Category Archives: Duiblog

Why Breathalyzers Don’t Measure Alcohol

That’s right: Breathalyzers don’t actually measure alcohol. What they actually detect and measure is any chemical compund that contains the methyl group in its molecular structure. There are thousands of such compounds — including quite a few which can be found on the human breath. And this machine that determines a person’s guilt or innocence will "see" all of those chemicals as alcohol — and report a falsely high "blood-alcohol" concentration (BAC).

Most breath machines used in DUI cases by law enforcement today employ a technology called "infrared spectroscopy". The DUI suspect breathes through a tube connected to the machine and a breath sample is captured in a small "sample chamber" inside the machine. Then beams of infrared energy are shot through the captured breath sample. If there are any compounds containing the methyl group, they will absorb some of this energy; the more of the chemical compound in the breath sample, the more energy is absorbed. The more energy that is absorbed, the less infrared energy that reaches sensors at the other end of the sample chamber. And the less energy that is detected by the sensors, the higher the "blood-alcohol" reading.

Problem: the machine is designed to simply assume that the chemical compound absorbing the energy is alcohol. If a person has any of these other compounds on his breath, called "interferents" by the engineers, he will get a falsely high BAC test result. And if there are two or three such compounds on his breath, the machine will read a cumulative result: it will add them up and falsely report the total as the blood-alcohol level.

So what kinds of compounds may be on a person’s breath that can cause false BAC readings in a DUI case? In one study of eight men, 69 different compounds containing the methyl group were discovered. "Trace Composition of Human Respiratory Gas", 30 Archives of Environmental Health 290. In another study invoviing 28 subjects, researchers found that teh "combined expired air comprises at least 102 various organic compounds of endogenous and exogenous origin". "Characterization of Human Expired Air", 15 Journal of Chromatographic Sciences 240. And Camnadian scientists have discovered over 200 such compounds. "The Diagnostic Potential of Breath Analysis", 21(1) Clinical Chemistry 5.

What are these compounds? Are there any on my breath?

Well, for starters, diabetics with low blood sugar can have high levels of acetone — which is "seen" as alcohol by Breathalyzers. And scientific studies have found that people on diets can have reduced blood-sugar levels, causing acetone hundreds of times higher than found in normal individuals. Frank and Flores, "The Likelihood of Acetone Interference in Breath Alcohol Measurements", 3 Alcohol, Drugs and Driving 1. And there are many other so-called "interferents". See, for example, "Excretion of Low-Molecular Weight Volatile Substances in Human Breath: Focus on Endogenous Ethanol", 9 Journal of Analytical Toxicology 246.

If you are a smoker, your Breathalyzer result is likely to be higher than expected. The compound acetaldehyde — reported by the Breathalyzer as "alcohol" — is produced in the human body as a by-product in metabolizing consumed alcohol, and eventually passes into the lungs and breath. Researchers have discovered that levels of acetaldehyde in the lungs can be 30 times higher in smokers than in non-smokers. Result: higher BAC readings on the machine.

And then there are the industrial compounds: paint, glue, gasoline, thinners, and other compounds contain the methyl group. No, you don’t have to drink the stuff: simply absorbing it through your skin or inhaling the fumes can result in significant levels of the chemical in your body for hours or even days, depending upon the "half-life" of the compound. So if you’ve painted a room or siphoned some gasoline in the last day or two, don’t breath into a Breathalyzer.

Some law enforcement officials say that this is not a problem, claiming that levels of the compound would have to be at toxic levels to raise a breath test result to .08% or higher. These officials are displaying their ignorance of the science involved — specifically, of the partition ratio. This is the ratio of the compound found in the breath to that found in the blood. With ethanol, the ratio is 2100-to-1, which means that, on average, there will be 2100 units of alcohol in the blood for every unit found in the breath.

These officials are using this ratio for all compounds, but every compound has its own ratio. Toluene (found in paint, glue, thinners, cleaning solvents. etc.), for example, has a partition ratio of only 7-to-1; a far greater amount of toluene in the blood will pass into the breath, and so a much smaller amount in the body will have a far greater impact on the breath machine.

The DUI Exception?

I have referred in many of my posts to a “DUI exception to the Constitution”, and have had numerous queries as to just what exactly this exception is.

There is, of course, no such “exception”. The term is one I have used for many years to characterize the increasing tendency in DUI cases to ignore the United States Constitution. It is easy for politically-sensitive legislators and judges to give in to the pressures of groups like Mothers Against Drunk Driving (MADD), particularly when there is no one to stand up for those whose rights are being violated. But the price is paid not only by the accused, but by all of us: it is the Constitution itself that is eroded. And the nature of our legal system is one of “precedent”: if it is permissible to ignore the Constitution in a DUI case today, then the precedent exists to ignore it in all cases tommorrow.

At some point I began using the term as the title of a lecture I’ve given to various groups of lawyers and laymen on the increasing danger to our Constitutional rights from the political pressures of well-intentioned but ignorant groups like MADD. The lectures have since been reproduced on a number of websites. For an example, see the transcript on Atlanta attorney William C. Head’s website.

Warning: Breathalyzer in Use

Have you ever noticed those "Warning: Microwave in Use" signs in restaurants? It’s for folks who have heart pacemakers: There is a risk that the electromagnetic interference (EMI) from the microwave will interfere with the electronic circuitry in the customer’s pacemaker and cause it to malfunction. This phenomenon, often called radio frequency interference (RFI), can be a recurring problem with any instrument containing electronic circuitry.

Now try to think of some place in your neighborhood that is chock full of electronic gizmos constantly transmitting RFI 24 hours a day. How about a police station? Powerful dispatch radio transmitters, radio transmitters in squad cars in the parking lot, walkie-talkies in every officer’s belt, cell phones, computer cathode ray tubes, microwave relays, electronic door locks, microwave ovens, fluorescent lighting — a veritable jungle of RFI. Now let’s put a Breathalyzer smack in the middle of this police station. An instrument filled with sensitive electronic circuitry that has to analyze tiny amounts of alcohol in breath to an accuracy of one tenth of a percent…..

Just a theory of some DUI defense attorney? Consider a report from the National Bureau of Standards, under contract with the National Highway Traffic Safety Administration to conduct accuracy testing on breath machines (referred to in the report as "Evidential Breath Testing" devices, or "EBTs"):

The Washington D.C. Metropolitan Police Department reported to NHTSA that EBTs were found to display erroneous BAC [blood-alcohol content] readings in the presence of electromagnetic fields from radio transmission…. Representatives of NHTSA and NBS were given a demonstration by police officers who routinely conduct breath testing using an EBT in a mobile van. One police officer operated his handheld radio within 1 foot of the EBT and demonstrated that the electromagnetic field could severely affect the analysis of alcohol samples.

The National Bureau of Standards subsequently conducted the testing and subsequently reported that

These results show that EMI is a potential problem with many of the EBT units currently in use….The states may have to take interim measures to determine the extent of their individual problems with EMI affecting EBTs.

The reaction by the federal government to this report was, perhaps, predictable. Afraid that it would undermine public confidence in law enforcement methods, the government classified the document and then buried it. However, it was later resurrected by a Minneapolis DUI law firm’s Freedom of Information Act lawsuit. Most manufacturers of breath machines today quietly offer an "RFI detector" as an option in their products. Unfortunately, these "detectors" are unreliable and, in any event, are rarely purchased by law enforcement agencies.

Note: all 50 states now make it a crime to drive with a blood-alcohol level of .08% or higher. In most cases, the only evidence of this comes from the breath machine. The breath cannot be re-analyzed. The machine cannot be cross-examined.

How to “Drive” Under the Influence While Sleeping

The DUI laws make it unlawful to drive (or, in some states, "operate") a vehicle while under the influence of alcohol (or over .08% blood-alcohol). That seems pretty clear: driving…vehicle…under the influence. Not really very complicated, is it? No, unless you’re an officer, a prosecutor or a MADD lobbyist trying to stretch the language of these laws to fashion a larger net.

How about that little word "driving", for example? Now just what does that really mean? Well, it means driving. Engine on, moving, steering, shifting, braking… that kind of thing, right?


Let’s take a look at a few examples of how law enforcement, prosecutors and courts have increasingly expanded that seemingly simple word to widen the DUI dragnet — by doing violence to the clear language and intent of the law.

- Engine off, car being pushed or towed….Let’s consider a case where the engine was off, but it was in motion — say, being towed? And the defendant was behind the wheel, steering: Is that driving?Yes, say some courts: "While a person is being towed, the person assumes responsibility for steering and braking the vehicle in a safe manner." State v. Dean (Oregon, 733 P.2d 105). Well, ok, maybe it’s not a huge stretch to include a towed car within the term "driving". At least it’s moving.

- Engine on, but vehicle parked….What if the car isn’t moving? What if the individual is just sitting behind the wheel of his car, parked but with the engine on, say, to keep the heater working?Many courts will require some movement of the vehicle, but others consider this "driving" or "operating".

- Engine on, but vehicle inoperable….An Ohio court had no trouble finding "driving" where the defendant was behind the wheel of her car, engine on — but stuck in the mud with two blown tires. City of Columbus v. Seabolt (607 N.E.2d 61).

- Engine off, vehicle parked….How about if the engine is off? If you’re just sitting behind the wheel of a parked car? More disagreement among the courts. The Colorado Supreme Court found "driving" where the defendant was behind the wheel of a car in a private parking lot, engine off — but the lights on. MVD vs.Warman (763 P.2d 558).

- Engine off, and vehicle inoperable….What if the car has a mechanical problem or is out of gas? If the car won’t start, how can it be driven? Not a problem, according to some courts anxious to sustain convictions.

Well, heck, next thing they’ll be arresting folks in their cars for "sleeping under the influence". Actually, hard as it may be to believe, they’ve been doing just that for quite awhile. There are plenty of appellate cases affirming DUI convictions where the defendant was asleep or unconscious in his car. – Engine on, "driver" asleep or unconscious….That’s "driving", say a number of courts. See, for example, Matter of Clayton (Idaho, 748 P.2d 401). Even in those cases where the engine was left on in cold weather so the heater could work.

Well, surely no one can say a person is driving if he is asleep AND the engine is off? – Engine off, "driver" asleep or unconscious….Amazingly, there is no shortage of courts willing to extend the crime of driving under the influence to individuals who are found asleep or unconscious in cars whose engines are turned off. In State v. Lawrence (849 S.W.2d 761), for example, a Tennessee court held that a defendant asleep on the driver’s side with the keys in his pocket was in sufficient physical control of the car to satisfy the statute. And in State v. Peterson (Mont. 769 P.2d 1221), a DUI conviction was sustained where the "driver" was found slumped onto the middle of the front seat; the car was off the roadway and the keys were in his pocket.

Don’t we want to encourage folks who think they may have had too much to drink to pull over and sleep it off? Why would we want to discourage this by arresting them? And what’s going on here with the word game? What does NOT constitute "driving"? Why are some courts so willing to support police and prosecutors from going far beyond the clear wording and intent of the laws?

The answer may be found in a Minnesota case, in which a conviction was sustained where the defendant was found in his pickup, engine off and with his head resting on the steering wheel. "The real purpose of the statute", the court wrote, " is to deter individuals who have been drinking intoxicating liquor from getting into their vehicles." State v. Juncewski (Minn., 308 N.W.2d 316)

Funny, I thought the "real purpose" of laws was to punish people who actually committed the crime — not just to send people to jail who came close. If the "real purpose" of the law is as stated by the Court, why didn’t the legislature just prohibit citizens "who have been drinking intoxicating liquor from getting into their vehicles"? Of course, then the guy working on his engine would get arrested for "getting into" his vehicle. And the guy changing a tire. And…..

Convicting the “Average” DUI Suspect

One of the greatest sources of error in breath-alcohol testing is the consistently recurring fallacy that the individual tested is perfectly average in certain critical physiological traits. Put another way, obtaining an accurate blood-alcohol reading in a DUI case is completely dependent on the validity of a number of assumptions. Unfortunately for the person being tested, these assumptions are usually incorrect: The person tested is rarely “average” in even one of these critical characteristics, let alone in all of them.

For example, all breath testing devices 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. Yet, the actual ratio in any given individual can vary from less than 1:1300 to more than 1:3000. So a DUI suspect with a true blood-alcohol level of .08 but a breath-to-blood ratio of, say, 1:1700 would have a .10 reading on an “accurate” breath testing instrument.

Put simply, these machines do not test individuals. Rather, they test the same “average suspect” over and over again, but using the individual subject’s breath.

Another example of the assumption of “averageness” can be found in urinalysis. When a DUI suspect’s urine is analyzed for blood-alcohol, a presumption exists that there are 1.3 parts of alcohol in the bladder’s urine for every 1 part of alcohol in the blood. This 1:1.3 ratio is as fallacious as the 1:2100 ratio’that is, it is based entirely on the ratio found in the average person. In fact, however, the actual ratio found in any given individual can vary greatly. And as the ratio is in error, so will be the final blood-alcohol reading.

Another example of this constant reliance on averages shows itself when the prosecutor in a DUI trial offers evidence of so-called “retrograde extrapolation”, or guessing backwards. The blood-alcohol level at the time of testing is not relevant to the charge, of course, and so the state will offer evidence to show what the level was when the defendant was driving. This is commonly done by “extrapolating” backward’that is, computing the earlier blood-alcohol level by estimating how much alcohol had been eliminated or “burned off” in the period between driving and testing. But this requires two assumptions: The blood-alcohol level was declining and the rate of elimination is known. This second assumption involves the further assumption that the “burn-off” rate was .015 percent per hour (sometimes the assumed rate is .02 percent). How does the prosecution know that the defendant was eliminating (assuming he was eliminating rather than absorbing) at that rate and not at .005 percent or .3 percent? Quite simply, the prosecution does not know: It merely assumes that the defendant eliminates at the average rate. And, of course, error in such an assumption translates into error in the extrapolation.

This ever-present “average person” in the DUI arena is not limited to chemical analysis. We even find him with the arresting officer in the field. When the officer administers the “nystagmus'’ test (“follow my finger with your eyes”) as part of the battery of field sobriety tests, he operates on the assumption that the suspect is “Mr. Average.” The officer has been trained to “read” at what angle the suspect’s eyes begin jerking. If it begins before 45 degrees, the suspect fails. And where does the magic figure of 45 come from? The average person.

Don Nichols, a pioneer among DUI defense attorneys, would point out to juries that his client is female, Chinese and deceased’despite obvious evidence to the contrary. He then explains that statistically there are more women than men in the world, more Chinese than any other nationality and more dead human beings than living ones. Statistically, then, the average person is female, Chinese and deceased’and so, according to the prosecution, must be his client. He also asks the jury how many of them have 2.3 children’the average in the United States.

So why does the state presume facts that are clearly untrue? Simple. It is convenient: it makes prosecution and conviction much easier.