Anthony R. Segura



Two Sugar Creek Center

77 Sugar Creek Center Blvd, Ste 565

Sugar Land, Fort Bend County, Texas 77478

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Alcohol Concentration

Chemical Testing in Texas

Under Texas law an individual is legally intoxicated if his alcohol concentration is .08 or greater.  Alcohol concentration can be determined by testing the blood, urine or breath.  “Alcohol concentration” means the number of grams of alcohol per: (1) 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 - Not Time of Test

An essential element of the crime of DWI is that the person is intoxicated at the time of driving.  Chemical tests 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 correlate the test result to alcohol concentration at the time of driving the prosecution may 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 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, what and when the person ate

Intoxilyzer 5000

Texas uses the Intoxilyzer 5000 to determine 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 then 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.   

The Intoxilyzer's manufacturer does not warrant that it is fit to accurately determine 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 determines 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.  

Free Consultation - Call Now

A failed breath / blood test does not mean automatic guilt.  The devices and procedures used to determine alcohol concentration are subject to challenge.  Sugar Land DWI Lawyer Anthony R. Segura offers a free initial consultation to discuss the circumstances of your case as well as the limitations of breath / blood testing instrumentation.  Call 281-242-7070 to schedule a free meeting with an experienced Fort Bend County DWI lawyer in Sugar Land, Texas 


Anthony R. Segura | 77 Sugar Creek Center Blvd, Suite 565 | Sugar Land, Fort Bend County, Texas 77478
Phone: 281-240-DWI-1 or 281-240-3941
Copyright © 2012. Anthony R. Segura. All rights reserved.