Conclusion

In some traditions and jurisdictions, for measured blood alcohol concentrations below 0.15‰, retrograde calculation to estimate offence-relevant BAC at the time of the incident is usually omitted, a practice that is historically rooted in uncertainties associated with earlier measurement techniques. Analysis of raw data from controlled drinking experiments with serial sampling to near-zero concentrations demonstrated comparable hourly elimination rates of approximately 0.13‰/h across different concentration intervals of the elimination curve.

In many forensic contexts, particularly when estimating minimum blood alcohol concentrations in favour of the subject, conservative elimination rates are applied, most commonly around 0.1‰/h. However, when examining alcohol elimination below 0.15‰ using linear regression, systematically lower elimination rates were observed. This transient underestimation can be compensated – while maintaining the minimum elimination rate – by shortening the back-calculation interval.

Thus, it is proposed that, for retrograde calculation of the minimum BAC at the time of the incident, a one-time deduction of 43 min be applied to the standard back-calculation interval for measured BAC values between 0.06 and 0.14‰, followed by continued calculation using an elimination rate of 0.1‰/h. Only for measured BAC values below 0.06‰ should retrograde calculation of the minimum BAC be omitted.