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Fighting Breathalyzer Results in Texas: How They Can Be Wrong

It happened. You got pulled over, the officer administered a breath test, and you blew over a 0.08. Now you’re going to have a DWI conviction on your record, and there’s nothing you can do about it.

This is what most people think if they register a positive BAC test result. What you may not know, though, is that breathalyzers are notoriously inaccurate. Breathalyzers have an inherent margin of error, and a number of other factors may also skew the results. Because of this, many Texans charged with DWIs may not actually be over the legal limit.

That’s the bad news. The good news is that an experienced Texas DWI lawyer not only knows this, but also how to raise doubts about breathalyzer results to fight your charges. This is something you really want to do, because a DWI conviction in Texas is life-changing.

Even a first-time offense costs between $5,000 and $24,000, and has long term consequences such as driver’s license suspensions, ignition interlock devices, and a criminal record that may come back to haunt you.

Let’s take a look at some of the many ways breathalyzers can be wrong, and how these sources of error could be useful to your case.

Inherent Margin of Error

Scientific studies have proven that breathalyzers have a 50% margin of error by comparing breathalyzer estimates of BAC to actual BAC. This means that a breathalyzer reading of 0.1% (well over the legal limit) represents an actual BAC of somewhere between 0.05% and 0.15%. That’s a huge difference.

Therefore, breathalyzer readings should not be considered per se evidence of DWI unless the reading is high enough to overcome the inherent margin of error. In Texas, this would be a reading of at least 0.16%. Unfortunately, in our state, that’s high enough to be considered an aggravating factor. Even so, this would fail to take into account the other potential sources of significant error discussed below.

Physiological Differences Among Drivers

Importantly, breathalyzers don’t directly measure BAC. They estimate BAC based upon the breath alcohol. To calculate the approximate BAC, breathalyzers multiply the breath alcohol level by a partition ratio that is based off of assumed averages.

The problem is that not everyone has the same partition ratio. The partition ratio can be affected by sex, body weight, breathing patterns, body temperature, and other physiological factors. This means that breath alcohol is not necessarily reflective of blood alcohol.


Parker County DWI Attorney

Breathalyzers must be regularly calibrated by a trained technician to work properly. In this process, the technician runs a sample with a known alcohol concentration through the device and tunes the device to match the sample concentration. If proper calibration procedures were not followed, the breathalyzer results are not admissible as evidence.

Your defense attorney can subpoena the maintenance and calibration records of the breathalyzer used at the time of your arrest. This can possibly be used as evidence that the equipment may not have been reliable.

Radio Frequency Interference

When most of us think about being pulled over by the police, we imagine the sound of police radios in the background. Well, those radios can in fact cause a breathalyzer to malfunction.

Some breathalyzers now have radio frequency interference (RFI) detectors to combat this problem, but not all of them. If the breathalyzer used to approximate your BAC does not have an RFI detector, the results may not be accurate.

Leftover Alcohol in the Driver’s Mouth

Ever notice that the taste of an alcoholic drink lingers in your mouth for quite a while after you’ve finished your drink? Or (pardon our bluntness here) that when you belch, you can taste alcohol for hours afterwards? Both of these factors can lead to an artificially high BAC reading from a breathalyzer.

That’s because a breathalyzer is designed to calculate BAC based on the alcohol vapor coming from the lungs, which is reflective of circulating alcohol levels in the bloodstream. However, alcohol from the mouth or stomach can also enter the sample chamber, often at a much higher concentration than would be found in the lungs. This can cause false high readings.

To prevent mouth-alcohol contamination, police are supposed to observe a suspected drunk driver for 15-20 minutes prior to administering a breathalyzer, known as the deprivation period. During the deprivation period, the officer is supposed to ensure that the driver does not burp, vomit, or put anything in his or her mouth. Any lingering alcohol should be gone by the end of the deprivation period, meaning that test results would be accurate.

However, it is impractical, and depending on location, dangerous, for police to observe a stopped driver for 15-20 minutes prior to administering a breathalyzer. Therefore, this protocol is rarely followed, meaning that the test results are most often subject to mouth alcohol contamination.

If You are Facing Texas DWI Charges

Weatherford TX DWI Lawyer

As you can see, there’s a lot of science behind proving conclusively that your blood alcohol was indeed over the legal limit at the time of your DWI arrest. It’s therefore often possible to contest test results.

However, to do this you need an experienced and knowledgeable DWI defense attorney who will leverage his or her knowledge to ensure the best possible outcome. Reach out to our office immediately to have the best chance at a positive outcome in your case.



About the Author:

Jeff Hampton has been practicing law in Texas in 2005, first in the Tarrant County District Attorney’s Office as a prosecutor, and now as a private attorney with the Hampton Eppes Law Group, protecting the rights of Texans who have suffered injury due to negligence or are facing criminal charges. His success in helping people with their legal troubles has been recognized by clients and peers alike, with a Top Attorney designation and 10/10 Superb Rating on Avvo, and a place on the National Trial Lawyers list of the Top 100 Trial Lawyers.

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