Understanding BAC (Blood Alcohol Content/Concentration) Levels
Points to remember
(Information compiled from a variety of sources: Virginia Tech's Alcohol Prevention Program -alcohol effects; National Highway Traffic Safety Administration; National Institute on Alcohol Abuse and Alcoholism; National Medical Association)
on Impaired driving
Determining your level of BAC
The first step in using any chart or computer program to estimate your BAC is to
determine the amount of alcohol you consume. The key is to think in terms of “standard drinks.” A standard drink is 0.5 oz. of alcohol. To calculate standard drinks you need to know the beverage size in ounces
and the percent alcohol content. Some alcoholic beverages are labeled by percent
alcohol by volume (i.e., 5%), but most beers are not.
WHAT IS BAC?
BAC (Blood Alcohol Content or concentration) is the percent of alcohol present in the blood. There
are various means of determining BAC. An absolute level can be obtained by drawing a sample of blood.
The most reliable estimate can be obtained via very accurate breathalyzers that take a sample of deep
lung air. These are often used by police departments, and are considered legal evidence in a court of law.
Handheld breathalyzers are less accurate, and while they are not considered legal evidence of
intoxication, they can be used by police to determine probable cause to obtain a BAC that is considered
legal evidence in a court of law.
The chart below explains the effects that BAC has on your ability to drive.
Click on the link below to dowload a PDF of the chart shown that is useful in estimating alcohol content:
WHAT IS A "STANDARD" DRINK?
Rate of Consumption
Blood alcohol concentration depends on the amount of alcohol consumed and the
rate at which the user's body metabolizes alcohol. Because the body metabolizes
alcohol at a fairly constant rate (somewhat more quickly at higher and lower alcohol
concentrations), ingesting alcohol at a rate higher than the rate of elimination results in a cumulative effect and an increasing blood alcohol concentration.
Consumption at a rate of one drink per hour will, for most people, maintain your current BAC.
Another gender based difference is in the elimination of alcohol. Although not explained, studies indicate that women eliminate alcohol from their bodies at a rate 10% greater than that of men.
It is important to remember that this difference in the eliminate rate is by far outweighed by gender differences related to distribution factors. Thus, women will, in most cases, reach higher BACs as their male counterparts that consume the same amount of alcohol.
The liver is responsible for the elimination of alcohol. The liver eliminates of 95% of ingested alcohol from the body through metabolism. The remainder of the alcohol is eliminated through excretion of alcohol in breath, urine, sweat, feces, milk and saliva. Healthy people metabolize alcohol at a fairly consistent rate. As a rule of thumb, a person will eliminate one average drink or .5 oz (15 ml) of alcohol per hour. Several factors influence this rate. In general, the rate of elimination tends to be higher when the BAC in the body is very high or very low. Elimination factors include rate of consumption, tolerance, and gender:
Alcohol can have significant effects on feelings, perceptions, and physiology. Although alcohol may give you a feeling of elation and aroused senses due to a lessening of inhibitions during the early stages of alcohol intoxication, alcohol is a depressant. It depresses the central nervous system—leading to slowed reactions, slurred speech, and ultimately, to unconsciousness. Alcohol progressively affects different brain areas. Alcohol first affects the part of the brain that controls inhibitions. When people lose their inhibitions, they may talk more, get rowdy, and do foolish things. After several drinks, they may feel “high,” but really, their nervous system is slowing down.
Alcohol acts fast because it is not digested like food. Instead, it moves directly into the bloodstream from the stomach and small intestine. It takes a long time for alcohol’s effects to wear off—as it takes approximately one hour for the liver to process the alcohol in one drink.