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Does a breath test really measure alcohol?

Of all the traffic laws that drivers on American roads are intended to understand and follow, DUI laws tend to be the most discussed and the most often revised and revisited. That's because while no one wants to invite impaired drivers to put others at risk on the road, the level of impairment that actually constitutes a risk and the best way to measure it are both controversial. With some contending that the effects of substances are so variable that drawing a line in the sand is difficult, and others pushing to increase penalties to discourage risky behavior, understanding how these laws operate in the real world can be frustrating.

This is especially true when it comes to the technology and processes involved in measuring impaired driving. One of the most common misconceptions that drivers have is that the mechanical breath testing devices used to estimate BAC are actually able to measure that number from the breath alone. This is simply not true.

How breath tests actually work

Breath tests do measure the amount of certain substances in the blood, and they do so by measuring the difference between a sample selection of regular air from the location and the breath sample provided. For this to work correctly, the breath test needs to be calibrated immediately before being used, and again after. It's also important to note that portable breath tests do not adequately measure ethanol on its own. Instead, they measure organic substances that fit the alcohol family of molecules. That means that in addition to ethanol, they can also pick up:

  • Paint thinner
  • Formeldahyde
  • Wood alcohol and other solvents
  • Acetone

All of these chemicals tend to be able to "trick" the breath test because they have similar properties to ethanol alcohol, and as a result, they may cause a field breath test to deliver a false positive. False positives are less common with an evidentiary breath test, usually given back at the station after the arrest, but some of the same issues seen in portable units do occasionally plague the larger and more robust units too.

If you are arrested

Oklahoma has a stringent implied consent law that punishes drivers who refuse to take a breath test with penalties that are similar to those involved in a DUI conviction. It also allows for that refusal to be used against you in court. As a result, the best thing you can do is to take the test, contact an attorney, and let your legal representative explore the ways in which a false breath test might have led to your arrest. Experienced DUI attorneys have the best resources for discovering what might have gone wrong and presenting it to the court on your behalf.

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Oklahoma City, OK 73105

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