How Reliable are ASD Tests? Part 2

Posted October 21, 2016

Last time I ended a discussion about the reliability of ASDs by saying ASDs lack 3 important safeguards that breath tests from evidentiary instruments have. These are:

Contemporaneous accuracy checks.
Pre-test observation period.
Duplicate tests within the tolerance of the instrument.

Accuracy checks on the ASD can be up to 28 days before a roadside breath test. That’s a significant amount of time for the ASD to be dropped, bumped, or exposed to dusty or extreme temperature conditions that might affect its calibration. Evidentiary instruments in the police office automatically have the accuracy checked just moments before each breath test, and they aren’t exposed to nearly the same everyday hazards as the smaller handheld ASD. So the ASD accuracy check ensures the device is accurate at the time of the check, but only infers it is accurate at the time of the roadside test, which it may or may not be.

When using evidentiary instruments in the police office, the test subject must be observed for at least 15 minutes before each breath test to ensure there is no burping, belching or consumption of alcohol that could produce a mouth alcohol effect. Mouth alcohol can give falsely high breath tests that are sometimes 100 mg% or more than they should be. Police using ASDs at the roadside aren’t required to do an observation period before the test, but they do need to ask when alcohol was last consumed and delay the test if there aren’t 15 clear minutes following the drink. By not doing the observation, there is a risk that the driver may burp or belch (potentially giving a false reading) or consume alcohol, that is never noticed or observed by the police officer.

Duplicate testing is a widely recognized method of enhancing test reliability whenever any instrument or analysis must be as reliable as possible. The 2 tests must give results that are within the tolerance of the device (that’s within plus or minus 10 mg% for evidentiary instruments) because if they aren’t, then one or both tests must be in error. This is a required procedure with the evidentiary instrument. Before the IRP legislation, only one ASD test was taken at the roadside, but the IRP procedure now allows the driver to request a second test on a second device.

This does increase the reliability of the test result (over having just one test), but still isn’t as reliable as ensuring two readings are within the tolerance of the ASD.  The problem is the ASD doesn’t generate an actual number in the  blood alcohol range where IRPs are issued; it gives only a WARN or FAIL message. The device still measures the blood alcohol level, but all numbers from 100 to 550 mg% are reported as FAIL, and all numbers from 60 to 99 mg% are reported as WARN. (For reference, 80 mg% is the criminal legal limit for blood alcohol. Many people also call this by the old terminology of  “point 08”.)  So, for example, two ASD tests could each gave a FAIL message, but if the underlying readings were 110 mg% and 210 mg% this would indicate something was seriously wrong with one or both readings, and no one would never know.

These 3 safeguards are required for evidentiary instrument breath tests for a reason: they make the test result the most reliable possible. In lacking these safeguards, ASD roadside tests are less reliable than evidentiary tests.

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