This paper presents some experimental results on the effect of temperature on breath alcohol concentration (BrAC) measurements, and discusses their relevance to breath tests. Ethanol concentration, breath temperature and breath flow have important influences on the results of breath tests. A working group, formed at the German Federal Health Office to investigate the forensic applicability of breath alcohol analysis, has recommended measuring the temperature of expired breath at the same time as measuring end-expired BrAC. An appropriate device for measuring breath temperature is described briefly. Graphs are given for measurements of: (1) BrAC and breath temperature during a drinking experiment with hyperventilation and mouth cooling; (2) BrAC at the temperature of 34 degrees C; (3) the course of breath temperatures at a high environmental temperature. The measurement of breath temperature and the conversion of BrAC to the reference temperature are necessary to obtain BrAC values that are comparable and independent of the environment, despite different body and mouth temperature, and to correct for conscious or unconscious influences on breathing technique. Breath alcohol measurements alone are too variable to be forensically acceptable.
Abstract