Beat the Breath Test or the Breath Test Beat You?

As a highly regarded DUI attorney, I invariably get asked “Well, how do I beat the breath test machine?” I always respond, “Don’t worry about beating the Breath test machine. Worry about it beating you.”

What I mean by this is that the machine can over-report your true Blood Alcohol Content. In other words, the alcohol in your veins can be less (sometimes very significantly less) than what the “magic” machine reports. These inaccuracies happen much more often than you might suspect.

First and foremost, the Breath Test doesn’t actually test how much you have to drink. As I previously wrote, these machines are not specific to alcohol. But beyond that even if it was specific only to ethyl alcohol to the exclusion of everything else, there are still so many variables that make us all different, and make the machine far from accurate, precise and reliable. It is specifically set to test the “average person”. Well, in the history of the world, the “average” person is dead, female and Chinese. Not a lot of dead people on trial. So trying to test based on the “average”, isn’t fair.

There are many physiological factors that can cause the Breath machine to beat you.

  1. long exhalation time into analyzer
  2. test made during the absorption phase of the blood alcohol curve when  arterial venous difference in concentration of alcohol is greatest
  3. presence of mouth alcohol when breath sample was analyzed
  4. re-breathing of the first exhalation a number of times before analysis of ethanol
  5. breath holding or  hypoventilation before sampling breath
  6. elevated body temperature hyperthermia
  7. non-specific method of analysis and presence of interfering substance
  8. Partition ratio

In the United States, all breath testing devices are set in a specific way. They depend on the assumption that the ratio between alcohol in the exhaled breath in deep lung air and alcohol in the blood is 1 to 2100. This ratio is called the “Partition Ratio”. To be very precise, the theory that the machine is based on is that the same weight of alcohol will be present in one cubic centimeter of pulmonary (lung) blood as in 2.1 liters of deep lung breath. However, these same exact machines in other countries have the partition ratio differently configured. For example in England, it is based upon a 1 to 2300 ratio.

Why does that matter? Well, the machine is designed to produce a reading based on that assumption. So if the assumption is wrong. The reading will be wrong every time. The truthfulness of the reading rises and falls on this one key ratio. Everyone is different. Stated more directly, not everyone has the same partition ratio. Not everyone is 1 to 2100. The actual ratio in any given individual can vary from less than 1:1300 to more than 1:3000. In fact, some peer reviewed research suggests that a person is not born with one set ratio and it can change over one’s lifetime.

To make sense if all of this let’s look at some real-world numbers. Suppose that the machine says that you have a 0.09 reading and  you have a partition ration of 1:1700, your true Blood Alcohol Content (BAC) would be below the legal limit of 0.08. Suppose the machine reads that you have a 0.10 reading and you have a partition ration of 1:1500, your true BAC would be 0.07.  So in essence, the machine has beat you.

Justin McShane

PA DUI attorney Justin J. McShane is the President/CEO of The McShane Firm, LLC - Pennsylvania's top criminal law and DUI law firm. He is the highest rated DUI attorney in PA as rated by Justin McShane is a double Board certified attorney. He is the first and so far the only Pennsylvania attorney to achieve American Bar Association recognized board certification in DUI defense from the National College for DUI Defense, Inc. He is also a Board Certified Criminal Trial Advocate by the National Board of Trial Advocacy, a Pennsylvania Supreme Court Approved Agency.

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