Just How Accurate Are Breath Testing Machines?

Posted by Joseph D. Lento | Nov 06, 2019 | 0 Comments

An investigation by The New York Times found what criminal defense attorneys have known about driving under the influence (DUI) law for some time, now: Breath testing machines are not always accurate.

New York Times Investigates Breathalyzers to Find Them Prone to Error

The New York Times recently published some investigative journalism about how accurate breath testing machines can be. They seemed shocked by how frequently they produced poor results, how often they were miscalibrated by the police officers using them, and how poorly they are maintained by police departments.

More recent editions of the machines rely on software, rather than mechanical processes. These are even scarier because problems may never get traced to the machine and there is a solid chance that no one ever realizes that a machine is providing incorrect results.

Unfortunately, these are all things that criminal defense lawyers have known about for a long time.

A Tentative Attempt at Scientific Accuracy, At Best

At best, breathalyzers are a tentative attempt to scientifically measure the amount of alcohol in someone's bloodstream. Blood alcohol content, or BAC, is the Holy Grail of DUI investigations – if a driver has a BAC at or above the legal limit of 0.08%, they are per se under the influence. Defending against DUI charges when there is this damning evidence against you is difficult.

But contrary to what police claim, breathalyzers don't measure someone's BAC. They measure a driver's BrAC – their breath alcohol content. That's the amount of alcohol that is on someone's breath, not in their blood.

The connection between BAC and BrAC is tight, but not foolproof: Alcohol-laden blood passes through the lungs, leaving alcohol behind at a known rate. When the driver exhales, the breath from their lungs will have that alcohol on it.

Therefore, a driver's BrAC should be closely linked to their BAC. However, the match is not always perfect. Environmental factors can skew the results, even if the breathalyzer is functioning perfectly.

In Reality, Another Overhyped and Overtrusted Police Tactic

But breathalyzers are rarely performing the way they are supposed to. They need constant calibration to make sure they are spitting out readings that are accurate. They also have to be administered correctly by police, which might make their arrest numbers go down.

These are things that are often overlooked or actively ignored by the police who use them to get people into serious legal trouble.

It's about time a major news outlet shone the limelight on this faulty police tactic and reveal it for what it really is – another example of the “revolutionary crime-solving technology” that brought us duds like bite mark analysis, handwriting experts, and hair matching evidence.

DUI Defense Lawyer Joseph D. Lento Serves Philadelphia

Joseph D. Lento is a DUI defense lawyer who helps people who have been accused of drunk or drugged driving in the Philadelphia area. Contact him online or call his law office at (215) 535-5353 if you have been accused of DUI and want to challenge the results of a breathalyzer.

About the Author

Joseph D. Lento

"I pride myself on having heart and driving hard to get results!" Attorney Joseph D. Lento passionately fights for the futures of his clients in criminal courtrooms in Philadelphia and across Pennsylvania as well as in New Jersey and nationwide. He does not settle for the easiest outcome, and instead prioritizes his clients' needs and well-being. With unparalleled experience occupying several roles in the criminal justice system outside of being an attorney, Joseph D. Lento can give you valuable behind-the-scenes insight as to what is happening during all phases of the legal process. Joseph D. Lento is licensed in Pennsylvania, New Jersey, and New York, and is admitted pro hac vice as needed nationwide. In the courtroom and in life, attorney Joseph D. Lento stands up when the bell rings!


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