Oklahoma DUI Intoxilyzer Breath Test Accuracy

Is an Intoxilyzer 5000/8000 breath test accurate?

How seldom a fact is accurately stated;
How almost invariably when a story has passed through the mind of a third person it becomes…
little better that a falsehood;
even though the narrator
is the most truth-seeking person in existence.

Many people, including lawyers, will look at a breath test result and say, “Oh, you scored a high number, you’ll be convicted”.  THIS DOES NOT HAVE TO BE TRUE, but it does show a total lack of understanding of the testing process and procedures.  We have trained extensively, understand how the machines work, and know what problems can occur in them and how to fight for you.

Your lawyer’s knowledge in this area of DUI litigation often is the difference between a conviction and being found NOT GUILTY.


  • Oklahoma law provides that a suspect can be tested by blood, breath or both.
  • Blood testing is generally considered to be the most reliable and accurate method. However, this is the least desirable for the police because it is more expensive and time consuming.  Additionally, blood testing would allow you to have a second test performed on your blood sample by your own expert.
  • Breath testing is more convenient, cheaper and is not subject to retesting. The machine is capable of preserving a sample.  The law allows retesting of any saved sample but it costs about $2 to retain the sample and no agency is willing to spend the money or subject itself to being rechecked.

To be clear, the police use the cheapest, most convenient, non-testable, scientifically debated chemical test when your freedom is on the line.

How is breath testing done?

  • Oklahoma uses two machines called, the Intoxilyzer 5000-D and the Intoxilyzer 8000, which are commonly called the “breathalyzer”. (Often called the Intoxiliar because of its inaccuracies.)
  • The Intoxilyzer 5000D costs about $7,500. Some models have been in service for 15 or more years.
  • The Intoxilyzer 5000-D is simply a computer based on very old technology. The brain of this thing is a Z-80 microprocessor, which was introduced in 1975, more than 30 years ago. Remember the “Radio Shack” TRS-80? Its processor was the Z-80.
  • The machine works on the theory of Infrared Spectrometry (IR), which is the absorption of infrared light. There is a light bulb at one end of the breath cylinder and at the other end is a filter wheel with three filters.  As you blow into the tube, the theory is that alcohol will absorb the light rays and not show up on the filter wheel.
  • The amount of breath actually measured is very small (only 81 cc.) and must be converted to a number we will understand. The conversion the machine makes would be similar to taking a paper towel tube and increasing it to the size of a 55-gallon drum.  Any error in the testing will be exaggerated by that amount.
  • The Intoxilyzer 8000 is the newest machine in Oklahoma and is touted as being greatly improved. Our experience with the machine has shown that it is actually LESS reliable in some areas. Bruce and John are the only attorneys in Oklahoma to own these machines and there are only ten owned by private attorneys in the world.  John and Bruce are the only Oklahoma attorneys who have taught other attorneys in Canada and throughout the US how the 8000 works and the problems with the machine.

How reliable is the breath test?

  • Close enough for government work! In Oklahoma, you will be given two tests and those tests must be within .03 of each other.  If your first test was .08, an acceptable second test could range from .05 (not intoxicated) to .11. This is a range of 75% and they tout the machines as being scientifically accurate? Would you accept such a variance from a thermometer, speedometer, medical test or toaster? Obviously not, but our state finds this “scientifically reliable” and acceptable when dealing with your personal liberty.
  • What are they hiding? Neither the State nor the manufacturer of the machine will allow anyone other than law enforcement to test the machine for its accuracy and reliability.  For a procedure to be accepted as accurate and reliable in the scientific community, it must be open and available for the scientific community to test and retest the procedure.  This is not permitted with the Intoxi-liar.
  • 2+2=5. Is this government math?  The number produced by the machine comes from a mathematical formula in the machine.  The manufacturer will not divulge this formula, claiming it is ‘proprietary’.  At this point, neither the government nor the courts are willing to divulge the secret formula that is used to determine your test value.  Literally—you could go to jail based on a secret formula!!
  • Why don’t they save a sample when your freedom is on the line? A sample of your breath could be saved for retesting for about $2, but the State chooses not to save it.  The courts have said they should save evidence, but if it is not saved, that’s okay.
  • A few of the many other issues that can affect the accuracy of a breath test are:
  1. Power surges
  2. Cell phones
  3. Body temperature
  4. Breath temperature
  5. Machine temperature
  6. Simulator solution temperature
  7. Radio frequencies
  8. Mouth contaminates (smokeless tobacco, dentures, denture adhesives, mints, lip balm, etc.)
  9. Physical problems
  10. Exposure to certain chemicals
  11. Diabetes
  12. Esophageal hernia
  13. Heartburn
  14. Liver disease
  15. Certain diet
  16. Disease of the lungs
  17. Periodontal (gum) disease
  18. Faulty bridge work
  19. Gastric reflux disease
  20. Fever
  21. Pre-menstrual
  22. Heart disease
  23. Airbags
  24. Certain medications
  25. Machine malfunctions
  26. Improper maintenance, and
  27. Improper training

The defense of a DUI case requires specialized knowledge about physics, chemistry, biology, anatomy, toxicology, pharmacology, and how these scientific disciplines interrelate.  Chemical testing for blood alcohol levels assumes that the subject is a:



            Average Person.

People are not the same and everyone’s body does not react in the same manner.  Common sense tells you this is true, yet the Government will prosecute as if you are identical to the “average person” in the State. Payton Manning averaged 357 yards per game last year but there was not a single game in which he threw for 357 yards. This is the same with the test. They are designed around an “average person” but you are never tested to see if your body is responding in an “average” manner.

Female Issues

Social Issues

Men account for an overwhelming majority of those arrested for DUI.  However, the percentage of female arrestees has increased rapidly in the last two decades. There are several social and psychological factors that account for the growing number of women accused of DUI.

Law enforcement officers’ attitudes towards women have changed over the past few decades.  It was once more likely for an officer to ensure that a female drunk driver got home safely rather than put her in a jail cell.

There is no doubt that the changing role of women in American society has played its part as well.  More women are in the workforce and subjected to the same stress as men.  These changing lifestyles leave women, like men, in situations that are more conducive to DUI arrests.

Gender/Test Bias

While the above issues are factors, the most pressing issue is test bias.  Studies have shown that women tend to score higher on breath testing machines.  This is because the machines are set for an average male’s lung capacity. This is inherently unfair to women and should be addressed by your lawyer.

Alcohol also affects women differently than men because women metabolize alcohol more slowly.  Women have less of the ADH enzyme.  This causes a larger proportion of the ingested alcohol to reach the blood system prior to being converted to acetate.  Also, women may experience fluctuations in hormone levels during their menstrual cycle that can affect the rate of alcohol metabolism.  This may make a woman more susceptible to elevated blood alcohol concentrations at different points in the cycle.

Due to many things that an expert DUI lawyer will know, a woman of the same size and drinking the same amount as a man will often show a higher BAC reading.  Men and women’s bodies are not the same but the machine used by the police assumes they are. You should consult a DUI attorney who is capable of protecting you from this bias.

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