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TEN ISSUES TO ADDRESS WITH THE JURY IN EVERY “NUMBERS” DUI BREATH CASE
By Kenneth N. Hamilton
Ventura County Public Defender
1. Everyone agrees that in the vast majority of cases where the driver is living, BAC at time of
driving is different than BAC at time of test because except during the short equilibrium period
(peak or plateau) BAC is going up or down.
2. Retrograde extrapolation used to estimate BAC at time of driving based on assumptions and
averages. “Extrapolation of a later alcohol test result to the time of the alleged offense is
always of uncertain validity and therefore forensically unacceptable.” (Dubowski, 1985.)
Averages include R factor (percentage of water weight) and beta factor (elimination rate.)
Assumptions include being post absorptive.
3. It is inappropriate to use retrograde extrapolation to estimate BAC at time of driving if client
is in absorptive state at time of driving. There is a general rule of thumb that alcohol is
completely absorbed somewhere between 30 minutes and 2 hours after the ingestion of
alcohol. (Posey, 2006.)
4a. Subjective indicators of alcohol consumption (also known as objective symptoms of
intoxication) can never demonstrate a client’s BAC and merely give an indication of recent
drinking.
4b. The most reliable indicator of whether a person is too impaired to drive is that a person’s
true BAC at the time of driving is .08 or over.
4c. The second most reliable indicator of whether a person is too impaired to drive is a person’s
driving pattern observed over a sustained period of time (e.g., DMV on-road driving test.)
There are 24 indicators of driving impairment and speeding is not an indicator.
4d. The least reliable indicator of whether a person is too impaired to drive is a driver’s
performance on field sobriety tests as subjectively evaluated by an officer who is tainted with
confirmation bias. Research indicates FST tests are highly susceptible to interpretation error
(Cole, 1994) and admitted for evidence of impaired driving, for which they have never been
validated. (Rubenzer, 2007.)
5. There is no way to know what your client’s actual partition ratio was at the time of a breath
test because it is always changing and there is partition ratio variation in the general public.
General partition ratio variability is admissible to raise doubt on A count. Post absorptive
partition ratios for 99.7% of the population in one study have been found to range between
1555:1 to 3005:1. (Dubowski, 1985.) When your client’s actual partition ratio is lower than
2100:1 a breath test will overestimate actual BAC.

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6. Research indicates BrAC (Breath Alcohol Content) is higher than a person’s true BAC when a
breath test is taken during the absorption phase. “Although there is good statistical correlation
between the alcohol concentration in different body tissues and fluids in the fully post
absorptive state, wide individual variations from the population mean alcohol partition values
exist. It is impossible to determine whether the post absorptive state has been reached at any
given time. Those factors make it impossible or infeasible to convert the alcohol concentration
of breath or urine to the simultaneous blood alcohol concentration with forensically acceptable
certainty.” (Dubowski, 1985.)
7. Research indicates BrAC is impacted by client’s breath temperature, the volume of breath
sample, and breath pattern (hypo- or hyperventilation). (Hlastala, 2010.)
8. Research indicates breath test results fail to accurately measure true BAC because additional
non-alveolar “breath” alcohol is exchanged from airway tissue in bronchial tubes and trachea.
(Hlastala, 2010.)
9. A breath test machine indirectly measures a microscopic amount of alcohol. Any
microscopic increase in the amount of alcohol measured due to inherent imperfections in the
breath test instrument will raise the purported BrAC results. The difference in the amount of
alcohol measured by a breath test instrument between BrAC readings of .07 and .12 is
minuscule.
10. Breath test instruments are generally not checked for their accuracy at different levels
(linearity); there is no confirmation work done to ensure that an instrument that can
theoretically accurately measure a BrAC of .10 can in fact accurately measure a true BrAC of .07
or .12.
Cases to review:
People v. McNeal (2009) 46 Cal.4th 1183: Both general and personal partition ratio evidence
challenge the accuracy of a defendant's reported blood-alcohol level, and therefore both can be
used to support an inference that, despite a high breath test result, the defendant was not
under the influence.
People v. Vangelder (2011) 197 Cal. App. 4th 1: The trial court committed prejudicial error in
refusing to allow expert testimony to be presented that would have raised doubts about the
reliability of the electrochromatograph/infrared and preliminary alcohol screening breath
testing devices. Under Veh. Code, § 23610, subd. (c), the expert provided enough of a
foundation to explain why he believed that the breath test samples were not representative,
based upon the problems in obtaining the samples that were inherent within the identified
variables of an individual's physiology.

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Borger v. Department of Motor Vehicles (2011) 192 Cal. App. 4th 1118: The trial court erred in
ruling that the presumptive validity of the BAC test results could be rebutted by testimony that
all “Intoxilyzer 5000” results have an inherent margin of error and might give a high BAC
reading. Were we to affirm and credit Williams's conclusion in this published opinion, we
would, in essence, rewrite section 13353.2, subdivision (a)(1) to provide that BAC test results of
less than 0.10 percent, as measured by the “Intoxilyzer 5000,” are presumptively invalid even if
the machine used is a certified test instrument maintained, calibrated, and operated in
compliance with title 17.
People v. Beltran (2007) 157 Cal.App.4th 235: In a trial for driving with a blood-alcohol content
(BAC) of 0.08 percent it was error to instruct the jury that it could infer BAC at time of driving
from two tests administered within three hours of when defendant stopped driving. In isolation
either of two BAC tests—the sole evidence upon which the jury could have concluded that
appellant had a BAC of 0.08 percent or greater when he was driving—were sufficient to allow
for the inference permitted by CALJIC No. 12.61.1. However, together they showed that
defendant’s BAC was rising from the time he was stopped until the tests were administered.
Both parties’ expert witnesses hypothesized that, assuming the reliability of the test results,
defendant’s BAC was under 0.08 percent when he was driving. Taken as a whole, the
connection between the proved fact (test result demonstrating a BAC of 0.08 percent or
greater within three hours of driving) and the inferred fact (BAC of 0.08 percent or greater at
the time of driving), which is an element of the charged crime, was not established beyond a
reasonable doubt.
Roze v. Department of Motor Vehicles (2006) 141 Cal.App.4th 1176: Cal. Code Regs., tit. 17,
compliance is plainly relevant to a trier of fact's independent assessment of the weight of test
evidence for purposes of proving unlawful blood alcohol concentration. Indeed, title 17
regulations apply to tests that determine the concentration of alcohol on the blood but not
those that determine only its presence. Laxity in complying with the regulations may
undermine the reliability of the test.
Title 17 regulations Relevant to Breath AlcoholTesting
17 CCR 1219.1 Blood Collection and Retention
17 CCR 1219.3 Breath Collection
17 CCR 1220.4 Expression of Analytical Results
17 CCR 1221.4 Standards of Procedure