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Documents of the NRPB: Volume 10 , No. 2

1998 ICNIRP Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic and Electromagnetic Fields (up to 300 GHz): NRPB Advice on Aspects of Implementation in the UK


Author(s):

S G Allen, P J Chadwick, P J Dimbylow, A F McKinlay, C R Muirhead, Z J Sienkiewicz and J W Stather

Summary:

Advice on the 1998 ICNIRP Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic and Electromagnetic Fields (up to 300 GHz).

A statement by the NRPB, and an abstract and executive summary of the document are given below.

This document has now been superseded by Documents of the NRPB, volume 15, nos 2 and 3.

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Statement by the National Radiological Protection Board

Background

  1. Guidance on restrictions on exposure to static and time-varying electric and magnetic fields and radiations (EMFs) was issued by the National Radiological Protection Board in 1993, together with a Board Statement summarising the scientific basis for the guidelines 1, 2. These guidelines have been widely accepted in the UK and used by central government departments, local authorities, professional bodies and industry.
  2. The restrictions on exposure to EMFs recommended by NRPB are based on biological data relating to thresholds for well-established direct and indirect effects of acute exposure. Direct effects are those resulting from the interaction of EMFs with the human body. For exposure to low frequency electric and magnetic fields, up to 100 kHz, the restrictions are intended to avoid the effects of induced currents on functions of the central nervous system. For radiofrequency (RF) fields, which include microwaves, the restrictions are intended to prevent the adverse effects of whole and partial body heating. Indirect effects are those resulting from an interaction between EMFs, an external object such as a vehicle or other mechanical structure and the human body. For these effects restrictions on exposure are set to avoid shocks at low frequencies and burns at RF frequencies.
  3. The recommendations to restrict exposure are based on the interactions of EMFs with body tissues and are termed basic restrictions. Compliance with the basic restrictions cannot, however, be generally determined directly. Investigation levels are therefore recommended as values of measurable field quantities for assessing whether compliance with the basic restrictions has been achieved. The exposure guidelines advised by NRPB incorporate conservative assumptions in their derivation and are considered to provide adequate protection for both workers and members of the public. No distinction is therefore made by NRPB between exposures received occupationally and those received by members of the public.
  4. There have been concerns that exposure to EMFs may be implicated in the development of long-term health effects, and in particular in the development of cancer. The NRPB Advisory Group on Non-Ionising Radiation has reviewed evidence from epidemiological studies for an association between the incidence of childhood and adult cancers and exposure to EMFs 3, 4, 5. It can be concluded from these reviews that there is no clear evidence of adverse health effects at the levels of EMFs to which people are normally exposed. The results of published epidemiological studies do not therefore provide a basis for restricting human exposure to EMFs 1, 2. The Advisory Group continues to keep this issue under active review and expects to publish a further report following publication of the UK National Childhood Cancer Study.

ICNIRP guidelines

  1. In April 1998, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) published guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields in the frequency range up to 300 GHz 6,7. These guidelines replaced previous advice issued in 1988 8 and 1990 9. The accompanying document on the ICNIRP guidelines by NRPB staff examines the recent recommendations by ICNIRP and provides advice on their scientific basis.

Board statement

  1. The Board has concluded that for occupational exposure the basic restrictions in the new ICNIRP guidelines do not differ in any significant way from those previously recommended by NRPB and have no implications for the UK guidelines. For members of the public, ICNIRP has generally included a reduction factor of up to five in setting basic restrictions across the frequency range to 300 GHz. There is, however, a lack of scientific evidence to support the introduction of these additional reduction factors. The Board believes that the existing UK advice by NRPB on limiting exposures for the general public already provides sufficient protection from direct and indirect effects and that any health benefits to be obtained from further reductions in exposure have not been demonstrated. It sees no scientific justification, therefore, for altering the advice previously given by NRPB on exposure guidelines for members of the public. It does, however, accept that other factors may need to be taken into account by government in establishing generally accepted exposure guidelines for the public.
  2. In relation to furthering knowledge on possible health effects of exposure to EMFs the Board supports the need for further epidemiological and experimental studies.

The Board's Statement reflects understanding and evaluation of the current scientific evidence as given in the supporting document. If and when further relevant information becomes available, the Board will review its advice.

1 NRPB. Statement by the National Radiological Protection Board: Restrictions on human exposures to static and time varying electromagnetic fields and radiation. Doc. NRPB, 4 No. 5, 1-5 (1993).

2 NRPB. Restrictions on human exposure to static and time varying electromagnetic fields and radiation: Scientific basis and recommendations for the implementation of the Board's Statement. Doc. NRPB, 4, No. 5, 7-63 (1993).

3 NRPB. Electromagnetic fields and the risk of cancer: Report of an Advisory Group on Non-Ionising Radiation. Doc. NRPB, 3, No. 1, 1-138 (1992).

4 NRPB. Electromagnetic fields and the risk of cancer: Summary of the views of the Advisory Group on Non-Ionising Radiation on epidemiological studies published since its 1992 report. Doc. NRPB, 4, No. 5, 65-9 (1993).

5 NRPB. Electromagnetic fields and the risk of cancer: Supplementary report by the Advisory Group on Non-Ionising Radiation (12 April 1994). Doc. NRPB, 5, No. 2, 77-81 (1994).

6 ICNIRP. uidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz). Health Phys., 74, No. 4, 494-522 (1998).

7 ICNIRP. Response to questions and comments on ICNIRP guidelines. Health Phys., 75, No. 4, 438-9 (1998).

8 INIRC. Guidelines on limits of exposure to radiofrequency electromagnetic fields in the frequency range from 100 kHz to 300 GHz. Health Phys., 54, No. 1, 115-23 (1988).

9 INIRC. Interim guidelines on limits of exposure to 50/60 Hz electric and magnetic fields. Health Phys., 58, No. 10, 113-22 (1990).

Abstract

In April 1998, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) published guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields in the frequency range up to 300 GHz. These guidelines replaced previous advice issued in 1988 and 1990. This document examines the recommendations of ICNIRP and provides advice on their scientific basis. Specific aspects of the ICNIRP guidelines are examined in comparison with current UK exposure guidelines recommended by NRPB. The application by ICNIRP of additional reduction factors for the derivation of exposure restrictions for the general public is particularly addressed. Examples of exposure situations in the UK where the ICNIRP electric and magnetic field reference levels for the general public might be expected to be exceeded, and where additional investigations of compliance with basic restrictions would be called for, are also provided. This advice reflects understanding and evaluation of the current scientific evidence as presented and referenced in this document.

Executive summary

Scope

  1. The National Radiological Protection Board has responsibility for providing advice on restrictions on the exposure of people to electric and magnetic fields and radiation (EMFs). These include static, power frequency (50 Hz) and other extremely low frequency (ELF) electric and magnetic fields, and radiofrequency (RF) fields and radiation. Guidance on restrictions on exposure to static and time-varying electromagnetic fields and radiation was issued in 1993 together with a Board Statement summarising the scientific basis for the guidelines 1, 2. These guidelines have been widely accepted in the UK and used by central government departments, local authorities, professional bodies and by the electricity generating and supply industry, and other industries.
  2. In April 1998, the International Commission on Non-Ionizing Radiation Protection (ICNIRP) published guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields in the frequency range up to 300 GHz 3. These guidelines replaced previous advice issued in 1988 4 and 1990 5. Further clarification of specific aspects of the guidelines and their application has been published by ICNIRP 6. This report reviews the recommendations of ICNIRP and provides advice on their scientific basis. Specific aspects of the ICNIRP guidelines are addressed in comparison with current UK exposure guidelines recommended by NRPB. In particular, the application by ICNIRP of additional reduction factors in deriving exposure restrictions for the general public is considered. Examples are provided of exposure situations in the UK where the ICNIRP electric and magnetic field reference levels for the general public might be expected to be exceeded and where additional investigations of compliance with basic restrictions would be needed.

Principles

  1. It is generally recognised that in establishing guidelines on standards of protection for exposure to EMFs, three broad scientific areas need to be addressed - epidemiology, biology and dosimetry.
  2. A substantial number of studies of human populations exposed to EMFs have been carried out. They have examined general health, birth outcome and cancer incidence. The NRPB Advisory Group on Non-Ionising Radiation has reviewed evidence from epidemiological studies on EMFs and the risk of cancer 7, 8, 9. It has concluded that there is no clear evidence of adverse health effects at the levels of EMFs to which people are normally exposed. In particular, in relation to concerns about the possible effect of EMFs on the development of cancer, the Advisory Group has concluded that epidemiological studies do not establish that exposure to EMFs is a cause of cancer although, taken together, they suggest that the possibility exists in the case of childhood leukaemia. At present though, there is no persuasive biological evidence that ELF electromagnetic fields can influence any of the accepted stages in carcinogenesis. There is no clear basis from which to derive a meaningful assessment of risk, nor is there any indication of how any risk might vary with exposure. In developing its advice, NRPB 1, 2 has therefore concluded that the published epidemiological data do not provide a basis for restricting human exposure to EMFs. ICNIRP has expressed the same view.
  3. NRPB guidance on restrictions on exposure is based on the available biological data describing thresholds for well-established direct and indirect effects of acute exposure. Direct effects are those resulting from the interaction of EMFs with the human body, whereas indirect effects are those resulting from an interaction between EMFs, an external object such as a vehicle or other mechanical structure and the human body. The advice, issued by ICNIRP, has followed the same approach.

Direct effects

  1. The adverse health consequences of direct effects of exposure to EMFs are addressed by a consideration of the biological responses to EMFs. Restrictions on exposure aim to limit the degree of interaction with the organs and tissues of the body to acceptable levels.
  2. The ubiquity of sources of static electric fields means it is not possible to recommend exposure restrictions to avoid completely the direct effects of human exposure to them. Guidance has been given for the avoidance of the annoying effects of the direct perception of electric charge on the surface of the body. The restrictions on acute exposure to static magnetic fields are based on avoiding acute responses such as vertigo or nausea and adverse health effects resulting from cardiac arrythmia and impaired mental function.
  3. For exposure to ELF fields, restrictions on exposure are expressed as values of current density induced in the body. The restrictions are intended to avoid the effects of induced electric currents on functions of the central nervous system, such as the control of movement and posture, memory, reasoning and visual processing. Exposure to much higher levels of EMFs has been reported to result in headaches and nerve and muscle stimulation.
  4. Heating is the established consequence of exposure to RF (including microwave) radiation. Restrictions on exposure are intended to prevent adverse responses to increased heat load and elevated body temperature resulting from whole and partial body exposure. Such responses include increased cardiac output associated with elevated skin blood flow and sweating. Increased body temperature may result in decreased mental function and other physiological changes. At very high whole body power absorption such exposures may result in headaches, nausea, dizziness and, eventually, circulatory collapse and loss of thermoregulatory control; in extreme cases such exposure can be fatal. For those exposures in which the distribution of absorbed power within the body is highly non-uniform, they are limited primarily by restrictions on localised heating. Such restrictions are intended to prevent the adverse effects of elevated local tissue temperatures.

Indirect effects

  1. An electrically grounded person touching an ungrounded metallic object in a static or ELF electric field may draw an electric current from the object and experience a microshock (spark discharge). A person touching a metallic object situated in a sufficiently intense RF field may experience a shock or burn. The possibility of occurrence of repeated microshocks, electric shocks and RF burns may be determined by the measurement of contact current. Such effects may be avoided by limiting the external electric field or by other engineering or administrative controls. Advice on this is given in the NRPB guidelines 2.

UK guidelines

  1. Restrictions on the effects of exposure to time-varying EMFs are based on biological considerations of their interactions with the body and are termed basic restrictions. Depending on frequency, the physical quantities used to specify the basic restrictions are: induced current density, specific energy absorption rate (SAR) and, for pulsed radiations, specific energy absorption (SA). The basic restriction on exposure to EMFs in the frequency range between 10 Hz and 1 kHz, which includes the power frequency of 50 Hz, is 10 mA m -2 and above 1 kHz it is frequency dependent. The basic restriction for EMFs with frequencies between 100 kHz and 10 GHz is 0.4 W kg -1 for whole body SAR. Higher values apply for partial body exposure.
  2. Compliance with the basic restrictions on exposure cannot be measured directly. Investigation levels are, therefore, recommended as values of electric field strength, magnetic field strength, magnetic flux density, power density and contact current. These are provided for the purpose of comparison with values of measured field quantities for investigating whether compliance with the basic restrictions is achieved. They have been developed using dosimetric models which assess the interaction of EMFs with the body. If the measured values are greater than the relevant investigation levels, it does not necessarily follow that the basic restrictions are exceeded but that further investigation is needed to assess compliance. No distinction is made between occupational exposure and that of members of the public. Further advice on assessments of exposure and compliance with the basic restrictions for complex exposure situations has recently been issued by NRPB 10.
  3. For electric fields, contact current investigation levels may be used to indicate whether there is a need to take appropriate action to prevent shock and/or RF burn.

ICNIRP guidelines

  1. In the development of its guidelines 3, the approach used by ICNIRP in establishing basic restrictions is the same as that recommended by NRPB. In addition, it has recommended reference levels which are intended to fulfil the same purpose as the NRPB investigation levels. ICNIRP states that compliance with the reference levels will ensure compliance with the relevant basic restrictions. If the measured value exceeds the relevant reference level, it does not necessarily follow that the relevant basic restriction will be exceeded. However, an investigation is indicated to assess compliance with the relevant basic restriction and to determine if additional protective measures are required.
  2. The basic restriction for occupational exposure to electric and magnetic fields with frequencies up to 1 kHz is 10 mA m -2 and above that it is frequency dependent. The value of 10 mA m -2 was chosen as less than one-tenth of the value of the current density above which thresholds for acute changes in excitability of the central nervous system are exceeded. This is the same value as recommended by NRPB for the UK. In addition, however, for exposures received by members of the general public, a reduction factor of five is applied, resulting in a basic restriction of 2 mA m -2. In its clarification, ICNIRP notes that compliance with this basic restriction may permit higher current densities in body tissues other than the central nervous system under the same exposure conditions.
  3. The basic restriction for occupational exposure to EMFs with frequencies between 100 kHz and 10 GHz is 0.4 W kg -1 for whole body SAR. Again, this is the same as the value recommended by NRPB. For exposures of the general public, a reduction factor of five is again applied, resulting in a basic restriction on whole body SAR of 0.08 W kg -1. The factor of five reduction also applies to the basic restriction on localised SAR, the values for those occupationally exposed and for the general public being 10 W kg -1 and 2 W kg -1 averaged over any 10 g of tissue. In the frequency range from 100 kHz to 10 MHz, basic restrictions on both induced current density and SAR apply.

Comment on ICNIRP guidelines

  1. Although there are some small differences in the basic restrictions and in the NRPB investigation levels and ICNIRP reference levels for occupational exposure, the practical implications are minor. Of greater substance, however, is the adoption of a reduction factor of up to five in setting basic restrictions for members of the general public. It is the view of NRPB that no scientific justification is provided in the ICNIRP guidelines for the introduction and choice of the additional reduction factors adopted in recommending exposure restrictions for the general public.
  2. In the case of frequencies up to 100 kHz, the approach used by ICNIRP is to limit the induced current density within the head, neck and trunk. These restrictions are explicitly intended to avoid acute changes in excitability of the central nervous system and other acute effects on brain function. The view of NRPB is that more stringent exposure restrictions for the general public are not justified on the basis of the scientific evidence presented. The current density chosen for occupational exposure is considered sufficiently conservative, in itself, to preclude the possibility of either acute or long-term effects on the nervous system.
  3. With regard to the direct effects of fields with frequencies between 100 kHz and 300 GHz, basic restrictions are intended to limit whole and partial body heating. The basic restrictions on whole body SAR for occupational exposure are accepted by ICNIRP as providing a large margin of safety for other limiting conditions such as high ambient temperature, humidity or level of physical activity. The restrictions are, therefore, assumed to provide an adequate level of protection for all exposed individuals under all working conditions and thus can be considered highly conservative. Hence it is the view of NRPB that the recommendation for more stringent restrictions for the general public lacks scientific justification. The reductions in SAR for the general public are explained by ICNIRP on the basis that the age and health status of members of the general public, and hence their sensitivity to thermal challenge, may be different from those of workers. ICNIRP notes that those with potentially higher thermal sensitivity include the frail and elderly, infants and young children, and people with diseases or taking medications that compromise thermal tolerance. However, no relevant data are used to quantify the exposure restrictions for members of the general public and no explicit biological data in support of the more restrictive general public limit are cited.
  4. ICNIRP sets reference levels for electric field strength at power frequencies to limit indirect effects of contact with electrical conductors in the field. In its clarification, ICNIRP notes that provided adverse health impacts of indirect exposure (such as microshocks) can be avoided, the general public reference levels at power frequencies can be exceeded provided that the basic restriction is not exceeded. In many practical exposure situations external power frequency electric fields at the reference levels will induce current densities in tissues of the central nervous system that are well below the basic restrictions. ICNIRP also notes in its clarification that recent dosimetry calculations carried out by NRPB indicate that the reference levels for power frequency magnetic fields are conservative guidelines relative to meeting the basic restrictions for both public and occupational exposures.
  5. ICNIRP sets reference levels for contact current for the general public that are lower by a factor of two than the value set for those occupationally exposed. This can be justified on the basis of the biological evidence: the average contact current needed to elicit equivalent effects for children and women have been reported to be one-half or two-thirds, respectively, those for men.

Occupational and general public exposure

  1. For occupational exposure there are a few situations where both NRPB investigation levels and ICNIRP reference levels may be exceeded. For exposures to electric fields this may occur beneath overhead power conductors and close to some transmitters. At higher frequencies, there are other situations where the levels may be exceeded - close to dielectric heaters and diathermy equipment and in some broadcast environments, for example. However, these exposures can be averaged over time. There are other situations in which occupational exposure to magnetic fields may exceed the reference levels. Exposures on trains and from induction heaters are examples. Medical, broadcast and dielectric heating exposures may exceed the reference level but, on further investigation, are often found not to result in the basic restrictions being exceeded.
  2. Where members of the general public can gain access to the workplace they also have the potential for exposure above reference levels. Normally they will be excluded from such areas. However, electric field exposure levels under power lines and magnetic field exposure levels close to some security systems may exceed the ICNIRP general public reference levels.

Conclusions

  1. For occupational exposure to EMFs, the new ICNIRP guidelines do not differ in any significant way from those previously recommended by NRPB and adopted for use in the UK.
  2. For members of the public, ICNIRP has generally included a reduction factor of up to five in setting basic restrictions. There is, however, a lack of scientific support for the introduction and choice of these reduction factors. It is considered that the existing UK guidelines on limiting exposure for the general public provide adequate protection and the health benefits to be obtained from further reductions in exposure have not been demonstrated.
  3. Further epidemiological, experimental and dosimetric studies related to assessing possible health effects of exposure to EMFs are desirable.

1 NRPB. Statement by the National Radiological Protection Board: Restrictions on human exposure to static and time varying electromagnetic fields and radiation. Doc. NRPB, 4, No. 5, 1-5 (1993).

2 NRPB. Restrictions on human exposure to static and time varying electromagnetic fields and radiation: Scientific basis and recommendations for the implementation of the Board's Statement. Doc. NRPB, 4, No. 5, 7-63 (1993).

3 ICNIRP. Guidelines for limiting exposure to time-varying electric, magnetic and electromagnetic fields (up to 300 GHz). Health Phys., 74, No. 4, 494-522 (1998).

4 INIRC. Guidelines on limits of exposure to radiofrequency electromagnetic fields in the frequency range from 100 kHz to 300 GHz. Health Phys., 54, No. 1, 115-23 (1988).

5 INIRC. Interim guidelines on limits of exposure to 50/60 Hz electric and magnetic fields. Health Phys., 58, No. 10, 113-22 (1990).

6 ICNIRP. Response to questions and comments on ICNIRP guidelines. Health Phys., 75, No. 4, 438-9 (1998).

7 NRPB. Electromagnetic fields and the risk of cancer: Report of an Advisory Group on Non-Ionising Radiation. Doc. NRPB, 3, No. 1, 1-138 (1992).

8 NRPB. Electromagnetic fields and the risk of cancer: Summary of the views of the Advisory Group on Non-Ionising Radiation on epidemiological studies published since its 1992 report. Doc. NRPB, 4, No. 5, 65-9 (1993).

9 NRPB. Electromagnetic fields and the risk of cancer: Supplementary report by the Advisory Group on Non-Ionising Radiation (12 April 1994). Doc. NRPB, 5, No. 2, 77-81 (1994).

10 Chadwick, P J. Occupational exposures to electromagnetic fields: The practical application of NRPB guidelines. Chilton, NRPB-R301 (1998).


 


Last reviewed: 26 November 2008