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DWI / DUI Chemical & Breath Tests

Generally, the most important piece of evidence in a Texas DWI case is the result of a breath, blood or urine test. It is important to understand the reliability issues of these tests and that there are ways to challenge the evidence collected against you. For example, the results of a Texas DWI breath test may be challenged if the test was given immediately after you belched or vomited because that can skew the results.

Depending on the facts of your case, your attorney may be able to challenge the accuracy of the test results, the way the blood or breath test was conducted, or how the evidence was handled. If you have been arrested and charged with a DWI, you should contact an experienced DWI attorney at (713) 222-6767 as soon as possible to determine your best legal options.

How BAC is Measured in Texas

Blood alcohol concentration can be measured using blood, breath or urine tests. Under Texas Penal Code Section 49.01(1), alcohol concentration means the number of grams of alcohol per:

  • 210 liters of breath;
  • 100 milliliters of blood; or
  • 67 milliliters of urine.

Blood tests measure blood alcohol concentration (BAC) directly while urine and breath tests provide indirect measurements. These chemical tests can be administered in addition to or in lieu of a field sobriety test, and the officer decides which test to offer. If you provide a BAC sample of .08 or more on any one of these tests, you are considered legally intoxicated and can be arrested for a DWI.

However, it’s important to know that even if you “pass” the test with a BAC of less than the .08 Texas legal limit, you still may be arrested if there is evidence that proves beyond a reasonable doubt that you lost the normal use of your mental or physical faculties was impaired by the consumption of alcohol.

Texas Legal Limit for BAC

The Texas legal limit for blood alcohol concentration is .08. This is determined using blood, breath or urine tests. While anyone who has a blood alcohol concentration (BAC) of .08 or more meets the definition of intoxicated, it is important to understand that a person may be arrested for a DWI with a BAC of less than .08 if he or she has ingested alcohol, a controlled substance, or a drug that resulted in the loss of normal use of mental or physical faculties.

Texas considers those under age 21 to be minors for purposes of DWI laws and any detectable amount of alcohol while operating a vehicle in a public place would constitute a DWI offense. For commercial drivers, the legal BAC limit is .04 and a DWI will result in your CDL being disqualified for 1 year or 3 years if you drive hazardous materials.

Increased Penalties for BAC of .15 or more

In September 2011, Texas lawmakers passed a new law that enhanced the penalties for people charged with their first DWI who have an “extreme” elevated blood alcohol level (Texas Penal Code Section 49.04(d)). Committing a DWI with a BAC of .15 or more is a Class A misdemeanor, which carries penalties upon conviction of:

  • A fine of up to $4,000
  • Up to 1 year in jail
  • Suspension of your driver’s license for up to 1 year

In addition to the penalties mentioned above, the court is required to order installation of an ignition interlock device for a 1-year period following license suspension for drivers with a BAC of .15 or more. The ignition interlock device requires a deep lung air sample to start the vehicle and periodic breath samples to monitor sobriety throughout the operation of the vehicle. You will be required to pay both the license reinstatement fees and the interlock license fee along with any costs necessary to maintain the device.

On top of the fines and legal fees associated with a DWI conviction, you will also have to pay DWI surcharges. DWI surcharges are essentially fees that you must pay annually for three years following a DWI conviction. Normally, surcharges increase with the number of DWI convictions. However, if you have a BAC that registers at or above .15, you will be required to pay $2,000 a year for three years regardless of the number of prior convictions on your record. If you fail to pay the surcharge within the required timeline, your license will be suspended.

Use of a Texas DWI Breath Test

Law enforcement officials in Texas most often use the Intoxilyzer 5000 machine to measure the blood alcohol concentration of suspected drunk drivers. The technology, which relies on a theory of infrared spectroscopy, was invented in 1984 and there have been very few updates since that time. The reliability issues for this technology are numerous and studies have shown a standard margin of error of approximately 20 percent.

Furthermore, the machine cannot differentiate between ethanol and other substances present in the mouth. The presence of mouthwash, dental work, or chewing gum may read as ethanol and result in elevated results. If someone’s temperature is above the standard 98.6 degrees, this could also result in a higher BAC reading.

Additionally, if the machine is not properly maintained, cleaned, or calibrated, the results could be compromised. A number of other factors such as weight, physical limitations or underlying medical conditions may also negatively impact a person’s results on a Texas DWI breath test.

Use of a Texas DWI Blood Test

The method used to analyze blood samples is gas chromatography and it is a direct way to measure blood alcohol concentration. Blood tests tend to be the most accurate of the three forms of chemical testing. A blood test usually is administered later in the investigation process than a breath test.

If the officer chooses to offer a blood test, he or she must first ask if you are willing to submit to a blood test. If you refuse a blood test, the officer must obtain a warrant before the blood can be drawn. In order to obtain the warrant, the officer must have probable cause to believe that you were driving while intoxicated.

There are numerous ways in which human error during the collection, handling, testing, or analysis phase can compromise blood test results. For example, contamination could occur if an antiseptic wipe is used to clean the area before the blood draw or if the equipment used to draw the blood is not sterile.

Similarly, if the sample was not properly stored either before or after arriving at the lab, the sample would be contaminated and cannot be accurately analyzed. It is also possible that certain medications may have an impact blood test results.

Use of a Texas DWI Urine Test

Urine testing is the least accurate of the three testing methods for measuring alcohol concentration. For this reason, urine tests are rarely used to measure alcohol concentration and are more likely to be used for drug testing purposes.

Urine tests are unreliable because the percent of alcohol in a person’s urine fluctuates greatly depending on bladder function and does not directly correlate with blood alcohol levels. Some studies have shown that alcohol content in urine is about 1.33 times the alcohol levels found in the blood. Aside from this, urine samples can also be contaminated due to errors in the lab.

Learn How a Houston DWI Attorney Can Help You

When you have been charged with a DWI, you need an aggressive and experienced DWI attorney on your side. Houston DWI defense attorney Ned Barnett has decades of experience in defending clients accused of DWI and he has a successful track record of challenging DWI evidence. Mr. Barnett is a board certified criminal lawyer and has certifications in DWI field sobriety testing, breath tests, and gas chromatography, which is the process used for DWI blood tests.

Ned Barnett has nearly 30 years of legal experience, which includes trying criminal cases as a state and federal prosecutor and more than 20 years as a criminal defense lawyer. Mr. Barnett is a knowledgeable and dedicated legal advocate who will fight aggressively to help you get the best possible outcome in your case.

If you or a loved one have been charged with a DWI, contact the Law Offices of Ned Barnett today at (713) 222-6767 to schedule a free, no-obligation, review of your case.