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Breath Alcohol Analysis

and the presumption of innocence
David Beyersdorf, Attorney > Criminal Law  > Breath Alcohol Analysis

Breath Alcohol Analysis

Our legal system is based on the principle that the accused is presumed innocent until proof is provided that demonstrates otherwise. The modern breathalyzer test is an example of where “scientific evidence that routinely deprives suspects and defendants of the presumption of innocence and results in wrongful convictions as well as unwarranted guilty pleas.”   In this article by Gerald Simpson, PhD. from Motorists.org, some of the pros and cons are discussed, as well as some solid advice as to how to handle this evidence in court.


In a 1983 law review article, Stephen G. Thompson observed that “Modern criminal justice is premised upon the requirement that a criminal defendant be proved guilty beyond a reasonable doubt before punishment can be meted out. This standard of proof is severe; its severity is based upon a collective societal judgment that the risk of error be borne by the state. As fundamental and unquestionable as this principle may seem, it is frequently tested when the interests of society appear urgent, immediate, and identifiable. In these instances, society often creates policies and systems which threaten the presumption of innocence.” Breath testing is a good example of the use of scientific evidence that routinely deprives suspects and defendants of the presumption of innocence and results in wrongful convictions as well as unwarranted guilty pleas. The reason for this is that breath testing as now employed does not accurately reflect the true or actual value of alcohol concentration in the venous blood or even in the breath of a human subject.

Scientific Problems

Current scientific research, published in respected peer-reviewed journals, now shows that results from breath alcohol analysis or breath testing are not sufficiently reliable for use in our courts. This represents a huge problem because breath testing has been used widely for this purpose for over 50 years and continues in widespread use on a daily basis.

What has now been demonstrated is that three important aspects of breath testing are faulty or even downright wrong. The very basis for breath testing in humans is the theory that ethyl alcohol (ethanol) in the blood is in equilibrium with the alveolar air in the lungs and that by measuring the concentration of ethanol in the end-expired air sampled by a breath machine, the amount of ethanol in the blood or breath can be reliably determined. Recent work by Michael Hlastala at the University of Washington Medical School in Seattle has shown that there is no such equilibrium and that breath testing therefore cannot work (google Michael P. Hlastala for further information).

Secondly, evidential breath testing has a very large margin of error, a minimum of +46%, meaning that for a given individual the breath test result can be anywhere from 0 to 46% higher than the actual amount of alcohol in the blood. This is the minimum amount of error that is indicated by the most recent scientific research. The actual amount could well be far greater. While it has been argued that this margin of error or uncertainty can be eliminated by criminalizing a certain amount of alcohol in the breath, rather than in the blood, the argument has no merit. This is because the rules of analytical chemistry require the amount of uncertainty in the blood breath conversion to be accounted for whenever the conversion is used. In the case of criminalizing a certain breath concentration, the 2100 conversion is used by the legislature to set the amount deemed to be illegal and the uncertainty reappears, i.e., when a blood alcohol concentration (BAC) of 0.08 grams/100 milliliters is divided by 2100 to yield a breath alcohol concentration of 0.08 grams/210 liters breath (google G. Simpson breath alcohol and Dominick Labianca). Moreover, setting the BrAC limit this way, without accounting for the margin of error, constitutes a legislative determination that breath test results are the exact equivalent of directly measured venous blood test results for measuring the alcohol load in a human subject. This determination is quite simply incorrect, and the legislature will have incorporated incorrect science into law.

Lastly, it has been recently shown that the “calibration” method used to ensure reliable performance of evidential breath machines does not work. The method used to “calibrate” these machines on a regular basis deals with only a fraction of the total error or uncertainty involved in a breath test result for a given individual; it simply ignores the major sources of error involved in results from evidential breath machines, e.g. error that occurs from assuming that the blood/breath ratio is 2100:l. Consequently, the actual amount of error in a breath test result for a given individual is unknown. This calibration method that has been used for over 50 years was put in place by those involved in the development of breath testing and supposedly uses appropriate principles of elementary analytical chemistry, those taught in sophomore courses on quantitative analysis. Unfortunately, these principles were not applied correctly when the calibration procedures were established and this has been ignored for far too long. As a result, the reliability of a breath test result for a given individual in simply unknown (google Dominick Labianca).

Legal Problems

Despite the fundamental scientific shortcomings of breath testing as used in criminal and civil cases, our courts continue to accept such evidence as an acceptable indicator of the inability to drive safely, blood alcohol concentration (BAC) and breath alcohol concentration(BrAC). Indeed, in a recently concluded hearing ordered by the New Jersey Supreme Court, the Special Master who conducted the hearing and issued a report concluding that breath testing is a reliable indicator of BAC. He did however recommend that corrections be made for breath temperature when the subject’s breath temperature deviates from that assumed by the breath test procedure. It is thus likely that the New Jersey Supreme Court, for whom the report was prepared, will reaffirm the reliability of breath testing.

There is still some hope, however, because the Special Master seems to have paid no attention to the existing U.S. Supreme Court requirements for the evaluation of proposed scientific evidence, as laid out in a 1990s case called Daubert. Doing the appropriate legal analysis of breath testing under what is known as Frye/Daubert standards as used in New Jersey should clearly demonstrate that breath test results do not qualify as scientific evidence and are therefore not admissible in criminal cases.

Another issue that should be taken to the U.S. Supreme Court involves the destruction of evidence when breath testing is are given. When a suspect is given a breath test, the breath sample is discarded, even though the technology to save the breath sample has been readily available for many years. This issue was taken to the U.S. Supreme Court in a California case called Trombetta many years ago (1984) and the court ruled that breath test samples need not be saved. It is time to revisit this issue because research done in the 1990s makes it clear that breath testing is far less reliable than blood testing, and far less reliable than the Trombetta court was led to believe, yet it is blood samples that are retained by forensic laboratories and breath samples are discarded. It is now clear that reanalysis of a breath sample can likely provide exculpatory evidence, contrary to the findings in Trombetta.

Breath testing devices are not specific for ethyl alcohol. There are at least 100 other volatile compounds that can cause false readings on a breath test device, and this is another reason the breath sample should be saved for reanalysis. A simple gas chromatography (GC) analysis, something that is available in forensic laboratories, can determine if any other compounds are contributing to, or are responsible for the entire reading. Under a U.S. Supreme Court case, Jackson vs. Virginia… (read the full article)