In all states, including Oregon, breath tests are used as per se evidence of someone's guilt for the crime of DUI. There is no other crime where someone is presumed guilty if a machine says he has a measurement over a certain level. What makes this reality even more disturbing is that breath test machines are inherently inaccurate.
Breath test machines work by measuring the alcohol concentration in a subject's breath. Whether or not that actually do this particularly well is a matter for a later post. Even if these machines are able to accurately measure a person's breath alcohol concentration, however, research indicates that breath and blood alcohol levels can be vastly different.
Dr. Michael P. Hlastala, Ph.D., a professor of Physiology, Biophysics and of Medicine Pulmonary and Critical Care Medicine at the University of Washington conducted experiments comparing breath test results to blood results. His research into this area shows that the results can vary by as much as 20% plus or minus.
This is a staggering figure when applied to a DUI case. Imagine a defendant who has a blood alcohol concentration of .067%. According to Dr. Hlastala's finding, it is perfectly possible for that person to register a .08 on the breath test. Such a reading would be used as per se evidence that the person was intoxicated even though his actual blood alcohol was well under the legal limit.
