Breath Tests

When you are stopped by the police and arrested for DWI, you may find yourself confronted with an officer requesting that you provide a breath test to determine the amount of alcohol in your system. If you consent to the test and if your results are above the legal limit, all is not lost and the results do not mean you will be convicted. At this point, you need to hire an experienced lawyer who knows how to fight DWIs with breath test results.

When you hire The Wilder Law Firm, you will be putting more than 25 years of experience working with DWIs and breath results to work for you. We have received extensive training in the science of breath testing, and will apply that knowledge to the facts of your case to determine the admissibility and/or validity of your breath results. Call us at 469-551-8609 and let us fight for you.

What is a Breath Test?

Although there are many makes and models of breath test machines, Texas uses the Intoxilyzer 9000 which operates on the theory of infrared spectroscopy. Infrared Spectroscopy is based on the principle that alcohol vapor (i.e. breath alcohol) passing through a sample chamber will absorb certain wavelengths of light. At one end of the chamber is a light source and at the other end of the chamber is a light receptor. The more alcohol that is present in the breath, the more light that will be absorbed as the breath passes through the sample chamber, thus fewer wavelengths of light will be detected by the receptor. A calculation is then performed by the machine that calculates the loss of light to an alcohol concentration.

Here is How We Challenge Breath Tests

There are many issues that can affect the accuracy of a breath test. Just looking at a printout with a number on it does not tell the whole story. There are many factors that can affect breath results that will be thoroughly investigated, but the initial inquiry always starts with making sure legal consent for the test was given. Here are some of the issues we will investigate to determine the admissibility and/or accuracy of your breath test:

  • Consent.
  • Breath or blood partition ratio.
  • Mouth alcohol.
  • Diabetes.
  • Testing while still absorbing alcohol.
  • Body temperature.
  • Breathing pattern.
  • Interferents such as acetone and acetaldehyde.
  • Radio frequency.
  • Maintenance and repairs.
  • Calibration and simulator solution.
  • 15 minute observation period.


In order for a breath test to be admissible, a person’s consent has to be freely and voluntarily given. If an officer tries to coerce a person into submitting to a breath test, the results could be inadmissible. An officer cannot tell a person if they pass the breath test, they will let them go, or that they will not be charged. The only information an officer can provide a person when asked to submit to a breath test are the consequences of failing or refusing the test as it applies to their driver’s license.

Blood/Breath Partition Ratio

The alcohol concentration in your breath is directly proportional to the alcohol concentration in your blood. This assumption is based on Henry’s Law which basically states that at a constant temperature (here 34 degrees celsius), the amount of alcohol in the blood will be proportional to the amount of alcohol in the breath. The accepted ratio is 2100:1. This means that 1 milliliter of blood has 2100 times more ethanol than 1 milliliter of breath from the lungs. Studies have shown that this ratio can vary between 1500:1 and 3000:1. When the breath machine is assuming a 2100:1 ratio and a person’s actual ration is 2200:1 or higher, an inaccurately high result will be reported.

Mouth Alcohol

If any alcohol gets regurgitated or burped back up into the mouth before a breath test, an inaccurate high reading can occur. Close attention has to be paid to what the person is doing on video before the breath test to ensure mouth alcohol does not play a role in a test.


Breath machines do not actually test for alcohol. They actually test for a molecule with a carbon/hydrogen bond. People in a state of Ketoacidosis could have a breath test result affected by that condition alone. Ketones can be read as alcohol by the breath machine, and diabetics can have higher amounts in their breath.

Testing While Still Absorbing Alcohol

Complete absorption of alcohol can take anywhere from 30-120 minutes. Food in the stomach is a main factor that can slow the absorption of alcohol. During the absorption phase, there is a difference in the amount of alcohol in the arteries and veins.

Body Temperature

A normal temperature is 37 degrees Celsius (98.6 degrees Fahrenheit).  For every 1 degree Celsius (1.8 degrees Fahrenheit) increase in body temperature, the 2100:1 partition ratio is affected and the breath results can increase as much as 7%. This might not play a major role with a BAC of .19, but it could play a huge role with a BAC of .083 (guilty or not) or a .155 (enhanced penalties to a Class A misdemeanor and mandatory breath device in your car).

Breathing Patterns

Your breathing pattern can affect the accuracy of a breath test. If you take a deep breath and hold it in before you blow into the machine, your breath results will be higher then if you just blew in a normal fashion. If you hyperventilate and are breathing heavy and fast before you blow, your results will be lower. I conducted my own personal study when being trained on intoxilyzer machines and found both to be true.

Interferents – Acetone and Acetaldehyde

Interferent detectors are put in breath machines to try and prevent other substances from being identified as alcohol. Acetone and Acetaldehyde can be read as alcohol by the breath machine, and if present with a non working interference detector, an inaccurate result will occur.

Radio Frequency

Believe it or not, radio frequency can be read as alcohol on a breath machine. The machine has a radio frequency interference detector in it to try and prevent radio frequency from affecting a test. Cell phones give this off and can affect a test.

Maintenance and Repairs

Maintenance and repair records of the machine have to be thoroughly investigated. I have seen machines where certain parts keep failing and need to be replaced. A pattern of constant “repairs” can raise a doubt as to the machine’s ability to provide accurate results. I have had cases where parts have failed right after my client gave a breath test. When parts finally quit working, it usually indicates that the part was in decline and not functioning as it was supposed to for some time. Thus it could have affected the results of my client’s test (raising doubt).

Calibration and Simulator Solution

The accuracy of any breath test depends on the accuracy of the machine’s calibration. If a machine is not properly calibrated, any results would not be reliable. Simulator solution calibration is always investigated. If the solution was not calibrated correctly, you will not be able to get an accurate result. Something as simple as investigating the expiration date can play a role in how reliable a breath result is.

15 Minute Observation Period

There is a 15 minute observation period where the breath operator has to be in the presence of the person giving the test. If this is not adhered to, the breath expert will not sponsor the test. I have had tests where the operator leaves the room or allows the person to use the restroom which is attached to the room the breath machine is in, thus not being in the presence of my client for the mandatory 15 minutes.

Our #1 Goal is Protecting Your Future

There are many issues when it comes to breath testing that must be investigated in order to most effectively represent someone accused of DWI. Your alcohol concentration only tells part of the story, and results above the legal limit do not mean you will get convicted. We have a vast amount of experience and have successfully fought breath test cases for more than two decades. With so much on the line, don’t trust your future to just any lawyer. Contact us at 469-551-8609 for the professional representation you need.

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We are passionate and determined about what we do, and we fight for our clients. If you’ve found yourself or a loved one in trouble, don’t give up hope. We have a criminal defense attorney who can help.


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