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Body Temperature and Breathalyzer Errors

Posted by attorney Luke Nichols

Few people know how breathalyzers work, and fewer realize how common it is for breathalyzers to produce faulty readings.

Breathalyzers (the machines that estimate a person’s BAC from that person’s breath) work on the principle that alcohol in a person’s blood evaporates into the lungs. The machine assumes that a greater amount of alcohol measured in the lungs is congruous with a greater amount of alcohol in the blood. However, as with all assumptions, there are flaws.

Anyone who has watched a pot of water boil knows that the warmer a liquid gets, the more it evaporates. Alcohol is the same. The higher a person’s body temperature is, the less accurate the breathalyzer will be. This inaccuracy occurs because breathalyzers do not take a person’s temperature; the breathalyzers simply assume that person’s body temperature is normal (98.6° Fahrenheit or 37° Celsius) when it calculates the BAC. However, if the driver’s body temperature is over 98.6°, the machine will return an erroneously high BAC reading. Consequently, if a person has a fever, is dressed too warmly, or is even left in a hot police car too long, his breath test results may be inaccurate.

If you are arrested for DUI and are hotter than normal, let the arresting officer know. Roll down the window, sit by the fan, drink water, and make sure that the arresting officer knows you are too hot. Informing the arresting officer will allow you to either have time to cool down or be able to testify in court that you were too hot when tested.

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