Breath alcohol testing


Breath alcohol measurement is based on Henry's law: the concentration of a volatile substance in the air above a fluid is proportional to the concentration of the volatile substance in the fluid. In case of blood alcohol content the following relation holds:

1 gram of ethanol in 1 liter (or 1kg) of blood corresponds to 0.5mg of ethanol in 1 liter of exhaled air.

Blood alcohol content (BAC) is usually measured in grams per liter (g/l or pro mille) or in percentage (% BAC).