ABC’s of BAC | Underage Drinking

| June 19, 2013


The ABC’s of BAC: Understanding Blood Alcohol Concentration and Alcohol Impairment

Source: National Highway Transportation Safety Administration,

Q: What is “BAC”?

A: The amount of alcohol in a person’s body is measured by the
weight of the alcohol in a certain volume of blood. This is called the
blood alcohol concentration, or “BAC.”

Alcohol is absorbed directly through the walls of the stomach and the
small intestine, goes into the bloodstream, and travels throughout the
body and to the brain.

Alcohol is quickly absorbed and can be measured within 30 to 70 minutes
after a person has had a drink.

Q: Does the type of alcohol I drink affect
my BAC?

A: No! A drink is a drink, is a drink.
A typical drink equals about half an ounce of alcohol (.54 ounces, to be
exact). This is the approximate amount of alcohol found in:

  • one shot of distilled spirits, or
  • one 5-ounce glass of wine, or
  • one 12-ounce beer.

Q: What affects my BAC?

A: How fast a person’s BAC rises varies with a number of factors:

  • The number of drinks. The more you drink, the higher the BAC.
  • How fast you drink. When alcohol is consumed quickly, you will
    reach a higher BAC than when it is consumed over a longer period of
  • Your gender. Women generally have less water and more body fat
    per pound of body weight than men. Alcohol does not go into fat
    cells as easily as other cells, so more alcohol remains in the blood
    of women.
  • Your weight. The more you weigh, the more water is present in
    your body. This water dilutes the alcohol and lowers the BAC.
  • Food in your stomach. Absorption will be slowed if you’ve had
    something to eat.

Q: What about other medications or drugs?

A: Medications or drugs will not change your BAC. However, if you drink alcohol while taking certain medications, you
may feel – and be – more impaired, which can affect your ability to
perform driving-related tasks.

Q: When am I impaired?

A: Because of the multitude of factors that affect BAC, it is very
difficult to assess your own BAC or impairment.
Though small amounts
of alcohol affect one’s brain and the ability to drive, people often
swear they are “fine” after several drinks – but in fact, the failure to
recognize alcohol impairment is often a symptom of impairment.

While the lower stages of alcohol impairment are undetectable to others,
the drinker knows vaguely when the “buzz” begins. A person will likely
be too impaired to drive before looking – or maybe even feeling –

Q: How will I know I’m impaired, and why
should I care?

A: Alcohol steadily decreases a person’s ability to drive a motor
vehicle safely. The more you drink, the greater the effect. As with BAC,
the signs of impairment differ with the individual.

In single-vehicle crashes, the relative risk of a driver with BAC
between .08 and .10 is at least 11 times greater than for drivers with a
BAC of zero, and 52 times greater for young males. Further, many studies
have shown that even small amounts of alcohol can impair a person’s
ability to drive.

Every State has passed a law making it illegal to drive with a BAC of
.08 or higher. A driver also can be arrested with a BAC below .08 when a
law enforcement officer has probable cause, based on the driver’s

The following chart contains some of the more common symptoms people
exhibit at various BAC levels, and the probable effects on driving

Blood Alcohol
Concentration (BAC)1

Typical Effects

Predictable Effects on Driving

  • Some loss of judgment
  • Relaxation
  • Slight body warmth
  • Altered mood
  • Decline in visual functions (rapid tracking of a moving
  • Decline in ability to perform two tasks at the same time
    (divided attention)
  • Exaggerated behavior
  • May have loss of small-muscle control (e.g., focusing
    your eyes)
  • Impaired judgment
  • Usually good feeling
  • Lowered alertness
  • Release of inhibition
  • Reduced coordination
  • Reduced ability to track moving objects
  • Difficulty steering
  • Reduced response to emergency driving situations
  • Muscle coordination becomes poor (e.g., balance, speech,
    vision, reaction time, and hearing)
  • Harder to detect danger
  • Judgment, self-control, reasoning, and memory are
  • Concentration
  • Short-term memory loss
  • Speed control
  • Reduced information processing capability (e.g., signal
    detection, visual search)
  • Impaired perception
  • Clear deterioration of reaction time and control
  • Slurred speech, poor coordination, and slowed thinking
  • Reduced ability to maintain lane position and brake
  • Far less muscle control than normal
  • Vomiting may occur (unless this level is reached slowly
    or a person has developed a tolerance
    for alcohol)
  • Major loss of balance
  • Substantial impairment in vehicle control, attention to
    driving task, and in necessary visual and auditory
    information processing
Information in this table shows the BAC level at which the
effect usually is first observed, and has been gathered from a
variety of sources including the National Highway Traffic Safety
Administration, the National Institute on Alcohol Abuse and
Alcoholism, the American Medical Association, the National
Commission Against Drunk Driving, and

Category: Alcohol, Child/Youth/Teens, Parents/Caregivers, Teachers, Young Adults - Alcohol

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