Elimination rates of breath alcohol

Legal driving limits are set coequally with 0.5 g/L blood alcohol concentration (BAC) or 0.25 mg/L breath alcohol concentration (BrAC) in Austria as well as in other European countries. As mostly some time elapses between BrAC measurement and driving offence, a back calculation of alcohol concentrations is often required. The calculation of hourly BrAC elimination rates can thereby help to avoid unnecessary variances. A study with 59 participants was performed under social conditions. BrAC was determined with the legally accredited Alcotest 7110 MK III A every 30 min, and concomitantly venous blood samples were drawn. Five hundred and four BrAC/BAC value pairs were evaluated. The overall mean peak BrAC was calculated with 0.456 mg/L (+/-0.119 mg/L standard deviation). The mean hourly BrAC elimination rate was overall determined with 0.082 mg/L per h (0.050-0.114, 95% range). Mean rate of females (0.087 mg/L h(-1)) and the according 95% limits were statistically significantly higher than of males (mean rate 0.078 mg/L h(-1), p<0.04). Our results confirm the possibility to implement hourly BrAC elimination rates, provided that adequate statistical ranges and basic forensic scientific rules that have been set up for alcohol back calculations are observed.