Discrepancies Between The Asd And Evidentiary Results - Dräger Alcotest 7410 GLC Operator's Manual

Alcotest 7410 GLC User's Manual

Discrepancies Between the ASD and Evidentiary Results

There may be occasions when the GLC
result does not correspond with the results
from the subsequent evidentiary test. For
example, an "F" result (indicating a BAC
greater than 100 mg%) was obtained on the
ASD but the subsequent result on an
approved instrument was less than 100
mg%. These discrepancies are due to one
(or a combination) of three reasons:
1. Time delay
There is a delay between the time of the
GLC test at the roadside and the time of the
breath test at the detachment. The BAC of
the subject does not remain constant during
this time. It will normally decline due to the
elimination process (approximately
15 mg%/hr). So the BAC at the time of the
GLC test is normally higher than at the time
of the evidentiary test, particularly if the
time delay is large.
2. Mouth alcohol
Mouth alcohol was discussed earlier. If the
observation period was not properly
observed, there may be residual alcohol in
the mouth at the time of the GLC test. This
will cause the ASD test to be higher than the
evidentiary test.
3. Tolerance of the instruments
All scientific instruments have a distinct
precision. It is often called the tolerance
and is expressed with a plus and minus
value (e.g. ± 10 mg%). No instrument will
give exactly the same result when analyzing
the same sample time after time (if that was
possible). The instrument will give one
result most of the time, but also results
which can be either slightly lower or higher
than the most common result.
The tolerance of an approved instrument
and the Alcotest 7410 GLC is ± 10 mg% of
the observed result. Any comparison of
results from these two instruments must
consider their tolerances. An apparent
discrepancy can occur when the tolerance of
either one or both of the units is at the
extreme. It is important to realize that a
discrepancy in this case does not mean an
error exists in either the ASD or the
evidentiary instrument.
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