Radio Frequency Interference in Breathalyzers

In February 1982, Smith & Wesson, a major manufacturer of DUI breath testing devices, notified law enforcement agencies that its Breathalyzer Model 1000 had been found to experience interference from radio frequency transmissions under certain DUI test conditions, resulting in false test results. Subsequent investigation suggested that the Breathalyzer Models 900 and 900A also were affected by various power levels.

The potential sources of radio frequency interference (RFI) within the law enforcement environment are numerous - for example, AM and FM radios, police station dispatchers, hand-held police transmitters, teletypes, and police radar units. Each of these may emit the kind of interference that could cause specific DUI breath alcohol test devices to render false results. It was then learned that the federal government (National Bureau of Standards) was testing for RFI sensitivity every type of breath testing device currently in use by law enforcement agencies in DUI investigations.

On September 10, 1982, Smith & Wesson issued a customer advisory suggesting that all breathalyzers used in drunk driving investigations be tested as a matter of preparedness for possible courtroom testimony to avoid the issue of RFI in breathalyzers.

Late in 1984, Smith & Wesson announced the availability of a kit designed to improve the Model 900A's resistance to RFI in DUi settings. In a customer advisory letter from Smith & Wesson's production manager, users of the machine were told that a "Kit I," consisting of a combination of a filter box and amplifier board was available for $147, and a "Kit II," consisting of only the filter box, was priced at $72. Additionally, the Model 900A could be converted by the factory for $171.

At about the same time, CMI came out with its state-of-the-art DUI breath testing instrument, the Intoxilyzer 5000. This new machine has an "RFI Detector." Obviously, the marketing of a kit and an "RFI Detector" to inhibit radio frequency interference constitutes a clear recognition of the problem. In view of such steps by manufacturers, it is difficult to imagine any prosecutor or witness in a DUi trial denying that the problem exists.

In May 1983, Don Nichols and Jim Kaster, Minneapolis DUI attorneys and editors of the Drinking/Driving Law Letter, obtained a copy of the National Bureau of Standards (NBS) preliminary report of test results for electromagnetic interference (EMI). The report was dated March 25, 1983. NBS was under contract with the National Highway Traffic Safety Administration (NHTSA) to conduct testing on evidential breath testers (EBTs) currently in use by law enforcement officials nationwide.

The report contained the "bottom line" results of RFI testing. Each of 16 unidentified instruments (the contract for testing specifically required that individual machines be identified by secret code only) were subjected to four different frequencies typically present in the police DUI investigation environment. Of the 16 units tested, only six showed minimal interference at each frequency; 10 of the 16 showed substantial susceptibility on at least one frequency. The report characterizes the potential effect of EMI on the testing of alcohol vapors in DUI cases as "severe." This characterization is found on page two of the report, where the writer is describing the first in-house demonstration of EMI to NHTSA representatives in March 1982:

"Early in 1982, the Washington D.C. Metropolitan Police Department reported to NHTSA that EBTs were found to display erroneous BAC [blood-alcohol content] readings in the presence of electromagnetic fields from radio transmission. NHTSA contacted LESL [Law Enforcement Standards Laboratory] and TSC [Transportation Systems Center], and it was agreed that if EBTs were susceptible to electromagnetic interference, action must be taken to solve the problem, and that it might be necessary to modify the NHTSA standard to include electromagnetic interference (EMI) susceptibility requirements. On March 24, 1982, representatives of NHTSA, TSC, and NBS were given a demonstration by police officers who routinely conduct breath testing using an EBT in a mobile van. One police officer operated his handheld radio within 0.3 m (1 ft.) of the EBT and demonstrated that the electromagnetic field could severely affect the analysis of alcohol samples."

As a part of Nichols and Kaster's FOLA, action, release was also sought of any preliminary drafts of the National Bureau of Standards (NBS) report on RFI and EMI, specifically, a preliminary report authored by Dr. John Adams of Boulder, Colorado. This report was rumored to be significantly different from the final report eventually released by the NHTSA. So different was the final edited version that it was reported that Dr. Adams asked to have his name removed from the list of those responsible, and, in fact, a review of contributors does not show the name of Dr. John Adams. The following are excerpts from the Adams report, which is entitled Effects for the Electromagnetic Fields on Evidential Breath Testers, written for the Electromagnetic Fields Division, National Bureau of Standards, Boulder, CO 80303:

Eight of the 16 units tested showed potential EMI problems under the specific test conditions of nominal 10 volts per meter electric field strength.

These results cannot be extrapolated to predict how individual EBTs would be affected at other levels of field strength or at other frequencies.

These results show that EMI is a potential problem with many of the EBT units in current use. The additional measurement techniques, standards, and test levels suggested in the section on "Future Efforts Needed" are needed to fully evaluate the effects of EMI on EBTs.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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