February 15, 2004
BAC: Blood Alcohol Content
Blood Alcohol Content (BAC) is the concentration of alcohol in a person’s blood.
Blood Alcohol Units
In the U.S., the most common gauge for measuring BAC is the concentration measured by volume as a percentage. A blood alcohol level of .08 percent (too impaired to drive in most states) means that 8 parts per 10,000 in the blood is alcohol. It may be abbreviated BAC% or %BAC.
Another common measure is percentage by weight, or grams of alcohol per 100 milliliters of blood, sometimes noted as g/100ml. Although blood alcohol test results are often described as a percentage by volume, most of the instruments used to determine it actually measure the weight.
The difference between percentage by weight and by volume is inconsequential for most of us, because they produce the same numbers. A BAC of 0.05% by volume is the same as 0.05 mg/ml.
BAC may also be given as mg%, which is similar to g/100ml. A level of 0.05% could be listed as 050 mg%.
Alcohol Metabolism Rates
HowStuffWorks.com briefly highlights how alcohol is metabolized:
Once absorbed by the bloodstream, the alcohol leaves the body in three ways:
- The kidney eliminates 5 percent of alcohol in the urine.
- The lungs exhale 5 percent of alcohol, which can be detected by breathalyzer devices.
- The liver chemically breaks down the remaining alcohol into acetic acid.
As a rule of thumb, an average person can eliminate 0.5 oz (15 ml) of alcohol per hour. So, it would take approximately one hour to eliminate the alcohol from a 12 oz (355 ml) can of beer.
BAC Charts
Moderation Management has a set of charts for approximating BAC based on our gender (male & female bodies metabolize alcohol differently), size, amount consumed, and elapsed time. The units used in the MM charts are “mg%”; a level of 080 there is the same as a BAC% of .08, the threshold at which most U.S. states prosecute for driving under the influence (DUI).
Comparing the one-hour-to-eliminate-one-drink rule to the MM charts, though, it appears the “average” person in question is 200-pound male or a 240-pound female, because if either of them has 3 drinks over 3 hours, their BAC will be under .01. A 120-pound woman is still going to be at .015 after consuming 3 drinks in a 6-hour period, and 160-pound man is likely to be at .012 after having 4 drinks in a 5-hour period.
Effects of alcohol based on BAC levels
The BRAD21.org website — Be Responsible About Drinking — was created by friends and family of Bradley McCue, who died of alcohol poisoning at 21. It includes a page which lays out the effects of alcohol, noting that “some users may become intoxicated at a much lower Blood Alcohol Concentration (BAC) level than is shown”.
| BAC | Effects |
|---|---|
| 0.02-0.03 | No loss of coordination, slight euphoria and loss of shyness. Depressant effects are not apparent. Mildly relaxed and maybe a little lightheaded. |
| 0.04-0.06 | Feeling of well-being, relaxation, lower inhibitions, sensation of warmth. Euphoria. Some minor impairment of reasoning and memory, lowering of caution. Your behavior may become exaggerated and emotions intensified (Good emotions are better, bad emotions are worse) |
| 0.07-0.09 | Slight impairment of balance, speech, vision, reaction time, and hearing. Euphoria. Judgment and self-control are reduced, and caution, reason and memory are impaired, .08 is legally impaired and it is illegal to drive at this level. You will probably believe that you are functioning better than you really are. |
| 0.10-0.125 | Significant impairment of motor coordination and loss of good judgment. Speech may be slurred; balance, vision, reaction time and hearing will be impaired. Euphoria. |
| 0.13-0.15 | Gross motor impairment and lack of physical control. Blurred vision and major loss of balance. Euphoria is reduced and dysphoria (anxiety, restlessness) is beginning to appear. Judgment and perception are severely impaired. |
| 0.16-0.19 | Dysphoria predominates, nausea may appear. The drinker has the appearance of a “sloppy drunk.” |
| 0.20 | Feeling dazed, confused or otherwise disoriented. May need help to stand or walk. If you injure yourself you may not feel the pain. Some people experience nausea and vomiting at this level. The gag reflex is impaired and you can choke if you do vomit. Blackouts are likely at this level so you may not remember what has happened. |
| 0.25 | All mental, physical and sensory functions are severely impaired. Increased risk of asphyxiation from choking on vomit and of seriously injuring yourself by falls or other accidents. |
| 0.30 | STUPOR. You have little comprehension of where you are. You may pass out suddenly and be difficult to awaken. |
| 0.35 | Coma is possible. This is the level of surgical anesthesia. |
| 0.40 and up | Onset of coma, and possible death due to respiratory arrest. |
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