Radio Frequency Interference in Breathalyzers

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The states may have to take interim measures to determine the extent of their individual problems with EMI affecting EBTs.

Dr. Richard F. Jensen, of Forensic Associates in Minneapolis, has offered the following comments concerning RFI:

Instrument failure because of radio frequency interference is a serious problem today. These problems can affect not only breath testing devices such as the Breathalyzer but also instruments in the forensic laboratories and clinical laboratories.

Radio frequency interference (RFI) is not a new or unique phenomenon. Communication systems employed by the armed forces in World War I experienced RFI, especially in areas where there was widespread use of radios in automobiles and airplanes. The complexity of radio communication has increased since that time, and the incidences of RFI have followed a similar pattern. A special-interest area of science, referred to as electromagnetic compatibility (EMC), has evolved out of this concern with RFI. In an effort to encompass the concerns of the entire electromagnetic spectrum, not just radio frequency, a broader designation has evolved: electromagnetic interference (EMI). (EMI and RFI will be used interchangeably in this discussion.) This discussion will deal specifically with radio frequency interference concerns: in evidential breath testing, in other forensic measurements, and in clinical laboratory measurements.

The preliminary research reported by the Electromagnetic Compatibility facility of the National Bureau of Standards has demonstrated that many evidential breath testing devices in DUI investigations experience EMI. At least 10 of the 16 instruments tested demonstrated some susceptibility to RFI. What this means, of course, is that the problem is one of a generic nature and is not limited to any specific instrument or manufacturer.

There are a number of opinions as to how radio frequency interferes with the performance of evidential breath test devices. The diversity of opinion results from the application of various theories and because the methods of measurement from one manufacturer to another differ in technology. In order to accurately evaluate the potential effect of radio frequency on evidential breath testing, it is imperative that each device be examined in its permanent location. A variety of procedures have been devised to accomplish this evaluation. All of these procedures are designed with a holistic approach where one must consider not only the instrument being tested but also its immediate surroundings and the involvement of the operator. The results of these site evaluations provide for a variety of important conclusions.

At the present time it may be that the breath testing instrument is the best potential detector for radio frequency in its environment. In keeping with a systems approach, the instrument will provide the precise data required for a site evaluation, particularly when coupled with a well designed evaluation protocol. All instruments are not equally susceptible to EMI. Therefore, it is appropriate to survey any given site with the instrument normally employed in that location.

Even if operators are well-trained and measurements are well documented in DUI investigations, RFI can occur. What then? There is absolutely no course of action except to decertify the affected instrument and immediately take it out of service. The instrument must remain out of service until the source of the interference is identified and eliminated or until the instrument can be modified to function in its environment. This course of action is dictated not only by the fact that these instruments are performing evidential analyses but also by the generally accepted practice of good analytical measurement. The concern should not be whether the results are high or low or whether they are to the benefit of the DUI defendant but simply whether or not they are accurate.

It is not my intent to discuss the details of the modification of breath test instruments in order to make them less susceptible to RFI. However, the task of modification is not an overly difficult one and should be undertaken if there is any indication that the instrument may potentially be affected by radio frequency in a manner that would cause erroneous results in DUI investigations. It is important to remember that the responsibility of electronic design is in the hands of the manufacturer and any subsequent modification must be coordinated by the manufacturer. Unfortunately, this is not often the case, Smith and Wesson has just recently offered a modification retrofit kit for the Model 900A.

The evidential testing of breath for alcohol concentration is not the only chemical test that may have the potential for interference of electromagnetic radiation. There are two additional areas that should cause intense concern. These are forensic analyses or examinations for the judicial system and clinical analyses for diagnostic purposes. The potential for interference is not only present in settings where these types of measurements are made, but there is the probability that the presence of an interference will cause a much larger deviation than those supposedly found in breath alcohol measurements. The Breathalyzer Model 900A, although capable of making accurate measurements, is not a sophisticated electronic instrument. Instruments such as gas chromatographs, mass spectrometers, and spectrophotometers are electronically more complex and therefore potentially more susceptible to the influence of electromagnetic radiation. In this great technological age there are literally an infinite number of instrumental measurements occurring on a regular basis. To attempt to discuss all of these measurements in detail would be impossible, but it is sufficient to state that there is the theoretical potential for radio frequency interference with each and every measurement. However, what should be of imminent concern are two specific areas of scientific measurement that could potentially affect each and every one of us directly at one time or another. As mentioned earlier, one area is forensic science and the other clinical chemistry. In the past decade both disciplines have enjoyed the benefits of great strides in technology. This is especially true in the complexity and number of instrumental measurements that are now being performed.Unfortunately, there are a couple of problems with this crude procedure. First, only the frequency used by the testing device is being tested; the procedure does not determine if frequencies used by any of dozens of other EMF-emitting devices in the area will be detected. Second, the calibration is usually done with the breath machine turned on but not during an actual capture and analysis - i.e., during operating conditions in an actual DUI investigation.

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