Truth is the breath test may not be indicative of the person's impairment because the breath test is not inevitably indicative of a person's BAC level
"It is generally recognized, as confirmed by the proffered testimony of the state chemist in the instant case, that "[b]ecause blood-breath ratios vary both between individuals, and at different times in the same individual, a breath test based on a 2100:1 blood-breath ratio may not accurately represent a particular individual's blood alcohol level." State v. Brayman, 110 Wash.2d 183, 751 P.2d 294, 297 (1988). The state chemist agreed that partition ratios can vary from 1600:1 to 3000:1, and further acknowledged that other experts have recognized an even greater variance in a small percentage of the population. The chemist explained that if the actual partition ratio were lower that 2100:1 because of factors such as body temperature or the ratio between red blood cells and blood plasma, a breath test would tend to overestimate blood alcohol; the opposite would be true if the partition ratio were higher than 2100:1. At its extremes, the variance could significantly affect test results."
No such thing as a true partition ratio relating a person's blood to breath because required parameters for a partition ratio to exist are never met
"We are not persuaded by the State's arguments that allowing defense counsel to cross-examine the state chemist concerning the variability of partition ratios would be inconsistent with the statutory scheme and lead to jury confusion. It is true that the Legislature has defined BrAC in terms of "the number of grams of alcohol per 210 liters of breath," Section 1200(1), and that permissive inferences may apply whenever a defendant's "alcohol concentration," as defined by statute, exceeds 0.08. But allowing testimony on the variability of partition ratios would not prevent the jury from accepting the statutory inference. Because defendant is charged with driving while under the influence rather than driving with an alcohol concentration exceeding the statutory limit, admitting scientifically accepted evidence concerning the variability of partition ratios will not negate a statutory offense or even an element of statutory offense;...
More significant language from Judges who understand science & physics
...rather, it will merely allow defendant to challenge the permissive inference and the State's charge that he was impaired ... We fail to see how such evidence would be confusing to the jury or unduly prejudicial to the State; to the contrary, not allowing defendants to reveal these scientifically recognized facts would make it difficult, if not impossible, for a defendant to challenge a test result that is admissible in generic DWI prosecutions only as a permissive inference on the ultimate question of impairment." [State v. Hanks, 772 A.2d 1087, 1092-93 ( Vt. 2001).]
Evidence of the fact that the blood to breath ratio is merely an average can get to the jury if the prosecution opens the door to the evidence
Use the Ratio Attack When Prosecution Expert Contradicts Defendant. This unfolds, as follows: o The state's expert witness is called to the stand and gives a list of the expert's qualifications. The expert next testifies about how breath testing works, skipping past the 2100 to 1 ratio. Having explained how breath testing works in general, the state's expert reviews the calibration and test records for the breath machine in question, and gives an opinion that everything was working just fine. o The prosecutor next tells the expert that the 135 lb. female defendant told the police officer she only had two drinks. This is followed up with this question: "What would the defendant's blood alcohol be after consuming two drinks?" The expert opines that at the most it would be .05%. o The prosecutor then asks: "How is it possible for the defendant to register a .10% BAC on a breath machine with only two drinks?" The ostensibly astonished expert says it cannot be so.
It is the breath machine that is false, and this is because the underlying assumptions of the machine are false
...Pretending to be equally dumbfounded the prosecutor asks, "What do you mean it cannot be so, the defendant said she only had two drinks?" o The expert replies that the defendant must not have told the officer the truth as to what she had to drink. Once the state's expert claims that the defendant is not telling the truth, the prosecution has opened the door to allowing the defense to tell the jury the truth about breath machines and their use of blood to breath ratios. The state's expert has called the defendant a liar. The variability in the 2100 to 1 presumed ratio is now relevant to defending the defendant's veracity. The defense should argue that it must be permitted to delve into the blood to breath ratio to expose the falsehood the state's expert presented to the jury. Explaining the variability in the 2100 to 1 ratio will allow the defense to explain to the jury that the defendant was telling the truth. With a lower ratio, two drinks could report out a .10% #.
Questions to ask Prosecutor's hired "expert"
Q: Even if the test was properly performed-which as now I understand you do not know-and even if the breath device was working properly, the defendant could still obtain a .10 % with only 2 drinks? A: No. Q: Not possible? A: Not possible. Q: Well, doesn't this breath device make some assumptions regarding the ratio of the alcohol in the defendant's blood to the defendant's breath? Q: The device makes an assumption that the concentration of alcohol in the blood is 2100 to 1 greater than it is in the breath? A: Yes. Q: That assumption is just an average? A: Yes. Q: Like any average it does not apply to everyone? A: True. Q: If the defendant's ratio was less than 2100 to one it would report out a higher alcohol level than she actually had? A: It would report out higher because the breath instrument is assuming her ratio is 2100 to one. Q: You do not know what the defendant's ratio is? A: No.
Key closing questions
Q: And so you do not know what defendant's true alcohol level is? A: Well, I know within a range. Q: And so you do not know what defendant's true alcohol level is? A: No, I do not know. Bring out the truth that the blood to breath ratio varies so much it exposes the falsehood that the state's expert presents to the court. Explaining the serious variability in the 2100 to 1 ratio will allow the defense to explain to the jury that the defendant was telling the truth. Breath machines assume that the concentration of alcohol in a person's blood is 2100 times greater than it is in the breath. Blood & breath are seldom found in equilibrium in human beings. A person's body temperature is not constant, and even the tightest wound is not sealed. Realistically, there is no partition ratio with respect to the blood and breath of human beings. The breath test is valid only if the defendant is the average. What is true for some people may not be true for others.