Dallas DWI Lawyer

Beer on the Breath – Principles behind the Breathalyzer

When police arrest a driver for DUI, they will typically administer a breath test to determine the driver's blood alcohol concentration, or BAC. BAC is essentially a measure of how much alcohol has been absorbed into a person's system; tests have also shown a correlation between a person's BAC and their level of intoxication.

This raises a question: since BAC is based on the amount of alcohol in a person's bloodstream, how can it be measured using a breath test? To answer this, we must take a look at how alcohol acts in the human body.

Alcohol is different from many other substances in that it is not digested. Rather, after a person consumes an alcoholic beverage, the alcohol is absorbed directly into the bloodstream through the mouth, throat, and/or intestinal tissue. Because of this, alcohol in the bloodstream is virtually unchanged, from a chemical perspective.

The blood-borne alcohol now travels throughout the body, eventually reaching the lungs. As the blood passes through the lungs, it will come across the alveoli, sac-like structures in the lungs which are responsible for removing carbon dioxide from and providing oxygen to the blood. At this point, because it is a volatile substance, some of the alcohol contained in the blood will evaporate and be released into the air inside the lungs. Now, when the person breathes out, this airborne alcohol will be expelled along with other waste gases.

The breathalyzer operates on the principle that the amount of alcohol carried on a person's breath is proportional to the amount of alcohol in their bloodstream, at a ratio of 1 to 2,100. In simpler terms, this means that every milliliter of blood will contain 2,100 times as much alcohol as every milliliter of air from the same person. By measuring the alcohol content of a person's breath and doing some simple mathematical calculations, the BAC of the person can be determined.

Of course, the breathalyzer is not foolproof. Any number of outside variables can influence breathalyzer readings one way or another. If you have been arrested for DUI based on your breath test results, remember that even the best breathalyzer has a potential for error. An experienced DWI lawyer will be able to help you by demonstrating these weaknesses in court.

For an experienced Dallas DWI lawyer, call the offices of Mark Lassiter at 214-457-1668.