Q. How does infrared technology work?
A. Infrared technology is used in several popular breath testing machines, most notably the BAC DataMasterTM and ithe National Dreager AlcoTest 7110 mk III use an Infrared detection is a process whereby an analysis is electronically conducted of the spectra of a beam of infrared radiation passed through the breath sample. We all know that for generations astronomers have been analyzing the chemical make-up of the stars by using a spectrometer to measure the various components of the spectrum generated by their light. This shared process is based upon the theoretically unassailable principle that no two chemical substances produce quite the same spectrum. Thus, the nature of a substance can be determined by analysis of the spectrum it produces which gives rise to the science of spectroscopy.
When the goal of infrared spectroscopy is determination of the presence and quantity of alcohol in human breath, infrared radiation is the source of the radiation which is measured. Infrared radiation can be produced by matter, as when a hot iron gives off heat, and can be absorbed by matter, as when a piece of metal subjected to infrared radiation gets hot. Infrared radiation ranges in wavelength from .75 to 100 microns. A micron, symbolized "m", is equal in length to one thousandth of a meter. That same length is sometimes expressed as a micrometer, or "mm". Part of the region, the vibrational portion, encompassing wavelengths of from 2.5 to 15 microns, is of primary importance in spectroscopic analysis of alcohol. In attempting to understand what goes on in an infrared breath testing device, two concepts of analysis should be kept in mind, qualitative (going to the nature of the substance being analyzed) and the quantitative (going to the concentration of the substance within the medium in which it is present).
Considering, first, the qualitative: When infrared radiation is directed at a compound such as ethyl alcohol, the molecules in that compound will absorb some of that radiation. This occurs when the covalent bonds at certain "signature" wavelengths are activated by the radiation. What those wavelengths are depends upon the compound. The pattern of infrared absorption can, therefore, be used for identifying molecules just as fingerprints can be used for identifying humans. Although on the surface it would seem quite a simple matter to identify a material based upon this technique, there's a hitch. More than one compound may absorb radiation at one or more of the same wavelengths. The only way to absolutely identify a compound is to identify all of its wavelengths. Our intended target, ethyl alcohol, has been proven to absorb radiation at major peaks of 3.39, 3.48, 7.25, 9.18, 9.50, and 11.5 microns, as well as some absorption at about a micron on either side of the peak. It also absorbs some, but less, radiation at secondary or shoulder bands, such as 3.42 microns. No other compound absorbs radiation at exactly those peaks and no others. Development of a commercially viable breath testing device to measure all of the frequencies at which alcohol absorbs would unquestionably be cost prohibitive. Therefore, each of the manufacturers has taken a different course whereby one major frequency is measured and other substances, such as acetone, which are likely to be found at or near the chosen frequency are either measured and subtracted or are electronically filtered out.
Since it is legal to operate a motor vehicle with some alcohol present in the blood, it is also necessary to make a quantitative determination of the amount of alcohol present. This side of any spectrometer therefore uses a principle known as Beer's Law (sometimes called the Beer-Lambert Law or the Bouguer-Beer Law). Beer's Law provides that the quantity of radiation absorbed by a substance (in this case alcohol) dissolved in a non-absorbing solvent (deep lung air) is directly proportional to the concentration of the substance and the path of the radiation through the solution. Beer's Law says that if one knows the amount of radiation absorbed, one can calculate the concentration of the substance responsible for the absorption.
Q. When applied to breath testing is this technique valid?
A. Maybe, and maybe not. Some researchers caution that the basic premise, the Beer-Lambert formula, is not predictive of the results of quantitative measurements, particularly when such measurements are anticipated over a wide range of sample concentrations.
One of the major problems with infrared techniques as presently employed in evidentiary breath testing is created by the fact that all commercially available machines do not trap a sample as does the Breathalyzer. Instead the technique employed is to pass the breath through a sample chamber which is fitted with the infrared source and a detector which measures the energy which is not absorbed by the sample. This means that the machines must employ a computer model to determine when the sample being expelled into the machine is from the deep lung or alveolar region (see, "The Blood Breath Partition Ratio"). This system creates difficulty when so-called "mouth alcohol" contained in the breath sample mimics the image that the machine's internal computer believes is an alveolar sample.
A misconception that is held by many, including many lawyers who represent client's charged with DWI, is that these machines contain "mouth alcohol detectors." They do not. The system employed in the DataMaster, detailed below, is to measure the rate of cooling across a thermistor. This is known as a slope detector. A too rapid rate of cooling will be interpreted by the device as "mouth alcohol" and the results will be reported as such. Even assuming that the slope detector system is valid, it is nonetheless possible for mouth alcohol to be "layered" atop alcohol contained in the alveolar sample as shown in the graph below. This will result in a cumulative mouth alcohol and alveolar sample and the slope detection system will be unable to differentiate between the two. The end product of such a situation is that reported BAC of the subject will actually exceed the true BAC by as much as 100%. On numerous occasions utilizing a DataMaster which our firm owns, we have substantiated that this problem can arise. For an actual example of such a situation utilizing our machine, click here (dial-up click here).
Q. How does the BAC DataMasterTM work?
A. When the subject blows into the device, the sample passes into a triangular tri-fold sample chamber which has been made continuous through the use of a mirror at the point where the chamber bends. This gives the chamber a continuous length of 1.1 meters notwithstanding its relatively small sample size. Controlled entirely by its software "brain," the DataMasterTM will first search and measure the interference present in the alcohol or 3.44 micron range. It accomplishes this by automatically moving this filter into position and measuring the decrease in transmission present in this range. Provided at least 1.5 liters have been delivered, when a the flow rate drops below 3.8 liters per minute and the realtime BAC curve is less than or equal to .001, the DataMasterTM will take a snapshot if the sample and report the analysis as the blood alcohol content of the subject utilizing a 2100 to 1 Blood Breath Partition Ratio. As noted above, both the minimum flow rate and the total amount of breath delivered are measured by the rate of cooling across a thermistor. After completing its alcohol measurement, the machine removes the alcohol filter and substitutes, in its place, the 3.37micron or acetone filter. The device then measures the absorption in this band and adjusts the alcohol determination by the results of the second test. It is not known what calculations are employed in making these determinations or whether different versions exist. Upon completion of the test, a self contained printer will provide multiple copies of the evidence ticket made in each test.
Q. How does the National Dreager AlcoTest 7110 MKIIITM work?
A. Manufactured by National Dreager at its Durango, Colorado plant, without a doubt, the AlcoTest MK III is the newest commercially viable breath testing device available. By all appearances the device is physically unimposing, measuring 15.8" long x 5.1" height x 10.4" depth. It weighs 16.5 pounds which gives it the size and "heft" of an old laptop computer. The device has a metal case coated in what appears to be a leatherette type of rubber or plastic. It has a hinged safety cover that is generally removed when in use and two latches to keep it in place when it is not. The top surface is dominated by an oval shaped well to house the thick black PVC sample hose. The hose is heated and contains a socket whereby the operator affixes a round white disposable plastic mouthpiece which also doubles as a saliva and particulate trap. Also mounted atop the device is a forty character alpha-numeric readout which describes, in a single line of text, the operation being performed, alerts the operator to perform required actions, conveys error messages and expresses the result in a percent of weight vs. volume. Likewise positioned on the top of the instrument is a small dot matrix printer which prints to a strip of paper roughly akin to a cash register tape.
Technically exciting, the AlcoTest 7110 MK III conducts not one but two tests. Further, each of the tests are conducted through two different modalities. The first test is by means of infrared spectrometry at the 9.5 m range. The second utilizes what Dreager calls "breakthrough" fuel cell technology. It is important to point out that utilization of this device will not inaugurate the "two test" system which is part of the regime of many states. The second, or fuel cell test, is conducted upon the same sample that was previously measured by the infrared detection system. This decision, as we see it, is a two edged sword. From one standpoint agreement of the two tests undoubtedly goes far to convince the trier of fact that the test result was an accurate representation of the motorist's BAC at the time he or she was tested. On the other hand, this system does little to dispel arguments that the arrestee's BAC had risen since the time of operation.
In use, the subject blows a steady and moderately long breath into the machine. Based upon personal observation and comparison, the breath is shorter than required for the DataMasterTM and much shorter, hence easier to blow than an early IntoxilyzerTM or BreathalyzerTM. It appears that the device utilizes a pressure sensor to determine the presence of deep lung air. While we cannot be 100 per cent certain at this preliminary stage, our best guess is that the sensor monitors the flow of air and upon achieving a peak moving toward a declination in pressure the optical system is activated. The sample is passed directly into a cuvette which the manufacturer describes as a "totally encapsulated optical bench to ensure no dust buildup on [the] infrared filter or any optics." A short optical chamber, hence smaller breath, is enabled by means of two gold plated parabolic mirrors that are placed at either end of the optical chamber. Thus, although the volume of the sample chamber is a mere 70 cc (10 cc smaller than the IntoxilyzerTM), the length is expanded seven times due to the arrangement of the mirrors and the placement of the infrared source and sensor. The infrared detector is fitted with a filter centered at 9.5 microns with a half bandwidth of 0.50 microns.
Selection of the 9.5 micron range, the absorbing frequency of the C-O bond of ethanol is, in the mind of Dreager, key to the improved performance of the device. In A New testing Device Using the 9.5 mm Ethanol Absorption, Dreager's B. Moreth noted that "a large variety of organic compounds are infrared active [in the 3.4 mm range] and the presence of a substance like toluene or methane would influence the reading on these multi-wavelength instruments without the possibility of correction." Theoretically therefore, by selecting this range, Dreager believes that it has circumvented these problems.
What makes the AlcoTest 7110 MK IIITM truly unique is the addition of an electro-chemical fuel cell to conduct a separate test with a totally unrelated technology. Well-known from the space program where fuel cell technology has been routinely used to generate electrical power since the mid 1960's, an electro-chemical fuel cell is an arrangement whereby a gas is passed between two electrodes through an electrolyte. Given the proper conditions, the passage of this gas will create an electrical current. Based upon a review of the manufacturer's literature, it is believed that in the AlcoTest 7110 MK IIITM, a tube, coated on both sides with finely divided platinum, contains a porous layer impregnated with an acetic electrolyte solution. The passage of a gas containing ethanol will cause the a minute current to flow, which current is measured and translated into an alcohol reading.
Q. How does an IntoxilyzerTM work?
A. While there are several different models of the IntoxilyzerTM in use in New York, since it is fairly typical, we will examine the 4011. The IntoxilyzerTM was originally marketed as the Omicron IntoxilyzerTM in 1971. Developed by Richard A. Harte, it was redesignated model 4011. In the Omicron IntoxilyzerTM, a beam of infrared light measuring 3.38mm to 3.40mm was passed through the sample whereupon a series of mirrors were employed to stretch out the focal length much in the fashion as employed in so-called reflecting telescopes. Although the instrument has changed over the years in many ways, its basic principle has remained constant. R. A. Harte, the Intoxilyzer's inventor, explained that principle in a 1971 article in the Journal of Forensic Science. Noting that the IntoxilyzerTM measured the absorption of infrared energy by a gas, following the Beer-Lambert Law, Harte wrote:
"The infrared wavelength used by the IntoxilyzerTM coincides with a major absorption band of ethyl alcohol, 3.39 microns, representative of C-H stretching, molecular bond vibrations. The infrared light source employs a proprietary, specially designed circuit which provides unusually high stability through a feedback control loop. This energy is modulated at a frequency of 330 Hertz. The modulated energy is then collimated by fused silica lenses and directed through a specially designed sample cell. At the other end of the cell, a second set of fused silica optics focuses the energy onto the face of a sensitive infrared photo conductor. The use of spherical concave mirrors in a clever optical design . . . permits multipass reflections to provide a long path length in a small package.
As the concentration of alcohol vapor increases in the cell, the amount of infrared energy reaching the detector falls in a predictable, exponential manner. The sample cell is kept heated to prevent moisture condensation on the optics and to prevent loss of alcohol in the condensate. The signal detected is electronically filtered at the source modulation frequency, and then is processed through a high gain, high sensitivity, low noise circuit and converted from an AC to a DC signal. This DC analogue signal, which is a representation of the exponential relationship between the energy transmitted through the cell and the concentration of alcohol in the cell, is linearized by a signal processing unit, and then passed through an analogue-to-digital converter, and displayed on a three-digit panel meter directly as percent blood alcohol, W/V.
The conversion to percent blood alcohol, W/V is based upon the established principle that alcohol in blood obeys Henry's Law and the experimentally confirmed finding that 2100 ml of a "substantially alveolar breath" sample as delivered at the mouth contains the same weight of alcohol as that simultaneously present in 1 ml of pulmonary arterial blood of otherwise normal composition . . ."
Unlike its wet chemistry predecessors such as the BreathalyzerTM, the 4011 does not require extensive preparation prior to administration. After the passage of about 10 minutes, a "ready" light, located at the top right corner of the display panel, will switch on. The operator will then pull the sample tube from the left hand side of the machine and connect it to the pump tube, after which the selector on the right hand side of the control panel will be turned to "Air Blank" and the machine purges. As with virtually every breath testing device, this is a vital step and ensures that no residual alcohol remains within the machine. Shutting off automatically, after about 30 seconds, the machine is now ready to use. The operator now selects the "Zero Set" mode and, while depressing the zero adjust knob, rotates the same until it digitally reads .000. The internal electronics of the machine will accept a non-blinking zero, a .001, .002 or a .003 as an acceptable starting point. In the event that the operator attempts to proceed with a setting other than that set forth above, the "ERROR" light will be activated and the printer will not run. A double thickness IBM card is then inserted into the printer, the machine is switched once again to "Air Blank" and, after a 30 second purge, the digital display will show the results of the blank test after which the printer will print the letter "A" followed by the two digit result on the card. The machine is then "re-zeroed" and the selector switch turned to "Breath" mode. The operator then disconnects the breath tube from the pump whereupon the subject is asked to blow into the breath tube to which a saliva trap has been attached. If the breath is being "properly given," a breath indicator lamp on the front panel will light, the numbers on the front panel will begin to rise and level off after the sample chamber is filled. After collection of the sample, the machine will print a "B" on the card followed by the first two digits of the result.