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Dallas Criminal Lawyer | Fort Worth Criminal Lawyer 

Courts have held breath testing science to be admissible.  The test for admission of scientific evidence are:

  • The underlying scientific theory must be valid
  • The technique applying the theory must be valid
  • The technique must have been properly applied on the occasion in question.

Breath Test Predicate

  • The proper use of a reference sample
  • The existence of periodic supervision over the instrument and operation by one who understands the existence the scientific theory of the instrument.
  • Proof of result of test by witnesses or witnesses qualified to translate and interpret the result so as to eliminate hearsay.

Testimony of an Intoxilyzer operator and a technical supervisor that an instrument was periodically tested to make sure it was working properly; that a test sample run demonstrated the machine was working properly; that the operator had been trained in the operation of the machine. and that the technical supervisor was certified by DPS, was sufficient predicate to admit the results of the Intoxilyzer tests.

Breath v. Blood Options

Although the implied consent statutes discuss options of using breath or blood gets the statutes do not give the suspect the right to choose one type of test or the other.  A police officer arresting a suspect for DWI is entitled to choose between asking as suspect to take a breath or blood test.  The officer need not track the language of Transportation Code Section 724.012 and ask the defendant to take a breath or blood test.  An officer does not have to give Miranda warnings to a suspect before asking for a breath sample.  A suspect does not have the right to counsel before deciding whether to give a sample   An invocation of the suspects right to an attorney will not later exclude evidence of a refusal to take a breath test.

Once the alcohol moves from the stomach into the blood, it will be distributed throughout the body by the blood.  Blood will carry alcohol to the various tissues and organs of the body, and will deposit the alcohol anthem in proportion to their water contents. Fat tissue contains very little water.  Thus very little alcohol will be deposited in the drinkers body fat.  As soon as the alcohol enters blood stream, the body starts trying to get rid of it.  Most of the alcohol a person drinks is eliminated by metabolism.  Metabolism is a process of chemical change.  Most of the metabolism of alcohol in the body takes place in the liver.  The speed of the reaction varies somewhat from person to person, and even form time to time for any given person.  On the average, however, a person blood alcohol concentration will drop by about 0.015 per hour. For example, if the person reaches a maximum BAC of 0.15, it will take about ten hours for the person to eliminate all of the alcohol.

Breath Test Facts

For the average sized male, a BAC of 0.015 is equivalent to about two thirds of the alcohol content of a standard drink (about two thirds of a beer, or glass of wine or shot of whiskey) For the average sized female, that same BAC would be reached on just one-half of a standard drink.  So the typical male will eliminate about two thirds of a drink per hour, while the typical female will bur up about one-half of a drink per hour.  It is the law that a BAC of 0.08 makes it unlawful to operate a vehicle.  But it is also unlawful to drive when under the influence of alcohol, and the law admits the possibility that a particular person may be under the influence at much lower BACs.  It depends on how much time the person spends drinking, or whether the person is a man or a woman or how large the person is, or whether the drinking takes place on an empty stomach, and certain other factors.

Breath Alcohol Testing

In Texas, a breath test or field sobriety test does not automatically prove you are guilty.  The weight of the chemical test evidence is presumptive of alcohol influence, not conclusive.  If there is no evidence to the contrary, the court may accept the legal presumption and conclude that the driver was or was not impaired on the basis of the chemical test alone. However, other evidence, such as testimony about the driver’s appearance, behavior or speech, for example, may be sufficient to overcome the presumptive weight of the chemical test.  It is possible for a person whose Alcohol Concentration at the time of arrest is above the per se or presumptive level legal limit to be acquitted of DWI. It is also possible for a person whose Alcohol Concentration at the time is below the per se or presumptive level to be convicted of DWI.

Evidentiary breath alcohol testing for traffic law enforcement utilizes instruments that determine the alcohol concentration in the breath of a subject.  Some use principles of spectroscopy, while others utilize gas chromatography. The instrument will accept a breath specimen if the subject maintains the minimum pressure continuously for at least five seconds, and if the alcohol concentration is changing by no more than 0.01 per second at the conclusion of the specimens delivery.  If these conditions are not met, an invalid test results.There are numerous fail safe features designed to test the accuracy and to increase the validity of the test.  If all tests pass, the instrument continues with the testing sequence.  In the course of the test, the instrument continues to check against unfavorable conditions that could affect the test.  It analyzes the contents of the sample chamber after each air blank to ensure that nothing remains that  would absorb the light.  The instrument also conducts a reference analysis on a solution with known alcohol concentration as a calibration check, requiring that the results be within 0.010 of the predicated value. Finally the instrument compares the results of the two subject specimens and requires that the two results, to be valid, differ by no more than 0.20.  If any improper testing condition or environmental source of error is detected, the instrument invalidates the test,  If a test is invalidated, the instrument will not print any test results.  Rather, INVALID TEST will appear on the test record, along with the reason for the invalidation.  A test record is said to be VALID if it has no invalidation messages, if the results are clearly printed, if all blank results are 0.00 and if it was signed by the operator.  The test record is INVALID if one of those four conditions are not met.

A breath alcohol test must be administered according to the rules established by the Texas Department of Public Safety.  A certified operator must conduct the test on a certified instrument used in a certified testing program that is under the supervision of a certified Technical Supervisor. An operator must remain in the presence of the subject for at least 15 minutes prior to the test and must exercise reasonable care that the subject places nothing in the mouth.  The operator must also use a fresh, disposable mouthpiece for each breath specimen tested.

Intoxilyzer Operator

All that is required is that the operator be certified and able to testify that the protocol for administering the breath test was followed.

Technical Supervisor & Instrument Certification

The technical supervisor’s job is to set out the safeguard in the intoxilzyer instruments and to vouch for the maintenance records for that particular instrument.  The technical supervisor will also be able to give an opinion as to the defendant’s intoxication and talk about retrograde extrapolation, if the relevant factors are known about the defendant.

The technical supervisor needs to bring certification records to court and answer questions that establish that the instrument was working properly onteh day the defendant submitted a breath sample.

Certification and maintenance records of breath test machines are admissible to show that the Intoxilzyer machine used to test the defendant’s alcohol concentration was working properly.  When a police agency substitutes one approved brand of breath testing equipment for another, the department needn’t reapply for certification of the entire breath testing program.  A new technical supervisor can lay the predicate for old tests by relying on the previous supervisor’s record as a basis for his opinion that the breath test machine was working properly.

It is no longer necessary for the defendant to be observed continuously for 15 minutes before the jury can consider the intoxilyzer result.  The rules still require the operator of the test to remain in the presence of the subject at least 15 minutes before the test.  Where a fact is raised with respect to this requirement, a defendant is entitled to an instruction that the jury disregard the test if it believes or has a reasonable doubt as to whether the 15 minute observation requirement was met.