Beating a DUI Breath Test in Court: The Partition Ratio

Law Offices of EJ Stopyro Orange County DUI Attorneys
DUI Lawyer in Orange County

You get pulled over after you’ve had two or three drinks with friends. You felt fine when you started driving and didn’t see a problem with driving home. But the cop smells alcohol on your breath and asks you to do some field sobriety tests. You do the tests and the cop doesn’t see any real problems. The cop then asks you to take a roadside breath test. Believing that you are not over the limit, you oblige and blow into the small handheld machine. Beeeep! Says the machine. And it’s off to jail you go with a 0.08% result on your breath test and a charge of DUI.. “How can this be” you think to yourself, as you sit handcuffed in the back of a police car. “I read that card the DMV gave me when I renewed my registration and according to the card I should be UNDER the limit,” you think. How can I be arrested for DUI.

The fact is, you may very well be below the legal limit and still produce a reading on a breath-testing device that is at or over the limit and result in a DUI arrest. Why? Because the breath-testing device has made an assumption about your physiology that may just be flat wrong. A skilled Orange County DUI attorney will tell you that a breath test does not directly measure the amount of alcohol in your blood. It only measures the alcohol in your breath. A breath testing device is programmed to ASSUME that the ratio between the alcohol vapor deep in your lungs (alveolar air) and the alcohol in your blood is fixed at 1:2100. This ratio is called a partition ratio.

In other words, the machine is programmed to assume that every 2.1 liters of your deep lung air contains the same amount of alcohol as 1 cubic centimeter of your blood. The machine measures the amount of alcohol in the air you expel and computes a result based on the assumption that YOUR partition ratio is 1:2100. But YOUR partition ratio may very well be something other than 1:2100. In fact, partition ratios vary from person to person from 1:1100 to 1:3000. So, for example, if your actual partition ration is 1:1500 and your actual blood-alcohol is .07%, the breath test will give a reading of .10% and falsely identify YOU as being over the legal limit and get you arrested for drunk driving or DUI.

Not only that, but YOUR partition ratio also varies from time to time—it’s not fixed. For example, when your body is absorbing alcohol—moving it from your stomach to your blood—your partition ratio will be higher. This will result in a breath test result that is higher than your actual blood alcohol.

For more information on partition ratios or any aspect of DUI defense call the Law Offices of EJ Stopyro at (949) 559-5500 for a free and confidential consultation or go to our website at www.EJEsquire.com.

Law Offices of EJ Stopyro

Orange County DUI Lawyer
DUI Attorneys in Orange County