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Calibration of Intoxilyzer

During a DUI investigation, one of the most critical pieces of evidence used against a drunk driving suspect is the breath test result. Kansas utilizes an Intoxilyzer 9000 machine to measure a person’s breath alcohol concentration (BrAC). The Kansas Department of Revenue (KDOR) is in charge of the breath testing policies and procedure in Kansas for DUI’s. They want the people of Kansas to just trust that the machines provide accurate readings. In fact, they don’t like it when they are questioned about the reliability or the machines. I especially enjoy cross-examining them when they are on the stand in a DUI trial. In a recent DUI case in Johnson County, KS District Court, the Kansas Department of Revenue stated that Kansas did NOT have a manufacturer’s instruction manual for the Intoxilyzer 9000. Then, at trial, while on the stand, they suddenly changed their mind and stated that they DID have one, but simply would not share it with me. Is there anything done to ensure that the breath testing results are accurate? Yes and no. While I have become very skeptical about breath testing, there are some procedures in place to try to provide more accurate results. One of those things is calibration and calibration checks. There is a difference between the two.

When the Intoxilyzer is calibrated, it is compared and actually altered so that it tests a specific known standard accurately. For the Intoxilyzer 9000, this calibration is done by the manufacturer of the machine, CMI. According to KDOR, when the machine is calibrated, it is calibrated against the “gold standard” at CMI.

When the Intoxilzer does a calibration check, it merely verifies that the unit is providing readings within tolerance. However, no actual corrections are made to the machine during this process. A calibration check is performed prior to any testing of actual breath. The machine does the calibration check against a known sample that is supposed to be .080. However, the machine is allowed to deviate plus or minus .005 in either direction during a calibration check, before it is allowed to proceed forward with testing actual breath. This is +/- 5%, (or +/- 0.005 grams). So, in Kansas, if the machine reads the known sample of .080 to be .085, it is still allowed to continue with a breath test. Obviously, this should be concerning. Moreover, how do we know that the “known” sample isn’t actually .070, such that the machine would then be overstating the readings by .015, yet still be determined reliable, despite being false? Then these false results are unfairly used in court against a DUI defendant?

There are two different types of calibration systems which can be utilized. Kansas uses dry gas cylinders which contain compressed air with a known ethanol concentration. The other way is via wet-bath systems that use simulator jars containing ethanol-laden liquid.

Kansas utilizes a dry gas cylinder containing ethanol vapor as the “known” sample to do the calibration checks. This cylinder is attached to the Intoxilyzer and prior to every breath test, the machine does a calibration check. It tests the known sample that is supposedly right at .080. So long as the reading is between .075 and .085, the machine proceeds forward with the test of the actual subject’s breath. This known sample is a cylinder that contains compressed air that has been saturated with ethanol molecules to a concentration of .080. As the gas is released, it produces a mixture of air and ethanol that provides a reading of .080.

To get accurate readings from an Intoxilyzer, not only does the machine itself need to be accurately calibrated, but the known .080 sample must be accurate as well. As with any device, to know that the measurements obtained are truly representative of accurate measurements, it requires a means of externally verifying its results. If the external verification is off, then the machine is off. This is part of the problem of relying on the machine to provide accurate result. First, they calibrate the machine itself to a “known” sample. This original “known sample” is never truly known, but rather tested with machines that have been calibrated as well. Second, that machine is “calibrate checking” against a new “known sample” prior to every actual test. This second “known sample” is not truly known either. Third, the known samples are changed out periodically.

Moreover, the Intoxilyzer 9000 is a machine that has wear and tear over time. The way it reads will change over time. However, breath alcohol testing devices do not use calibration check results of the standard alcohol solution (SAS) reading to “re-adjust” themselves to the known standard. Instead, it is up to the qualified breath technician to ensure that the calibration values obtained are within the acceptable range. The unit will only be truly calibrated when service work is performed by an authorized repair technician. To make matters worse, each Intoxilyzer 9000 receives periodical software updates as well as changing out the “known” sample. What is this actually doing regarding calibrations? Supposedly nothing, but I have seen an Intoxilyzer start providing a series of different levels of results for calibration checks after changes were made to the machine.

When KDOR is questioned at trial about how the machine hasn’t been actually calibrated for some time, the prosecuting attorney will often counter with something like, "Your car doesn't stop working because you haven't performed an annual oil change.” That is so short sited. While your car might still actually drive, it isn’t working optimally. Yes, the Intoxlizer might still give a reading even if it hasn’t been maintained or recently calibrated, but that doesn’t mean it’s a correct reading.

This is especially concerning because in Kansas, if the machine provides reading outside of tolerance (i.e. it reads the known sample to be higher than .085) it doesn’t mean the machine is sent off for calibration or maintenance. No, the machine is simply allowed to start over again and again until it finally reads the known sample to be within tolerance.

When reviewing calibration records from a specific Intoxilyzer, it is normal to see fluctuations that are both positive and negative of the target value (a neutral bias). For a target value of 0.080 grams, you should see fluctuations above and below the .080 target, within the acceptable range. However, when an instrument starts to display readings that are usually higher or always lower than .080, it is time for a re-calibration of the device, as the instrument has drifted high or low in its calibration bias. The historical performance of an Intoxilyzer is relevant information a criminal defense lawyer might want to use. The results of calibration checks done over a period of time are instructive as to the bias of the device. Alas, if the machine has a history of overstating the known sample, then isn’t it likely that it also overstated the person’s actual breath alcohol concentration?