Challenging a DWI Breath Test

Published on November 25, 2020 Science & DWI

Updated: Nov 25, 2020 @ 12:15 pm

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After arresting a driver who is suspected of driving while intoxicated, law enforcement officers can ask him or her to submit to a DWI breath test. The results of these tests, however, are not always accurate, so if you were charged with Driving While Intoxicated, you should call a Houston DWI defense attorney who can evaluate the evidence against you and help ensure that any inaccurate test results are thrown out.

Understanding Roadside DWI Breath Tests

Breath tests are used to calculate the amount of alcohol in a person’s blood by testing his or her exhaled breath. If a person’s Blood Alcohol Content (BAC) registers at .08 percent or higher, he or she is considered intoxicated. While this may seem like a relatively straightforward test, the reality is that breath testing is problematic for a number of reasons.

For instance, breathalyzers don’t actually measure the amount of alcohol in the blood, but calculate alcohol that has already evaporated from the blood system and traveled to the person’s airway. While there is a relationship between the amount of alcohol in the breath and in the blood, there are quite a few factors that could affect this relationship, including:

Temperature, as the warmer a person’s body temperature is, the higher his or her BAC reading will be;
Breathing technique, as those with shallower breaths often have higher BAC results; and
Breath/blood partition ratio, which takes into account the volume of blood from which the ethanol in a person’s breath originated, but can be impacted by the rate at which a person’s body absorbs alcohol.

Fortunately, a skilled DWI lawyer can help determine whether any of these factors played a role in someone’s BAC test and if so, can help cast the results of that test into question.

Improper Administration & Maintenance

DWI Police Stop Not only can breathalyzers produce inaccurate results because of a person’s temperature, breathing technique, or breath/blood partition ratio, some results are actually attributable to improper calibration of the machine.

Breathalyzers are also supposed to be maintained regularly, but this maintenance is often overlooked or neglected, which can have a significant effect on the results of a test.

Similarly, breathalyzer tests must be administered in a certain way that requires specific training.

For instance, officers must wait 15 minutes before administering breath tests to ensure that no residual mouth alcohol is present when testing. Officers who fail to fulfill this duty could significantly skew the results of a driver’s test. The cleanliness of the mouthpiece, whether the officer was properly certified to administer the test, and whether the external standard checks fell within the acceptable range, can also affect a person’s results. Fortunately, evidence of improper maintenance or administration can be used to counter any results presented by state prosecutors when charging a person with a DWI.