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Prosecutors mistakenly convince jurors the Breathalyzer Test is the standard in determining DUI

When you think about it, someone charged with DUI faces a court date by machine. After the Breathalyzer indicates a blood-alcohol content (BAC) of .08% or higher, one has failed the test and, “Presto,” is declared drunk.

Breathalyzer happens to be the brand name for a collection of devices made by one manufacturer, Smith & Wesson, which later sold to National Draeger. Breathalyzer is the uniform name for instruments made to measure alcohol in the blood: Intoxilyzer, Intoximeter, AlcoMate, AlcoScan, AlcoHAWK, Alcotest, Alcosensor, Alcolizer, Datamaster and BreathKey.

Breathlyzers Do Not Measure BAC

The machine does not determine an individual's level of intoxication, as this varies by a subject's individual alcohol tolerance, according to the online encyclopedia, Wikipedia. The BAC test result can vary between individuals consuming identical amounts of alcohol based upon race, gender, weight, genetic make-up, metabolic rate, sleep deprivation and even, stress.

Breath analyzers do not measure BAC or concentration. Blood tests do. Instead, the machines estimate BAC indirectly by measuring the amount of alcohol in one’s breath. Breath testers can be affected by temperature and will output false readings if not adjusted or recalibrated to account for ambient or surrounding air temperatures. The temperature of the subject also is important.

Breathing patterns also affect breath test results. One study found that the BAC readings of subjects decreased 11-14% after running up one flight of stairs and 22–25% after running up two flights. Another study found a 15% decrease in BAC readings after vigorous exercise or hyperventilation. Hyperventilation for 20 seconds has been shown to lower the reading by approximately 10%. On the other hand, holding your breath for 30 seconds can increase the breath test result by 15%.

Prosecutors Tell Jurors Breathalyzers Are Foolproof

If the Breathalyzer indicates a BAC of .08% or higher, the person usually will be charged with two offenses: DUI of alcohol and driving with a BAC of .08% or higher. That person by law will be presumed guilty of both offenses with the burden of proof weighing on the accused.

Prosecutors assure jurors these machines are accurate scientific instruments — so accurate and reliable they feel certain finding the defendant, “guilty beyond a reasonable doubt,” based solely upon the machine.

However law enforcement agencies are beginning to abandon machines in favor of blood tests. Just how accurate and reliable are these “state-of-the-art” breath machines? -- not very, according to documents from the Commonwealth of Virginia Department of Forensic Science (DFS).

VA Attorney Piloting More Accurate “Measure”

Attorney Robert F. Keefer of Harrisonburg, Virginia, filed a demand under the Freedom of Information Act for records concerning the machine used in Virginia, the Intoxilyzer 5000. The device is the most commonly used machine in the United States the past 15 years. Keefer submitted the DFS data to support replacing machines with upgraded models. Following are quotes from the documents:

”Funding of this request will allow the agency to replace instruments (Intoxilyzer 5000) which are 9-10 years old and for which replacements are not available. These instruments are outdated and the manufacturer is no longer maintaining parts. Plus, current instruments demonstrate two generations of technological advancement.”

“In response to, “What are the expected results to be achieved if this request is funded?” this answer was given: “To replace outdated, unstable and unreliable breath alcohol instrumentation used by police officers throughout Virginia to certify whether a driver is or is not impaired.”

But prosecutors give jurors the same line: “The machines are accurate, reliable and state-of-the-art.” It’s proof that someone testing 0.08 or above is deemed guilty beyond a reasonable doubt.

Bob Battle
100% of my practice is devoted to serious traffic defense and criminal litigation in state and federal courts