How BAC is Calculated

The use of breath analyzers in drivers dates back as far as the 1940’s. While not the most accurate of tests, it is considered by law enforcement to be the best available test for detecting whether or not drivers are over the limit for driving without impairment.

The breath detector is used based on it’s ability read the blood alcohol concentration (BAC) in a person’s system. The limits considered safe here in the great state of Alabama where “We Dare Defend Our Rights” is 0.08. But what does that mean, exactly?  To understand it better, it helps to know how the breath analyzers work. How is it possible that a person can breathe into a machine and it detect how much they’ve had to drink?

While it is of utmost importance for public safety and individual safety that impaired drivers be taken off the road, it is also important to know how the limit is determined. It’s true that blood tests and urine tests are more accurate than a breath test, but those tests are impractical in roadside stops. The breath analyzer is by far more likely to be used.

When a person consumes alcohol, it gets absorbed by the mouth, throat, stomach, intestines, and bloodstream. Because alcohol is not digested upon absorption, nor is it chemically changed in the bloodstream, when the blood goes through the lungs, some of the alcohol moves across the membranes of the lung’s air sacs. These airsacs (alveoli) allow the alcohol evaporates to be exhaled.

The BAC is based on a ratio of breath alcohol to blood alcohol as 2100:1. So 2100 milliliters(ml) of alveolar air contains the same amount of alcohol as 1 ml of blood. The American Medical Association has determined that a person can become impaired when the blood alcohol level reaches 0.05. A reading of 0.08 indicates that there are 0.08 grams of alcohol per 100 ml of blood.

There’s quite a math formula that goes into determining how much alcohol a person can consume (based on their body size/weight/type.) To avoid making an error in judgment, make the decision not to drink and drive.