The Science of Blood Alcohol Concentration (BAC)
Blood Alcohol Concentration (BAC) measures the percentage of ethanol present in a person's bloodstream (e.g., a BAC of 0.08% indicates 0.08 grams of alcohol per 100 milliliters of circulating blood). Once ingested, approximately 20% of ethanol is absorbed directly through gastric mucosa and 80% through the upper small intestine, dispersing into total body water.
Widmark Equation & Biological Gender
Developed by Swedish physician Erik Widmark, the distribution factor r quantifies the body water distribution volume (0.68 for men vs. 0.55 for women). Because adipose tissue holds minimal water compared to lean tissue, women generally experience higher peak BACs from identical ethanol doses.
Metabolic Rate of Alcohol Clearance
Hepatic alcohol dehydrogenase (ADH) enzymes metabolize ethanol at a zero-order kinetic rate of approximately 0.015% BAC per hour (equivalent to roughly one standard drink per hour). Neither caffeine, cold showers, nor exercise can accelerate this constant physiological rate.
Stages of Alcohol Impairment
- 0.02% – 0.05%: Mild euphoria, warmth, minor relaxation, relaxation of social inhibitions.
- 0.05% – 0.08%: Noticeably lowered alertness, reduced coordination, delayed tracking of dynamic obstacles.
- 0.08% (Federal Statutory Driving Limit): Significant degradation in visual perception, hazard reaction time, and balance. It is illegal to operate a motor vehicle at or above this threshold in all 50 US states.
- 0.10% – 0.20%: Pronounced motor ataxia, dysarthria (slurred speech), gastrointestinal nausea.
- 0.30%+: Critical hazard of central respiratory depression, coma, and fatal alcohol toxicity.