Attacking the principles of breath testing
This is my second post on articles from the American Academy of Forensic Sciences Journal. An article that jumped out immediately was "Paradigm Shift for the Alcohol Breath Test" by Michael P. Hlastala.
Breath testing was developed to determine a person's blood alcohol level. All states define intoxication of terms of the level of alcohol in a person's blood. The best way to test is that is of course to take a blood sample; however, that takes time; breath testing and easy and quick. Something that can be done by a police officer.
Breath testing is based on the scientific principle that there is an exchange between air and the blood system. You breath in air, which is transferred to your blood system in the lungs. Breath testing is based on the idea that you can estimate a person's blood alcohol content based on the levels in their deep lungs - alveolar air. A mathematical formula is used, which is recognized as being an assumption. The formula is basically an average, which does not apply to everyone.
For any test to be valid, the underlying facts must be valid. According to Dr. Hlastala, the facts supporting breath testing are far from settled. At the beginning of his paper he notes:
In spite of the considerable effort that has gone into the studies attempting to validate the breath test, forensic scientists and toxicologists still have only a basic understanding of the physiological aspects of the the alcohol breath test (ABT) and associated limitations.
The "old paradigm" assumes the amount of alcohol in the breath remains constant as it goes through the lungs. It turns out that is not accurate. In fact, the amount varies - sometimes significantly. The result is that the actual blood alcohol level may be over or under-represented.
The new paradigm recognizes that alcohol is deposited in the airway surfaces during both inspiration and expiration. It also recognizes that the alcohol that comes out in the breath test comes from airway surfaces rather than the alveolar region.
The conclusion reached in the article was:
It is time for forensic scientists to re-examine the ABT to consider the importance of alcohol interaction with the airway tissue during both inspiration and expiration. the result of this interaction is that the breath test is fairer for some subjects than others. Another consequence is that the BrAC continues to increase as the subject continues to exhale. The resulting end-exhaled breath concentration is only partially related to BAC. And, therefore, the ABT exhibits much more variability than previously recognized.
The author recommends decreasing the importance of relying on threshold levels - especially for determining penalties. he also recommends that some margin of error be recognized. Of course, that will never happen, but it something to consider when you have a client that is only slightly over the limit. Based on this research, they may or may not be legally intoxicated.
In Texas, limits are important for not only determining whether someone is guilty or not, but also for determining whether certain conditions are going to be imposed - such as a interlock device. The validity and accuracy of the breath test results is therefore critical.
This article does not break new ground - problems with breath testing have long been recognized. Those problems must be explored - especially in marginal cases. Where someone's future hinges on a machine, the least we can do is make sure the machine is accurate.
