Tell R A, Harlen F
J Microw Power. 1979 Dec;14(4):405-24. doi: 10.1080/16070658.1979.11689176.
This report examines the bases for developing radiofrequency exposure standards which can be related to the thermogenic properties of electromagnetic fields. A review of selected biological effects, including dosimetric data and simulation of human thermodyanmic characteristics that are pertinent to standards development, is presented. Based on the analogy of thermal-stress standards that have been developed for hot industrial environments, limits on increases of body temperature are proposed as criteria for limiting exposure to radiofrequency fields, i.e., occupational exposures involving deep heating of the whole body should not increase core temperature in excess of 1 degree C. Since energy deposition from exposure to some RF fields is likely to be non-uniform and may be high in tissues that are not adapted to high rates of absorption or dissipation of thermalizing energy, means are needed to adjust focal thermal loading against the whole-body averages. A limit on core temperature is inadequate when focal elevations of temperature are close to the limits for protein denaturation, as may well occur even though the core temperature may rise less than 1 degree C. Safety limits for the general population are also discussed and here the permissible thermal load should be low enough to cause no more than an insignificant increase in core temperature. Areas needing further research to reduce the uncertainties in developing safe exposure limits for man are delineated. Even in highly adverse environmental conditions the gross thermal load and consequential heat stress from exposure to radiofrequency fields at the 10 mW/cm2 level will be small compared with that generated by any physical effort. On the basis of available data, it is concluded that the safe value for continuous exposure to 10 mW/cm2, widely used in Western countries, appears to provide an adequate margin of safety for both occupational and environmental exposure for frequencies above about 1 GHz. This limit may well be too high (perhaps by an order of magnitude) for some frequencies below 1 GHz where body resonances cause a significant increase in energy deposition and where local temperature rises occur. At the same time the present averaging period of 0.1 h seems unjustifiably short.
本报告探讨了制定与电磁场热效应相关的射频暴露标准的依据。文中对一些选定的生物效应进行了综述，包括剂量学数据以及与标准制定相关的人体热力学特性模拟。基于已为高温工业环境制定的热应激标准，建议将体温升高的限制作为限制射频场暴露的标准，即涉及全身深度加热的职业暴露不应使核心体温升高超过1摄氏度。由于暴露于某些射频场时的能量沉积可能不均匀，且在不适应热能快速吸收或消散的组织中可能很高，因此需要采取措施根据全身平均值来调整局部热负荷。当局部温度升高接近蛋白质变性的极限时，仅限制核心温度是不够的，即使核心温度升高可能不到1摄氏度，这种情况也很可能发生。文中还讨论了一般人群的安全限值，此处允许的热负荷应足够低，以使核心体温升高不超过微不足道的程度。文中划定了为减少制定人类安全暴露限值时的不确定性而需要进一步研究的领域。即使在高度不利的环境条件下，与任何体力活动产生的热负荷相比，暴露于10 mW/cm²水平的射频场产生的总热负荷和相应的热应激也将很小。根据现有数据得出结论，西方国家广泛使用的连续暴露于10 mW/cm²的安全值，对于频率高于约1 GHz的职业和环境暴露而言，似乎提供了足够的安全裕度。对于某些低于1 GHz的频率，该限值可能过高（可能高出一个数量级），因为人体共振会导致能量沉积显著增加并出现局部温度升高。同时，目前0.1小时的平均时间似乎短得不合理。
