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The scientific determination of alcohol intoxication is always an estimate regardless if the expert is an ordinary police officer armed with a breathalyzer or a forensic toxicologist armed with the most sophisticated laboratory . This is because over 90 million Americans who drink have different body chemistries and physical constitutions that exhibit extraordinary variation in the behavioral effects of alcohol our society has decided to criminalize as “intoxication”. The crime of “drunkenness has been the most common misdemeanor since colonial times. It’s hard not to admit a class or moral bias against intoxication, and it may very well be the perfect example of how the law reaffirms moral boundaries. See Criminal Law lecture #13 (optional reading) if you’re interested in legal distinctions between the act and status of intoxication as public indecency.

It’s also no secret that about 17,500 automobile deaths a year (about 40% of all traffic deaths) and over 2,000,000 automobile injuries are alcohol-related. Alcohol abuse, despite signs of decline, is still at epidemic proportions. That’s why the law doesn’t require full-fledged forensic toxicologists for routine, ordinary alcohol intoxication testing. Those people’s services are better put to use on attempted overdose cases or whether children were exposed to lead paint, for example. Instead, judges have been taking the word of police officers for decades, and the law is replete with numerous examples of precedent where police officer testimony carries the same weight as expert testimony, or at least testimony of the “skilled witness” type.


In 1938, Dr. R.N. Harger developed the first testing instrument, called the Drunkometer, which was followed in 1941 by the Intoximeter, developed by Glenn Forester, and the Alcometer, developed by Prof. Leon Greenberg. All of these machines were designed to take a deep air sample (breath from the alveolar sacs, the site of gas exchange in the lungs) and calculate the rate or proportion of alcohol-in-blood to alcohol-in-breath. This proportion is known as the partition rate, and since 1938, it has been generally accepted that the ratio is approximately 1 to 2,100. All breath testing instruments since then have this ratio built into their circuitry, and sometime during the 1950s, the estimated alcohol-in-blood using this proportion became referred to as BAC (blood alcohol concentration, the percent weight by volume, or % w/v, based upon grams of alcohol per cubic centimeter of blood or 210 liters of breath).

NHTSA (the National Highway Traffic Safety Administration) and LEAA’s National Highway Administration played a key role during the 1970s and 80s in encouraging the proper training of police officers so that they would have sufficient foundation to admit HGN (horizontal gaze nystagmus) testing and other field sobriety tests such as finger-to-nose, walk-and-turn, or the one-leg stand. In spite of opposition by ophthalmologists and other medical people (at least 60 different physical conditions cause nystagmus), NHTSA and the police community managed to convince most judges, prosecutors, and lawmakers that these techniques were reliable, and in some states became the equivalent of “non-scientific” Frye-approved techniques. Field sobriety testing is now part of every basic policy academy curriculum (at least eight hours of training is required in most states). Perhaps it might be instructive to examine this “skilled witness” standard in some detail; State v. Superior Court 149 Ariz. 269 (1986):

HGN and other field sobriety tests need not be held on the basis of the Frye principle of “general acceptance” since when administered by a trained police officer are sufficiently reliable to corroborate and establish, but not to quantify, probable cause. The police witness, though not necessarily college trained, will nevertheless be considered an expert in a non-scientific category for which no expert testimony is required.

The story of nystagmus testing is a story about the dispensing of true scientific evidence and a devaluation of whatever meaning the word “expert” has. Little support for its reliability can be found outside of police training manuals (for example: any eye doctor will tell you that wearing contact lenses makes a difference but police manuals say it makes no difference at all), AND this may sound like a harsh criticism, but it’s the one area of police science where the less college education one has, the more steadfast and credible the “skilled witness” will be in advocating its reliability (at least in knowing what 45 degrees or an eye jerk looks like). Judges tend to blindly accept these tests, and some prosecutors have attempted to use HGN as direct evidence instead of probable cause. Roadside testing (other than HGN) does not require probable cause, and it may make sense to refer to two (2) categories of tests: 3 STEPS OF HGN TESTING:

1. Eye jerks following an object moved laterally

2. Eye jerks trying to use peripheral vision

3. Point at which jerking first occurs estimates BAC: 40 degrees equals .10; 35 degrees equals .15; 30 degrees is .20+

Tests that require the suspect to do something (so-called evidentiary tests), including blow into a tube, give blood, stand on one leg, walk a line, touch their nose, HGN. The issue is whether these sufficiently reliable techniques constitute a search or a frisk, and most states have gotten around this with implied consent laws that trigger something akin to a search incidental to arrest.

Test that don’t require the suspect to do anything (so-called preliminary tests), including erratic driving, slurring, having bloodshot eyes, the odors associated with alcohol. The issue is whether these roadside techniques or checkpoints constitute an invasion of privacy, are searches under plain view, and are the basis of probable cause or just reasonable suspicion. (Discussion question: Write a checklist of things you would recommend looking for, in addition to those mentioned above, that would constitute a “DUI offender profile”.)

Sometime around 1984, Smith & Wesson sold off its Breathalyzer Division, and although such devices were around prior to that date, this is the year of the first truly automatic machine that found its way into most police departments — the Breathalyzer Model 1000. NHTSA, DOT (the Department of Transportation), and the National Safety Council all contributed to the popularity of these (“DOT-approved”) devices and the market-mania that accompanies today’s debates over whether the Intoxilyzer 5000 is better than the Breathalyzer 7410, other various Intoximeters/Intoxilyzers or portable handheld devices. Mobile units tend to be used at checkpoints or in school demonstrations.


The best medico-legal scientific method for determining anything close to “impaired judgment” is an estimate of the amount of alcohol that has flowed through the blood vessels of the brain. Theoretically, a blood sample drawn from the brain’s blood vessels (or from spinal fluid) would yield the most accurate results. However, for practical purposes, blood samples are usually drawn from the arm, and there is little or no research on circulatory systems regarding whether arms are the best place to estimate brain alcohol concentration (some people may have poor circulation in one or more extremities).

With blood tests, the law allows a suspect to have an analysis done at a laboratory of their own choice. Two samples are therefore drawn at the same time (as close to the traffic stop as possible), one vial for the police and another vial for the suspect’s hospital. A preservative (sodium fluoride or mercuric chloride) must be added to the vials, otherwise putrefaction begins in a matter of hours. The vials must also not be exposed to sunlight or heat.

The most commonly used laboratory test for alcohol in a blood sample is called the dichromate oxidation method (a type of chemical test). This involves using ready-made ampoules consisting of a mix of chromium dichromate and sulfuric acid. If anything containing alcohol is introduced into this solution, a residue of chromic sulfate will form due to oxidation. The unconsumed amount of dichromate or the chromic sulfate formed is then measured which gives the percentage of alcohol in the sample expressed in percent weight per volume, which is exactly the same formula for estimating BAC.

Many states require a blood test in all traffic fatality incidents, and with most commercial drivers (who are held to be intoxicated at a much lower, .04%, standard). Congress also (under the Uniform Vehicle Code) withholds federal highway funds from any state that does not use intoxication standards of .10% or .08% for all drivers. At the state level, these standards translate into what are called “per se” laws, making it illegal per se to be in physical control of a vehicle while having an alcohol concentration above .08%. The UVC presumes any concentration of .08% or more is “under the influence”, anything .05% or less is “not under the influence”, and anything between .05% and .08% shall not give rise to any presumptions, but can be considered with other competent evidence in a police determination of “under the influence” or not. A “per se” law gives a jury no choice but to consider the defendant intoxicated.

As with all intoxication testing, if the technique, method, or instrument used produces a digital display and a printout, the witness testifying for the prosecution need not be a chemist or scientist. Occasionally, the “professional quality” of a laboratory comes into question and/or the chain of evidence, but typically, it’s the police officer or someone else who talked to the defendant that testifies as an expert in what is called retrograde extrapolation. The expert states that they know when the drinking started and ended, the absorptive interval of time, and when the person last ate (one reason why police ask these questions early on in DUI stops). This witness then extrapolates backward in time from the BAC estimation to the time of driving, accounting for the full ingestion and absorption of alcohol, and is questioned as to whether it is scientifically impossible (with reasonably certainty) for the person to be below the legal limit at the time of the offense. The prosecution is never required to produce such a witness; the mere mention that they can is often admissible and persuasive in many cases. Some states do not allow the defense any opportunity to present their own extrapolation evidence. (Discussion question: Defend the seemingly one-sided and unfair practice of retrograde extrapolation from a prosecutorial viewpoint, then argue against it from a defense viewpoint. Devote equal time to each side.)


Urine normally contains about 1.3 times as much alcohol as blood, but attempts to relate this to BAC depend on a number of bladder conditions. If alcohol is consumed with a full bladder (the person has not voided themselves), the test would produce a false negative (inaccurately underestimate). If the person consumed alcohol with an empty bladder and had not voided, the test would produce a false positive (inaccurately overestimate). Urinalysis tests, most of the time, are not favorable to the defendant. Higher concentrations of alcohol in urine will occur over a longer period of time than in blood.

Law enforcement practice is to take two (2) samples, at 30-minute intervals, preferably the latter sample after the bladder has been emptied. Again, precautions must be made to add preservative and keep the samples from exposure to light and heat. Urinalysis requires a bit more sophisticated laboratory equipment than for blood testing. One of three (3) laboratory methods are used: (1) chemical tests; (2) biochemical tests; and (3) gas chromatography. Gas chromatography is the most widely used because it can distinguish alcohol from ketones and aldehydes (a problem that exists with diabetics and people with other disorders that blood tests are not capable of controlling for). While chromatography produces a printout and lends itself to quantitative analysis, it always requires the expert testimony of a scientist to be admissible in court. This is because chromatography results are subject to both quantitative and qualitative interpretation.


It’s important that police departments choose professional, high-quality vendors to get their supplies (ampoules, vials, preservatives, chemicals) from. At a minimum, there should be lot numbers on each and every product which indicates manufacturer testing and quality control procedures.

It’s also important that packaging and preservation of evidence be consistent. The FBI has taken the lead in proposing standards (paper or plastic), but some laboratories have their own preferences, and police departments often run out of certain supplies and make do with what’s on hand (which should be avoided). Bottled specimens sent to any lab should also have expiration dates on them, following whatever guidelines are listed on the preservative’s brochure. There should also be independent corroboration (a statement by witnesses) of the sample being collected, packaged, and mailed out (chain of evidence).

Laboratories themselves, in order to be considered “professional”, must adhere to rigorous internal and external controls. Externally, they should be site visited or audited by outsiders on a regular basis as part of a certification or accreditation process. Internally, they should have excellent record-keeping and quality controls. It must be assured that all chemical reagents are fresh as things like dichromates and permanganates tend to have short shelf life. Instruments must be calibrated and standardized (using equilibrator solutions) after every use. Instruments, syringes, vials, and flasks used in alcohol testing should never be cleaned or sterilized in alcohol solutions. Boiling, likewise, will often trap alcohol-related impurities or distillates into the equipment. Containers must not be contaminated with foreign substances, and this includes the air. Exposure to air not only contributes to putrefaction of alcohol samples but transmits oxidizable organic materials that may produce false positives.


Breath tests are an indirect yet most practical way of estimating alcohol intoxication. They have the advantages of being able to produce digital display and printed readout (calculated in terms of BAC per the built-in 1 to 2,100 ratio), results obtainable in minutes (as opposed to long waits for laboratory reports), a short chain of evidence (custody), low operator skill requirements, low cost, and little invasiveness of the human body. They have the disadvantages of breath samples being difficult to preserve (silica gel is about the only thing), relying upon cooperation of the suspect, requiring a waiting period of 15-20 minutes (to eliminate residue mouth alcohol), interference from foreign sources (RFI or radio frequency interference), and interference by other objects/odors in mouth. Police have no constitutional duty to preserve breath samples (under Brady rules), and there’s usually no requirement for a second test sample (as with blood or urine, although some departments do perform a second test).

Police officers are the experts when it comes to breath testing. They typically attend a breath testing school, and are taught only that which the designers of the instrument feel it is necessary for the officer to know and which they feel he/she can understand and relate to others. A lot is left out, and if a defense attorney tries asking probing questions about the digestive tract and respiratory systems, they will quickly be perceived as trying to discredit an honest, hard-working officer with irrelevant scientific nonsense. “I’m an operator, not a scientist” is the usual response from a non-scientific expert.

Nevertheless, most states have constructed elaborate certification systems which are a sought-after training by police officers. Becoming certified in breath testing offers some degree of protection from challenges to professionalism. The following is an example from the system in North Carolina:

Approximately 5,000 law enforcement officers in North Carolina have been trained and certified as Chemical Analysts on the Intoxilyzer 5000 breath alcohol testing instrument. Each year about 1,000 officers are certified for the first time. The initial training on the Intoxilyzer is a one-week school in which law enforcement officers receive training on law, rules and regulations, theory, science of alcohol and the human body, and hands-on use with the Intoxilyzer. Chemical Analysts are required to attend a one-day recertification class every two years in order to maintain their permits. Approximately 2,000 Chemical Analysts are recertified annually. A training class is also provided on portable breath alcohol test devices. Approximately 2,500 officers complete that training each year. In addition to providing Law Enforcement Training, Forensic Tests for Alcohol’s 14 field staff members are responsible for maintaining the 252 Intoxilyzer 5000 breath test units located in 162 law enforcement test sites throughout the state.

There are actually three (3) different types of breath testing instruments: (1) desktop models, such as the Intoxilyzer 5000, the kind we’ve been discussing, although modern infrared devices are also becoming common; (2) PBTs, or Preliminary Breath Testing devices; and (3) PASDs, or Passive Alcohol Screening Devices.

PBTs (like the ALERT models or Intoximeters) are sometimes referred to as handheld “roadside” devices or “portables”, and are about the size of a pocket calculator. They require a person to blow into a balloon or a plastic tube about the size of a cigarette. Most PBTs are calibrated to give a “pass-fail” reading, set at .05% (for no presumption but the collection of other corroborative evidence) or .08% (for a presumption of intoxication). A few models give a digital readout of the estimated BAC. These devices are intended to be used for preliminary purposes only, as screening devices along with an officer’s other observations. They are not normally admissible in court on the factual issue of intoxication, but they are active devices, requiring the suspect to do something, hence they are likely to be considered as legitimate search evidence under plain view, incident to arrest, or some other doctrine.

PASDs (like England’s Lion Alcometer), by contrast, are portable passive devices that sniff or sample the air around a person. They are about the size of a flashlight, consisting of a miniature fan (to pull the air in), a salt-based alcohol sensing device, a sensitivity knob, and an indicator light. A PASD is held in front of a person’s face (for as long as it takes to exhale) or in the head area of the driver’s compartment (once they have left the vehicle). The latter technique is inappropriate when there are open bottles of alcohol in the vehicle and/or drinking passengers. Passive devices often give false positives in the presence of car exhaust, perfume, aftershave, hair oil, and airborne contaminants. By adjusting the sensitivity knob for such considerations, passive devices often give false negatives (anything less than maximum sensitivity works in the favor of the suspect). PASDs work best in temperate climates (those consistently around 70 degrees), and tend to be less sensitive in cold weather and more sensitive in warm weather. Like PBTs, PASDs are not designed to be admissible in court as a substitute for BAC readouts. However, they effectively counter the challenge of a suspect who says they haven’t been drinking.


As with most machines, error is classifiable into operator and equipment failure. However, alcohol intoxication theory may be more fundamentally flawed. The 1:2,000 partition ratio (which has been assumed true since 1938) and is an integral part of the internal calibration of all machines may NOT be reliable. There’s scientific research that the true ratio varies from 1:1000 to 1:3000, depending upon the individual. Just to name a few differences: females absorb, distribute, and eliminate alcohol 10% faster than males; heavy people have different tolerances in their stomach linings; and physically fit people have different tolerances in their lung sacs. Some judges are aware of this, and exercise a little leniency, or give-and-take, when the estimated BAC is a close call. For example, if the state’s standard is .08%, a court might permit and closely consider challenges for police estimations in the .09% or .10% range. However, it’s pretty much hopeless to raise a defense challenge in a case where the BAC is .12%, .13%, or higher.

There’s also controversy surrounding the conventional wisdom of charts that imply a connection or nexus between certain BAC ranges and certain behaviors. Aside from the seriousness of the matter, almost everyone has heard the joke that “you should be in a coma” with that much alcohol. Various other charts or popular “drunk wheels” showing how to calculate BAC based on amount and body weight are a step in the right direction, but are likewise controversial. As previously mentioned, there are at least 60 different pathologies other than alcohol intoxication (even personality disorders) which produce similar behavioral symptoms. It’s generally accepted that alcohol affects higher cerebral functions (like judgment and self-restraint), but only at higher levels is there anything like problems with nerve impulses or muscular control. (Discussion: Has society set the standard for alcohol-related impairment too low or too high? Defend your answer by relating your choice of a specific BAC range to possible social harms.) Here’s a typical BAC range chart:

0.03 – 0.12 Euphoria Euphoria, sociability, talkitiveness Self-confidence, decreased inhibition Diminuation of attention, judgment and control Beginning of sensory-motor impairment Loss of efficiency in finer performance tests 0.09 – 0.25 Excitement Emotional instability, loss of critical judgment Impaired perception, memory, comprehension Decreased sensatory response, reaction time Reduced visual acuity, peripheral vision Sensory-motor incoordination, impaired balance Drowsiness 0.18 – 0.30 Confusion Disorientation, confusion, dizziness Exaggerated emotional states Disturbances of vision and/or perception Increased pain threshold Staggering and slurred speech Apathy, lethargy 0.25 – 0.40 Stupor Inertia, approaching loss of motor functions Lack of response to stimuli Inability to stand or walk Vomiting, incontinence Impaired consciousness, sleep or stupor 0.35 – 0.50 Coma Complete unconsciousness Depressed or abolished reflexes Subnormal body temperature Incontinence Impairment of circulation and respiration Possible death 0.45 + Death Death from respiratory arrest

Some defense attorneys claim there are at least 30 different ways to “beat” a DUI rap, even more for opinion evidence of the field sobriety nature. The following is a short list of the most commonly seen DUI defenses:

1. Operator Error – in general, not following the operator’s manual, which is sometimes countered by a good faith argument, but specific errors, like not following the 20-minute rule, cannot be overlooked.

2. Improperly Dedicated Power Source – the power circuit should be grounded and surge-protected. Also, there should be no cameras, microwaves, coffee pots, toaster ovens, or other electrical appliances that can cause “spikes” on the same circuit or even in the same room. Sometimes, defense attorneys will take a picture of the police room.

3. Radio Frequency Interference – RFI occurs when a component of the machine acts as an antenna. Also, no cellular or cordless phones should be used in the area at the time. However, testing device manufacturers have made great strides in producing equipment nowadays that locks out, checks, or otherwise controls for RFI.

4. Mouth Contamination – some of the things that cause early “spikes” in the readout are menthol tobacco (smokeless), mints, lozenges, denture adhesive, lip balm, breath spray, recent dental work, asthma inhalers, and pepper spray. If readouts are “spiking”, a flatline or plateau in the readout indicates the desired alveolar air.

5. Environmental Contamination – some of the things in the air that cause “spikes” include solvents in the workplace (Brasso), hair spray, nail polish, and airplane glue.

6. Physical Condition of Suspect – a variety of things affect accurate readout, including:

Hyperventilation – being upset, crying, vomiting, for example

Sitting down and bending forward – this pushes air up from the stomach

Gastric reflux – if the suspect has gas or indigestion

Diabetes – if the suspect’s sugar levels are off

Liver malfunction or disease – as well as renal dysfunction

Tuberculosis – TB can get trapped permanently in the machine

Prescription drugs – Nyquil, Sinus medication, Antabuse, many others

Diet – if the suspect has been fasting or is on a high-protein regimen

Body temperature – if because of illness or menstruation. The general rule is that a one degree elevation in body temperature equals an increase of .03% in BAC.

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H. Michael Steinberg Esq.
Attorney and Counselor at Law
The Colorado Criminal Defense Law Firm of H. Michael Steinberg
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