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The Liquid Ruler

Posted on June 14, 2013 in Blood Testing

One of the myths that I am determined to dispel is the idea of “perfection” in DUI blood testing. I have had far too many clients come to me and indicate that they have heard from friends, family, and shockingly even other attorneys, that because they took a blood test in their case, there is nothing that can be done to help them. This statementis 100% inaccurate.

I am a man of science. I believe strongly in supporting scientific endeavors to further the goals of society. However, an inherent necessity in the accuracy and integrity of the scientific process is understanding and recognizing the limitations of the method that you are using. Unfortunately, I am often confronted by Criminalists and Prosecutors who eitherhave little understanding as to how the blood is actually tested in DUI cases in Arizona, or who refuse to acknowledge the multitude of errors that can, and do, occur in the crime labs in Maricopa County. This is problematic for numerous reasons, but especially because this absolutism tends to infect the rest of the population, tainting the mindset ofpotentially innocent DUI suspects, and even worse, tainting the minds of potential jurors that are supposed to be impartial in court. As an attempt to halt the further perpetuation of this cycle, I want to provide a brief glimpse into the inner workings of gas chromatography.

Head Space Gas Chromatography is the gold standard in forensic alcohol testing. If done correctly, it uses a series of scientific principles to measure the alcohol concentration in the air above a blood sample, to determine the alcohol concentration (relatively accurately) contained within that blood sample. But, there are limitations onthis procedure that are completely overlooked by its most zealous advocates.

One of these limitations is that Gas Chromatography requires the use of a “liquid ruler.” What this means is that the way your alcohol concentration is measured, is by comparing the amount of alcohol found by the machine in a Defendant’s blood sample to the amount found by the machine in a different liquid that is not a Defendant’sblood sample. Thus, the calculations are done by comparison. In most crime labs, the machines use things called “calibrators” as the substance that alcohol is compared to, i.e. it is the “liquid ruler.” The Criminalist programs the machine using these calibrators, by inserting .02%, .1%, .2%, and .4%. solutions into themachine, then “teaching” the machine to remember and recognize these amounts. The machine will then compare all the various Defendant samples that come through the machine to these calibrator amounts, and determine how high or low a blood alcohol concentration is by comparing it to those 4 examples.

In principle, this is an appropriate way to measure an unknown concentration. Problematically in Arizona, the regulations surrounding the creation and storage of these calibrators are non-existent, and as a result there are questions about the reliability of the ones that are used. Recent investigations into Scottsdale and Phoenix Crime Labs have producedalarming information that there is a high likelihood that the amount of alcohol contained within the calibrators is actually markedly lower than it should be. Meaning, what the machine is taught to recognize as a .1% alcohol concentration is actually less than that, making the Defendant’s sample concentration appear higher that what it should bereported as. One can easily see the problem here. People’s blood results are consistently being reported as significantly higher than they actually are. It is a problem that is cause for alarm and needs to be addressed because in a DUI case, every percentage point counts. Even one percentage point can be the difference between a guilty verdict and anot-guilty verdict, and a day in jail or weeks in jail.

If you are accused of DUI, and you think that the reported results are higher than they should be, you may be a victim of this liquid ruler problem. You need to consult an DUI.

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