HOUSTON/FORT BEND DUI/DWI

Anthony R. Segura

Anthony R. Segura

Fort Bend/HOUSTON DWI Attorney

Chemical Testing in Texas

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Under Texas law an individual is legally intoxicated if his/her alcohol concentration is .08 or greater. A person's alcohol concentration can be determined by testing the blood, urine or breath.  “Alcohol concentration” means the number of grams of alcohol per:

     (a)         210 liters of breath;

     (b)         100 milliliters of blood; or

     (c)            67 milliliters of urine.

Blood testing is generally considered to be the most reliable and accurate, while urine tests are regarded as the least precise.  If you are arrested for DWI in Texas you will most likely be asked to give a sample of your breath.  Breath testing is the most commonly utilized method because it is the least expensive to administer.  The scientific community is sharply divided over the accuracy and reliability of breath testing procedures.  The police do not save the sample of breath tested.  Thus it is not available for re-testing by an independent laboratory.  

Time of Driving vs. Time of Test

An essential element of the crime of DWI is that the person is intoxicated at the time of driving.  However, chemical tests only reflect a person's alcohol concentration at the time of testing.  A person's alcohol concentration at the time of driving may have been higher, lower or the same.  In order to link the test result to alcohol concentration at the time of driving the prosecution may attempt to present expert testimony concerning alcohol concentration at the time of driving.  The process the expert uses to relate the test result back to the time of driving is known as retrograde extrapolation.  However, in order for the expert to offer an opinion which will be admissible at trial, the court must find that the expert's opinion will be reliable.  Factors effecting reliability include:

          (a) the length of time between the offense and the test(s)

               administered;

          (b) the number of tests given and the length of time between each

               test; and

          (c) whether, and if so, to what extent, any individual characteristics

               of the defendant were known to the expert.  These

               characteristics and behaviors might include, but are not limited

               to,

1)      weight and gender

2)      typical drinking pattern

3)      tolerance for alcohol

4)      how much the person had to drink on the day or night in question,

5)      what the person drank,

6)      the duration of the drinking spree

7)      the time of the last drink, and

8)      how much and what the person had to eat either before, during, or after the drinking.

Intoxilyzer 5000 - Breath Testing Device

The State of Texas uses the Intoxilyzer 5000 to determine a person's breath-alcohol concentration.  The Intoxilyzer's manufacturer claims the device works on the principle of Infrared Spectrometry.  A sample of the subject's breath is collected in the device's sample chamber.  At one end of the chamber is a light bulb.  At the other end is a light detector.  The machine measures the amount of light that passes through the chamber when no alcohol is present.  This is this compared with the amount of light passing through the chamber after a sample of the subject's breath is introduced.  In theory, the alcohol in a breath sample will absorb some of the light, thus the less light that passes through a breath sample the higher the concentration of alcohol.  The Intoxilyzer has a computer chip which processes the results of the test to arrive at a specific alcohol concentration.  The calculations the device performs are unknown as the manufacturer refuses to release the computer code.   

You may be interested to learn that the Intoxilyzer's manufacturer does not warrant that it is fit to accurately determine the alcohol concentration in human breath.   In addition, there is no way to check the accuracy of results obtained by using this device because the State refuses to preserve breath specimens for future testing.   

Officer Decides Between Breath, Blood or Urine Test

Under Texas law the officer has the right to determine which type of sample to request.  For example, if the officer requests a breath sample and you will consent only to a blood test, your license is subject to suspension as a refusal.  However, if you submit to a chemical test you have the right to have a physician, qualified technician, chemist, or registered professional nurse take an additional sample of your blood for analysis.  Your request must be made within two hours of your arrest and the police are not required to transport you for testing.  

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