Measurement of electric- and magnetic-field strengths from industrial radio-frequency (6-38 MHz) plastic sealers

This paper describes the results of occupational radio-frequency (RF) field strength measurements on RF plastic sealers and compares the results to the ANSI C95.1-1974 personnel exposure standard. The RF sealers are characterized according to operating frequency, duty cycle, and nominal power output. The field strength monitors used in these measurements were constructed and calibrated for near-field exposure measurements by the National Bureau of Standards and Narda Microwave Corporation. Near-field measurements were necessary because RF sealer operators were less than one free space wavelength from the sealers. Results of these measurements showed that at least 60 percent of the RF sealers emitted electric field strengths in excess of the ANSI C95.1-1974 guideline (200 V/m). In addition, at least 29 percent of the RF sealers exceeded the ANSI guideline for magnetic field strength exposure (0.5 A/m). All measurements have been corrected for duty cycle (typically 0.050 to 0.200). Several valuable observations were also made during the surveys. First, shielding can substantially reduce operator exposure. Second, exposure from adjacent sealers can be comparable to that received from the RF sealer being surveyed. Third, all RF sealers surveyed were operated by women. Finally, field strengths measured at seven anatomical locations showed considerable differences.