The Relationship between Blood Alcohol Concentration (BAC) and Breath Alcohol Concentration (BrAC): A Review of the Evidence

This report concerns the relationship between blood-alcohol concentration (BAC) and breath-alcohol concentration (BrAC), and observations about the blood/breath ratio (BBR) of alcohol. This important ratio is used in European Union (EU) countries when statutory BrAC limits are derived from the preexisting BAC limits.

Scientific articles reporting BBRs of alcohol either involve controlled drinking experiments or tests made with apprehended drivers. The participants in controlled laboratory studies are usually healthy volunteers who consume moderate amounts of alcohol after which nearly simultaneous samples of breath and blood are taken for analysis of alcohol. Under some circumstances apprehended drivers provide specimens of breath and blood for determination of alcohol. The results furnish information about the BBR of alcohol under real-world conditions and are probably more relevant to consider because of the wider range of BAC encountered.