What is alcohol burn off and how does it effect retrograde extrapolation?
Alcohol “burn off” is the concept that the human body metabolizes and burns off alcohol over time. That is to say, that during the normal operation of the human body, absorption and elimination of alcohol occurs through either sweating it out or urination. Alcohol is consumed and initially resides in the stomach where a small portion is absorbed in the lining of the stomach and the rest moves through into the intestines where the alcohol is absorbed and carries on to the brain and central nervous system whereupon a person becomes impaired or inebriated. While this is occurring, alcohol is sweating out the pores and is being eliminated as waste through urination. Similar to the process of consuming food where solid food resides in the stomach and then moves into the intestines where it is absorbed to the extent that the body will utilize the nutrients and the rest of it is eliminated as waste.
About 20% of the alcohol that is consumed will be absorbed in the stomach lining and the rest will be absorbed in the intestines as it moves through. This is why the consumption of food in particular greasy and fatty foods can slow down the digestion or metabolism of alcohol and this is why one may not initially feel the effects of alcohol with the consumption of food but may experience impairment later in time. This can become particularly difficult if a person is stopped or arrested on a full stomach and initially blows a low PBT and yet is taken to the police station and 45 minutes later asked to blow in a machine. It is possible that there could be a rising blood alcohol content or BAC at that time because alcohol is only being absorbed into the body at that time as the food has made its way out of the stomach.
As to the elimination rate of alcohol, the standard rule of thumb is that the body can metabolize roughly .02 or roughly one drink per hour so consequently one 12 ounce beer consumed in hour should not leave an individual impaired; something more than one beer per hour however could result in impairment. Police departments in some states are fond of a concept known as “retrograde extrapolation” which is largely hocus-pocus science but some experts espouse retrograde extrapolation to try to indicate what a defendant’s BAC was at a given moment in time. This is really hocus-pocus because different people’s absorption rate will change based on their body chemistries, size, degree of fat versus muscle, and what they ate. In fact, the same person’s absorption rate can change based on what they ate or drank in a particular evening. Consequently, trying to extrapolate backwards to determine what a person’s BAC was at the time of arrest or at the time of an accident based on what their BAC was when tested an hour or two later is somewhat ridiculous; but there are experts out there that the government relies upon to prove a BAC number. Happily we don’t see too many cases with retrograde extrapolation involvement in Maryland and that is probably because in Maryland the law is written that the BAC cannot be over .08 at the time of “testing” whereas in other states it may be from the time of the accident or from the time of an arrest. Writing the legislation to reflect from the time of testing is actually more useful so that issues of retrograde extrapolation can be largely avoided.