Significance of a Breath Temperature on a San Diego DUI breath test machine

San Diego DUI Breath Testing can be performed or operate on a principle - that the measured breath sample has a temperature of 34 degrees Centigrade.

Whenever a periodic accuracy check, or a calibration takes place on any make or model of breath testing machine with a wet bath simulator, the simulator solution must be heated to 34 degrees (plus or minus one half of one degree) and maintained through the use of a thermostat.

A higher rise - or upward departure - in temperature is a source of significant error in San Diego DUI Breath Alcohol (BrAC) readings.

This source of error is why the newer, more sophisticated machines both measure the temperature of the expired breath, and, when necessary, make the required correction based upon a temperature of anything other than 34 degrees. (The Draeger 7110 Desktop breath tester has this feature. But the Draeger machine is not used in San Diego County.)
San Diego DUI Breath Test machines incorrectly assume that the temperature of expired breath is 34 centigrade.

Studies have shown that the true average temperature of expired breath is higher - 35.5. There is a 6.9% error for every degree high, or 10.35%.

If a person has an average breath temperature of 35.5 and blows a reported ".08%" into a breath test machine that subtracted for breath temperature above 34 degrees what would his level be? .07% (rounded) or exactly 0.07172% BAC (6.9 x 1.5 =.1035 x.08 = .00828 -.08 =.07172).

Breath temperature is the temperature of the exhaled breath as it leaves the mouth.

Breath temperature is not the same as one's core body temperature. Body Temperature itself varies by region. Extremities are cooler than the core.

Air is inhaled at room temperature which - if close to normal - must be heated by the body.
As air passes into the body, past the nose or mouth, down the trachea, into the lungs it cools the surrounding services by direct temperature differential and by evaporation of the moisture from the mucus surfaces.

Air is going to be as warm as it gets at the end of the inhalation.

Then as the air is exhaled, it redeposits some of the moisture to the surrounding tissue and mucus, according to the top worldwide Breath Test Expert - Dr. Michael Hlastala of the University of Washington.

This cools the air, so the temperature should be an "average" of 35 Centigrade at the time of exhalation. This conclusion is based on the new, more comprehensive study.

The outdated six person study upon which the 34 degree standard was originally and incorrectly based. There is quite a breadth of the range of that statistical sample, 31 to 35 C. That means one person in 6 had a breath temperature of 31C and one 35 C. However, the other 4 had to be clumped real close to 34C to counter act the 31C reading.

The breath test result can also be increased by having a person hold his or her breath before blowing. Reason: it increases the temperature of the breath. (The machine assumes the breath is 34C. The higher the temperature, the higher the result on the readout.)

Here is a related excerpt from a Breath Testing / Body Temperature study entitled: "Effect of Hyperthermia on Breath-Alcohol Analysis" - "Discussion"

These results show clearlv that mild hyperthermia in humans does not alter the standard decay curve of BAC (and therefore the net kinetics of ethanol metabolism), but does significantly distort the BrAC decay curve to an extent which would cause serious inaccuracy for prediction of BAC. The magnitude of this distorting effect of core temperature is too large (up to 23% with mild hyperthermia) to be ignored in breath-testing procedures. In contrast to the situation provoked by hypothermia 131. such error in the case of hyperthermia increases the likelihood of a suspect being unjustly convicted.

Ethanol intoxication may accompany several situations which can significantly elevate core temperature. For example, core temperature may be significantly elevated by fever, consumption of certain drugs (for example, amphetamines, heavy physical exertion, or exposure to high ambient air or water temperatures as found in saunas or hot tubs. Consequently, it seems warranted, from a judical viewpoint, to insure that any possible variation in core temperature be detected durlng forensic assessment of BAC from BrAC.

For this specific reason as well as others relating to temperature influences, we recommend that direct monitoring of breath temperature be incorporated into BrAC analyzers to provide automatic temperature compensation. Breath temperature measurement would be suitable because it reflects mouth temperature, which in turn reflects core temperature. Until such instrumentation becomes routinely available. it may be necessary to rely solely on blood analysis in cases of potential abnormality of core temperature. The foregoing solution, however. is impractical in the case of hypothermia due to the difficulty of blood sampling caused by cold-induced peripheral vasoconstriction 13.18).

Furthermore, the use of invasive sampling in cases of "suspected" hyperthermia is obviously undesirable. Rather than relying on direct blood-alcohol analysis, it seems more reasonable using present BrAC instrumentation, to attempt to correct for possible error of BrAC resulting from altered body temperature by measuring the body temperature at some site and applying a "correction factor" to the measured BrAC value. This approach has been suggested for hypothermia, using the correction factor determined in vivo of 7.3% . 'C-' decrease in rectal temperature. This factor closely approximates the in vitro correction factor of 6.8% . OC-I determined by Dubowski. Similarly, we suggest the expediency of utilizing the mean distortion index of 8.6% . "C-I, determined herein, as a suitable correction factor for the perturbing effect of hyperthermia on BrAC. A suitable body site would be the mouth, a common and socially acceptable site at which to measure core temperature. In contrast to the present experimental situation, which used rapid body cooling by water immersion, correction of BrAC based on altered mouth temperature would have great validity under the conditions of slow body cooling typical of forensic science assessment.

Thus, the measurement of a test subject's mouth temperature before breath sampling for BrAC offers two advantages. It would screen for possible departures from thermia and would provide an opportunity to adjust BrAC by use of an appropriate temperature correction factor.

In summary, mild hyperthermia or hypothermia can significantly distort BrAC and lead to serious inaccuracy of predicted BAC. Feasible methods now exist to remedv this problem. [Glyn R. Fox,' Ph.D. and John S. H a y w a r d , ' Ph.D. Effect of Hypert herrnia on Breath-Alcohol Analysis Fox. G. R. and Hayward. 1. 5.. "Effect of Hyperthermia on Blrath-Alcohol Analysis," Journal of Forensic Sciences. JFSCA, Vol. 34. No. 4, July 1989, pp. 830-841.]

2008© San Diego County DUI Law Center
- All Rights Reserved