Even if you’ve never been stopped on suspicion of drunk driving in California, you probably know that a “Breathalyzer” or other breath-testing machine is often used during a DUI stop to estimate how much alcohol is in a driver’s bloodstream.
What you may not know, however, is how these machines work – or that, if the machine is not calibrated and operated correctly, a false test result can put you at risk of a conviction even if you were not breaking any laws.
Currently, California and other states prohibit driving a motor vehicle if your blood alcohol concentration (BAC) is 0.08 percent – 0.04 percent for drivers of commercial vehicles. A breath test is one way to estimate the percentage of alcohol in the bloodstream.
Different breath testing machines use different methods to estimate blood alcohol levels. The Breathalyzer uses a chemical reaction, while the Intoxilyzer and DataMaster use IR spectroscopy.
Each device first collects a breath sample by having the test subject breathe into the device. If the test subject has eaten, ingested, or taken medications recently false positive can result. A breath sample that is too small or does not collect air from the bottom of the lungs can also produce a false reading.
Once the device has a breath sample, it passes the sample through a chemical mixture or through an IR spectroscope. The device then measures the color change associated with the chemical reaction and looks for alcohol molecules in the breath sample. It expresses the result in terms of blood alcohol concentration.
Because all breath testing machines are essentially laboratory test devices, they require the same calibration and attention to detail as any laboratory equipment. If they are not calibrated correctly, if the sample is too small or is corrupted, or if the device is operated incorrectly, the results cannot be trusted.