Part 5: How does a DWI (driving while intoxicated) investigation in Austin, Texas work? Basics of the Breath Test

DWI, Austin, Breath Test, breath alcohol

Posted on: November 11, 2013



Chapter 72, Section 724.016 of the Texas Transportation Code provides that the analysis of the breath specimen in a DWI arrest in Texas.  Here are some of the highlights.  Breath testing in Texas must be performed according to the rules of the Texas Department of Public Safety and by an individual possessing a valid certificate issued by the Texas Department of Public Safety for this purpose.

The Department has created the Office of the Scientific Director, Breath Alcohol Testing Program, as the responsible officer to administer these regulations and qualifications.  The Science Director will hold at least a bachelor’s degree with a major in chemistry, or as an alternative a major in another scientific field with a minor in chemistry, and in addition, he or she must have specialized knowledge in the area of alcohol testing. 


The Office of the Scientific Director, Alcohol Testing Program, Texas Department of Public Safety (hereinafter referred to as the scientific director) shall approve and certify all breath test instruments to be used for evidential purposes.

In order to be approved each instrument must meet the following criteria:

1.            Breath specimens collected for analysis shall be essentially alveolar (deep lung) in composition.

2.            The instrument shall analyze a reference sample or analytical test standard the result of which must agree plus or minus 0.01g/210l of the predicted value or such limits as set by the scientific director.


1.            a period during which an operator is required to remain in the presence of the subject.  An   operator shall remain in the presence of the subject at least 15 minutes before the test and should exercise reasonable care to ensure that the subject does not place any substances in the mouth.   Direct observation is not necessary to ensure the validity or accuracy of the test result; 

2.            the breath alcohol testing instrument and reference sample device must be operated by either a certified operator or technical supervisor and only certified personnel will have access to the instrument;

3.            the use of a system blank analysis in conjunction with the testing of each subject;

4.            the analysis of a reference sample, the results of which must agree with the reference sample predicted value within plus or minus  0.01g/210 L, or such limits as set by the scientific director.   This reference analysis shall be performed in conjunction with subject analyses;

5.            all analytical results shall be expressed in grams of alcohol per 210 liters of  breath (g/210 L);

6.            maintenance of any specified records designated by the scientific director;

7              supervision of certified operators and testing techniques by a technical supervisor meeting the qualifications set forth in section 19.6 of this title (relating to Technical Supervisor Certification);

8.            designation that the instrumentation will be used only:

                A.  for testing subjects that are suspected of violating any statute or rule that defines intoxication in terms of alcohol concentration;

(h)          Technical supervisors, when required, shall provide expert testimony by direct testimony or by written affidavit concerning the approval of techniques, methods and programs under their supervision. 

Rule 19.5 Operator Certification

3.            Prior to initial certification as an operator of a breath test operator an applicant must successfully complete a course of instruction meeting the criteria set forth in section 19.7 of this title (relating to Approval of Courses of Instruction).

4.            Prior to certification as an operator of a breath alcohol testing instrument, an applicant must satisfactorily complete examinations, prepared and given by the scientific director or a designated representative, which shall include the following:

                (A)          a written examination;

(B)          a practical examination establishing proficiency in the operation of the instrument and reference sample device on which the operator is to be certified and the proper completion of all required reports and records.  The practical examination will involve the completion of simulated subject analyses and/or practical test (s).  If the simulated subject analyses and/or practice tests are not completed correctly and/or there are one or more errors in the reports or records the applicant will be offered a second set of simulated subject analyses.  Any error(s) in the second set of analyses will result in a failure of the practical examination;

(C)          failure of the written and/or practical examination will cause the applicant to be ineligible for reexamination for a period of 30 days.  A subsequent failure will require that the candidate attend and satisfactorily complete the initial course of instruction for certification of a breath testing operator.

5.            Upon successful completion of the requirements for certification, the scientific director will issue the individual an operator certificate valid for a period of time designated by the scientific director or until the next examination for renewal unless inactivated or suspended. 

(1)          A practical examination in accordance with subsection (a)(4)(B) of this section establishing proficiency of the operator in the operation of the instrument and reference sample device on which the operator is certified and the proper completion of all required reports and records.  The operator will be evaluated on the basis of the ability to:


                (A)          use proper techniques;

(B)          follow established procedures including, but not limited to, the operation of the instrument and reference sample device and the proper reporting procedures for analysis results;


(2)          The satisfactory biennial completion of a course of instruction, the contents of which should include, but not be limited to topics such as:


                (A)  a brief review of the theory and operation of the breath alcohol test equipment;

                (B)  a detailed review of the breath alcohol analysis and reporting procedures;

                (C)  a discussion of procedural updates resulting from recent court decisions and legislation;

                (D) a discussion of current issues in the field of breath alcohol testing;

                (E)  a written examination.

 (8)         expert testimony by direct or by written affidavit concerning all aspects of breath alcohol testing within an assigned area.

(A)          advanced survey of current information concerning alcohol and its effects on the human body;

(B)          operational principles and theories applicable to the program;

(C)          instrument operations, maintenance, repair and calibration;

(D)          legal aspects of breath alcohol analysis;

(E)          principles of instruction;

(4)          knowledge and understanding of the scientific theory and principles as to the operation of the instrument and the reference sample device;

The course must include:

               (1)  three hours of instruction on the effects of alcohol on the human body;

                (2)  three hours of instruction on the operational principles of the breath alcohol testing instrument to be used.  This instruction shall include:

                                (A)          a functional description of the testing method; and

                                (B)          a detailed operational description of the method with demonstrations;

                (3)  five hours of instruction on Texas legal aspects of breath alcohol testing;

                (4)  three hours of instruction on supplemental information which is to included nomenclature

                     Appropriate to the field of breath alcohol testing;

                (5)  10 hours of participation in a laboratory setting operating the breath testing equipment. 

Laboratory practice will include the analysis of reference samples, as well as the analysis of breath samples from actual drinking subjects and completion of all required records and reports needed for documentation;

                               (6)  examination time (approximately three hours) which will be considered part of the course.

Chapter 49 of the Texas Penal Code covers all of the Intoxication and Alcoholic Beverage Offenses.   

Legislatively, the State of Texas has “Alcohol Concentration” in Section 49.01 (1) “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. 

The statutory definition of “Alcohol Concentration” sets a uniform partition ratio in all human beings in Texas as 2100 milliliters of breath is equal to 1 milliliter of blood.  The breath testing instruments used in Texas are programmed as such.  This is despite the fact studies show variance in partition ratios.  One study by Kurt Dubowski, showed a range of 1706 to 3063 to 1 partition ratio for a sample of healthy adult males in the full post absorptive state under laboratory conditions.   Another study by A.W. Jones, showed partition ratios with ranges between 1837 and 2863 in the post absorptive state and 990 to 2863 while in the absorptive phase.

This is a pretty hyper-technical analysis of attacking the partition ratio in breath testing machines, but it is relevant.  Legislatively, the 210 liters of breath was chosen as an average partition ratio based at least partially on a recommendation from Dubowski.  The problem with averages is that once you start using them the numbers you achieve based on those averages are flawed. 

See, Clinical Chemistry, Vol. 33, No. 2, 1987, 261-268 “Accuracy and Precision of Breath-Alcohol Measurements for a Random Subject in the Postabsorptive State,” by G. Simpson for more comprehensive information on the subject of partition ratios.

Now that we have talked about some of the basic legal concepts behind breath testing in Texas, we will talk more comprehensively in our next Blog the “Texas Breath Alcohol Testing Program” and the used of the Intoxilyzer 5000, which is the chief breath testing device used in the State of Texas.  


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