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Houston DWI Attorney for Breathalyzer Tests

Learn The Role Breath Tests Play in a DWI Arrest in Texas

In Texas, if you are pulled over for a traffic stop, and the police officer suspects you are driving while intoxicated due to alcohol, he or she will likely request that you perform field sobriety exercises. Depending on the outcome of those exercises, the officer will probably arrest you, because those exercises are designed to cause a person to fail. Sober people fail sobriety tests every day. Once under arrest, the officer will ask you to blow your breath into an Intoxilyzer, which is more commonly known as a breathalyzer. If the resulting breath alcohol concentration (BrAC) is at or above the legal limit, you are per se intoxicated in Texas. The good news is that the prosecution has to prove that you were intoxicated at the time you were DRIVING. The breath test is usually 45 minutes or longer from the time of driving. Breath (BrAC) and blood (BAC) alcohol legal limits in Texas are as follows:

  • 21 years old or older: 0.08%
  • Commercial driver (CDL): 0.04%
  • 20 years old or younger: any detectable amount

Many DWI arrestees assume that if they are tested with a BrAC number above the legal limit, they are automatically assumed to be guilty. Though the latter may be true—i.e., there's an assumption you are guilty—it does NOT mean you are in fact legally guilty. In fact, retaining a lawyer who has proven experience in DWI criminal defense and breath tests can be the difference between a DWI conviction and a dismissal of the charge or a not guilty verdict. Doug Murphy, a reputable DWI criminal defense lawyer in Houston, Texas, not only knows the law, the flaws, and inaccuracies associated with breath testing—Doug has a proven track record and reputation for successfully winning breath and blood test cases at trial.

Review the below information to learn more about how breathalyzers more often than you may think produce inaccurate results. That's something to think about when it comes to your DWI charge and your search for an experienced criminal defense attorney who can help maximize the possibility that your case will have a successful outcome. Contact Doug Murphy today to discuss the specifics of your case.

Breath Test Equipment Used in Houston, Texas

The Intoxilyzer 9000 is now the only breath test machine used throughout all of Texas. The machine has only been in use for a very short time in Texas, but other states, like Colorado, Georgia, and New York, have been using it for several years.

Like most older breathalyzers, the Intoxilyzer 9000 is based on the theory of infrared spectrometry (IR), the absorption of infrared light. The Intoxilyzer 9000 looks for the presence and amount of alcohol in a breath sample. It uses infrared light to both identify and quantify ethyl alcohol, because ethyl alcohol absorbs infrared light in a unique way. The pattern of absorption is used to identify alcohol, and the amount of absorption is used to quantify alcohol in a breath sample. The Intoxilyzer 9000 provides analytical results in grams of alcohol per 210 liters of breath, as required by Texas Penal Code § 49.01(1)(a).

Breath Testing: Machine Miscalculations & Unreliability

Breath testing is problematic for a number of reasons. First, a breathalyzer doesn't measure the amount of alcohol in either the brain or the blood. Breathalyzers measure alcohol that has evaporated from the blood system and then travels into the person's airway. But the machine (and police officers) assume that the amount of alcohol in the breath is the same as that in the blood. This is an incorrect assumption. Though the relationship exists, it varies according to multiple factors.

Factors Affecting the Relationship Between Alcohol in Blood and Alcohol in Breath

There are three main factors that can alter the link or relationship between alcohol levels in the blood versus what is determined on the breath via the breathalyzer: (1) temperature; (2) breathing technique; and (3) breath/blood partition ratio.


The temperature of your breath can make all the difference. The warmer your body temperature, the faster alcohol diffuses from blood into your lungs. The warmer your body temperature, the higher the BAC reading will be. Compounding this factor is the fact that our temperatures vary by degrees. The breathalyzer assumes your temperature is 34 C. Just one degree above 34 C is enough to increase a person's BAC by 7%.

Breathing Technique

The way you breathe can impact the BAC reading just as much if not more than body temperature. If you are a shallow breather, then your BAC results could be as high as 20% more than the true BAC level. Breathing is not controlled, and there is no method to determine how a person breathed at the moment they blew into the breathalyzer.

Breath-to-Blood Partition Ratio

The partition ratio is the fundamental principle behind breathalyzer technology. All breathalyzers used in any state of the United States, including Texas, proportion the relationship between breath and blood at 2100 to 1. Thus, for every part alcohol on the breath, there is 2100 times greater alcohol in the blood. The idea is simple using this ratio: if 2100 cubic centimeters of deep lung air was analyzed for alcohol, the result would be equal to the amount of alcohol in a milliliter of blood.

Studies, however, indicate the very opposite. Research has identified that this ratio is misleading, and something closer to the truth is a range rather than a strict ratio. This ratio range can be anything from 990 cubic centimeters of deep lung air to 3005 cubic centimeters of deep lung air representing 1 milliliter of blood. If your ratio is below 2100, which can very realistically be the case, then the BAC is artificially high, and your arrest could have been unwarranted. Your breath-to-blood partition ratio will vary from your mother's, your brother's, or your friend's, and it can even change for you over time.

This breath-to-blood partition ratio is further compounded by the stages of absorption. We all absorb alcohol at different rates. In fact, it can take anywhere between one and five hours to absorb alcohol fully if you consumed alcohol on a full stomach, and between one and two hours if you consumed alcohol on an empty stomach. Breath tests, however, assume that you are in the post-absorptive phase. Without knowing the absorption phase, it is nearly impossible to know if the BAC level is indicative of your actual state.

It's not that the breathalyzer machine, in this case, does not work, it's more about the purpose of its use not correlating or identifying properly with the results. The machines are designed only to provide an estimate, not a certainty, but officers use it as though the result is definitive.

Test Bias

Breathalyzers are not set for the average female, but for the average male. Females generally score higher on average than males, and the latter is in part the reason. In fact, the machine assumes each person blowing into it is of the same sex and average weight, and due to this assumption, results can vary, which also means it can vary on the side of error that is to your legal, emotional, and financial detriment.

Health Conditions

Your health or health condition at the time of the test can also impact the breathalyzer results. Specifically, a test may be affected if you have diabetes, heartburn, liver disease, gum disease, heart disease, fever, or, among other things, are on certain medications. Some diets even affect the test, specifically the ketogenic diet, which can have the same effect on the body as diabetes.

Radio Frequency Interference

The Intoxilyzer 9000 is susceptible to interference from radio frequency. If strong or close enough, radio frequency from a cell phone or a peace officer's radio can cause the instrument to malfunction. The 9000 is equipped with an automatic detection device, but it is not fully accurate. If interference happens, the BAC reading will be affected, and the results could be suppressed.

In Texas, the law and law enforcement are well aware of these problems, but they don't care; they care more about convictions. The Intoxilyzer 9000 allows for a variance of .20 between two breaths. As such, law enforcement can give you two tests, and the results may be within .02 of each other. This is a problem. Consider, if your first test was .08, and the second test resulted in a BAC at either .06 or .10, one reading establishes you below the legal limit while the other reading puts you well above the legal limit. Is this acceptable? According to Texas law and practice, it is. In fact, it is deemed "scientifically reliable," which means a charge and subsequent conviction could be left to chance, but for an experienced attorney, like Doug Murphy, who can recognize these problems and challenge them effectively.

Breath Testing: Poorly Maintained Breathalyzers

Not only can the breathalyzer produce inaccurate results when it is working properly, but it can also produce inaccurate results when it has not been maintained or calibrated properly. Breathalyzers are supposed to be maintained regularly, and if not, they become faulty. There are guidelines that advise how to maintain breathalyzers, including routine maintenance. There are a lot of things going on at a police station, and maintenance is often overlooked or neglected. When this happens, faulty results happen.

Breathalyzers ultimately require a lot of love and attention to work properly over time. If maintenance is not upkept, a breathalyzer's accurate functioning capabilities are reduced. Doug Murphy is the lawyer who can help you get your case dismissed. Of course, all cases are different with their unique facts and circumstances, but Doug Murphy is thoroughly knowledgeable of the faults and failures of breath tests, and he exposes these faults and failures strategically during your defense.

Breath Testing: Poorly Administered Tests

The Intoxilyzer 9000 is extremely new to the state of Texas, and all officers must be trained in its operation. As always, bad breath tests come down to the poor administration of the Intoxilyzer. Below are some things to keep in mind if you are requested to give a breath sample:

  • Did the officer observe the proper waiting period of 15 minutes before administering the test? The 15-minute waiting period, according to the Texas Breath Alcohol Program Operator Manual, is to "ensure that there is no residual (mouth) alcohol present."
  • Was the mouthpiece used or unused? A clean, unused mouthpiece must be used each time.
  • Was the officer certified on the Intoxilyzer? If not, he was not permitted to administer the test.
  • Was the external standard check results fall within an acceptable range? The standard range is .075 to .085; if it was not within this range, then that is grounds to suppress the results.

It should also be noted that there are other capabilities associated with the Intoxilyzer 9000 that could be useful, such as the ability to produce histograms. The state of Texas, however, has determined it will neither use the instrument to its utmost functionality nor provide all the information that the instrument is capable of producing.

Contact Our Houston DWI Lawyer for Breathalyzer Tests

At Doug Murphy Law Firm, P.C., we devote our resources and capabilities to defending our clients' rights. We have decades of proven experience and a reputation earned in the courtroom for successful results. Attorney Doug Murphy is a Board Certified criminal defense lawyer and a Board Certified DWI lawyer who not only fights on behalf of his clients but constantly gives back to the legal community to teach other attorneys how to do the same. Contact Doug Murphy online or at 713-229-8333 today to discuss the circumstances of your case.

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