error on these devices. The police readily admit that their devices can be out by as much as .01% when functioning properly. If they are properly programmed, a “Warn” on an ASD should display if the subject is at .06%. But what happens if the subject is at .045% and they then blow on an ASD where the previous subject was at .220% or some such high level?
The simple answer is it would be another case where an innocent person receives an Immediate Roadside Prohibition.
We gave this information to the RCMP because we couldn’t find it in the literature. It was clear to us that the subsequent test could be contaminated by the previous. We don’t know what they did with the information that we gave them, but it may have influenced the new procedure.
Interesting, however, is that on one of the new ASD calibration sheets used by the police to record the calibration test results, there is now a box for the officer to record the results of a blank test.
Our first thought was that this was simply to give the impression that someone was actually testing whether the device functioned. That was a major problem that we exposed last year. It may still have been the case. But of course, we have now accumulated records for a few hundred ASDs since the new testing procedure was introduced.
We had already over 2000 pages of ASD records going back over 2 years. Now we have a few hundred more, some for calibration tests performed as recently as August 15, 2012. And the interesting thing that we are seeing is that when the officers perform the blank tests, often enough they are discovering that the devices are reporting false positives for alcohol. And, confirming what we first reported, after a few minutes or more tests, the alcohol typically dissipates.
We’re sure this wasn’t the result that they hoped for when they introduced the blank tests. But it is clear on the face of the police records that you can blow false positives for alcohol on an Approved Screening Device if you blow shortly after someone who has been drinking.