BAC or blood alcohol concentration is the measure of how much alcohol a person has in their system. Although two different people can experience very different effects from the same number of drinks, two people will experience more or less the same effects if they have the same BAC. This is why BAC is used as a measure in DUI cases—it is seen as more “scientific.” But the ways we test and prove BAC are not always so reliable.
In DUI cases, BAC is established one of two ways:
- By testing it directly in a blood test. This allows a lab to see exactly how much alcohol is in a given amount of your blood. If properly gathered, the blood sample will show BAC very reliably, albeit with some margin of error.
- By calculating it indirectly with a breath test. A breath test device uses an infrared scanner to see how much alcohol vapor is in the breath coming from deep in the lungs. It then uses a formula to estimate how high BAC must have been to exhale that much alcohol vapor. This formula is fairly accurate for most people, but breath tests are not as reliable as blood tests.
In some cases a urine test can also be used, though this is less common.
All of these methods of testing are open to errors, especially when police officers or lab technicians do not follow state-required rules known as Title 17 rules.
How does BAC affect my DUI case?
In California, BAC is the heart of most DUI cases. For example:
- If your BAC was .08% or above, you ca be convicted of DUI. But if your BAC was below .08%, the prosecution has to prove you were impaired in order to convict you.
- If your BAC was .15% or more, or .20% or more, you have “excessive BAC” and will face extra penalties. If convicted of a DUI with .20% BAC or higher, you will also face mandatory alcohol treatment.
- If you can establish that your BAC was right around the .08% mark, you can often negotiate a generous plea bargain for a non-DUI charge. If there is no evidence of your BAC at all, you may be able to get your case dismissed.
One of the most important moves your DUI lawyer can make is to attack the BAC evidence, either by attacking the blood test or the breath test, and try to get it suppressed. If the prosecution cannot use the test results, their case against you frequently collapses.
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