DWI Breath Test Accuracy
Throughout the United States, it is illegal for drivers over the age of 21 to operate a motor vehicle with a blood alcohol content (BAC) of .08 percent or higher. For commercial drivers and those under the age of 21, this legal limit is much lower.There are three tests that can be used to determine BAC: breath, blood, and urine. Of the three tests, the breath test is most often used, due to its cost-efficiency and convenience. This form of testing is also less intrusive than drawing blood from the driver.
There are several brands of breath-testing machines, with the Intoxilyzer 5000 and BAC Datamaster being the most common.
The breath test works by analyzing a deep lung breath sample from the driver to determine his or her blood alcohol content. In order to administer the test, the officer will have the driver blow into a plastic tube until asked to stop.
Most breath-test machines use infrared spectroscopic analysis. Alcohol vapors in the breath sample absorb light waves at a certain frequency. This means that the more alcohol there is, the more light absorbed. To determine the alcohol concentration, the breath-testing device measures the amount of light that goes to a receptor at the other end of the chamber – the less light there is, the higher the alcohol content. The machine then uses a standard ratio to determine the BAC.
Unfortunately, breath-testing machines are not always accurate. For example, a machine may have difficulty determining the difference between the alcohol from a deep lung sample and mouth alcohol. Mouth alcohol can be caused by vomiting before the test or dental products that can trap alcohol in the mouth (e.g., dentures or a crown). Gum, mints, and mouthwash may also contribute to mouth alcohol.
It is also important that the machine be maintained and calibrated properly. A defense attorney may ask to see the maintenance logs to determine if the machine was functioning properly before you were asked to submit a breath sample.
If you have recently been charged with drunk driving, you should contact an experienced defense attorney.Your attorney may be able to question the DWI breath test accuracy. It can help your case if your attorney is able to prove that your breath test results were inaccurate.
