The legal BAC limit for adult drivers in Texas is .08%. If you hold a commercial driver's license, the legal limit is .04%, even if you drive your private vehicle and not a commercial vehicle. If your BAC is .15% or above, you could face enhanced penalties raising a first DWI from a Class B to a Class A misdemeanor.
It's important to remember that both breath and blood tests for BAC can be inaccurate. An inaccurate breath test can be the result of:
- Problems with the machine
- Improper calibration and maintenance of the machine
- Improper storage of sensitive scientific equipment
- Improper training of the officer using the equipment
- Improper use of the equipment
- Something you ate, like very ripe fruits, kombucha, vanilla extract, protein bars, hot sauce, lip balm, vinegar, sugar-free gum, and yeast breads
- Something you used like mouthwash or cough and cold remedies
- Shallow breathing, holding your breath, or keeping your mouth closed
- Health conditions like diabetes, asthma, and acid reflux
While breath tests purport to be an accurate measurement of the alcohol in your blood, they don't actually measure the amount of alcohol in the blood or affecting the brain. A breathalyzer measures alcohol that evaporates from the blood system that travels into your airway. While police may assume that the amount of evaporated alcohol measured in a person's breath is the same as the amount in the blood, this is incorrect. Some studies show a margin of error of 50% for breath tests compared to blood BAC tests.
You also shouldn't assume that blood BAC tests are infallible. Some common problems with blood testing include:
- Improper storage and collection of samples
Collecting samples with a gap in time between the arrest and collection can lead to a blood sample with a higher BAC than you had while driving. Everyone metabolizes alcohol at different rates. Moreover, if a properly trained medical professional doesn't collect the sample, they may inadvertently compromise the blood sample's integrity. If blood samples aren't stored at the proper temperature, it can lead to fermentation and an inaccurate BAC.
- Chain of custody
If someone fails to seal a sample, mislabels it, or doesn't document the chain of custody, the sample can be compromised.
- Inaccurate blood test results
If delays occur before testing a blood sample, fermentation or other degradation can occur. Police and lab techs may try to account for this by using retrograde extrapolation, asking you for your height and weight and the time you were drinking. But these extrapolation methods don't account for specific medical conditions you may have or your individual metabolic rate.
RECOMMENDATION: Hire an attorney with experience interpreting and challenging police BAC measurements, including the science behind BAC measurements and technical knowledge of the instruments and testing processes involved.