Radio frequency interference (RFI) or electromagnetic interference can arise when radio signals transmitted in proximity to a breath testing instrument are amplified in a way indistinguishable from electronic signals generated by the instrument during an analysis. Most instruments are shielded from such interference, have RFI detectors that prevent testing if significant RFI sources are present or both. Breath testing protocols typically prohibit the use of handheld transmitters in the proximity of the instrument while it is being operated (National Safety Council, 1992). Subject testing protocols that include the analysis of air blanks, known alcohol samples and agreement of duplicate subject test results can be used to demonstrate the lack of RFI.
Portions of the above were taken from Garriott, Medical-Legal Aspects of Alcohol, 4th ed 2003.
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