DUI enforcement is discussed in the May 2010 “Police
The Law Enforcement Magazine” in an article entitled:
“Drug and Alcohol Enforcement.”
Basically, the DUI cops admit the shortcomings of breath
testing gadgets and estimators. This could help
San Diego DUI lawyers in their cases.
Here’s some astonishing DUI excerpts:
EVIDENTIARY BREATH TESTERS
MOST EVIDENTIARY BREATH TESTERS in
use today employ infrared spectroscopy
to measure BAC. The operating principle
of infrared spectroscopy or spectrophotometry
is that every substance will absorb
infrared light at wavelengths unique
to that substance. When a breath sample
is introduced into the sample chamber of
a breath analyzer, infrared light is beamed
through the transparent chamber toward
a photocell on the opposite side.
Any alcohol present in the breath sample
will absorb the relevant wavelengths
of light, and the more alcohol present
in the sample, the more light is absorbed.
The analysis is specific for ethanol, so other
volatiles in the sample (such as acetone,
produced by diabetics and some dieters)
that contributed to falsely high readings
in more primitive devices have no effect.
Some accused drunk drivers will claim
their BAC reading came from mouth
or stomach alcohol. A denture or other
mouth structure or the stomach gas coming
from a burp can contain alcohol. Pretest
water and observing the subject for burping
are supposed to prevent these claims,
but people still try.
Fact is, both mouth and stomach sources,
if measured as lung air… will begin to
dissipate with exhalation, so the BAC level
in the sample will decrease as the subject
empties his or her lungs. Modern testers used
by police in the field employ platinum fuel
cells to measure BAC. Breath samples pass
through electrodes coated with a thin layer
of platinum black. Any alcohol present in
the sample is oxidized, releasing electrons.
The free electrons pass from one electrode
to the other, creating a current. The
current is proportional to the amount
of alcohol in the breath sample.
PAS Tests (Hand-held gadgets)
PAS tests/PBTs don’t have slope detectors,
and they can be fooled by some
other organic compounds. They are
reliable enough for field work, although
most states do not allow their
results to be introduced in court as
evidence. Their main function is
to assist the officer in establishing
probable cause for the arrest.
There is a fourth technology for
measuring BAC, used primarily in
consumer-grade electronic breath
testers. Semiconductor-based devices
can detect alcohol in a breath
sample, but their measurements of
BAC are unreliable. They are prone
to false positives, showing a BAC
when there is no alcohol present.
They are also prone to contamination,
and the sensors require
recalibration or replacement every
six months to preserve whatever accuracy
they do have. Few consumers
will bother to do this. No state
allows the results from a semiconductor-
based tester to be used as evidence
of BAC, and the U.S. Department
of Transportation rejects them as well…
Much of what these DUI cops say is not
scientifically supported.
However, San Diego DUI criminal defense
attorneys know much of this is supported:
BAC reading can come from mouth
or stomach alcohol. A denture or other
mouth structure or the stomach gas coming
from a burp can contain alcohol. Pretest
water and observing the subject for burping
are supposed to prevent these claims..
PAS Tests (Hand-held gadgets)
PAS tests/PBTs don’t have slope detectors,
and they can be fooled by some
other organic compounds.