Tuesday, 15 March 2011 15:26

Radiofrequency Fields and Microwaves

Rate this item
(1 Vote)

Radiofrequency (RF) electromagnetic energy and microwave radiation is used in a variety of applications in industry, commerce, medicine and research, as well as in the home. In the frequency range from 3 to 3 x 108 kHz (that is, 300 GHz) we readily recognize applications such as radio and television broadcasting, communications (long-distance telephone, cellular telephone, radio communication), radar, dielectric heaters, induction heaters, switched power supplies and computer monitors.

High-power RF radiation is a source of thermal energy that carries all of the known implications of heating for biological systems, including burns, temporary and permanent changes in reproduction, cataracts and death. For the broad range of radiofrequencies, cutaneous perception of heat and thermal pain is unreliable for detection, because the thermal receptors are located in the skin and do not readily sense the deep heating of the body caused by these fields. Exposure limits are needed to protect against these adverse health effects of radiofrequency field exposure.

Occupational Exposure

Induction heating

By applying an intense alternating magnetic field a conducting material can be heated by induced eddy currents. Such heating is used for forging, annealing, brazing and soldering. Operating frequencies range from 50/60 to several million Hz. Since the dimensions of the coils producing the magnetic fields are often small, the risk of high-level whole-body exposure is small; however, exposure to the hands can be high.

Dielectric heating

Radiofrequency energy from 3 to 50 MHz (primarily at frequencies of 13.56, 27.12 and 40.68 MHz) is used in industry for a variety of heating processes. Applications include plastic sealing and embossing, glue drying, fabric and textile processing, woodworking and the manufacture of such diverse products as tarpaulins, swimming pools, waterbed liners, shoes, travel check folders and so on.

Measurements reported in the literature (Hansson Mild 1980; IEEE COMAR 1990a, 1990b, 1991) show that in many cases, electric and magnetic leakage fields are very high near these RF devices. Often the operators are women of child-bearing age (that is, 18 to 40 years). The leakage fields are often extensive in some occupational situations, resulting in whole-body exposure of operators. For many devices, the electric and magnetic field exposure levels exceed all existing RF safety guidelines.

Since these devices may give rise to very high absorption of RF energy, it is of interest to control the leakage fields which emanate from them. Thus, periodic RF monitoring becomes essential to determine whether an exposure problem exists.

Communication systems

Workers in the fields of communication and radar are exposed only to low-level field strengths in most situations. However, the exposure of workers who must climb FM/TV towers can be intense and safety precautions are necessary. Exposure can also be substantial near transmitter cabinets that have their interlocks defeated and doors open.

Medical exposure

One of the earliest applications of RF energy was short-wave diathermy. Unshielded electrodes are usually used for this, leading possibly to high stray fields.

Recently RF fields have been used in conjunction with static magnetic fields in magnetic resonance imaging (MRI). Since the RF energy used is low and the field is almost fully contained within the patient enclosure, the exposure to operators is negligible.

Biological Effects

The specific absorption rate (SAR, measured in watts per kilogram) is widely used as a dosimetric quantity, and exposure limits can be derived from SARs. The SAR of a biological body depends upon such exposure parameters as frequency of the radiation, intensity, polarization, configuration of the radiation source and the body, reflection surfaces and body size, shape and electrical properties. Furthermore, the SAR spatial distribution inside the body is highly non-uniform. Non-uniform energy deposition results in non-uniform deep-body heating and may produce internal temperature gradients. At frequencies above 10 GHz, the energy is deposited close to the body surface. The maximum SAR occurs at about 70 MHz for the standard subject, and at about 30 MHz when the person is standing in contact with RF ground. At extreme conditions of temperature and humidity, whole-body SARs of 1 to 4 W/kg at 70 MHz are expected to cause a core temperature rise of about 2 ºC in healthy human beings in one hour.

RF heating is an interaction mechanism that has been studied extensively. Thermal effects have been observed at less than 1 W/kg, but temperature thresholds have generally not been determined for these effects. The time-temperature profile must be considered in assessing biological effects.

Biological effects also occur where RF heating is neither an adequate nor a possible mechanism. These effects often involve modulated RF fields and millimetre wavelengths. Various hypotheses have been proposed but have not yet yielded information useful for deriving human exposure limits. There is a need to understand the fundamental mechanisms of interaction, since it is not practical to explore each RF field for its characteristic biophysical and biological interactions.

Human and animal studies indicate that RF fields can cause harmful biological effects because of excessive heating of internal tissues. The body’s heat sensors are located in the skin and do not readily sense heating deep within the body. Workers may therefore absorb significant amounts of RF energy without being immediately aware of the presence of leakage fields. There have been reports that personnel exposed to RF fields from radar equipment, RF heaters and sealers, and radio-TV towers have experienced a warming sensation some time after being exposed.

There is little evidence that RF radiation can initiate cancer in humans. Nevertheless, a study has suggested that it may act as a cancer promoter in animals (Szmigielski et al. 1988). Epidemiological studies of personnel exposed to RF fields are few in number and are generally limited in scope (Silverman 1990; NCRP 1986; WHO 1981). Several surveys of occupationally exposed workers have been conducted in the former Soviet Union and Eastern European countries (Roberts and Michaelson 1985). However, these studies are not conclusive with respect to health effects.

Human assessment and epidemiological studies on RF sealer operators in Europe (Kolmodin-Hedman et al. 1988; Bini et al. 1986) report that the following specific problems may arise:

  • RF burns or burns from contact with thermally hot surfaces
  • numbness (i.e., paresthesia) in hands and fingers; disturbed or altered tactile sensitivity
  • eye irritation (possibly due to fumes from vinyl-containing material)
  • significant warming and discomfort of the legs of operators (perhaps due to current flow through legs to ground).


Mobile Phones

The use of personal radiotelephones is rapidly increasing and this has led to an increase in the number of base stations. These are often sited in public areas. However, the exposure to the public from these stations is low. The systems usually operate on frequencies near 900 MHz or 1.8 GHz using either analogue or digital technology. The handsets are small, low power radio transmitters that are held in close proximity to the head when in use. Some of the power radiated from the antenna is absorbed by the head. Numerical calculations and measurements in phantom heads show that the SAR values can be of the order of a few W/kg (see further ICNIRP statement, 1996). Public concern about the health hazard of the electromagnetic fields has increased and several research programmes are being devoted to this question (McKinley et al., unpublished report). Several epidemiological studies are ongoing with respect to mobile phone use and brain cancer. So far only one animal study (Repacholi et al. 1997) with transgenic mice exposed 1 h per day for 18 months to a signal similar to that used in digital mobile communication has been published. By the end of the experiments 43 of 101 exposed animals had lymphomas, compared to 22 of 100 in the sham-exposed group. The increase was statistically significant (p > 0.001). These results cannot easily be interpreted with relevance to human health and further research on this is needed.

Standards and Guidelines

Several organizations and governments have issued standards and guidelines for protection from excessive exposure to RF fields. A review of worldwide safety standards was given by Grandolfo and Hansson Mild (1989); the discussion here pertains only to the guidelines issued by IRPA (1988) and IEEE standard C 95.1 1991.

The full rationale for RF exposure limits is presented in IRPA (1988). In summary, the IRPA guidelines have adopted a basic limiting SAR value of 4 W/kg, above which there is considered to be an increasing likelihood that adverse health consequences can occur as a result of RF energy absorption. No adverse health effects have been observed due to acute exposures below this level. Incorporating a safety factor of ten to allow for possible consequences of long-term exposure, 0.4 W/kg is used as the basic limit for deriving exposure limits for occupational exposure. A further safety factor of five is incorporated to derive limits for the general public.

Derived exposure limits for the electric field strength (E), the magnetic field strength (H) and the power density specified in V/m, A/m and W/m2 respectively, are shown in figure 1. The squares of the E and H fields are averaged over six minutes, and it is recommended that the instantaneous exposure not exceed the time-averaged values by more than a factor of 100. Furthermore, the body-to-ground current should not exceed 200 mA.

Figure 1. IRPA (1988) exposure limits for electric field strength E, magnetic field strength H and power density


Standard C 95.1, set in 1991, by the IEEE gives limiting values for occupational exposure (controlled environment) of 0.4 W/kg for the average SAR over a person’s entire body, and 8 W/kg for the peak SAR delivered to any one gram of tissue for 6 minutes or more. The corresponding values for exposure to the general public (uncontrolled environment) are 0.08 W/kg for whole-body SAR and 1.6 W/kg for peak SAR. The body-to-ground current should not exceed 100 mA in a controlled environment and 45 mA in an uncontrolled environment. (See IEEE 1991 for further details.) The derived limits are shown in figure 2.

Figure 2. IEEE (1991) exposure limits for electric field strength E, magnetic field strength H and power density


Further information on radiofrequency fields and microwaves can be found in, for instance, Elder et al. 1989, Greene 1992, and Polk and Postow 1986.



Read 7821 times Last modified on Wednesday, 17 August 2011 18:36

" DISCLAIMER: The ILO does not take responsibility for content presented on this web portal that is presented in any language other than English, which is the language used for the initial production and peer-review of original content. Certain statistics have not been updated since the production of the 4th edition of the Encyclopaedia (1998)."


Radiation: Non-Ionizng References

Allen, SG. 1991. Radiofrequency field measurements and hazard assessment. J Radiol Protect 11:49-62.

American Conference of Governmental Industrial Hygienists (ACGIH). 1992. Documentation for the Threshold Limit Values. Cincinnati, Ohio: ACGIH.

—. 1993. Threshold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati, Ohio: ACGIH.

—. 1994a. Annual Report of ACGIH Physical Agents Threshold Limit Values Committee. Cincinnati, Ohio: ACGIH.

—. 1994b. TLV’s, Threshold Limit Values and Biological Exposure Indices for 1994-1995. Cincinnati, Ohio: ACGIH.

—. 1995. 1995-1996 Threshhold Limit Values for Chemical Substances and Physical Agents and Biological Exposure Indices. Cincinnati, Ohio: ACGIH.

—. 1996. TLVs© and BEIs©. Threshold Limit Values for Chemical Substances and Physical Agents; Biological Exposure Indices. Cincinnati, Ohio: ACGIH.

American National Standards Institute (ANSI). 1993. Safe Use of Lasers. Standard No. Z-136.1. New York: ANSI.

Aniolczyk, R. 1981. Measurements of hygienic evaluation of electromagnetic fields in the environment of diathermy, welders, and induction heaters. Medycina Pracy 32:119-128.

Bassett, CAL, SN Mitchell, and SR Gaston. 1982. Pulsing electromagnetic field treatment in ununited fractures and failed artrodeses. J Am Med Assoc 247:623-628.

Bassett, CAL, RJ Pawluk, and AA Pilla. 1974. Augmentation of bone repair by inductively coupled electromagnetic fields. Science 184:575-577.

Berger, D, F Urbach, and RE Davies. 1968. The action spectrum of erythema induced by ultraviolet radiation. In Preliminary Report XIII. Congressus Internationalis Dermatologiae, Munchen, edited by W Jadassohn and CG Schirren. New York: Springer-Verlag.

Bernhardt, JH. 1988a. The establishment of frequency dependent limits for electric and magnetic fields and evaluation of indirect effects. Rad Envir Biophys 27:1.

Bernhardt, JH and R Matthes. 1992. ELF and RF electromagnetic sources. In Non-Ionizing Radiation Protection, edited by MW Greene. Vancouver: UBC Press.

Bini, M, A Checcucci, A Ignesti, L Millanta, R Olmi, N Rubino, and R Vanni. 1986. Exposure of workers to intense RF electric fields that leak from plastic sealers. J Microwave Power 21:33-40.

Buhr, E, E Sutter, and Dutch Health Council. 1989. Dynamic filters for protective devices. In Dosimetry of Laser Radiation in Medicine and Biology, edited by GJ Mueller and DH Sliney. Bellingham, Wash: SPIE.

Bureau of Radiological Health. 1981. An Evaluation of Radiation Emission from Video Display Terminals. Rockville, MD: Bureau of Radiological Health.

Cleuet, A and A Mayer. 1980. Risques liés à l’utilisation industrielle des lasers. In Institut National de Recherche et de Sécurité, Cahiers de Notes Documentaires, No. 99 Paris: Institut National de Recherche et de Sécurité.

Coblentz, WR, R Stair, and JM Hogue. 1931. The spectral erythemic relation of the skin to ultraviolet radiation. In Proceedings of the National Academy of Sciences of the United States of America Washington, DC: National Academy of Sciences.

Cole, CA, DF Forbes, and PD Davies. 1986. An action spectrum for UV photocarcinogenesis. Photochem Photobiol 43(3):275-284.

Commission Internationale de L’Eclairage (CIE). 1987. International Lighting Vocabulary. Vienna: CIE.

Cullen, AP, BR Chou, MG Hall, and SE Jany. 1984. Ultraviolet-B damages corneal endothelium. Am J Optom Phys Opt 61(7):473-478.

Duchene, A, J Lakey, and M Repacholi. 1991. IRPA Guidelines On Protection Against Non-Ionizing Radiation. New York: Pergamon.

Elder, JA, PA Czerki, K Stuchly, K Hansson Mild, and AR Sheppard. 1989. Radiofrequency radiation. In Nonionizing Radiation Protection, edited by MJ Suess and DA Benwell-Morison. Geneva: WHO.

Eriksen, P. 1985. Time resolved optical spectra from MIG welding arc ignition. Am Ind Hyg Assoc J 46:101-104.

Everett, MA, RL Olsen, and RM Sayer. 1965. Ultraviolet erythema. Arch Dermatol 92:713-719.

Fitzpatrick, TB, MA Pathak, LC Harber, M Seiji, and A Kukita. 1974. Sunlight and Man, Normal and Abnormal Photobiologic Responses. Tokyo: Univ. of Tokyo Press.

Forbes, PD and PD Davies. 1982. Factors that influence photocarcinogenesis. Chap. 7 in Photoimmunology, edited by JAM Parrish, L Kripke, and WL Morison. New York: Plenum.

Freeman, RS, DW Owens, JM Knox, and HT Hudson. 1966. Relative energy requirements for an erythemal response of skin to monochromatic wavelengths of ultraviolet present in the solar spectrum. J Invest Dermatol 47:586-592.

Grandolfo, M and K Hansson Mild. 1989. Worldwide public and occupational radiofrequency and microwave protection. In Electromagnetic Biointeraction. Mechanisms, Safety Standards, Protection Guides, edited by G Franceschetti, OP Gandhi, and M Grandolfo. New York: Plenum.

Greene, MW. 1992. Non Ionizing Radiation. 2nd International Non Ionizing Radiation Workshop, 10-14 May, Vancouver.

Ham, WTJ. 1989. The photopathology and nature of the blue-light and near-UV retinal lesion produced by lasers and other optic sources. In Laser Applications in Medicine and Biology, edited by ML Wolbarsht. New York: Plenum.

Ham, WT, HA Mueller, JJ Ruffolo, D Guerry III, and RK Guerry. 1982. Action spectrum for retinal injury from near ultraviolet radiation in the aphakic monkey. Am J Ophthalmol 93(3):299-306.

Hansson Mild, K. 1980. Occupational exposure to radio-frequency electromagnetic fields. Proc IEEE 68:12-17.

Hausser, KW. 1928. Influence of wavelength in radiation biology. Strahlentherapie 28:25-44.

Institute of Electrical and Electronic Engineers (IEEE). 1990a. IEEE COMAR Position of RF and Microwaves. New York: IEEE.

—. 1990b. IEEE COMAR Position Statement On Health Aspects of Exposure to Electric and Magnetic Fields from RF Sealers and Dielectric Heaters. New York: IEEE.

—. 1991. IEEE Standard for Safety Levels With Respect to Human Exposure to Radiofrequency Electromagnetic Fields 3 KHz to 300 GHz. New York: IEEE.

International Commission on Non-Ionizing Radiation Protection (ICNIRP). 1994. Guidelines on Limits of Exposure to Static Magnetic Fields. Health Phys 66:100-106.

—. 1995. Guidelines for Human Exposure Limits for Laser Radiation.

ICNIRP statement. 1996. Health issues related to the use of hand-held radiotelephones and base transmitters. Health Physics, 70:587-593.

International Electrotechnical Commission (IEC). 1993. IEC Standard No. 825-1. Geneva: IEC.

International Labour Office (ILO). 1993a. Protection from Power Frequency Electric and Magnetic Fields. Occupational Safety and Health Series, No. 69. Geneva: ILO.

International Radiation Protection Association (IRPA). 1985. Guidelines for limits of human exposure to laser radiation. Health Phys 48(2):341-359.

—. 1988a. Change: Recommendations for minor updates to the IRPA 1985 guidelines on limits of exposure to laser radiation. Health Phys 54(5):573-573.

—. 1988b. Guidelines on limits of exposure to radiofrequency electromagnetic fields in the frequency range from 100 kHz to 300 GHz. Health Phys 54:115-123.

—. 1989. Proposed change to the IRPA 1985 guidelines limits of exposure to ultraviolet radiation. Health Phys 56(6):971-972.

International Radiation Protection Association (IRPA) and International Non-Ionizing Radiation Committee. 1990. Interim guidelines on limits of exposure to 50/60 Hz electric and magnetic fields. Health Phys 58(1):113-122.

Kolmodin-Hedman, B, K Hansson Mild, E Jönsson, MC Anderson, and A Eriksson. 1988. Health problems among operations of plastic welding machines and exposure to radiofrequency electromagnetic fields. Int Arch Occup Environ Health 60:243-247.

Krause, N. 1986. Exposure of people to static and time variable magnetic fields in technology, medicine, research and public life: Dosimetric aspects. In Biological Effects of Static and ELF-Magnetic Fields, edited by JH Bernhardt. Munchen: MMV Medizin Verlag.

Lövsund, P and KH Mild. 1978. Low Frequency Electromagnetic Field Near Some Induction Heaters. Stockholm: Stockholm Board of Occupational Health and Safety.

Lövsund, P, PA Oberg, and SEG Nilsson. 1982. ELF magnetic fields in electrosteel and welding industries. Radio Sci 17(5S):355-385.

Luckiesh, ML, L Holladay, and AH Taylor. 1930. Reaction of untanned human skin to ultraviolet radiation. J Optic Soc Am 20:423-432.

McKinlay, AF and B Diffey. 1987. A reference action spectrum for ultraviolet induced erythema in human skin. In Human Exposure to Ultraviolet Radiation: Risks and Regulations, edited by WF Passchier and BFM Bosnjakovic. New York: Excerpta medica Division, Elsevier Science Publishers.

McKinlay, A, JB Andersen, JH Bernhardt, M Grandolfo, K-A Hossmann, FE van Leeuwen, K Hansson Mild, AJ Swerdlow, L Verschaeve and B Veyret. Proposal for a research programme by a European Commission Expert Group. Possible health effects related to the use of radiotelephones. Unpublished report.

Mitbriet, IM and VD Manyachin. 1984. Influence of magnetic fields on the repair of bone. Moscow, Nauka, 292-296.

National Council on Radiation Protection and Measurements (NCRP). 1981. Radiofrequency Electromagnetic Fields. Properties, Quantities and Units, Biophysical Interaction, and Measurements. Bethesda, MD: NCRP.

—. 1986. Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields. Report No. 86. Bethesda, MD: NCRP.

National Radiological Protection Board (NRPB). 1992. Electromagnetic Fields and the Risk of Cancer. Vol. 3(1). Chilton, UK: NRPB.

—. 1993. Restrictions On Human Exposure to Static and Time-Varying Electromagnetic Fields and Radiations. Didcot, UK: NRPB.

National Research Council (NRC). 1996. Possible health effects of exposure to residential electric and magnetic fields. Washington: NAS Press. 314.

Olsen, EG and A Ringvold. 1982. Human corneal endothelium and ultraviolet radiation. Acta Ophthalmol 60:54-56.

Parrish, JA, KF Jaenicke, and RR Anderson. 1982. Erythema and melanogenesis: Action spectra of normal human skin. Photochem Photobiol 36(2):187-191.

Passchier, WF and BFM Bosnjakovic. 1987. Human Exposure to Ultraviolet Radiation: Risks and Regulations. New York: Excerpta Medica Division, Elsevier Science Publishers.

Pitts, DG. 1974. The human ultraviolet action spectrum. Am J Optom Phys Opt 51(12):946-960.

Pitts, DG and TJ Tredici. 1971. The effects of ultraviolet on the eye. Am Ind Hyg Assoc J 32(4):235-246.

Pitts, DG, AP Cullen, and PD Hacker. 1977a. Ocular effects of ultraviolet radiation from 295 to 365nm. Invest Ophthalmol Vis Sci 16(10):932-939.

—. 1977b. Ultraviolet Effects from 295 to 400nm in the Rabbit Eye. Cincinnati, Ohio: National Institute for Occupational Safety and Health (NIOSH).

Polk, C and E Postow. 1986. CRC Handbook of Biological Effects of Electromagnetic Fields. Boca Raton: CRC Press.

Repacholi, MH. 1985. Video display terminals -should operators be concerned? Austalas Phys Eng Sci Med 8(2):51-61.

—. 1990. Cancer from exposure to 50760 Hz electric and magnetic fields: A major scientific debate. Austalas Phys Eng Sci Med 13(1):4-17.

Repacholi, M, A Basten, V Gebski, D Noonan, J Finnic and AW Harris. 1997. Lymphomas in E-Pim1 transgenic mice exposed to pulsed 900 MHz electromagnetic fields. Radiation research, 147:631-640.

Riley, MV, S Susan, MI Peters, and CA Schwartz. 1987. The effects of UVB irradiation on the corneal endothelium. Curr Eye Res 6(8):1021-1033.

Ringvold, A. 1980a. Cornea and ultraviolet radiation. Acta Ophthalmol 58:63-68.

—. 1980b. Aqueous humour and ultraviolet radiation. Acta Ophthalmol 58:69-82.

—. 1983. Damage of the corneal epithelium caused by ultraviolet radiation. Acta Ophthalmol 61:898-907.

Ringvold, A and M Davanger. 1985. Changes in the rabbit corneal stroma caused by UV radiation. Acta Ophthalmol 63:601-606.

Ringvold, A, M Davanger, and EG Olsen. 1982. Changes of the corneal endothelium after ultraviolet radiation. Acta Ophthalmol 60:41-53.

Roberts, NJ and SM Michaelson. 1985. Epidemiological studies of human exposure to radiofrequency radiation: A critical review. Int Arch Occup Environ Health 56:169-178.

Roy, CR, KH Joyner, HP Gies, and MJ Bangay. 1984. Measurement of electromagnetic radiation emitted from visual display terminals (VDTs). Rad Prot Austral 2(1):26-30.

Scotto, J, TR Fears, and GB Gori. 1980. Measurements of Ultraviolet Radiations in the United States and Comparisons With Skin Cancer Data. Washington, DC: US Government Printing Office.

Sienkiewicz, ZJ, RD Saunder, and CI Kowalczuk. 1991. Biological Effects of Exposure to Non-Ionizing Electromagnetic Fields and Radiation. 11 Extremely Low Frequency Electric and Magnetic Fields. Didcot, UK: National Radiation Protection Board.

Silverman, C. 1990. Epidemiological studies of cancer and electromagnetic fields. In Chap. 17 in Biological Effects and Medical Applications of Electromagnetic Energy, edited by OP Gandhi. Engelwood Cliffs, NJ: Prentice Hall.

Sliney, DH. 1972. The merits of an envelope action spectrum for ultraviolet radiation exposure criteria. Am Ind Hyg Assoc J 33:644-653.

—. 1986. Physical factors in cataractogenesis: Ambient ultraviolet radiation and temperature. Invest Ophthalmol Vis Sci 27(5):781-790.

—. 1987. Estimating the solar ultraviolet radiation exposure to an intraocular lens implant. J Cataract Refract Surg 13(5):296-301.

—. 1992. A safety manager’s guide to the new welding filters. Welding J 71(9):45-47.
Sliney, DH and ML Wolbarsht. 1980. Safety With Lasers and Other Optical Sources. New York: Plenum.

Stenson, S. 1982. Ocular findings in xeroderma pigmentosum: Report of two cases. Ann Ophthalmol 14(6):580-585.

Sterenborg, HJCM and JC van der Leun. 1987. Action spectra for tumourigenesis by ultraviolet radiation. In Human Exposure to Ultraviolet Radiation: Risks and Regulations, edited by WF Passchier and BFM Bosnjakovic. New York: Excerpta Medica Division, Elsevier Science Publishers.

Stuchly, MA. 1986. Human exposure to static and time-varying magnetic fields. Health Phys 51(2):215-225.

Stuchly, MA and DW Lecuyer. 1985. Induction heating and operator exposure to electromagnetic fields. Health Phys 49:693-700.

—. 1989. Exposure to electromagnetic fields in arc welding. Health Phys 56:297-302.

Szmigielski, S, M Bielec, S Lipski, and G Sokolska. 1988. Immunologic and cancer related aspects of exposure to low-level microwave and radiofrequency fields. In Modern Bioelectricity, edited by AA Mario. New York: Marcel Dekker.

Taylor, HR, SK West, FS Rosenthal, B Munoz, HS Newland, H Abbey, and EA Emmett. 1988. Effect of ultraviolet radiation on cataract formation. New Engl J Med 319:1429-1433.

Tell, RA. 1983. Instrumentation for measurement of electromagnetic fields: Equipment, calibrations, and selected applications. In Biological Effects and Dosimetry of Nonionizing Radiation, Radiofrequency and Microwave Energies, edited by M Grandolfo, SM Michaelson, and A Rindi. New York: Plenum.

Urbach, F. 1969. The Biologic Effects of Ultraviolet Radiation. New York: Pergamon.

World Health Organization (WHO). 1981. Radiofrequency and microwaves. Environmental Health Criteria, No.16. Geneva: WHO.

—. 1982. Lasers and Optical Radiation. Environmental Health Criteria, No. 23. Geneva: WHO.

—. 1987. Magnetic Fields. Environmental Health Criteria, No.69. Geneva: WHO.

—. 1989. Non-Ionization Radiation Protection. Copenhagen: WHO Regional Office for Europe.

—. 1993. Electromagnetic Fields 300 Hz to 300 GHz. Environmental Health Criteria, No. 137. Geneva: WHO.

—. 1994. Ultraviolet Radiation. Environmental Health Criteria, No. 160. Geneva: WHO.

World Health Organization (WHO), United Nations Environmental Programme (UNEP), and International Radiation Protection Association (IRPA). 1984. Extremely Low Frequency (ELF). Environmental Health Criteria, No. 35. Geneva: WHO.

Zaffanella, LE and DW DeNo. 1978. Electrostatic and Electromagnetic Effects of Ultra-High-Voltage Transmission Lines. Palo Alto, Calif: Electric Power Research Institute.

Zuclich, JA and JS Connolly. 1976. Ocular damage induced by near-ultraviolet laser radiation. Invest Ophthalmol Vis Sci 15(9):760-764.