Breathalyzer "Science" Shown Defective

Breathalyzer “Science” Shown Defective

Accuracy of science behind Breathalyzer tests provides defense in DUI cases

In the landmark case, People v. Timmie Lance McNeal, the California Supreme Court recognized that Breathalyzer tests produce variable [and inaccurate] results for different people, and unanimously ruled that juries can consider the accuracy of Breathalyzer tests to rebut the presumption of intoxication in DUI cases.  This ruling represents a major victory for California DUI defense attorneys, who have long-held the “science” used in Breathalyzer tests is highly questionable. 

Henry’s Law

Breathalyzer devices measure the amount of alcohol vapor in a person’s breath (presumably representing the level of alcohol contained in the person’s lungs, after being consumed, absorbed in the blood, and circulated throughout the body), and use a breath-to-blood ratio to convert the breath-alcohol level to an estimated blood-alcohol level.  Currently, a nationally accepted scientific formula, known as “Henry’s law,” is used to accomplish this breath-to-blood conversion.  However, the problem is that breath-to-blood ratios vary greatly from person to person, and are influenced by many factors which are not taken into account by the Breathalyzer devices – such as body temperature, atmospheric pressure, medical conditions (such as the person having a lung condition, like asthma, or only having one lung) and the precision of the measuring device.  In other words, the same Breathalyzer result for one person could show severe intoxication, while for another person it could show complete sobriety! 

California’s DUI Law

The Supreme Court’s holding in McNeal resolved inconsistencies between California’s two different DUI laws, where results from Breathalyzer tests under one law simply establish a presumption of intoxication, whereas in the other law, those same results define legal intoxication (essentially creating an irrebuttable presumption). 

Law 1 – Presumption of Intoxication.  California’s first DUI law requires proof that a driver was intoxicated, such as slurred speech and bloodshot eyes, and Breathalyzer tests may be used to establish a legal presumption of intoxication – jurors may presume someone is drunk if the Breathalyzer test shows a blood-alcohol level of at least 0.08 percent. 

Law 2 – Definition of Intoxication.  California’s second DUI law, passed by the Legislature in 1981 and updated in 1989, defined a drunk driver as someone with a blood-alcohol level of 0.08 percent, regardless of the person’s behavior or appearance.  Then, a 1994 Supreme Court decision extended that definition to include Breathalyzer results – meaning Breathalyzer tests showing a blood-alcohol level of at least 0.08 percent provide definitive evidence of legal intoxication.  The effect of this 1994 ruling was to bar drivers charged with this second law from attacking the accuracy and variability of Breathalyzer tests. 

Since this ruling, DUI defense attorneys have been unable to dispute Henry’s law as a basis for challenging the breath-test results or defending against DUI charges. 

McNeal Decision

In its unanimous decision, Justice Carol Corrigan explained that “defense evidence is relevant to rebut the presumption that the defendant was intoxicated, but not to remove the presumption altogether.”  Prosecutors believe this ruling will seriously hamper their ability to win convictions in DUI cases. 

The takeaway is that the Supreme Court’s decision in McNeal essentially overrules previous laws restricting DUI defense strategies, and provides drivers with an extremely strong weapon in their arsenal to combat DUI convictions.  If you’ve been charged with a DUI based on a Breathalyzer test, especially if your test results are very near the legal limit (0.08-1.00 percent), don’t wait – contact us today!