What is the Rising Blood Alcohol Defense?

Posted by Jon Ibanez on November 30th, 2015

California DUI law requires that a person’s blood alcohol content be at a 0.08 percent or higher at the time they were driving. However when a person drinks, their blood alcohol content is either rising or falling. This means that, at the time the driver was actually driving, his or her blood alcohol content could have been lower than the chemical test reading.

When a person drinks, alcohol enters the blood stream after it is absorbed through the walls of the stomach and the small intestine. This process is called absorption and during this time, the person’s blood alcohol content will continue to rise. When the person stops drinking, absorption stops and a person’s blood alcohol content peaks. After the person’s blood alcohol content peaks because they have stopped drinking, it then begins to fall.

If we were to chart a person’s blood alcohol content as they drink, stop drinking, and begin sobering up, we would see a lopsided bell curve, rising sharply and falling gradually. The more alcoholic drinks are and the faster someone drinks them, the quicker the blood alcohol content rises.

A person’s BAC can be determined in several ways. The first is with a preliminary alcohol test (also known as a “PAS” test) which is a pre-arrest breathalyzer. The PAS test is a field sobriety test is not mandatory. The chemical test, on the other hand, is mandatory and can be either a blood test or a breath test after a person has been lawfully arrested for a California DUI.

If only one test is done and only one BAC level determined, we’ll only where on the curve the person was at the time they took the test. In other words, there’s no way to determine whether the person’s blood alcohol content was rising or falling.

When there are two BAC readings at two different times, however, we can determine whether a person’s BAC is rising or falling because one reading will be higher than the other.

Take, for example, a person who is pulled over at midnight for drunk driving. Following the stop at around 12:20am, the officer does a PAS test. The PAS test indicates that the driver’s BAC is 0.09 percent. Because the driver is over the legal limit of 0.08 percent, the driver is arrested on suspicion of a California DUI. Following the arrest, the driver provides a blood test for the mandatory chemical test. The blood test is performed at 12:45am and the results show a blood alcohol content of 0.14 percent.

This is a rise of 0.05 percent in the 25 minutes between the PAS test and the blood test. Therefore, if you to track the BAC level backwards in time to the last point the person was driving at midnight, it is possible that the driver’s blood alcohol content was as low as 0.05 percent.

Conversely, it is also possible that the later BAC reading is higher than the earlier reading which would indicate that the driver’s blood alcohol content was falling.  Therefore, unfortunately, it is also possible that it was much higher at the time they were driving.

While this may serve as a defense to California Vehicle Code section 23152(b) – driving with a 0.08 percent blood alcohol content or higher – it may not serve as a defense to California Vehicle Code section 23152(a). If a person “drives under the influence,” they can still be convicted of a California DUI under California Vehicle Code section 23152(a). To prove that a person is “driving under the influence,” the prosecution typically uses the officer’s observations of poor performance of field sobriety tests, poor driving, and the “objective symptoms of intoxication.”

If the prosecution, however, cannot prove that a person was under the influence, it may be possible to they were under the legal limit of 0.08 percent at the time they were driving using the rising blood alcohol defense.  

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