6
Occupational exposure standards and guidelines
Many countries have now established RF health protection standards or guidelines. There have been a number of in-depth reviews of current RF standards (Czerski, 1985; Stuchly, 1987; Sliney, 1988; Repacholi, 1990). Most of the early standards addressed the microwave region only (300 MHz-300 GHz) because of the introduction and proliferation of radar, telecommunications, and radio and TV broadcasting. Later the vastly expanded use of the electromagnetic spectrum was recognized, especially at lower frequencies where concerns were raised about RF exposures from induction heaters, heat sealers and other industrial applications.
RF exposure standards have also been proposed by groups of countries, such as the European Community and the Council for Mutual Economic Assistance. A proposal for a Directive of the Council of the European Communities was published in March 1993. The proposal on the minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents included electromagnetic fields and waves. Following the advice of the European Parliament, the Commission submitted an amended proposal in July 1994, which was adopted in August 1994. The European Committee for Electrical Standardization (CENELEC) published a prestandard (ENV 50166 part 2) in January 1995, which will be reviewed for adoption as a full standard in three years. The Commission of Mutual Economic Assistance Standard 5801-86, established in 1986, had been incorporated into the regulations of several Eastern European countries in the following years. The maximum exposure levels in the various standards can differ by two orders of magnitude. It is speculated that these differences result from: (a) the physical and biological effects data selected as the basis for the standards; (b) the interpretation of these data; (c) the different purposes to be served by the standards; (d) the compromises made between levels of risk and degrees of conservatism; and (e) the influence of preceding standards in each particular nation. In recent years, an increasing number of countries have adopted limits identical or very close to those recommended by INIRC/IRPA.
6.1. ICNIRP guidelines
The INIRC/IRPA guidelines for frequencies between 100 kHz and 300 GHz were published in 1988 and were based on a whole-body average SAR of 0.4 W/kg (IRPA, 1988). Under conditions where the whole-body average SAR might not exceed the whole-body average limit, several reports (Conover et al., 1992; Dimbylow, 1988; Gandhi et al., 1985, 1986; Chou and Guy, 1985; Stuchly et al., 1985, 1986a, 1986b; Williams and Mild, 1991; Erickson and Mild, 1985) indicate that under certain conditions peak values of local SAR in the extremities (particularly the wrists and ankles) can exceed the whole-body limit value by a factor of 300 at certain frequencies.
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Safety in the use of RF heaters and sealers
ICNIRP is currently revising these RF guidelines as follows: for occupational exposure in the frequency range of 10 to 100 MHz, an SAR of 0.4 W/kg should not be exceeded when averaged over any 6-minute period and over the whole body. In head, neck and trunk, the local SAR should not exceed 10 W/kg averaged over 6 minutes and over any 10-g mass. For other parts of the body, the corresponding local SAR is 20 W/kg averaged over 6 minutes and 10 g.
The field strength limits in table 1 for frequencies between 10 MHz and 100 MHz are derived from the whole-body average SAR value of 0.4 W/kg. A limitation of the body-to-ground current to 100 mA per limb provides a means of complying with the basic restrictions.
Table 1. ICNIRP occupational exposure limits to radiofrequency fields
Frequency range |
Unperturbed electric |
Unperturbed magnetic |
Body current to ground |
|
|
field strength (rms) |
field strength (rms) |
through one limb |
|
ƒ (MHz) |
E (V/m) |
H (A/m) |
B(µT) |
I(mA) |
10-100 |
61 |
0.16 |
0.2 |
100 |
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