Ever look at the alcohol chart sent out in the mail by the DMV regarding how many drinks over a period of hours a person may drink at a certain weight and be under the legal limit? Ever think, okay I can have five drinks over a four-hour period or one drink per hour and be okay to drive? Unfortunately, we’re not getting all the information and if one follows the general guidelines sent out by the DMV, a DUI arrest may ensue. (DMV Chart)
First, let’s look at the definition for a “drink”. If we look at the Merriam-Webster Dictionary the noun “drink”, is defined as “a liquid suitable for swallowing; alcoholic beverages; a draft or portion of liquid”. However, DUI alcohol experts who do calculations to correlate the number of “drinks” per a specific blood alcohol level define a “drink” as a twelve-ounce beer, a four-ounce glass of wine, or one-and-a-half ounces of hard spirits. Unless one is drinking beer from a can or a bottle, it is difficult to know the exact ounces of alcohol being ingested.
In addition, inconsistencies in alcohol content in these specific types of drinks are also problematic as you may have a five percent light beer while a heavier beer may have eight percent. Wines and hard liquors also vary in their alcohol content depending on the brand and type. (Alcohol Contents) All of these variables make it impracticable to rely on a specific number of drinks during a specific time period in trying to assure that one is legal to drive.
The other problem in determining if one is under a .08 (it is illegal to drive in California with a .08 percent or greater alcohol content in your blood) is the difficulty in determining what one’s blood alcohol concentration is at a specific time.
Alcohol absorption explains how alcohol travels through one’s body and over time goes from a zero blood alcohol concentration, up to the highest blood alcohol concentration and then back down to zero. Alcohol absorption may be categorized in three phases. As soon as one starts drinking, the alcohol level starts to rise. This is the ascending portion of the blood alcohol curve. During this phase the alcohol that is going into one’s body is greater than the alcohol that is being eliminated by the body through the liver. This phase goes on for as long as alcohol is ingested and for some time after the drinking stops. The amount of time that elapses between the time of the last drink and the end of the ascending portion of the curve (or the highest alcohol concentration) depends on factors such as whether or not there is food in the stomach and the pace of the drinking. For example, if there is rich food in the stomach and/or more alcohol ingested later in the evening at a faster pace than earlier, the time that the person reaches the peak alcohol level, after they stop ingesting alcohol, may take longer. However, if only a little food is in the stomach and/or the alcohol is drank at an even pace over a period of time, the peak will be reached quicker once the person stops ingesting alcohol.
The second phase of alcohol absorption is called the plateau or peak. This phase is reached some time after the person has stopped drinking and reaches their highest alcohol concentration. This is when the rate of absorption is equal to the rate of elimination. Expert opinions vary as to how long this phase lasts. Some say it ends in a matter of minutes while others say it may last for up to an hour.
The last phase of alcohol absorption is the descending or elimination phase. This is where there is very little absorption going on in the body and the body is eliminating the alcohol primarily through the liver. This phase goes on until all of the alcohol has been eliminated from the body. Most experts will say that alcohol eliminates at a rate of .015 to .02 percent per hour.
When determining if a person is below a .08 when driving there are a couple of issues that arise in a DUI case regarding the three phases of the blood alcohol curve (BAC). (Example of BAC) The most frequently used, is what is called the “rising defense”. This occurs when a person just finished drinking, and soon thereafter drives. Police stop the person, and then, some time later they are given a breath or blood test. In a case where the blood alcohol is close to the legal limit, the person at the time of driving could have been below a .08. Then, at the time tested, their blood alcohol level rises, because they were still on the ascending portion of the curve when they were driving, and the test results are at a .08 or greater. This is a “rising defense”, because the person is actually below a .08 at the time of driving, which is a defense in a DUI case (it is illegal to DRIVE with a .08 or greater - Vehicle Code), and then rises to a .08 or above, after the driving has stopped.
Another issue that arises is when someone drinks quite a lot of alcohol the night before and then gets up the next morning believing they are fine to drive. They are stopped by police, tested and are above the legal limit. Since alcohol eliminates from the body at .015 to .02 per hour, if someone goes to bed at 2:00 am and is at a .20. At 8:00 am that morning they could still be at a .11 alcohol level if they eliminate alcohol at a .015 rate per hour. In this case the person would have been a higher level at the time of the stop and then when eventually tested would have been at a lower level, because they are the elimination portion of the curve.
The science behind a DUI case is important to acknowledge and remember when deciding whether or not to drive. Unfortunately, even if tested before leaving friends or a restaurant does not solve the issue as blood alcohol levels fluctuate. Counting drinks is also imprecise, as the size and alcohol content will influence the true alcohol concentration of the person’s blood. The only real choice is not to drive, because one cannot guesstimate their blood alcohol level at a specific time and then determine that it is going down instead of up or that since they are ascending they will stay below a .08 blood alcohol concentration until they arrive at home. It is always a gamble to drink and drive, but if you are arrested on suspicion of DUI one definitely needs to seek counsel from someone who knows the science behind the law.