NCJ Number
13577
Journal
Journal of Forensic Sciences Volume: 19 Issue: 2 Dated: (APRIL 1974) Pages: 325-326
Date Published
1974
Length
2 pages
Annotation
TECHNICAL EXPLANATION OF SITUATIONS IN WHICH CHANGES IN BAROMETRIC PRESSURE MAY AFFECT THE RESULT OBTAINED FROM BREATH-ALCOHOL TESTING DEVICES.
Abstract
IF A FIXED VOLUME OF BREATH, MEASURED OR UNMEASURED, OBTAINED AND ANALYZED AT EXISTING AMBIENT PRESSURE, HAS BEEN EMPLOYED, THE RESULT IS INDEPENDENT OF BAROMETRIC PRESSURE. THUS, AT A GIVEN CONCENTRATION OF ALCOHOL IN PULMONARY ARTERIAL PLASMA, THE AMOUNT OF ALCOHOL IN THE SAME VOLUMES OF BREATH COLLECTED AT DIFFERENT BAROMETRIC PRESSURES IS THE SAME. THIS FOLLOWS FROM THE FACT THAT THE PARTIAL PRESSURE OF A VOLATILE SOLUTE IN EQUILIBRIUM WITH A DILUTE SOLUTION IS PROPORTIONAL TO ITS MOLE FRACTION IN SOLUTION (HENRY'S LAW). PUT ANOTHER WAY, THE SOLUBILITY OF A GAS AT A GIVEN TEMPERATURE IS PROPORTIONAL TO THE EQUILIBRIUM PRESSURE OF THE GAS ABOVE THE SOLUTION. ANY PROCEDURE WHICH INVOLVES COLLECTION OF A BREATH SPECIMEN AT ONE PRESSURE AND MEASUREMENT OR REGULATION OF THE VOLUME ANALYZED AT A DIFFERENT PRESSURE WILL, OBVIOUSLY, REQUIRE A CORRECTION OF THE RESULT OBTAINED FOR THE BAROMETRIC PRESSURE DIFFERENCE IF THE MAGNITUDE OF THE CHANGE IS SIGNIFICANT. A RECENT EXPERIMENTAL STUDY EMPLOYING ONE MAKE OF INSTRUMENT DEMONSTRATED ITS INDEPENDENCE OF BAROMETRIC PRESSURE. THE REASON ASSIGNED FOR THIS INDEPENDENCE WAS THAT THE SUBJECT MUST LIFT AN 87-G WEIGHT IN THE COLLECTING CHAMBER AS HE EXPIRES, ASSURING A CONSTANT VOLUME FOR EACH SAMPLE. THIS REASON IS INCORRECT. (AUTHOR ABSTRACT)