Breath tests measure energy absorbed by certain chemical compounds — which can include substances other than alcohol.
It’s a common scene in movies or television: a person is pulled over on suspicion of drunk driving and immediately made to blow into a small portable machine (known as a breathalyzer). The police then declare that this person is driving drunk and lock them up. But what exactly does a breathalyzer measure? Can the police really prove that someone was drunk by testing their breath?
As a general rule, California law prohibits operating a motor vehicle if you have a blood alcohol content (BAC) of .08 percent or higher. In some situations, such as if you hold a commercial driver’s license or are under the age of 21, the BAC is lower. The police can measure BAC in two primary ways: through a blood test or a breath test.
How Breath Tests Work
Although many people believe that breathalyzers or breath tests measure the amount of alcohol in your system, this is not actually true. Breath tests measure any chemical compound that has the methyl group as part of its structure. There are thousands of chemical compounds other than alcohol that contains the methyl group — which means that you could have a positive breath test despite not having any actual alcohol in your system.
When a driver is stopped for a DUI, he may be asked to take a breathalyzer test at the side of the road. It’s important to know that you do not have to submit to this roadside test unless you are under age 21 or currently on DUI probation. After you are arrested for a DUI, however, you are required to take a chemical breath or blood test. You will be asked to breathe into a tube, where a machine captures a breath sample. These machines generally use infrared spectroscopy to shoot light energy through a captured breath sample. Any compounds that contain the methyl group will absorb this energy. The more energy that is absorbed by the same, the more of that chemical compound is present in a breath sample. The breath test reading is based on how much of that light energy reaches the sensor on the other side of the machine. The less light that reaches the sensor, the higher the blood alcohol content (BAC) reading.
As mentioned above, there is a significant flaw in this process. A chemical breath test machine assumes that if the light is absorbed by a breath sample, the chemical compound absorbing the energy is alcohol. The machine does not analyze or measure the type of compound that is actually absorbing the light; it only reports the amount of energy absorbed. This then translates into a BAC reading. Any number of compounds other than alcohol can result in a false positive BAC reading. These compounds can be something consumed by the person taking the test, or even something produced by a person’s body if he has certain medical conditions or is on a special diet.
If you have been arrested for driving under the influence even though you did not actually consume alcohol, you will need an experienced DUI lawyer. In Tustin, California, contact the Chambers Law Firm at 714-760-4088 or dchambers@clfca.com to learn more about how we can defend you against false positive breath test results. Our initial consultations are always free!
