Section 70 Breath Temperature

• Library: DWI Experts and the Science of Chemical Tests 2014

The strongest second-line defense is the issue of breath temperature versus the temperature of the calibration check of the machines. Missouri breath testing machines currently do not account for breath temperature at the time of blowing into the machine or adjust breath test samples from individuals. More modern machines do take into account the breath temperature measurement and make the appropriate adjustment down of the BAC estimate. Several modern machines perform this adjustment for a more accurate and fair reading.

The average breath temperature has been determined to be 35°C, or 1° higher than the 34°C that Missouri machines are calibrated and calibration-checked. Though 1° may not seem like a big deal, it is a big deal because the breath result will overestimate the BAC by 6.59% to 8.62% for every degree of breath temperature. See:

· G. Schocknecht & B. Stock, The Technical Concept for Evidential Breath Testing in Germany, Proceedings of the 13th Int’l Conference on Alcohol, Drugs and Traffic Safety, Adelaide, Austl. (1995)

· Dale A. Carpenter & James M. Buttram, Breath Temperature: An Alabama Perspective, 9 INT’L ASS’N CHEM. TESTING NEWSLETTER 16, 16 (1998)

The MSHP (Missouri State Highway Patrol) included in a Type II (Type II breath analyzer permittee) manual the figure of 7% per degree, so what is good for the MSHP could be good to use in civil cases but not in criminal cases. The MSHP estimate is also a figure between the 6.59% and 8.62% figures from different scientific studies. In forensics, the reporting doubt always goes to the accused so, forensically, the 8.62% figure should be used in criminal cases.

The lower-than-7% figures have been proposed by both Alan W. Jones and Kurt Dubowski. Alan W. Jones, Effects of Temperature and Humidity of Inhaled Air on the Concentration of Ethanol in a Man’s Exhaled Breath, 63 CLINICAL SCI. 441...