Breath Alcohol Concentration Tests Can Vary As Much As 20%

While the states contend that the science behind Breath Alcohol Testing is reliable, researchers are finding flaws with the science upon which Breath Alcohol Testing is based. 

Lung physiology researcher Dr. Michael P. Hlastala, Ph.D. Professor of Physiology, Biophysics and of Medicine Pulmonary and Critical Care Medicine of the University of Washington tested the consistency of measurements from breath alcohol concentration (BrAC) testing machines and compared them to measurements of blood alcohol concentration (BAC) measurements.  Dr. Hlastala discovered that the results could vary by as much as plus or minus 20%.

In his research, Dr. Hlastala states that:

. . . subjects with larger lung volume may have a lower BrAC than a subject with a small lung volume because these subjects do not need to exhale as great a fraction of their vital capacity as subjects with smaller lung volume to fulfill the minimum volume exhalation required before stopping exhalation (usually ~1.5 liters). A person with smaller lung volume must breathe farther into the exhaled breath, resulting in a greater BrAC-to-BAC ratio.   Michael P. Hlastala, Invited-Editorial on "The Alcohol Breath Test," 93 Journal of Applied Psysiology 405 (2002).

According to this research, breath testing machines based on the "average" person can result in a bias favoring individuals with large lung capacities causing a low BrAC-to-BAC ratio, and against individuals with small lung capacities causing a higher BrAC-to-BAC ratio.

Stated another way, a person legally under the influence with a 0.08 blood alcohol concentration and with large lung capacity may inaccurately measure 0.064 BrAC on a breath alcohol concentration test machine.   A person not considered to be under the influence with a 0.067 blood alcohol concentration and with a small lung capacity may inaccurately measure 0.08 BrAC on a breath alcohol concentration test device.

Post by Kentucky Attorney Stephen J. Isaacs, Isaacs Law Office.

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Comments

[Sharon Rainer]

My sister was pulled over after having three beers.  The cop gave her two standard tests to see if she was drunk.  She passed the walking the line test and holding her head back.  He made her blow into a device and did not give her the numbers.  Took her to the station and had her blow in the table machine an hour and a half later.  Why would they have her blow twice?

Response:
It appears the cop gave your sister only one of the standard field sobriety tests - which compromises the test. The breath test by the road is to establish probable cause for an arrest, but is not valid unless the cop waits 20 min from the time of the stop before giving her the test per statute.