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Joseph Coupal - Friday, March 26, 2010
As stated previously, often the most significant evidence against a defendant is the result of the breath test. While every breath test operator in Massachusetts must be certified to operate the Alcotest 7110 (the only breath testing device approved in this state for DUI prosecutions), when it comes to convincing jurors about how this device arrives at accurate numbers, many of these same officers have difficulty. Another major issue with the “science” behind breath testing devices is the role of temperature. In order for Henry’s Law to be properly applied when the breathalyzer converts breath alcohol to blood alcohol (see previous posting), the device assumes a constant body temperature of 34 degrees celsius. This is why the simulator (which generates the middle number in a breath test) heats the solution to 34 degrees to approximate the temperature of the subject’s breath going into the machine. However, in reality not everyone has a constant breath temperature of exactly 34 degrees. Some people have a normal, but slightly higher breath temperature or may be running a slight fever without other obvious symptoms. A higher breath temperature will always result in an artificially high breath test reading, even with a properly functioning breath test device. Even though it is extraordinarily easy to do, the operators of the Alcotest in Massachusetts are not required to test their subjects’ actual temperature before administering breath tests. Given the many other shortcomings of these devices, properly explaining this issue helps to generate reasonable doubt in the minds of jurors.

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