BAC Measurement

How Blood Alcohol Content is Measured

After alcohol is absorbed into the bloodstream it leaves the body in two ways. A total of about ten percent leaves through the breath, perspiration, and urine. The remainder is broken down through the process known as metabolism.

Trained and experienced police officers can develop remarkably accurate assessments of individual levels of alcohol impairment. However, it is virtually impossible for the casual observer to judge another's BAC without the use of a precision breath alcohol tester.

What Happens at Different BAC Levels?

Breathalyzer measurements can also predict other alcohol related behaviors. While Individual responses to alcohol differ, the BAC chart below is representative of the stages and effect of alcohol at various breath alcohol concentrations.

BAC Level Effects from Alcohol
0.02 - 0.03 BAC No loss of coordination, slight euphoria and loss of shyness. Mildly relaxed and maybe a little lightheaded.
0.04 - 0.06 BAC Feeling of well-being, lower inhibitions, and relaxation. Judgment is slightly impaired. Minor impairment of reasoning and memory, and less cautious. Your behavior can become exaggerated and emotions (ex. happiness or sadness) felt more intensely.
0.07 - 0.09 BAC Impairment present in everyone. Driving skills such as vision, steering, lane changing and reaction time are impaired along with balance, speech, and hearing. Feelings of Euphoria in some. Self-control and caution are reduced. Riskier behaviors displayed. Judgment, reason and memory suffer. You are likely to believe that you are functioning better than you really are.
0.08 BAC is legally impaired and it is illegal to drive at this level.
0.10 - 0.12 BAC Significant impairment to motor coordination and loss of good judgment. Speech may be slurred; balance, vision, reaction time and hearing will be impaired. Probably not thinking straight.
0.13 - 0.15 BAC Very obviously drunk. Severe impairment to judgment, perception, and major motor skills. Very slow reaction time. Blurred vision, loss of balance and slurred speech. Feelings of well being starting to be replaced by anxiety and restlessness (dysphoria). Vomiting common.
At .15 BAC you are 380 times more likely to be in a fatal crash than you are sober.
0.16 - 0.19 BAC The drinker has the appearance of a "sloppy drunk." At this point, most drinkers begin to feel incapacitated. Many social drinkers will pass out. Nausea begins to set in and the drinker has difficulty focusing on any object.
The average BAC among fatally injured drivers is 0.17, which is also the average BAC nationally for persons arrested for drunk driving.
0.20 BAC Out of it. Confused. Dizzy. Requires help to stand or walk. If injured may not feel the pain. Nausea and vomiting. The gag reflex is impaired and you can choke if you do vomit. Blackouts are likely.
0.25 BAC All mental, physical and sensory functions are severely impaired. Near total loss of motor function control. Increased risk of asphyxiation from choking on vomit and of seriously injuring yourself by falls or other accidents.
0.30 - 0.40 BAC Extremely life threatening. You have little comprehension of where you are. You may pass out suddenly and be difficult to awaken. Complete unconsciousness. Coma is possible. This is the level of surgical anesthesia. Death may occur.
Over 0.45 BAC death will occur in most people

The body (in actual fact the liver) can metabolize only a certain amount of alcohol per hour. No matter how much or how fast alcohol is consumes, the body can only dispose of it at a rate that is generally accepted as being 1 standard drink per hour. Allowing for individual variations in weight, percent body water, percent body fat, and food intake, the amount of alcohol from one standard drink will peak, in the blood stream, within 30 to 45 minutes.

The rapid consumption of four or five drinks in one or two hours (see binge drinking) overwhelms the liver with much more alcohol than it can handle. As a result BAC rapidly increases and continues to do so until drinking is stopped or decreased to a rate of less than one drink per hour. Excessively rapid drinking as frequently practiced on campus will invariably lead to dangerously high BAC levels.

Time to Sober Up

Alcohol leaves the body of at a conservative rate of about 0.5 oz. alcohol per hour or .015 percent of blood alcohol content (BAC) per hour. This is an average rate at which the liver can metabolize (burn off) alcohol. The result is that it can take many times longer to sober up than it took to become intoxicated.

Hours to Rid the Body of Alcohol = Peak BAC/.015

Someone with a BAC of .16, or twice the legal driving limit will require over 10 hours to be completely sober and after 5 hours may still not be under the legal driving limit.

Many late night revelers never think about the time it takes to sober up. Driving or performing safety sensitive duties the morning after can put anyone at risk. If an individual’s breath alcohol content is .20 after an evening of heavy drinking at 1:00 AM, they may not be under the legal driving limit of .08 BAC until approximately 9:00AM later that morning. Imagine how long it might take for the individual to be under the US Department of Transportation’s BAC limit of .02.