Development of a source-exposure matrix for occupational exposure assessment of electromagnetic fields in the INTEROCC study

Abstract

To estimate occupational exposures to electromagnetic fields (EMF) for the INTEROCC study, a database of source-based measurements extracted from published and unpublished literature resources had been previously constructed. The aim of the current work was to summarize these measurements into a source-exposure matrix (SEM), accounting for their quality and relevance. A novel methodology for combining available measurements was developed, based on order statistics and log-normal distribution characteristics. Arithmetic and geometric means, and estimates of variability and maximum exposure were calculated by EMF source, frequency band and dosimetry type. The mean estimates were weighted by our confidence in the pooled measurements. The SEM contains confidence-weighted mean and maximum estimates for 312 EMF exposure sources (from 0 Hz to 300 GHz). Operator position geometric mean electric field levels for radiofrequency (RF) sources ranged between 0.8 V/m (plasma etcher) and 320 V/m (RF sealer), while magnetic fields ranged from 0.02 A/m (speed radar) to 0.6 A/m (microwave heating). For extremely low frequency sources, electric fields ranged between 0.2 V/m (electric forklift) and 11,700 V/m (high-voltage transmission line-hotsticks), whereas magnetic fields ranged between 0.14 μT (visual display terminals) and 17 μT (tungsten inert gas welding). The methodology developed allowed the construction of the first EMF-SEM and may be used to summarize similar exposure data for other physical or chemical agents.

Figure 1

Quartile plots (25^th and 75^th percentiles) for EMF sources in the SEM with the highest and lowest _cwGM for E-, H-, and B-fields for operator position by frequency band. Estimates without whiskers (i.e. “transmission lines”, “electric forklift truck” and “sewing machine”) were obtained from only one measurement. To indicate within-source variability, the graphs include estimates for the first and third quartiles = e^{[ln(cwGM)±0.675ln(cwGSD)]}, where 0.675 is the z-value for the 75th percentile.

Figure 2

Operator position E-field measurements for two RF sources (i.e. aircraft radar and dielectric heater) collected from documents covering the time span 1986–2004. Data points and corresponding confidence ratings (i.e. the size of the point) were obtained by averaging the available data by year. The lines represent modeled linear regressions based on the averaged data.

Figure 3

E-field measurements versus distance for OEMD data used to estimate the confidence-weighted mean exposure for the source “continuous shortwave diathermy” in the SEM. The bubbles represent data points with size proportional to the assigned rating level. The lines represent modeled exponential regression lines (dashed line, weighted) with y-axis in the linear (left graph) and logarithmic (right graph) scales. No ratings were assigned to these measurements below 1 or above 2. Thus, the “Rating” legend only includes a scale of sizes between these levels.