NMA DUI/DWI Fact Sheet ( PDF )
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By Gerald D. Simpson, Ph.D.
P.O. Box 1551
Thousand Oaks, CA 91358

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, the prosecution must provide evidence of proof beyond a reasonable doubt to satisfy the requirement for sufficiency of the evidence. If this is not done, the State’s case cannot even proceed to the defense putting on its case, and a directed verdict is ordered. The prosecution must provide an unequivocal identification of ethyl alcohol and show that it is responsible for the entire reading produced by the breath test device. Without this, the evidence would appear to be insufficient for a reasonable juror to conclude guilt beyond a reasonable doubt.

Lack of Regulation and Oversight

In addition to scientific and legal problems, there is inadequate Federal and State regulation of breath testing devices and procedures. Because a criminal charge is involved, regulation should be at least as strict as it is for medical or clinical laboratories for which 95% confidence limits are used to meet a standard of reasonable medical certainty. Breath testing is actually a clinical chemistry analysis because alcohol concentration is being measured in a human body fluid (breath). Consequently, when used for legal purposes in criminal cases, regulations should require at least 95% confidence limits (some have argued that 99% confidence limits are appropriate to meet a standard of beyond a reasonable doubt).

Fundamentally, however, breath testing involves measurement of the concentration of ethyl alcohol in air and the rules of basic analytical chemistry require that the concentration be measured and the margin of error for that measurement be properly determined and reported along with the result. Analytical chemistry, the fundamental course that college sophomores take, has been accepted as scientific fact for at least 100 years.

Consider a political poll in which one candidate gets 49% of the vote and the other 51% of the vote, and the margin of error in the poll is +/- 4%. Since the result is within the margin of error, the race is too close to call. Confidence limits are part of how the margin of error is determined. If one wants to be 95% certain that a subject’s BAC or BrAC are not being over-stated by the breath machine result, an appropriate correction factor must be used. For example, most statutes now criminalize driving with a BAC of 0.08% or a BrAC of 0.08 grams/210 liters of breath, and to be 95% certain that the 0.08% limit is in fact exceeded, a person would have to have a test result 40% greater than 0.08%, which is 0.112%. For 99% confidence limits the result must be 46% greater than 0.08%, or 0.117%. At best, however, statutes and courts allow only +/- 0.01% for the margin of error in breath test results. At 0.08% this amounts to a 12% correction factor, rather than 40% or 46% indicated by the most recent scientific research (another way to phrase it would be that for a measured result of 0.08%, the actual BAC would be 46% less, or 0.044% for 99% confidence limits).

As stated earlier, current regulation is inadequate. The Federal agency charged with oversight of breath testing devices is NHTSA of the U.S. Department of Transportation. They have established lists of conforming products for evidential breath testers (EBTs) and preliminary breath testers (PBTs). Evidential breath testers are bench top devices that have multiple safeguards built in by design to help prevent things like operator error, tampering, to identify mouth alcohol and to prevent false positive readings from compounds other than ethanol that can be in the breath. Preliminary breath testers (PBTs) are pocket-sized devices that are not designed for evidential use, so they typically have none of these safeguards. In general, EBTs are considerably more accurate and have better reproducibility (precision) than pocket PBTs. The design features of EBTs are there for a reason.

When a case goes to trial, the prosecution will attempt to establish the reliability (accuracy) of the breath tester used by showing it is included on the NHTSA list of conforming products for EBTs. To qualify for inclusion on this list, the device must be able to correctly measure the concentration of an alcohol vapor sample generated by what is known as a breath alcohol simulator. This is a bench-top device that generates alcohol vapor samples having a known concentration of alcohol in air.

There are fundamental problems with this approach. Firstly, it has been found that some PBTs can qualify for inclusion of the EBT list, even though these pocket devices are not even designed for evidential use. What this means is that the NHTSA test criteria used for determination of inclusion on the EBT list are so inadequate that they cannot distinguish between a bench top EBT and a pocket PBT. Secondly, when a prosecutor claims the breath test result is reliable because it is on the NHTSA list, he/she is claiming the device is reliable when used to test human subjects. However, NHTSA does not use human subjects to establish inclusion in the EBT list. They use a breath alcohol simulator. Since no human testing is done by NHTSA, it is not possible to know if the breath test devices are reliable when used on human subject. This is true for both EBTs and PBTs. It is thus not clear how a device can be “approved” for human use when no human testing has been done by NHTSA to establish that “approval.”

Almost as though the above differences between and oversight of clinical laboratories compared to forensic laboratories are not great enough, there is more. Both clinical laboratories and forensic laboratories carry out blood alcohol analyses. Clinical and medical laboratories do only blood analyses; they do not use breath testing to determine alcohol concentrations in the blood or breath because it is not considered to be sufficiently reliable. Clinical laboratories also subscribe to the College of American Pathologists (CAP) blind, third party proficiency testing program. In doing so, each laboratory is informed what the margin of error is for the blood alcohol analyses they perform. Forensic laboratories employ no such proficiency testing (blind, third party testing) for either blood or breath analyses, so the margin of error is not known for their results. The reason for these differences can probably be traced to strong Federal oversight of all clinical laboratories under the Clinical Laboratories Improvement Act (CLIA) passed by Congress.

Interestingly, clinical laboratories perform alcohol analyses in a manner that is consistent with good scientific practices and with the legal requirements of Frye/Daubert. But when it comes to alcohol analyses for legal purposes, where the criminal standard of proof is beyond a reasonable doubt, forensic laboratories use methods and procedures that fall far short of what is required of clinical laboratories and the requirements of Frye/Daubert.

Unfortunately, regulation and oversight of breath testing is not improving, it is getting worse. In California, the State Department of Health has until recently been in charge of breath testing oversight in forensic laboratories and use of bench top EBTs have always been required for an evidential breath test. PBTs are now available with a printer that produces a paper record of the breath test results, and these are now being used for evidential use in some counties, with the blessings of the State Attorney General, despite the objections lodged by the State Department of Health. The California Legislature enacted the California Code of Regulations, setting down the requirements for breath testing devices and procedures that forensic laboratories must follow, and the state Department of Health is responsible for oversight and enforcement of these requirements. They are also involved in administering quality control evaluation of blood tests done in forensic laboratories but this does not consist of blind, third party tests. There is no proficiency testing program for breath testing and this is unacceptable from a scientific standpoint. Under the PBT program now being used, “calibration” checks are now done by CHP officers using alcohol in dry gas samples having a known concentration, rather than trained, licensed, forensic laboratory personnel who were used prior to this, as required by the Code of Regulations. It is not clear why the Attorney General, who is the chief law enforcement officer in the state, has decided he can override the law that the legislature has put in place.

Now that PBTs are being used for evidential testing, the following is not uncommon. A driver is pulled over because a taillight is not working. The California Highway Patrol (CHP) officer smells alcohol when the driver is questioned. The driver is then asked to perform what are called field sobriety tests (FSTs), which are a series of balance and walking tests the officer instructs the driver to perform. The chances of passing these tests, even for a sober person, are slim to none. The driver is then asked to take a PBT test, something that is voluntary under the law, and the officer is required to inform the driver of this. But when the driver refuses to blow into the PBT, the officer tells him that if he refuses, he will be arrested and taken to the station for an evidential test. So the driver relents, blows into the hand-held PBT, and the result is above the 0.08 limit. The officer then informs the driver he is under arrest, goes to the trunk of the police cruiser and brings out a PBT attached to a printer. The driver is informed that this is his evidential test, and since it will be too will be greater than 0.08%, the driver is taken to the station and booked for DUI. It will be interesting to see how long it will take for these practices (use of PBTs for evidential breath tests) to be used state wide and then perhaps nation wide.

Know Your Rights

Drivers need to know what their rights are in order to minimize the chances of wrongful arrest and conviction. A driver has the right to politely refuse to answer any questions about drinking. It is likely that the officer will persist in an attempt to get the driver to admit to alcohol consumption to make their case stronger. There is, however, little chance that a driver’s explanations will keep an arrest from happening, so it is better to remain silent about anything having to do with alcohol consumption.

A driver does have to take the FSTs, because they are not verbal communications, and refusal can be used against the driver in court. If there are factors in play that compromise FST performance, such as poor balance or nystagmus due to injuries or prescription drugs the officer must be told about them in order to include them in his report. Hyperventilation prior to the breath test will significantly lower the test result. If the driver has had exposure to paints or solvents or is diabetic or has asthma, the officer must be asked to include these in his report as well. Refusal of a blood or breath test can be helpful in some jurisdictions and harmful in others for avoiding conviction at trial, and usually results in suspension of the suspect’s driver’s license.


The current status of breath testing is, as it has been for some 50 years, about the same as the status of DNA Fingerprinting was when if first began to be used in our courts. Forensic scientists adopted this methodology and began presenting it in courts as powerful evidence to identify suspects who left their DNA at the crime scene. At this time, like breath testing now, there was virtually no oversight or outside regulation of DNA Laboratories. Like breath testing, outlandish claims of accuracy and probability of a match were commonplace by those in the forensic science community, even under oath.

As time passed, very capable and informed defense attorneys were able to raise enough doubt about the claims that were being made that evaluation of the method by the National Academy of Sciences (NAS) was initiated. As a result, most of the scientifically unacceptable aspects of the procedures and methods used by DNA Laboratories were corrected, based on the recommendations of NAS committee members. This is precisely what must be done with breath testing. NAS consists of members of the main-stream scientific community, not forensic scientists. Indeed, forensic science is not one of the disciplines even represented in the National Academy of Sciences (google National Academy of Sciences). NAS must be enlisted to evaluate the scientific merit of breath testing methods and procedures. If this is not done, the 50 year history indicates that neither the forensic science community nor our courts will solve the problem.

An immediate fix for the problems with breath testing is to inform jurors and judges that there are large unknown uncertainties in breath test results, and this must be factored into decisions of innocence or guilt of drunk driving. Long term solutions await development of direct, non-invasive blood alcohol tests. Breath testing is now and will always be too unreliable to use for legal purposes, and when evaluated by NAS, this will eventually be shown to be true.

This article is excerpted from the book: CSI/Forensic Fraud Cover-up by John Kelly who can be reached at: