BAC Calculation Guide and Resources
The
estimation of a person's blood alcohol content (BAC) has become particularly
important in recent years for legal reasons. Increasingly strict drunk
driving laws and stiffer legal consequences for those who commit crimes
while alcohol-impaired have recently made the estimation of BAC very important.
There are several methods that can be used for BAC calculation, although
Stowell and Stowell (1998)* showed that none of the methods were of great
accuracy and that none of the methods were superior to the others. There
are many websites which contain a BAC estimator and there are many different
opinions of how to accurately calculate BAC. The following are links to
sites that contain useful information on how to estimate BAC.
The
most commonly used formula is referred to as the "Widmark formula".
It can be summarized in the following formula:#
[(# of drinks)(# oz. ethanol/drink)(0.0514 lbs. ethanol/oz.ethanol)(1.055
g ethanol/ml)]/[(weight of person in lbs.) * Widmark "r" value]
* 100 - (B * time) where "r" refers to the percentage of body
mass that contains alcohol (total body mass - mass of fat and bone), and
B is the hourly decrease in BAC.
The US Department of Transportation uses a slightly different formula
which is essentially an updated "Widmark formula": %
[(# of drinks)(# oz. ethanol/drink)(23.36 grams ethanol/oz.)(0.806
ml H2O/ml blood)]/[(weight of person in lbs./2.2046 lb/kg)(TBW)(1000g/kg)]
* 100 - (B * time) where TBW refers to the total body water volume and
B is the hourly decrease in BAC.
The two above methods are generally the most reliable and accurate, although complex factors such as alcohol clearance rate, total body water content, and food consumption will ultimately affect BAC at any given time and add to the inaccuracy of the estimation methods. An article by Professor Craig with additional information can be seen in the Alcohol Inquirer (ver 2).
*Ref: Stowell, A.R.; Stowell, L.I. Estimation of blood
alcohol concentrations after social drinking. Journal of Forensic Sciences.
43 (1), pp. 14-21, 1998.
# Ref: Ed Kuwatch, Esq. Defense attorney (Widmark
method)http://www.dui-california.com/blood-alcohol-level.htm
%Ref: National Highway Traffic Safety Administration (Herbert
Moskowitz, Ph.D.) http://www.nhtsa.dot.gov/people/injury/alcohol/bacreport.html