Blood Alcohol Concentration

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Blood Alcohol Concentration

When a person drinks alcohol, the alcohol is absorbed from the stomach and small intestine into the bloodstream. The amount of alcohol in the blood is called blood alcohol concentration (BAC). As blood travels to the brain, the alcohol in the blood produces the signs and symptoms of inebriation, or drunkenness. BAC is expressed as the weight of alcohol in a fixed volume of blood, for example, grams per liter.

In addition to how much a person drinks, several factors affect the amount of alcohol in the blood. Eating along with drinking alcohol decreases the amount of alcohol that can be quickly absorbed into the blood. Having more than one drink in an hour causes the BAC to increase rapidly. The percentage of body fat in a person's total weight also affects BAC. More fat means less body water into which the alcohol can distribute, thus increasing BAC. This is why women

Concentration UnitCountryLegal Limit
Percent weight/volume (% w/v)United States0.10 g/100 ml
Milligrams per 100 milliliter (mg/dl)Britain80 mg/100 ml
Milligrams per milliliter (mg/ml)Netherlands0.50 mg/ml
Milligrams per gram (mg/g)Sweden0.20 mg/g
Milligrams per gram (mg/g)Norway0.50 mg/g
50(0.05%)There may be no observable effects on behavior, but thought, judgment, and restraint may be more lax and vision is affected. More errors in tasks that require divided attention such as more steering errors, and increased likelihood of causing an accident.
80(0.08%)Reaction time for deciding and acting increases. Motor skills are impaired. The likelihood of a crash increases to three to four times the likelihood when sober.
100(0.10%)Six times as likely to be involved in a crash. Reaction time to sights and sounds increases. Physical and mental coordination are impaired; movement becomes noticeably clumsy.
150(0.15%)Twenty-five times as likely to be involved in a crash. Reaction time increases significantly, especially in tasks that require divided attention. Difficulty performing simple motor skills. Physical difficulty in driving.
200(0.20%)One hundred times as likely to be involved in a crash. Motor area of brain significantly depressed, and all perception and judgment distorted. Difficulty standing, walking, and talking. Driving erratic.
300(0.30%)Confusion and stupor; inability to track a moving object with the eyes. Passing out is likely.
400(0.40%)Coma is likely.
450–500(0.45–0.50%)Death is likely.
source: Mothers Against Drunk Driving (MADD) and the National Safety Council.

generally have a higher BAC than men after having the same number of drinks.

Laws in the United States establish limits on how high a person's BAC can be while driving. The legal limit in the United States is 0.10 grams per 100 milliliters of blood, or a BAC of 0.10 percent. Some state laws set an even lower BAC. Law enforcement officers use Breathalyzer machines to measure BAC. The measurement of alcohol concentration in the breath is converted into a measurement of alcohol concentration in the blood.

see also Alcohol: Chemistry; Breathalyzer; Driving, Alcohol, and Drugs; Drug Testing Methods and Analysis.

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Blood Alcohol Concentration

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