Blood Alcohol Charts and Commentary

Blood alcohol charts are generalizations that are based on total body weight and gender, and the charts assume complete and immediate absorption of the alcohol contained in the so-called "standard drink." This assumption is, of course, medically and scientifically wrong, but the charts are useful as a gauge to determine what a person's blood alcohol is after a specified number of drinks.

Whenever a person consumes alcohol, several complex metabolic processes take place. Generally, these are described as absorption, distribution and elimination of the alcohol from the body.

During the absorption phase, alcohol from a beverage is processed in the stomach and small intestine. Approximately 20% of alcohol can be absorbed through the stomach wall, but the majority of alcohol is processed in the small intestine. Depending upon whether a drinking subject has eaten food, the process of absorption can be slower and some of the alcohol will be broken down if trapped in the stomach. Thus, drinking on a full stomach will slow the absorption rate. On average, however, alcohol is absorbed within 45 minutes, but absorption can take upwards of three hours.

The distribution phase marks the phase where alcohol is distributed throughout the body. As with the absorption phase, this can also only be described in general terms. Arterial blood picks up the alcohol from the small intestines and begins distributing it throughout the body, dropping off alcohol at various points in the body like Hansel and Gretel's breadcrumbs.

Blood alcohol charts (and perhaps more importantly, breath alcohol devices such as the Datamaster) assume complete equilibrium of alcohol throughout the body. According to the charts and breath testing devices, the amount of alcohol in the lungs is the same as in the brain, where alcohol has its known impairing effect. Medically and scientifically, this isn't true; distribution is not uniform, and the blood alcohol content of one big toe versus the other will not be equal.

Distribution and equilibrium are important when considering that alcohol mixes with water. More specifically, alcohol mixes primarily with the body's water content, which is concentrated in muscle tissue and, more importantly, the brain. (Until alcohol reaches the brain, there can be absolutely no impairing effect by alcohol, even if a person's big toe measures 0.15 BAC.) Because there is very little water in fatty tissue and bone, there will similarly be very little alcohol in these portions of the body. Men have generally much more water in their bodies than women, and women have more fatty tissue on average than men. An average man's body is composed of 68% water, whereas the average woman is 55% water. Again, however, these averages are only just that: an average. This means that half of the world's male population is more than 68% water-weight and the other half less than 68% water-weight.

The elimination phase is also something that can be addressed only in general. Alcohol is "burned off" by a metabolic process assisted by the liver. The liver produces an enzyme called alcohol dehydrogenase, which acts as a catalyst to speed up the interaction of oxygen and alcohol and essentially "burns" off the alcohol. The byproduct of this process is carbon dioxide and water, which is why people have to use the bathroom more often while drinking alcoholic beverages. On average, the average person burns off alcohol at a rate of 0.015 grams per hour. Thus, a person who reaches a blood alcohol content of .080 will be, on average, .065 one hour later.

In truth, a person who is drinking under normal conditions will be absorbing, distributing, and eliminating alcohol throughout the course of drinking, and it is extremely difficult to precisely gauge what a person's blood alcohol is at a given point in time.

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