Breath Temperature: The Joker in the Deck of Breath Testing

     Infrared breath testing devices such as the Intoxilyzer 5000 rely on certain assumptions.   Since a report of the National Safety Council in 1952 it has been assumed that there is a constant 2100:1 ratio between the amount of alcohol in the blood versus the amount in a person’s breath.  Similarly, it has been assumed that the average temperature of expelled human breath is 34 degrees centigrade.

World class researchers such as A.W. Jones have consistently found that breath temperature variability affects test results.  The Fox and Hayward study published in he Journal of Forensic Sciences demonstrated that for every one degree increase in core body temperature a person’s breath alcohol concentration would increase by 8.6 percent.  In the mid-1990’s three studies of hundreds of individuals found that the average breath temperature was 35, 35.1, and 34.9 degrees respectively, for an overall average of 35 degrees.  Therefore, it appears that an “average” person whose breath  measured by an Inotoxilyzer 5000 is .087 has, according to these studies,  a blood alcohol concentration of .079, even if you ignore every other confounding factor except breath temperature.

Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website Written by Allen Trapp who is board certified by the National College for DUI Defense and the author of Georgia DUI Survival Guide Visit Website

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