Safety in the use of RF heaters and sealers

microwaves. In other studies (Szmigielski et al., 1982; Szudzinski et al., 1982), the chronic microwave exposure of mice at 2 to 8 W/kg resulted in an SAR-dependent increase in the progression or development of spontaneous mammary tumours or chemically induced skin tumours. Body temperatures were not raised but the authors suggest a possibility of inhomogeneous heating at the highest level of exposure. A further experiment (Szmigielski et al., 1988) showed that exposure at 4 to 5 W/kg followed by the application of a "sub-carcinogenic" dose of a carcinogen to the skin, a procedure repeated daily, eventually resulted in a threefold increase in the numbers of skin tumours appearing.

Some epidemiological studies have investigated groups of adults with RF or assumed RF exposure and cancer incidence or mortality (Lilienfield et al., 1978; Robinette et al., 1980; Milham, 1988; Armstrong et al., 1994; Szmigielski, in press). The results were varied in that in some studies there was no effect, while in other studies associations between RF exposure and various cancers were found. Some of these studies are subject to methodological shortcomings or uncertainties, such as crude exposure assessments, lack of analysis of confounding (except for age), paucity of reported details of analysis, etc. The overall assessment of these studies suggests that certain findings of excess lung cancer in two of them (Robinette et al., 1980; Armstrong et al., 1994) may warrant further investigation, but that uncertainties in exposure assessments currently preclude any conclusions. For other cancer sites, indications of associations were either absent or difficult to evaluate for methodological reasons.

5.3. Conclusion

Although there remains a great deal unknown about the health implications of RF radiation, the potential thermal hazard is understood and should be given serious consideration. The deposition of RF energy in the human body tends to increase the body temperature. During exercise, the metabolic heat production can reach levels of 3 to 5 W/kg. In normal thermal environments, a SAR of 1 to 4 W/kg for 30 minutes produces average body temperature increases of less than 1 °C in healthy adults. Thus, an occupational RF guideline of 0.4 W/kg SAR leaves a margin of protection against complications due to thermally unfavourable environmental conditions.

In conclusion, exposure conditions experienced by some RF heater operators can cause elevated body temperatures. At these elevated temperatures, reproductive and teratogenic effects may occur in heater operators. In addition, eye irritation, RF burns, and neurological problems (hand numbness, diminished two-point discrimination and carpal tunnel syndrome) have been documented for heater operators.

14