One of the most neglected areas of attack upon the Intoxilyzer 5000 by Texas criminal defense lawyers defending DWIs is the assumption the temperature of a DWI suspect’s breath is 34 degrees Centigrade (or 93.2 degrees Fahrenheit).
Heat is the driving force behind Henry’s Law and the inner workings of the Intoxilyzer 5000. Heat causes the ethanol in a person’s blood to evaporate into their breath inside the lungs. The higher the temperature, the more ethanol goes into the breath.
The Intoxilyzer 5000 is certified to give accurate results for water solutions (the reference sample) of ethanol carefully maintained at a temperature different from the human body. However, the machine is never checked for accuracy using samples provided by living human beings at a core body temperature of 98.6 degrees Fahrenheit.
The Intoxilyzer programing assumes the breath temperature from a DWI suspect is 93.2 F. But not all investigators agree that expired human breath is at this temperature. This is critical since the higher the core body temperature, and thus higher breath temperature, the more the Intoxilyzer will overestimate the breath alcohol concentration of the person providing a sample. Amazingly, the Intoxilyzer as no way to measure a person’s breath temperature at the time a sample is collected.
Studies show for every 1.8 degree Fahrenheit (1 degree C) increase in breath temperature there is a 6.8% overestimation of the measured breath alcohol, compared to that of a simultaneous blood alcohol sample. This means an Intoxilyzer 5000, measuring a person blowing into the machine with a breath temperature of 98.6 degrees F, is calculating an ethanol concentration about 20% too high. Consequently, many persons providing breath samples are being unjustly charged with DWI and are being wrongly convicted.