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Why are DUI breath tests inaccurate?

There are a number of different reasons why alcohol breath tests are unreliable indicators of blood alcohol content, and in the event of test, it's best to understand the nuances, capabilities and admissibility of the various types of breath tests.

Types of breath tests
There are a few different types of breath testing devices, each with their own capabilities and capacity for accuracy. The most common breath testers are evidential testers, non-evidential testers and disposable testers. Evidential testers are the most accurate, but require frequent maintenance and calibration, so they're are not particularly efficient for patrol officers to use. Non-evidential testers, on the other hand, are frequently used by police to determine intoxication.

A Preliminary Breath Test (PBT) performed by a police officer will most likely be conducted with a non-evidential tester. These devices are notoriously inaccurate, as they are designed to measure an alcoholic compound found in many places in nature, so there is a possibility of contamination.

Because of these inaccuracies, PBT tests can determine cause for arrest, but any BAC data is inadmissible in court. If you are nervous about taking a PBT test, many DUI lawyers note that the test is voluntary, and refusal to take it cannot lead to more than light fines a small fine. However, commercial drivers who refuse a breath test may be charged with a misdemeanor.

How does a breath tester work?
In essence, an alcohol breath tester detects the presence of methyl compounds in a person's breath. Most use a process called infrared spectroscopy, which produces frequencies and determines the type of molecules present in the air by looking at the way certain wavelengths are absorbed. DUI lawyers note that there are a number of pitfalls in the technology.

For one, contamination, especially among widely-used law enforcement PBT testers, is a possibility. The testers detect chemicals in the methyl group, which include gasoline, paint thinner and acetone, which can appear naturally in the breath of a diabetic. People who suffer from acid reflux disease may produce a false high BAC score as well. Lawyers also point out that a breath test is designed to determine the amount of alcohol in your blood, but measures it on your breath, a completely different source.

Because the device is making this conversion to determine sobriety, elements like the environment and a person's physiology will likely have an effect on her test results.