Radio Frequency Interference in Breathalyzers

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The responsibility of forensic science is to provide the judicial system with the results of the scientific examination of physical evidence. These results are most often interpretations based on an instrumental analytical measurement. In addition to the classical types of examinations accomplished by the use of both the stereo and compound microscopes, the instruments employed by forensic scientists have expanded to a wide variety of sophisticated electronic devices of which many are computer controlled. These instruments are most often in laboratories that are associated with law enforcement personnel. With the increased use of communications equipment by law enforcement agencies in DUI cases and the proliferation of radio frequencies employed by these agencies, scientific equipment in the forensic science laboratory is being exposed to more and varying electromagnetic radiation than ever before. Because of this potential for radio frequency interference, the analytical measurements and the interpretations based on those measurements may be incorrect. Does this mean that under these circumstances there is no chance for an accurate measurement? Absolutely not. All that needs be done is to employ the rules that govern good analytical measurements in any area of science. First, all measurements must be performed at least in duplicate, meaning two separate measurements are made on the same sample. The purpose of this procedure is to substantially reduce the effect of a systematic error in DUi testing, of which RFI is but one example. Systematic errors are those that can arise from identifiable sources that can occur in a sporadic manner and that generally are the cause of large, unpredictable deviations of the measured quantity. Second, these duplicate analyses must be accompanied by well designed and systematic programs of quality control and proficiency testing.

The concerns outlined above can and should be expressed also for the clinical chemist and the measurements that are made on physiological samples for the purposes of diagnosing medical problems. The majority of clinical laboratories have sound programs of quality control and proficiency testing. However, there are very few clinical tests or procedures performed in duplicate, a practice that does not count for or ensure the absence of systematic error. Systematic errors can be from an infinite number of sources. The only way in which the presence or absence of a systematic error can be assured in an analytical measurement is by making that measurement in duplicate: two separate measurements on the same sample. Recently a sheriffs deputy in southern Minnesota related to me, They don't like us to use our radios in the hospital; it louses up their tests. Need more be said?

Finally, let it be said that this concern for radio frequency interference in drunk driving investigations is not an overreaction. It is a scientific fact: One area of technology simply has not caught up with another. Radio frequency interference is a product of today's technological demands interacting with yesterday's design and manufacturing methods.

Note: The prosecution may counter the DUI defense attorney attack in a DUI trial by pointing out that the machine has an RFI detector. The problem with such detectors is that they are simply not reliable. First, as repeated tests have demonstrated, there is a segment of the frequency band to which the detector is essentially blind. If there is a source of interference from a device emitting electromagnetic waves in this frequency range, it will not be detected.

Second, the detectors are rarely calibrated correctly. Most law enforcement agencies are unqualified to perform a complete maintenance and calibration. Commonly, the instrument will be sent back to the manufacturer for annual calibration of the various fail-safe devices (RFI detector, mouth alcohol detector, interferent detector, ambient air flag, etc.). In the meantime, the machine is often calibrated by police officers by simply using something like a hand-held police radio. The device may be activated three or four times from three or four different angles and distances from the breath machine; if the RFI detector is triggered, it is considered calibrated for DUI testing purposes

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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