Ultra High Rate of Alcohol Elimination in Drinking Drivers

Although the world’s top forensic alcohol toxicologist, A.W. (Wayne) Jones was born in Wales, he spent most of his professional life in the forensic laboratory in Sweden. His groundbreaking research on alcohol elimination rates in drinking drivers has shaped how courts understand impaired driving cases across North America and Europe. The study I am about to describe comes from his 2008 paper in the International Journal of Legal Medicine.

An analysis was conducted of the BACs of double blood samples collected from drinking drivers in Sweden, approximately one hour apart. A total of 1,090 drivers participated in the study. The mean alcohol elimination rate was 19 mg/100mL per hour. This is not unexpected, as drinking drivers are typically heavier drinkers than social drinkers, who have an average alcohol elimination rate of 15 mg/100mL per hour.

The 97.5 percentile for the rate of alcohol elimination in drinking drivers ranged between 11 and 31 mg/100mL per hour. This wide range demonstrates why forensic experts cannot simply apply a standard elimination rate to every case. Each driver’s metabolic profile is unique.

Only 21 drivers (2.2%) had an apparent rate of alcohol elimination of less than 10 mg/100mL per hour. This unusually slow rate may have been due to the drivers being in the rising or plateau phases of the BAC curve rather than the elimination phase. When a driver is still absorbing alcohol, back-calculation becomes much more complex.

The study also determined the rates of alcohol elimination in 21 drivers who had the highest alcohol elimination rates, as shown in the attached table. These ultra-high alcohol elimination rates occurred in drivers with a BAC of between 271 and 518 mg/100mL, with a mean BAC of 405 mg/100mL. To put this in perspective, the legal driving limit in Canada is 80 mg/100mL. These drivers had BACs five to six times above the legal limit.

The mean rate of alcohol elimination in these extreme cases was 33 mg/100mL per hour, with a remarkable range of 20 to 62 mg/100mL per hour. The driver with the highest alcohol elimination rate – 62 mg/100mL per hour – was a 42-year-old male who provided his first blood sample at 9:00 a.m. with a BAC of 453 mg/100mL. His second sample, taken 70 minutes later, showed a BAC of 381 mg/100mL.

These ultra-high alcohol elimination rates have significant implications for forensic back-calculations. If a defence expert assumes a slow elimination rate of 15 mg/100mL per hour, the calculated BAC at the time of driving could be artificially inflated. Conversely, assuming an ultra-high rate could benefit the defence. The truth lies in the individual driver’s drinking history.

Those who drink alcohol to reach a BAC exceeding 300 mg/100mL (3.0 g/L) have probably been drinking continuously for several days or weeks. This pattern of chronic drinking is associated with the development of cellular and functional tolerance, so that people can appear relatively sober and are sufficiently alert to walk and attempt to drive a motor vehicle – despite having BACs that would incapacitate a social drinker.

Prolonged heavy drinking also leads to dispositional or metabolic tolerance, which can account for the faster rate of alcohol elimination and give a steeper slope in the post-peak BAC elimination phase. For forensic experts, understanding these ultra-high alcohol elimination rates is essential for accurate back-calculation and fair courtroom testimony.

Reference

Jones, A.W. “Ultra-Rapid Rate of Ethanol Elimination from Blood in Drunken Drivers with Extremely High Blood Alcohol Concentrations” International Journal of Legal Medicine, 122: 129-134, 2008