It is now well established that a subject’s manner and mode of breathing just prior to providing breath for analysis can significantly alter the concentration of alcohol in the breath sample. Hyperventilation has been shown to lower the breath alcohol concentration by as much as 20%. Holding your breath for a short time (20 seconds) before exhalation increases the alcohol concentration in exhaled air by as much as 15%. Be on the lookout for forced agreement between the two breath samples. An officer can watch the BrAC rise on the second sample. When it gets close to the reading of the first sample, he can tell the subject to stop blowing, to ensure that the two samples are not more than .02 apart.
Since at least 1950 34°C has been the accepted breath temperature used for breath testing purposes. Professor Harger made this decision in 1950 after examining six subjects whose recorded range was between 31°C and 35°C. However in 1996, a much larger study of 700 subjects concluded that the average was 35°C-a full degree higher than Harger’s adopted temperature. Fox & Hayward compared the effects of hyperthermia and hypothermia on breath alcohol results. They found that average increase in Breath Alcohol Concentration over Blood Alcohol Concentration was 8.6°C for each degree Celsius increase in deep-core body temperature.
These are just two of the more basic issues we encounter in DUI defense. Although some lawyers think “anyone can do DUI,” the odds are that those lawyers are not familiar with these issues and will not invest the work required to gain the knowledge. No matter where you are, if you interview a lawyer and he or she cannot discuss these matters, keep looking.