MAGNETIC-FIELD CHARACTERISTICS OF ELECTRIC BED-HEATING DEVICES

Measurements of the flux density and spectra of magnetic fields (MFs) generated by several types of electric bed heaters (EBH) were made in order to characterize the MFs to which the fetus may be exposed in ute ro from the mother's use of these devices. Data on MFs were gathered f rom more than 1,300 in-home and laboratory spot measurements. In-home measurements taken at seven different positions 10 cm from the EBHs de termined that the mean flux density at the estimated position of the f etus relative to the device was 0.45 mu T (4.5 mG) for electric blanke ts and 0.20 mu T (2.0 mG) for electrically heated water beds. A rate-o f-change (RC) metric applied to the nighttime segment of 24 h EMDEX-C personal-dosimeter measurements, which were taken next to the bed of v olunteers, yielded an approximate fourfold to sixfold higher value for electric blanket users compared to water-bed heater users. These same data records yielded an approximate twofold difference for the same m easurements when evaluated by the time-weighted-average (TWA) MF expos ure metric. Performance of exposure meters was checked against standar d fields generated in the laboratory, and studies of sources of varian ce in the in-home measurement protocols were carried out. Spectral mea surements showed that the EBH's measured produced no appreciable high- frequency MFs. Data gathered during this work will be used in interpre ting results from a component of the California Pregnancy Outcome Stud y, which evaluates the use of EBHs as a possible risk factor in miscar riage. (C) 1996 Wiley-Liss, Inc.