It is the alcohol in your blood that affects your ability to safely drive a motor vehicle. Because of the many causes of alcohol on the breath, only one of which is alcohol in the blood, and the fact that the alcohol content of your breath is, at best, loosely correlated with the alcohol content of your blood, the relationship between alcohol on your breath and your ability to safely drive a motor vehicle is actually pretty weak. So, why are breath testers (aka intoxylizers) in such wide use around the globe for determining levels of intoxication? Economics. It is cheaper and more expedient to test the breath of an individual than to draw and then test their blood by lawful and forensically approved methods. While cheaper, nearly everyone will agree that breath testing is less accurate than blood testing to establish a particular blood alcohol content. How much less accurate is breath testing than blood testing is hotly debated.
The debates center around three fallacies as follows:
The first fallacy is that breath is not blood and, therefore, a breath test is not a blood test. But you knew that already, right?
The second fallacy is that the breath generated in everyones' deep lungs (aka alveolar air) carries the same number of alcohol molecules when their blood alcohol content contains the same concentration of alcohol. This is simply wrong. The "breath/blood partition ratio" that the industry of breath instruments programs into their instruments is one gram of alcohol per 210 liters of breath. However, this ratio of 1:2100 is an average, not the truth about you or me. In fact, this ratio varies between 1:1300 to more than 1:3000 across the population. This difference across the population can and likely does account for innocents getting wrongfully accused as well as guilty people getting away with DUI. More vividly, my deep lung air might contain more alcohol than your breath, even though our blood alcohol content is the same. And, most likely, neither one of us has exactly a 1:2100 ratio at any given time. So, the industries' instruments are not designed for you and me, but for the population in general.
The third partial-fallacy, is that these breath instruments are in proper working order, properly maintained, properly calibrated, operated under ideal conditions (temperature, wind, etc.), actually testing deep lung air, and operated by someone with adequate training, who is, at a particular time, administering the tests in strict compliance with their training.
So, back to economics... After these alarming fallacies were exposed over many years of agressive and skilled litigation of DUI's, resulting in many people being found not guilty of DUI, California's legislature, along with many other state legislatures endeavored to write into law what might be viewed as a new law violation: Driving with a BREATH alcohol content which tests .08% or greater on instruments which presume a 1:2100 blood/breath partition ratio.
The Supreme Court of California affirmed on appeal the inadmissibility of testimony of an individual’s partition ratio, especially when the defendant exhibited clear signs of alcohol intoxication. Here the court looked to legislative intent to discourage drunken driving therefore a conviction based on alcohol measured by breath as amended by statute would stand. People v. Bransford, 884 P.2d 70 (Cal. 1995).
Say it ain't so!? Yes, the Supreme Court favored the California Legislature's one-size-fits all pragmatism over the pursuit of justice in the individual case. Sounds great until you're the one looking at a DUI case based on a Breath Alcohol test result narrowly above the legal limit, doesn't it? (Advertisement: If you are facing such a charge in Santa Barbara, and believe that your unique breath partition ratio may have over represented your blood alcohol percentage, then contact me at 805-892-4922 right away to discuss how you might be able to successfully defend your case).