Breath temperature and DUI alcohol levels
Why is breath temperature important in DUI cases? Breath temperature and DUI alcohol levels can affect test results. As this website has mentioned in other articles about breath testing, your breath temperature is strongly associated with the level of alcohol measured. Breath temperature and DUI alcohol levels are a known problem. Warmer breath corresponds with higher measurements of known alcohol levels, and cooler breath corresponds with lower measurements of the same known samples.
Modern breath testing machines have a temperature sensor, that can detect readings and measure the exhalation breath temperature, and correct the resulting breath alcohol concentration to the reference temperature of 34 degrees celsius.
The whole reason for the interest in the breath temperature of subjects testing for alcohol concentration is the well known influence of temperature on breath readings, under the scientific principle known as Henry’s Law.
Henry’s Law describes the proportional relationship of the concentration of a particular volatile substance in the liquid phase, to the concentration of the gaseous phase of the same compound at equilibrium. Accordingly, when the temperature of the liquid phase increases (in breath testing for DUI cases, the core body temperature), the concentration of the compound (in DUI cases, for ethanol), in the gaseous phase (breath), will increase.
For people that have a fever, have medical problems or issues, or are ovulating, there is a natural increase in body temperature, which can affect the final reading of alcohol.
One question that has been discussed in scientific literature is whether or not the 34 degrees celsius temperature is even correct, or whether it should be adjusted. Why the 34 degree standard temperature in the first place, knowing that body temperature is not a constant?
The origin of the thirty four degree celsius figure as the average breath temperature seems to predate the modern scientific studies, which show the average is higher – some 34.4 degrees to 35.1 degrees celsius. The use of the 34 degree figure seems to date to one publication, by Harger, from 1950.