Wednesday, June 19, 2019

How Temperature Effects the Police Breath Testing Machines

The temperature of a suspect's exhaled breath is a key area of ​​challenge when defending driving while inoxication (DWI) breath test prosecutions. It's also one of the most overlooked. DWI criminal defense attorneys should become familiar with this technical aspect of breath testing and prepare themselves to use it for their client's advantage.

Heat is the driving force behind Henry's Law and the inner workings of the breath testing machines. Heat causes the alcohol in a person's blood to evaporate into their breath inside their lungs. According to Henry's Law, the higher the temperature the more alcohol goes into the breath. The significant point is the police breath testing machines assume the temperature of a DWI suspect's breath is 34 degrees Centigrade (or 93.2 degrees Fahrenheit). But at the time of the breath test the temperature of the suspect's breath is unknown.

The machines are certified to give accurate results for a reference sample of alcohol carefully maintained at a temperature different from the human body. Core body temperature for human beings is 37 degrees Centigrade (or 98.6 degrees Fahrenheit). However, the machine is never checked for accuracy using samples at a core body temperature of 37 degree C.

Again, the machine's program assumes the breath temperature from a DWI suspect is 34 degrees C. But not all investigators agree a person's breath is this temperature. This is critical since the higher the core body temperature (and thus higher breath temperature), the more the breath test machines will overestimate the breath alcohol concentration of the person providing the sample. Remarkably, the police machines have no way to measure a person's breath temperature at the time of sample collection.

Studies show for each one (1) degree C (or 1.8 degree F) increase in breath temperature there is a 6.8% overestimation of the calculated breath alcohol concentration (compared to a simultaneous blood alcohol analysis). This means a breath testing machine measuring a person with a breath temperature of 37 degrees C (98.6 degrees F) is calculating an alcohol concentration about 20% too high. Consequently, many persons providing breath samples are being unjustly charged with DWI and are being wrongly convoked because of these police breath testing machines.

Source by Stephen Gustitis

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