It is illegal to have a blood-alcohol concentration (BAC) of .08% or greater while driving a vehicle. It is not illegal to have a BAC of .08% or greater while blowing into a breathalyzer after a DI arrest at a police station. In other words, just because a breath test shows a level of, say, .09%, it does not mean that the blood alcohol level when the suspect was driving an hour earlier was the same .09%.
So what was the blood alcohol level when driving?
Well, we’ll never know: There is no evidence of the BAC at the time of actual driving. However, it is highly probable that it was .09%, since the body is constantly either absorbing or eliminating alcohol and the blood alcohol level is therefore constantly rising or falling. If it was falling, then we can expect the BAC when driving was higher — maybe .10% or more. But if it was rising…..
Let’s take a typical drunk driving arrest. The subject — let’s call her “Janet” — finishes dinner by throwing down “one for the road”, a 12-ounce can of beer containing .05% alcohol. Janet is stopped by an officer soon after leaving the restaurant, alcohol is smelled on her breath and she is given field sobriety tests. She does marginally well but the officer arrests her for DUI and takes her into the police station for breath testing. About 45 minutes after drinking the alcohol, Janet breathes into the breathalyzer. The result: .09%. She is booked and his driver’s license confiscated.
It will take, on average, about one hour for the alcohol to be absorbed and reach peak levels of concentration in the blood, thereafter to be eliminated from the body. This is only an average; it can vary from 15 minutes to 2 hours; some invidividuals can reach peak concentration ten times faster than others. Dubowski, “”Absorption, Distribution and Elimination of Alcohol: Highway Safety Aspects”, Journal on Studies of Alcohol, Supp. 10 (July 1985).
This makes trying to estimate earlier BAC levels no better than a rough guess, and scientists have uniformly condemned the practice. See, for example, “Breath Alcohol Analysis: Uses, Methods and Some Forensic Problems”, 21 Journal of Forensic Sciences 9.
Applying averages to Janet, though, we can expect the last drink to have had little if any effect on her blood-alcohol concentration while she was driving. By the time she is being tested at the station 45 minutes later, however, she is reaching peak concentration. In other words, Janet’s blood alcohol concentration has been rising. At about 120 pounds, we can estimate (read “guess”) that the can of beer has increased her BAC by about .031%.
Translation: the breathalyzer reading of .09% at the station indicates a BAC while driving of only .06%. She is not guilty. But the “evidence” will convict her.
Just to make things worse….As I indicated, attempts to guess BACs when driving earlier than when tested have been condemned by scientists. This makes things tough for prosecutors. Solution? As I discussed in a post on my personal DUIblog, “Whatever Happened to the Presumption of Innocence?“, most states today have passed laws — contrary to scientific truth — which rebuttably presume that the BAC at the time of being tested is the same as at the time of driving!
In other words, unless a defendant charged with drunk driving can prove that his blood alcohol content was different than when tested, the jury will be instructed that they must find that it is the same. In effect, the defendant is presumed to be guilty based upon the breathalyzer reading. And since there is no evidence of the BAC when driving, there is no way for the defendant to rebut the presumption. These laws do, however, make getting convictions much easier.
If you need to consult with a Los Angeles DUI lawyer or Orange County DUI attorney, contact The Law Offices of Lawrence Taylor at 888-777-3449. With offices in Los Angeles, Orange County, Riverside, and north San Diego County, the firm has limited its practice to DUI defense exclusively for 33 years and is consistently top-rated in surveys of Southern California attorneys and consumers.