Comparison of venous blood alcohol concentrations and breath alcohol concentrations measured with Draeger Alcotest 9510 DE Evidential

• The relationship between BAC and BrAC was examined under realistic drinking conditions.
• The conversion factor Q varied between 1571:1 and 2394:1.
• A constant conversion factor for forensic issues concerning higher BACs could not be presented.

Most comparisons of blood alcohol concentrations (BAC) and breath alcohol concentrations (BrAC) are either derived from drinking trials with rigid drinking protocols or from investigative authorities’ data with considerable time differences between the determination of BAC and BrAC. In general, only comparisons of relatively low BAC–BrAC pairs are available. Therefore, the relationship between BAC and BrAC was examined even for high BAC above 2 g/kg.The results of a large-scale drinking test under realistic conditions with 78 test persons and short time intervals between BAC and BrAC measurements are presented.It was shown that the conversion factor Q varies greatly (between 1571:1 and 2394:1) and increases with increasing BAC. A constant conversion factor that is suitable for variable forensic purposes could not be presented.