Breathalyzer and Breath Test Accuracy

DUI Breath Test gifThe "Implied Consent" laws of California provide that if you are arrested for drunk driving, you are presumed as a condition of the privilege to drive to have impliedly consented to chemical testing. If you refuse to submit to testing, your driving privilege can be suspended. The chemical test will normally consist of your choice of breath or blood analysis; a urine sample can be taken instead if neither breath nor blood is readily available.

In the past, the prosecutor's case solely on the testimony of the arresting officer. The evidence against the defendant consisted entirely of the officer's observations of the defendant and of his opinion as to sobriety. But the pitfalls were many. The police officer's word could be challenged, and there was nothing to corroborate his observations. The validity of his opinion could be questioned and his opinion often had little special education or training behind it. Perhaps most important, the prosecutor had to fit the DUI defendant within a vague, ill-defined category entitled "under the influence." At no time could the prosecutor offer any evidence but outward symptoms and opinions, and at no time could he even spell out the DUI offense beyond such amorphous phrases as "substantial impairment."

Two factors led to a drastic change in this situation. The first was the advent of advanced scientific techniques within criminalistics laboratories. Increasingly, law enforcement was turning to scientific methods of detection in proving criminal conduct. Then, in 1938, the American Medical Association set up a "Committee to Study Problems of Motor Vehicle Accidents"; at almost the same time, the National Safety Council established a "Committee on Tests for Intoxication." Studies by these committees resulted in a recommendation that legal standards be set for determining the intoxication of a driver by chemical testing. Although there was some disagreement among the prominent medical members of the committees, the consensus recognized that any individual who had .15 percent alcohol in his blood could be presumed to be under the influence of alcohol; anyone having less than .05 percent of alcohol could be presumed to be not under the influence; and those individuals falling in the .05 - .15 percent midrange might or might not be under the influence - that is, the test would not be conclusive. The .15 level was lowered in 1960 by the recommendations of both committees to .10 percent (this vacillation of medical experts, incidentally, should give added ammunition to defense counsel for cross-examination). Since then, many states have lowered it even further - to .08 percent.

Armed with these findings and recommendations, prosecuting agencies throughout the country were able to obtain legislation requiring any driver to submit to chemical testing when requested by an officer. If the driver refused, these implied consent statutes automatically imposed sanctions, usually in the form of license suspension, regardless of the driver's guilt. When a blood-alcohol reading was obtained from the test, still other statutes determined what presumption, if any, was to be drawn legally from the reading, and the jury was to be instructed accordingly.

The prosecution in a DUI case was now armed with not merely the opinion of one officer, but with "science"; he could now "prove" to the jury what the chemical state of the defendant's body was at the time of the arrest. Furthermore, he could now define for the jury exactly what "under the influence" consisted of; quite simply, it meant having a blood-alcohol reading in excess of .08 or.10 percent. Prosecuting a DUI case became largely a matter of obtaining a blood-alcohol reading and comparing it to the statutory presumptive levels.

But even this was not enough. Backed by increasing public hysteria and the attendant political pressures, prosecutors have succeeded in obtaining the passage of so-called DUI "per se" laws. These laws make it illegal simply to drive with a blood-alcohol level in excess of a certain amount - usually .10 or .08 percent. No longer is intoxication even relevant: The crime of DUI consists entirely of driving while having a given physiological condition. Under such statutes, chemical evidence has taken on even greater importance. The accused's right to jury trial in a DUI case has increasingly been supplanted by "trial by machine" - that is, innocence or guilt is largely determined by a breath analyzing device.

Yet, blood-alcohol tests in drunk driving cases were designed only to corroborate the observations of witnesses, not to take their place. Many scientific studies have been completed and many statistics compiled concerning the validity of the recognized blood-alcohol testing methods and the presumptive levels in DWI cases. There is considerable disagreement within the medical and scientific communities as to any conclusions that can be drawn. There are still many unanswered questions regarding breath, blood, and urine tests and their correlation with impairment of driving ability. Individual tolerances to alcohol are completely ignored, as are the individual physiological differences in absorption and elimination. Testing devices used in DUI investigations vary in quality, and none of them is without numerous sources for error.

Nevertheless, the significance of chemical evidence in a DUI case is considerable. Many judges, for example, will not even permit a drunk driving defendant to enter a plea at his arraignment until the results of the blood or urine analysis are returned from the crime lab. Prosecutors in many, if not most, courts will use the blood-alcohol reading in a given DUI case as a gauge in plea bargaining. If a reading is below .08 percent, for example, a traffic violation may be offered in lieu of a plea of guilty; if the reading is between .08 and .09 percent, a plea to the lesser-included offense of reckless driving may be offered; and if the figure is .10 percent or over, the prosecutor will probably insist on a straight plea as charged. Sentencing, too, is affected in many courts by the blood-alcohol level. As an example, one jurisdiction imposes one day in jail for each point over .10 percent in the defendant's blood-alcohol reading, resulting in an eight-day sentence for a drunk driving suspect with a level of .18 percent. And, of course, chemical evidence is all-important in a DUI per se case.

The most commonly used test is breath analysis. Although generically referred to as a "breathalyzer" (the brand name of one of the earliest models, manufactured by Smith and Wesson), California police agencies use a variety of different makes and models of breath machines - usually at DUI sobriety checkpoints or at the police station. However, all have one thing in common: they are prone to a wide variety of problems and are reliably inaccurate (see the discussion of "Breathalyzer Accuracy" on this website). And an experienced attorney specializing in DUI defense should have the expertise necessary to find the flaws in a given breath test and to demonstrate for a jury the machine's defects.

To cite but one example, breathalyzers are controlled by a primitive computer which calculates the blood-alcohol level of the subject by assuming he/she is average in all ways — despite the fact that individual physiology and alcohol metabolism varies greatly (they do not, for example, distinguish between "he" and "she", despite the fact that alcohol metabolism varies considerable between the sexes). In fact, you may be surprised to learn that these machines do not even measure alcohol! Most use infrared spectroscopy technology to detect the presence of a "methyl group" in the molecules on a subject's breath. However, thousands of chemical compounds contain the methyl group in their molecular structure. Studies have documented over 100 of them on the human breath, including acetone (found in diabetics and people on diets) and such products as paint, thinner, glue, gasoline — most of which can be breathed in as vapors or absorbed through the skin (to be breathed out hours later and registered by a breathalyzer as "alcohol").

Analysis of a blood sample for alcohol is generally more accurate than breath analysis, but problems exists with this method as well: lack of sterilization, preservatives and/or refrigeration; coagulation; vial mix-ups; fermentation of the blood in the vial; etc.

Clearly, the pendulum in DUI cases has swung too far in the opposite direction: The results of all-too-fallible blood-alcohol tests are today accorded far more stature than they deserve. This is a reality that the DUI defense attorney must learn to deal with. He must constantly struggle to de-sanctify the DUI testing procedures. Certainly, he must convince the jury that the procedure used in the case was not only generally unreliable but faulty as applied to the defendant.

The DUI lawyer will discover one benefit from this general feeling of reverence or mysticism toward the blood-alcohol reading. Many prosecutors, particularly inexperienced ones, will present the testimony of the police officer as almost an afterthought, relying instead on the blood-alcohol evidence to convict. Never mind that the officer can testify that the defendant was falling down and incoherent, the prosecutor will hurry on so that he can display the magic number to the jury. This is a common but serious tactical mistake, and one that the DUI lawyer should take advantage of by shifting the focus of the trial from the defendant to the blood-alcohol test. The issue is changed subtly from the intoxication of the defendant to the accuracy of the testing procedure. Prosecutors can be protective of their chemical evidence and will concentrate their efforts on defending against the attacks of defense counsel on the breath machine, urinalysis, or blood analysis. The ultimate question in the jury's mind will subtly shift from one of whether the defendant was under the influence to one of whether the test was valid. If it was not valid, the defendant may well be acquitted, regardless of other damning evidence. In other words, the DUI defense lawyer has succeeded in putting the blood-alcohol test on trial.

The results of breath alcohol testing are susceptible to attack by an experienced and specialized DUI attorney.

Many breath alcohol analysis systems fail to differentiate between the ethanol in alcohol and that of other compounds containing ethanol. Scientific study has shown that breathalyzers are not specifically designed for ethyl alcohol (a compound found in ethanol). These machines can, and often will, detect other compounds similar to that of ethyl alcohol and will identify them improperly as ethanol. Hence, a suspect with other compounds in their system can have an inaccurately high result in a breath test.

This potential problem is most common in the infrared analyzer that most agencies use currently. The reasoning is that many of these types of breath analyzers are not specifically designed to detect ethyl alcohol. They are designed to detect just a portion of ethyl alcohol known as the methyl group. The methyl group is absorbed by the infrared light in the analyzer and results in a positive blood-alcohol result. Any compound with the methyl molecular group can be identified by the infrared analyzer as ethanol.

There are over 1000 known compounds that contain the methyl molecular group. Many of those compounds, such as acetone, are commonly found on the human breath. Several scientific studies have found that many compounds containing the methyl group can be found on the breath at any time. The infrared breath analyzers detect these methyl groups and assume it to be ethanol.

Other common situations that can give false readings include:

  • Diabetics patients
  • People on weight reduction systems
  • Fasting
  • Long-term smokers can have higher blood-alcohol results since they have a greater amount of acetaldehyde in the lungs
  • Alcoholics
  • Absorbed inhalants such as paint fumes, glue fumes, or lacquer fumes
  • Accidental absorbing of gasoline
  • And even some bread products.

As defense DUI experts can testify, the design of these breathalyzers are also an area of concern. The on-board computer used by these machines makes assumptions on the individual being tested. The machine automatically assumes the suspect is of average physiological make up. This is a fatal flaw to the results. The individual being tested, more often than not, is not of average make up. Thus the test can be inaccurate.

For example, all breath-testing machines used by police depend on the assumption that the ratio between alcohol in the exhaled breath and alcohol in the blood is 1 to 2100. In fact, the machine is designed to produce a reading based on that assumption; the accuracy of the reading is directly tied to the accuracy of the presumption. The actual ratio in any given individual can vary from 1:1300 to 1:3000, or even more widely. Thus a person with a true blood-alcohol level of .08% but a breath-to-blood ratio of 1:1700 would have a .10% reading on an accurate breath testing instrument.

Unfortunately, these breath analyzers do not test individuals and their unique physiological make up. Each test will give a result based on an average person's breath and breathing patterns.

These scenarios are just an example of several flaws can be brought up by an experienced DUI lawyer.

For further information about breath and blood alcohol testing, as well as about our law firm, see Lawrence Taylor’s videos on this site.

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