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Science Fails to Trump Law When It Comes to Breathalyzer Tests
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In a recent decision, the California Supreme Court ruled that in challenging the reading of breathalyzers in DUI cases, testimony to prove malfunctioning of an instrument is admissible, but general scientific evidence refuting the accuracy of all breathalyzers is inadmissible in evidence.

Terry Vangelder had been convicted of drunk driving following the reading of a breathalyzer though he showed little sign of any impairment during field sobriety tests.


Vangelder was stopped for allegedly driving at 125 MPH on Highway 163. As soon the Highway Patrol car apprehending him flipped on its overhead lights Vangelder pulled over. He admitted to having a few glasses of wine with dinner and agreed to an Alco Sensor test which showed a 0.086 blood alcohol content. He was immediately arrested. A breathalyzer test at the county jail confirmed a 0.08 blood alcohol consumption level which was just at the legal limit. He took another blood test which reported 0.087 BAC.

At trial, Vangelder called Dr. Michael P. Hlastala, a professor of medicine at the University of Washington as an expert witness to prove that breathalyzer readings were often inaccurate and were an inaccurate method of deciding the level of drunkenness.

Hlastala testified that the tests were inaccurate, “because the basic assumption that all of the manufacturers have used is that the breath that [is] measured is directly related to water in the lungs, which is directly related to what’s in the blood. And in recent years, we’ve learned that, in fact, that’s not the case.”

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He explained that breathalyzer readings are influenced by many other factors besides the level of alcohol in the blood, and other factors include the depth of breathing, temperature of breathing, the ratio of red blood cells to total blood volume and others.

However, the court allowed the prosecutor to strike out the entire part of the expert testimony that could have suggested the basis of drafting the laws [accuracy of breathalyzers] could be challenged.

The court observed, “We conclude that when the legislature employed the word ‘breath’ in section 23152(b), it had in mind the air that is exhaled into a properly working and calibrated breath-testing machine … Although Dr. Hlastala may hold scientifically based reservations concerning these legislative conclusions, we must defer to and honor the legislature’s reasonable determinations made in the course of its efforts to protect the safety and welfare of the public.”


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