A law enforcement grade Breathalyzer
A breathalyzer or breathalyser (a portmanteau of breath and analyzer/analyser) is a device for estimating blood alcohol content (BAC) from a breath sample. Breathalyzer is the brand name of a series of models made by one manufacturer of breath alcohol testing instruments (originally Smith and Wesson, later sold to National Draeger), and is a registered trademark for such instruments.[1] In Canada, a preliminary non-evidentiary screening device can be approved by Parliament as an approved screening device, and an evidentiary breath instrument can be similarly designated as an approved instrument. The U.S. National Highway Traffic Safety Administration maintains a Conforming Products List of breath alcohol devices approved for evidentiary use,[2] as well as for preliminary screening use.[3]
A 1927 paper produced by Emil Bogen,[4] who collected air in a football bladder and then tested this air for traces of alcohol, discovered that the alcohol content of 2 litres of expired air was a little greater than that of 1 cc of urine. However, research into the possibilities of using breath to test for alcohol in a person's body dates as far back as 1874, when Anstie made the observation that small amounts of alcohol were excreted in breath.[5]
Also, in 1927 a Chicago, IL corner-chemists by the name of W.D. McNalley invented a breathalizer in which the breath moving through chemicals in water would change color. One interesting use for his invention was for house wives to test whether their husbands had been drinking before letting them in the house.[6]
The first practical roadside breath-testing device intended for use by the police was the drunkometer. The drunkometer was developed by Professor Rolla H. Harger in 1938.[7] The drunkometer collected a motorist's breath sample directly into a balloon inside the machine. The breath sample was then pumped through an acidified potassium permanganate solution. If there was alcohol in the breath sample, the solution changed colour. The greater the colour change, the more alcohol there was present in the breath.
In late 1927, in a case in Marlborough, England, a Dr. Gorsky, Police Surgeon, asked a suspect to inflate a football bladder with his breath. Since the 2 liters of the man's breath contained 1.5 ml of ethanol,[dubious – discuss] Dr. Gorsky testified before the court that the defendant was "50% drunk".[8] Though technologies for detecting alcohol vary, it is widely accepted that Dr. Robert Borkenstein (1912–2002), a captain with the Indiana State Police and later a professor at Indiana University at Bloomington, is regarded as the first to create a device that measures a subject's blood alcohol level based on a breath sample. In 1954, Borkenstein invented his Breathalyzer, which used chemical oxidation and photometry to determine alcohol concentration. Subsequent breath analyzers have converted primarily to infrared spectroscopy. The invention of the Breathalyzer provided law enforcement with a non-invasive test providing immediate results to determine an individual's breath alcohol concentration at the time of testing. Also, the breath alcohol concentration test result itself can vary between individuals consuming identical amounts of alcohol due to gender, weight, and genetic pre-disposition.
When the user exhales into a breath analyzer, any ethanol present in their breath is oxidized to acetic acid at the anode:
CH3CH2OH(g) + H2O(l) → CH3CO2H(l) + 4H+(aq) + 4e-
At the cathode, atmospheric oxygen is reduced:
O2(g) + 4H+(aq) + 4e- → 2H2O(l)
The overall reaction is the oxidation of ethanol to acetic acid and water.
CH3CH2OH(l) + O2(g) → CH3COOH(l) + H2O(l)
The electrical current produced by this reaction is measured by a microprocessor, and displayed as an approximation of overall blood alcohol content (BAC) by the Alcosensor.
Breath analyzers do not directly measure blood alcohol content or concentration, which requires the analysis of a blood sample. Instead, they estimate BAC indirectly by measuring the amount of alcohol in one's breath. Two breathalyzer technologies are most prevalent. Desktop analyzers generally use infrared spectrophotometer technology, electrochemical fuel cell technology, or a combination of the two. Hand-held field testing devices are generally based on electrochemical platinum fuel cell analysis and, depending upon jurisdiction, may be used by officers in the field as a form of "field sobriety test" commonly called PBT (preliminary breath test) or PAS (preliminary alcohol screening) or as evidential devices in POA (point of arrest) testing.
There are many models of consumer or personal breath alcohol testers on the market. These hand-held devices are generally less expensive than the devices used by law enforcement. Most retail consumer breath testers use semiconductor-based sensing technology, which is less expensive, less accurate, and less reliable than fuel cell and infrared devices.
All breath alcohol testers sold to consumers in the United States are required to be certified by the Food and Drug Administration,[9] while those used by law enforcement must be approved by the Department of Transportation's National Highway Traffic Safety Administration.[10]
Manufacturers of over-the-counter consumer breath analyzers must submit an FDA 510(k) Premarket Clearance to demonstrate that the device to be marketed is at least as safe and effective, that is, substantially equivalent, to a legally marketed device (21 CFR 807.92(a) (3)) that is not subject to Premarket Approval (PMA). Submitters must compare their device to one or more similar legally marketed devices and make and support their substantial equivalency claims.[11] The devices are cleared as "screeners" which means they have met the requirements used by the FDA for detecting the presence of alcohol in the breath. Screener certification does not mean that the device can measure breath alcohol content accurately. Many breath analyzers cleared by the FDA are very inaccurate when it comes to BAC measurement. No semiconductor device has ever been approved for evidential use (to stand-up in a court of law) by any State Law Enforcement Agencies or the U.S. Department of Transportation.
A Breathalyzer in action.
The breath alcohol content reading is used in criminal prosecutions in two ways. The operator of a vehicle whose reading indicates a BAC over the legal limit for driving will be charged with having committed an illegal per se offense: that is, it is automatically illegal throughout the United States to drive a vehicle with a BrAC of 0.08 or higher. One exception is the State of Wisconsin, where a first time drunk driving offense is normally a civil ordinance violation.[12] The uniformity is due to Federal guidelines, since motor vehicle laws are States'; in earlier years the range of the threshold varied considerably between States. The breath analyzer reading will be offered as evidence of that crime, although the issue is what the BrAC was at the time of driving rather than at the time of the test. Some jurisdictions now allow the use of breath analyzer test results without regard as to how much time passed between operation of the vehicle and the time the test was administered.[citation needed] The suspect will also be charged with driving under the influence of alcohol (sometimes referred to as driving or operating while intoxicated). While BrAC tests are not necessary to prove a defendant was under the influence, laws in most states require the jury to presume that he was under the influence if his BrAC is found and believed to be over 0.08 (grams of alcohol/210 liters breath) when driving.[citation needed] This is a rebuttable presumption, however: the jury can disregard the test if they find it unreliable or if other evidence establishes a reasonable doubt.
Infrared instruments are also known as "evidentiary breath testers" and generally produce court-admissible results.[citation needed] Other instruments, usually hand held in design, are known as "preliminary breath testers" (PBT), and their results, while valuable to an officer attempting to establish probable cause for a drunk driving arrest, are generally not admissible in court. Some states, such as Idaho, permit data or "readings" from hand-held PBTs to be presented as evidence in court. If at all, they are generally only admissible to show the presence of alcohol or as a pass-fail field sobriety test to help determine probable cause to arrest. South Dakota does not permit data from any type of breath tester, and relies entirely on blood tests to ensure accuracy.
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Breath testers can be very sensitive to temperature, for example, and will give false readings if not adjusted or recalibrated to account for ambient or surrounding air temperatures. The temperature of the subject is also very important.[citation needed]
Breathing pattern can also significantly affect breath test results. One study found that the BAC readings of subjects decreased 11–14% after running up one flight of stairs and 22–25% after doing so twice. Another study found a 15% decrease in BAC readings after vigorous exercise or hyperventilation. Hyperventilation for 20 seconds has been shown to lower the reading by approximately 32%. On the other hand, holding one's breath for 30 seconds can increase the breath test result by about 28%.[citation needed]
Some breath analysis machines assume a hematocrit (cell volume of blood) of 47%. However, hematocrit values range from 42 to 52% in men and from 37 to 47% in women. A person with a lower hematocrit will have a falsely high BAC reading.
Research indicates that breath tests can vary at least 15% from actual blood alcohol concentration. An estimated 23% of individuals tested will have a BAC reading higher than their true BAC. Police in Victoria, Australia, use breathalyzers that give a recognized 20% tolerance on readings. Noel Ashby, former Victoria Police Assistant Commissioner (Traffic & Transport), claims that this tolerance is to allow for different body types.[13]
Many handheld breath analyzers sold to consumers use a silicon oxide sensor (also called a semiconductor sensor) to determine the blood alcohol concentration. These sensors are far more prone to contamination and interference from substances other than breath alcohol. The sensors require recalibration or replacement every six months. Higher end personal breath analyzers and professional-use breath alcohol testers use platinum fuel cell sensors. These too require recalibration but at less frequent intervals than semiconductor devices, usually once a year.
Calibration is the process of checking and adjusting the internal settings of a breath analyzer by comparing and adjusting its test results to a known alcohol standard. Law enforcement breath analyzers are meticulously maintained and re-calibrated frequently to ensure accuracy.
There are two methods of calibrating a precision fuel cell breath analyzer, the Wet Bath and the Dry Gas method. Each method requires specialized equipment and factory trained technicians. It is not a procedure that can be conducted by untrained users or without the proper equipment.
The Dry-Gas Method utilizes a portable calibration standard which is a precise mixture of alcohol and inert nitrogen available in a pressurized canister. Initial equipment costs are less than alternative methods and the steps required are fewer. The equipment is also portable allowing calibrations to be done when and where required.
The Wet Bath Method utilizes an alcohol/water standard in a precise specialized alcohol concentration, contained and delivered in specialized simulator equipment. Wet bath apparatus has a higher initial cost and is not intended to be portable. The standard must be fresh and replaced regularly.
Some semiconductor models are designed specifically to allow the sensor module to be replaced without the need to send the unit to a calibration lab.[citation needed]
One major problem with older breath analyzers is non-specificity: the machines not only identify the ethyl alcohol (or ethanol) found in alcoholic beverages, but also other substances similar in molecular structure or reactivity.
The oldest breath analyzer models pass breath through a solution of potassium dichromate, which oxidizes ethanol into acetic acid, changing color in the process. A monochromatic light beam is passed through this sample, and a detector records the change in intensity and, hence, the change in color, which is used to calculate the percent alcohol in the breath. However, since potassium dichromate is a strong oxidizer, numerous alcohol groups can be oxidized by it, producing false positives. This source of false positives is unlikely as very few other substances found in exhaled air are oxidizable.
Infrared-based breath analyzers project an infrared beam of radiation through the captured breath in the sample chamber and detect the absorbance of the compound as a function of the wavelength of the beam, producing an absorbance spectrum that can be used to identify the compound, as the absorbance is due to the harmonic vibration and stretching of specific bonds in the molecule at specific wavelengths (see infrared spectroscopy). The characteristic bond of alcohols in infrared is the O-H bond, which gives a strong absorbance at a short wavelength. The more light is absorbed by compounds containing the alcohol group, the less reaches the detector on the other side—and the higher the reading. Other groups, most notably aromatic rings and carboxylic acids can give similar absorbance readings.[14]
Some natural and volatile interfering compounds do exist, however. For example, the National Highway Traffic Safety Administration (NHTSA) has found that dieters and diabetics may have acetone levels hundreds or even thousand of times higher than those in others. Acetone is one of the many substances that can be falsely identified as ethyl alcohol by some breath machines. However, fuel cell based systems are non-responsive to substances like acetone.
A study in Spain showed that metered-dose inhalers (MDIs) used in asthma treatment are also a cause of false positives in breath machines.
Substances in the environment can also lead to false BAC readings. For example, methyl tert-butyl ether (MTBE), a common gasoline additive, has been alleged anecdotally to cause false positives in persons exposed to it. Tests have shown this to be true for older machines; however, newer machines detect this interference and compensate for it.[15] Any number of other products found in the environment or workplace can also cause erroneous BAC results. These include compounds found in lacquer, paint remover, celluloid, gasoline, and cleaning fluids, especially ethers, alcohols, and other volatile compounds.
Breath analyzers assume that the subject being tested has a 2100-to-1 partition ratio[16] in converting alcohol measured in the breath to estimates of alcohol in the blood. If the instrument estimates the BAC, then it measures weight of alcohol to volume of breath, so it will effectively measure grams of alcohol per 2100 ml of breath given. This measure is in direct proportion to the amount of grams of alcohol to every 1 ml of blood. Therefore, there is a 2100-to-1 ratio of alcohol in blood to alcohol in breath. However, this assumed partition ratio varies from 1300:1 to 3100:1 or wider among individuals and within a given individual over time. Assuming a true (and US legal) blood-alcohol concentration of .07%, for example, a person with a partition ratio of 1500:1 would have a breath test reading of .10%—over the legal limit.
Most individuals do, in fact, have a 2100-to-1 partition ratio in accordance with William Henry's law, which states that when the water solution of a volatile compound is brought into equilibrium with air, there is a fixed ratio between the concentration of the compound in air and its concentration in water. This ratio is constant at a given temperature. The human body is 37 degrees Celsius on average. Breath leaves the mouth at a temperature of 34 degrees Celsius. Alcohol in the body obeys Henry's Law as it is a volatile compound and diffuses in body water. To ensure that variables such as fever and hypothermia could not be pointed out to influence the results in a way that was harmful to the accused, the instrument is calibrated at a ratio of 2100:1, underestimating by 9 percent. In order for a person running a fever to significantly overestimate, he would have to have a fever that would likely see the subject in the hospital rather than driving in the first place. Studies suggest that about 1.8% of the population have a partition ratio below 2100:1. Thus, a machine using a 2100-to-1 ratio could actually overestimate the BAC. As much as 14% of the population has a partition ratio above 2100, thus causing the machine to under-report the BAC. Further, the assumption that the test subject's partition ratio will be average—that there will be 2100 parts in the blood for every part in the breath—means that accurate analysis of a given individual's blood alcohol by measuring breath alcohol is difficult, as the ratio varies considerably.
Variance in how much one breathes out can also give false readings, usually low.[17] This is due to biological variance in breath alcohol concentration as a function of the volume of air in the lungs, an example of a factor which interferes with the liquid-gas equilibrium assumed by the devices. The presence of volatile components is another example of this; mixtures of volatile compounds can be more volatile than their components, which can create artificially high levels of ethanol (or other) vapors relative to the normal biological blood/breath alcohol equilibrium.
One of the most common causes of falsely high breath analyzer readings is the existence of mouth alcohol. In analyzing a subject's breath sample, the breath analyzer's internal computer is making the assumption that the alcohol in the breath sample came from alveolar air—that is, air exhaled from deep within the lungs. However, alcohol may have come from the mouth, throat or stomach for a number of reasons.[citation needed] To help guard against mouth-alcohol contamination, certified breath-test operators are trained to observe a test subject carefully for at least 15–20 minutes before administering the test.
The problem with mouth alcohol being analyzed by the breath analyzer is that it was not absorbed through the stomach and intestines and passed through the blood to the lungs. In other words, the machine's computer is mistakenly applying the partition ratio (see above) and multiplying the result. Consequently, a very tiny amount of alcohol from the mouth, throat or stomach can have a significant impact on the breath-alcohol reading.
Other than recent drinking, the most common source of mouth alcohol is from belching or burping. This causes the liquids and/or gases from the stomach—including any alcohol—to rise up into the soft tissue of the esophagus and oral cavity, where it will stay until it has dissipated. The American Medical Association concludes in its Manual for Chemical Tests for Intoxication (1959): "True reactions with alcohol in expired breath from sources other than the alveolar air (eructation, regurgitation, vomiting) will, of course, vitiate the breath alcohol results." For this reason, police officers are supposed to keep a DUI suspect under observation for at least 15 minutes prior to administering a breath test. Instruments such as the Intoxilyzer 5000 also feature a "slope" parameter. This parameter detects any decrease in alcohol concentration of 0.006 g per 210 L of breath in 0.6 second, a condition indicative of residual mouth alcohol, and will result in an "invalid sample" warning to the operator, notifying the operator of the presence of the residual mouth alcohol. PBT's, however, feature no such safeguard.
Acid reflux, or gastroesophageal reflux disease, can greatly exacerbate the mouth-alcohol problem. The stomach is normally separated from the throat by a valve, but when this valve becomes herniated, there is nothing to stop the liquid contents in the stomach from rising and permeating the esophagus and mouth. The contents—including any alcohol—are then later exhaled into the breathalyzer.[18]
Mouth alcohol can also be created in other ways. Dentures, for example, will trap alcohol. Periodontal disease can also create pockets in the gums which will contain the alcohol for longer periods. Also known to produce false results due to residual alcohol in the mouth is passionate kissing with an intoxicated person. Recent use of mouthwash or breath fresheners can skew results upward as they can contain fairly high levels of alcohol.
Absorption of alcohol continues for anywhere from 20 minutes (on an empty stomach) to two-and-one-half hours (on a full stomach) after the last consumption. Peak absorption generally occurs within an hour. During the initial absorptive phase, the distribution of alcohol throughout the body is not uniform. Uniformity of distribution, called equilibrium, occurs just as absorption completes. In other words, some parts of the body will have a higher blood alcohol content (BAC) than others. One aspect of the non-uniformity before absorption is complete is that the BAC in arterial blood will be higher than in venous blood. Laws generally require blood samples to be venous.
During the initial absorption phase, arterial blood alcohol concentrations are higher than venous. After absorption, venous blood is higher. This is especially true with bolus dosing. With additional doses of alcohol, the body can reach a sustained equilibrium when absorption and elimination are proportional, calculating a general absorption rate of 0.02/drink and a general elimination rate of 0.015/hour. (One drink is equal to 1.5 ounces of liquor, 12 ounces of beer, or 5 ounces of wine.[19])
Breath alcohol is a representation of the equilibrium of alcohol concentration as the blood gases (alcohol) pass from the (arterial) blood into the lungs to be expired in the breath. The venous blood picks up oxygen for distribution throughout the body. Breath alcohol concentrations are generally lower than blood alcohol concentrations, because a true representation of blood alcohol concentration is only possible if the lungs were able to completely deflate. Vitreous (eye) fluid provides the most accurate account of blood alcohol concentrations.
The breath analyzer test is usually administered at a police station, commonly an hour or more after the arrest. Although this gives the BrAC at the time of the test, it does not by itself answer the question of what it was at the time of driving. The prosecution typically provides an estimated alcohol concentration at the time of driving utilizing retrograde extrapolation, presented by expert opinion. This involves projecting back in time to estimate the BrAC level at the time of driving, by applying the physiological properties of absorption and elimination rates in the human body.
Extrapolation is calculated using five factors and a general elimination rate of 0.015/hour.
For example: Time of breath test-10:00pm...Result of breath test-0.080...Time of driving-9:00pm (stopped by officer)...Time of last drink-8:00pm...Last food-12:00pm
Using these facts, an expert can say the person's last drink was consumed on an empty stomach, which means absorption of the last drink (at 8:00) was complete within one hour-9:00. At the time of the stop, the driver is fully absorbed. The test result of 0.080 was at 10:00. So the one hour of elimination that has occurred since the stop is added in, making 0.080+0.015=0.095 the approximate breath alcohol concentration at the time of the stop.
The photovoltaic assay, used only in the dated Photo Electric Intoximeter (PEI), is a form of breath testing rarely encountered today. The process works by using photocells to analyze the color change of a redox (oxidation-reduction) reaction. A breath sample is bubbled through an aqueous solution of sulfuric acid, potassium dichromate, and silver nitrate. The silver nitrate acts as a catalyst, allowing the alcohol to be oxidized at an appreciable rate. The requisite acidic condition needed for the reaction might also be provided by the sulfuric acid. In solution, ethanol reacts with the potassium dichromate, reducing the dichromate ion to the chromium (III) ion. This reduction results in a change of the solution's color from red-orange to green. The reacted solution is compared to a vial of non-reacted solution by a photocell, which creates an electric current proportional to the degree of the color change; this current moves the needle that indicates BAC.
Like other methods, breath testing devices using chemical analysis are somewhat prone to false readings. Compounds that have compositions similar to ethanol, for example, could also act as reducing agents, creating the necessary color change to indicate increased BAC.
There are a number of substances or techniques that can supposedly "fool" a breath analyzer (i.e., generate a lower blood alcohol content).
A 2003 episode of the popular science television show MythBusters tested a number of methods that supposedly allow a person to fool a breath analyzer test. The methods tested included breath mints, onions, denture cream, mouthwash, pennies and batteries; all of these methods proved ineffective. The show noted that using items such as breath mints, onions, denture cream and mouthwash to cover the smell of alcohol may fool a person, but, since they will not actually reduce a person's BAC, there will be no effect on a breath analyzer test regardless of the quantity used, if any, it appeared that using mouthwash only raised the BAC. Pennies supposedly produce a chemical reaction, while batteries supposedly create an electrical charge, yet neither of these methods affected the breath analyzer results.[20]
The Mythbusters episode also pointed out another complication: It would be necessary to insert the item into one's mouth (e.g. eat an onion, rinse with mouthwash, conceal a battery), take the breath test, and then possibly remove the item — all of which would have to be accomplished discreetly enough to avoid alerting the police officers administering the test (who would obviously become very suspicious if they noticed that a person was inserting items into their mouth prior to taking a breath test). It would likely be very difficult, especially for someone in an intoxicated state, to be able to accomplish such a feat.[20]
In addition, the show noted that breath tests are often verified with blood tests (which are more accurate) and that even if a person somehow managed to fool a breath test, a blood test would certainly confirm a person's guilt.[20] However, it is not clear why a negative breath test would be verified by a subsequent blood test.
Other substances that might reduce the BAC reading include a bag of activated charcoal concealed in the mouth (to absorb alcohol vapor), an oxidizing gas (such as N2O, Cl2, O3, etc.) that would fool a fuel cell type detector, or an organic interferent to fool an infrared absorption detector. The infrared absorption detector is more vulnerable to interference than a laboratory instrument measuring a continuous absorption spectrum since it only makes measurements at particular discrete wavelengths. However, due to the fact that any interference can only cause higher absorption, not lower, the estimated blood alcohol content will be overestimated.[citation needed] Additionally, Cl2 is rather toxic and corrosive.
A 2007 episode of the Spike network's show Manswers showed some of the more common and not-so-common ways of attempts to beat the breath analyzer, none of which work. Test 1 was to suck on a copper-coated coin such as a penny. Test 2 was to hold a battery on the tongue. Test 3 was to chew gum. None of these tests showed a "pass" reading if the subject had consumed alcohol.
On the other hand, products such as mouthwash or breath spray can "fool" breath machines by significantly raising test results. Listerine mouthwash, for example, contains 27% alcohol. The breath machine is calibrated with the assumption that the alcohol is coming from alcohol in the blood diffusing into the lung rather than directly from the mouth, so it applies a partition ratio of 2100:1 in computing blood alcohol concentration—resulting in a false high test reading. To counter this, officers are not supposed to administer a PBT for 15 minutes after the subject eats, vomits, or puts anything in their mouth. In addition, most instruments require that the individual be tested twice at least two minutes apart. Mouthwash or other mouth alcohol will have somewhat dissipated after two minutes and cause the second reading to disagree with the first, requiring a retest. (Also see the discussion of the "slope parameter" of the Intoxilyzer 5000 in the "Mouth Alcohol" section above.)
This was clearly illustrated in a study conducted with Listerine mouthwash on a breath machine and reported in an article entitled "Field Sobriety Testing: Intoxilyzers and Listerine Antiseptic" published in the July 1985 issue of The Police Chief (p. 70). Seven individuals were tested at a police station, with readings of 0.00%. Each then rinsed his mouth with 20 milliliters of Listerine mouthwash for 30 seconds in accordance with directions on the label. All seven were then tested on the machine at intervals of one, three, five and ten minutes. The results indicated an average reading of 0.43 blood-alcohol concentration, indicating a level that, if accurate, approaches lethal proportions. After three minutes, the average level was still 0.020, despite the absence of any alcohol in the system. Even after five minutes, the average level was 0.011.
In another study, reported in 8(22) Drinking/Driving Law Letter 1, a scientist tested the effects of Binaca breath spray on an Intoxilyzer 5000. He performed 23 tests with subjects who sprayed their throats and obtained readings as high as 0.81—far beyond lethal levels. The scientist also noted that the effects of the spray did not fall below detectable levels until after 18 minutes.
- ^ U.S. Trademark Reg. No. 661,636
- ^ http://www.dot.gov/ost/dapc/testingpubs/20071217_CPL_EBT.pdf
- ^ http://edocket.access.gpo.gov/2009/pdf/E9-29822.pdf
- ^ Bogen E (June 1927). "The Diagnosis of Drunkenness—A Quantitative Study of Acute Alcoholic Intoxication". Cal West Med 26 (6): 778–83. PMC 1655515. PMID 18740360. //www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pmcentrez&artid=1655515.
- ^ Professor Robert F.Borkenstein — An Appreciation of his Life and Work.
- ^ "Test a Tippler's Breath" Popular Science, August 1927, p. 56, bottom of page.
- ^ "Rolla N. Harger Dies; Invented Drunkometer", New York Times, August 9, 1983.
- ^ This is not now regarded as one of forensic medicine's finest moments.Mitchell, C. Ainsworth (March/April 1932). "Science and the Detective". The American Journal of Police Science (Northwestern University) 3 (2): 169–182. DOI:10.2307/1147200. JSTOR 1147200.
- ^ FDA > CDRH > Product Classification Database Search
- ^ Retrieve Pages
- ^ http://www.fda.gov/CDRH/DEVADVICE/314.html
- ^ WI DOT
- ^ Holroyd, Jane (16 May 2006). "Breathalyser's 20 per cent tolerance defended". Sydney Morning Herald. http://www.smh.com.au/news/national/breathalysers-20-per-cent-tolerance-defended/2006/05/15/1147545242026.html.
- ^ "Infrared spectroscopy". Organic Chemistry Resources Worldwide. Archived from the original on 2006-08-31. http://web.archive.org/web/20060831211510/http://organicworldwide.net/infrared/. Retrieved 2012-01-12.
- ^ Buckley TJ, Pleil JD, Bowyer JR, Davis JM (1 December 2001). "Evaluation of methyl tert-butyl ether (MTBE) as an interference on commercial breath-alcohol analyzers". Forensic Science International 123 (2): 111–8. DOI:10.1016/S0379-0738(01)00534-5. http://linkinghub.elsevier.com/retrieve/pii/S0379073801005345.
- ^ Forensic-Evidence.com: Biological Evidence/ Breath Tests for Blood Alcohol Determination: Partition Ratio
- ^ Jones AW (March 1982). "Quantitative measurements of the alcohol concentration and the temperature of breath during a prolonged exhalation". Acta Physiol. Scand. 114 (3): 407–12. DOI:10.1111/j.1748-1716.1982.tb07002.x. PMID 7136772.
- ^ Kechagias S, Jönsson KA, Franzén T, Andersson L, Jones AW (1999). "Reliability of Breath-Alcohol Analysis in Individuals with Gastroesophageal Reflux Disease". Journal of Forensic Sciences 44 (4): 814. PMID 10432616.
- ^ http://rethinkingdrinking.niaaa.nih.gov/WhatCountsDrink/WhatsAStandardDrink.asp
- ^ a b c Mythbusters, Season 1, episode 6. First aired November 7, 2003.
