Foot currents and ankle SARs induced by dielectric heaters.
Conover-DL; Moss-CE; Murray-WE; Edwards-RM; Cox-C; Grajewski-B; Werren-DM; Smith-JM
Bioelectromagnetics 1992; 13(2):103-110
Foot currents and ankle specific absorption rates (SARs) were measured as functions of radiofrequency electromagnetic fields encountered by operators of dielectric heaters. Operators of 15 dielectric heaters used to heatseal plastic materials were studied. Frequencies ranged from 6.5 to 65 megahertz (MHz), and the duty cycle was 20% or less during any 6 minute period of heater operation. Currents through both feet to the ground were measured by having the operator stand on a bilayered sensor. Voltage measurements and sensor impedances were used to calculate foot currents. Each foot current value was a short term average over a 1 second duration. Ankle SARs were calculated from the foot current data. Electric and magnetic field strengths were measured after the operator moved away from the normal working position. Foot current maxima ranged from 3 to 617 milliamperes (mA). About 27% of the heaters generated foot currents that exceeded 250mA, and about 20% exceeded 350mA, all of which were above the 200mA limit proposed for occupational exposure by the American National Standards Institute (ANSI). The highest ankle SAR obtained was about 176 watts per kilogram (W/kg). This was more than eight times that recommended in ANSI C95.1-1991 (20W/kg), for a part body extremity SAR.
NIOSH-Author; Bioelectric-effects; Electrical-fields; Electromagnetic-radiation; Nonionizing-radiation; Occupational-exposure; Radiation-hazards; Electrical-measurement