Alcohol (BAC, Gender, etc)

What is BAC?

BAC = “Blood Alcohol Concentration”

The ratio of alcohol to blood in the body.

Factors That Determine BAC


Alcohol does not affect men and women equally. Research indicates that alcohol’s effects on females tend to be stronger and last longer. This is because women produce a smaller amount of alcohol dehydrogenase, an enzyme that breaks down alcohol in the stomach. As a result, women reach a peak BAC about 20 percent higher than men do when consuming the same amount of alcohol.

Body Weight

Your weight affects the percentage of alcohol in your blood. A heavier person has more body fluids with which the alcohol will mix, and thus will have a lower BAC.

Strength of the Drink

The stronger the alcohol content in the beverage consumed, the higher the BAC will rise. A 1.5 oz. shot of 80 proof spirits (straight or in a mixed drink), a 5 oz. glass of wine and a 12 oz. bottle or can of beer contain equivalent amounts of alcohol.

Size of Drink

A larger drink will contain more alcohol and result in a higher BAC than a smaller drink of the same alcohol strength. For example, a 24-ounce beer contains twice as much alcohol as a 12-ounce beer of the same brand.


Food in the stomach does not absorb alcohol, but it might slow the rate at which alcohol is absorbed. All consumed alcohol will get into the blood eventually. Trying to prevent becoming intoxicated by drinking only on a full stomach will just result in a well-fed drunk!

Time Spent Drinking

The faster a person consumes alcohol, the more quickly BAC will reach its peak. Spreading out drinking over time will result in a lower peak BAC, other factors being equal. For example, the BAC would reach a higher level if a person had three drinks in one hour then if a person had one drink each hour for three hours.

How Alcohol is Measured in the Body

People may drink the same amount of a beverage, but the percentage of alcohol in the blood depends on gender, body weight, strength of the drink, size of the drink, whether there is food in the stomach, and time spent drinking.

The Greater the Blood Alcohol Concentration (BAC), the Greater the Risk of Being Involved in a Fatal Crash

Young drivers between the ages of 16 to 19 with a BAC of 0.02 to 0.05 percent (one to two drinks) are at least seven times more likely to be killed in a crash than a sober driver of any age.

At 0.08 percent (three to four drinks), they are 40 times more likely to be killed than a sober driver and 20 times more likely to be killed than a 55-year-old driver at the same BAC level.

By 0.12 percent BAC (four to six drinks) a 16- to 19-year-old is 90 times as likely to die in a traffic crash as a sober driver.

Having the facts is only part of making careful decisions about alcohol use. Analyze your attitudes and behavior by answering the following self-assessment.

Effects of Carbonation

  1. Can speed up absorption
  2. The pyloric valve controls the rate at which the alcohol passes into the small intestine
  3. Carbonation stimulates the opening of the pyloric valve, allowing more rapid absorption of the fluid

Sequence of Effects on the Body

  1. Judgment
    The first part of the body affected by alcohol is the brain, particularly the part of the brain that allows you to think clearly and make good decisions. Its sedative effects impair judgment in a way that is usually not noticed by the drinker. The part of the brain that controls social inhibitions is also affected, causing people to say and do things they normally would not. These effects start with just one drink.
  2. Muscle Control
    The second part of the body affected by alcohol is muscle control. Due to the small muscles in the eye being very susceptible to the effects of alcohol, vision can be significantly affected, even at low alcohol levels.
  3. Effects of Alcohol on Driving Ability
    The following table summarizes the effects of alcohol on vision:
Type of VisionEffects of Alcohol on Driving Ability
Visual Acuity, or Sharpness of VisionAlcohol can cause vision to become blurry, making it more difficult to perceive the traffic scene and make good driving decisions.
Side, or Peripheral VisionWhen sober, most people have about 180 degrees of side vision. Even while looking straight ahead you can detect objects moving at the side. As BAC rises, side vision decreases.
Color DistinctionColor plays an important role in the highway transportation system. Alcohol reduces your ability to distinguish colors, decreasing your ability to perceive the full traffic scope.
Night VisionAlcohol decreases your night vision, reducing your ability to automatically and quickly regulate the amount of light entering the eyes.
Distance JudgmentAlcohol decreases your ability to accurately judge distances. Determining how far objects are from your vehicle is a critical driving skill.
FocusThe eye is able to change focus rapidly from objects close by to objects far away. Alcohol slows this ability, reducing the ability to see hazards clearly soon enough to respond properly.

Here are some of the ways in which different numbers of drinks consumed in one hour may affect a 150-pound adult. The beverage in these examples is beer (12 ounces).Alcohol’s Impact on Behavior

After One Drink, Inhibitions Are Lowered
A person may be less critical of him or herself and others, and judgment begins to be affected. Coordination may also be affected. (BAC: 0.02-0.03 percent).

After Two Drinks, Reaction Time Will Be Slower
A person may appear relaxed and friendly. Reaction time begins to slow. (BAC: 0.04-0.05 percent).

After Three Drinks, Judgment Is Not Sound
A person will not think clearly and may do or say things that are rude or unreasonable, and reasoning is less reliable. Reaction time slows down. (BAC: 0.06-0.07 percent).

After Four Drinks, Hearing, Speech, Vision and Balance Are Adversely Affected
A person may have difficulty enunciating words. As eye muscles become more relaxed, focusing and tracking becomes more difficult. Although the drinker may not be aware of it, reaction time is greatly slowed. (BAC: 0.08-0.09 percent).

After Five Drinks, Most Behaviors Are Affected
Body parts do not seem to work together. Speech may be slurred. Performing any task that requires the use of hands and feet is difficult. Walking without stumbling also is difficult. (BAC: 0.10-0.11 percent).

After 12 Drinks, A 150-Pound Person’s BAC Would Be About 0.30 Percent
At this level, a coma or deep sleep is not unusual. If there is enough alcohol in the stomach when the person passes out, the blood-alcohol level will continue to rise. If the BAC reaches 0.40 percent, the person may fall into a deep coma and die.

Elimination of Alcohol

Once alcohol reaches the bloodstream, the body immediately begins to eliminate it. It does so in three ways:

  • Breath. Approximately 8 percent of alcohol is eliminated by breathing (exhalation). This is why you might be able to detect the odor of an alcoholic beverage on a drinker,s breath.
  • Sweat. About 2 percent of alcohol is eliminated by sweating. It may be possible to detect the odor of an alcoholic beverage on a drinker’s body.
  • Oxidation. The majority of alcohol (90 percent) is removed by the liver as it burns up the alcohol through a process called oxidation.

On average, BAC is eliminated from the body at a rate of .015-.017% per hour.


BAC and Time

Some drinkers try all sorts of things to sober up. In reality, coffee, fresh air, exercise and cold showers will not help. Neither will sleep. Time is the only thing that will sober you up. It takes a lot longer than most people think for the body to eliminate alcohol. If fact, it takes between 75-90 minutes or longer for the body to eliminate the alcohol contained in one standard-size drink. While some very large males (over 250 pounds) can eliminate this amount of alcohol in about one hour, it takes much longer in everyone else. The figure below depicts a drinking scenario that demonstrates the actual rate of elimination.

Say a person starts drinking at 9 p.m. and continues to drink until 1:30 a.m., drinking at a rate of about 2 drinks per hour. This graph depicts the scenario, showing the alcohol level on the vertical axis and the time of day along the horizontal axis.

By 1:30 a.m., the drinker has reached a BAC of about 0.14 percent. Note that the alcohol level continues to rise for at least 30 minutes after drinking has stopped. This is because it takes a while for alcohol to be fully absorbed into the bloodstream, causing this drinker’s BAC to rise even more.

By 2 a.m., the drinker’s BAC has peaked and the body continues its efforts to eliminate the alcohol at an average elimination rate of about 0.015 percent per hour. At 7:30 a.m. the next morning, this drinker will still have a BAC of 0.08 percent.  This drinker is still legally intoxicated and a danger behind the wheel. If they chose to drive to work, school or elsewhere, they can be arrested for DUI.

The elimination of alcohol continues, but the drinker is still impaired (0.05 percent BAC) at 9:30 a.m.! It is not until 1 o’clock in the afternoon of the next day that the drinker’s alcohol level is back down to zero. Even at that point, the drinker could still be impaired by the effects of a hangover.

The bottom line is that it takes much longer for the body to eliminate alcohol than most people think. That is one reason why it is so important to separate alcohol from driving.

Alcohol and Driving

All states have per se laws which make it illegal to drive with a BAC of .08 of higher. However, a driver can be arrested with a BAC lower than .08 if a law enforcement officer has probable cause to believe the driver is impaired. As noted above, impairment can occur at BAC levels as low as .02.

Crash Risk

The greater the blood alcohol concentration, the greater the risk of being involved in a fatal crash. At a BAC of .05, a driver’s risk of crashing begins to increase rapidly. At a BAC of .08, the crash risk increases exponentially.

The 16-20 year old age group has a highest crash risk at all BAC levels. At a BAC of .05, this age groups crash risk is 4.09 and it rises to 9.51 at the.08 BAC level compared to a sober driver.

The 21-34 year old age group has the second highest crash risk by BAC level. At a .05 level, this age groups crash risk is 3.33 and it rises to 6.87 at the .08 level compared to a sober driver.

The 35 plus age group has the lowest crash risk at all BAC levels. At a BAC of .05, this age groups crash risk is 2.92, and it rises to 5.56 at the .08 BAC level compared to a sober driver.


Risk of Fatal Crash Involvement by BAC and Age


(Source: (IIHS,2015)