Some considerations relating to SHE Safety Code 23 Working with time-varying electromagnetic fields (EMF) Circumstances surrounding the drafting and issuing of STFC SHE Code no. 23 (SC23), Working with time-varying electromagnetic fields (EMF), included recognition of the likelihood that before too long an EU Directive requiring compliance with specific electromagnetic field limits would come into force. The EU Directive 1 in question was originally issued in 2004, and was intended to be transposed into national law by 2008, but objections to the directive led to postponement 2 of the date for transposition to 2012 and then to 2013, and finally to the repeal of the original 2004 directive and its replacement by a revised directive 3 issued in 2013. The original EU Directive was based on the 1998 Guidelines 4 from the International Commission on Non-Ionising Radiation Protection (ICNIRP), and since the EU Directive was intended to cover workers, the directive simply adopted the occupational exposure limits from the ICNIRP Guidelines. But whereas the ICNIRP limits were essentially recommendations, the EU Directive would make these same limits legally enforceable, would introduce dissuasive 5 penalties, and could in principle be enforced with the pathological enthusiasm occasionally experienced in areas covered by other EU directives. The most vocal objections to the EU limits related to their impact on the use of Magnetic Resonance Imaging (MRI) machines in health care and in fact the most visible changes in the revised directive relate to magnetic field limits. SHE Code 23 simply adopted the ICNIRP 1998 occupational limits for STFC staff, and used the ICNIRP s reference levels for general public exposure as action values above which formal consideration through risk assessment and EMF surveying must be given to the health and safety of staff and others exposed to EMFs 6. In the meantime, in 2009 the ICNIRP issued a statement 7 saying that it reconfirms the 1998 basic restrictions in the frequency range 100 khz 300 GHz until further notice, and in 2010 the ICNIRP issued revised guidelines 8 covering the 1 Hz 100 khz region. At the time of writing of this note (June 2016), no more recent guidance on EMF levels has been posted on the ICNIRP web site 9. The purpose of the ICNIRP Guidelines is essentially to define limits or basic restrictions for the magnitudes of circulating electric currents and energy absorption 1 Directive 2004/40/EC of the European Parliament and of the Council of 29 April 2004. 2 Directive 2008/46/EC of the European Parliament and of the Council of 23 April 2008, and Directive 2012/11/EU of the European Parliament and of the Council of 19 April 2012. 3 Directive 2013/35/EU of the European Parliament and of the Council of 26 June 2013. 4 Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz), Health Physics 74 (1998) 494. 5 2013/35/EU, Article 9. 6 SC23, Section 3.2. 7 ICNIRP Statement on the Guidelines for Limiting Exposure to Time-Varying Electric, Magnetic, and Electromagnetic Fields (up to 300 GHz), Health Physics 97 (2009) 257. 8 Guidelines for Limiting Exposure to Time-Varying Electric and Magnetic Fields (1 Hz to 100 khz), Health Physics 99 (2010) 818. 9 http://www.icnirp.org/en/publications/index.html. considerations-she-sc23 Page 1 of 6
within the human body in order to limit sensory effects and adverse health effects, but since it is impractical to measure these fundamental quantities, limits have to be set in terms of proxies measurable external electromagnetic fields and models have to be used to relate limits or reference levels for external electromagnetic fields to the fundamental circulating currents and energy absorption within the human body. The ICNIRP Guidelines note that if measured values are higher than reference levels, it does not necessarily follow that the basic restrictions have been exceeded, but a more detailed analysis is necessary to assess compliance with the basic restrictions 10. It should be noted that levels at which adverse health effects occur are substantially higher than levels at which sensory effects occur. Fig. 1 shows a comparison between the 1998 and 2010 ICNIRP Guidelines. Whilst the 2010 revision reduced general-public electric-field reference levels below 50 Hz and occupational reference levels in the khz MHz region, the same 2010 revision increased both general-public and occupational magnetic-field reference levels below ~100 khz. It can be seen that in the 100 khz 10 MHz region the 1998 and 2010 sets of reference levels do not completely overlap; this is due essentially to differences between restrictions on current density to prevent effects on nervous system functions and restrictions on energy absorption to prevent heating of tissue; and, presumably, in these cases, the lower limits should be adopted. The ICNIRP occupational reference levels are set essentially to avoid the induction of sensory effects, and the general-public reference levels are set significantly lower because members of the public are unaware of their exposure to EMF [and] individual members of the public cannot reasonably be expected to take precautions to minimize or avoid exposure 11. Fig. 2. shows a comparison between the action values in the 2004 and 2013 EU Directives. The 2013 directive introduced high and low action levels (ALs); for both electric and magnetic fields, the low ALs are the same as the 2010 ICNIRP occupational 12 values. For electric fields, the high ALs are greater than the low ALs by a factors 2.0 3.6 in the frequency range 50 Hz 10 MHz, and for magnetic fields the high ALs are greater than the low ALs by factors 1 12 in the frequency region below 300 Hz. It is not immediately apparent in the 2013 EU Directive exactly how the high action levels were determined; the directive says that the physical quantities, ELVs [exposure limit values] and ALs, laid down in this Directive are based on the recommendations of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) and should be considered in accordance with ICNIRP concepts, save where this Directive specifies otherwise 13. But the 2010 ICNIRP Guidelines, whilst they say nothing specific about high action levels, do anticipate exposure in controlled environments, where workers are informed about the possible transient effects of such exposure 14 (e.g. faint flickering in the periphery of the visual field), at levels roughly an order of magnitude higher than the 2010 ICNIRP occupational references levels, and the 2013 EU Directive notes 15 that the high ALs should be applied only if workers are made fully aware in advance of the possible 10 ICNIRP 1998, page 508. 11 ICNIRP 1998, page 508. 12 The 2014 and 2013 EU Directives cover workers, not the general public. 13 2013/35/EU, introductory section, paragraph 15. 14 ICNIRP 2010, page 825. 15 Annex II, Section B. considerations-she-sc23 Page 2 of 6
sensory effects. However, in all cases, the high ALs are said to be consistent with exposure limit values below which adverse health effects will not occur. Fig. 3 shows a comparison between the current SC23 action and limit values, the EU 2013 action levels, and the ICNIRP 2010 reference levels. The following may be noted: o at 50 Hz the 2010 ICNIRP electric-field general-public reference level is the same as the SC23 action value, although below 25 Hz it is now half the SC23 action value; o between 3 khz and 1 MHz the 2010 ICNIRP electric-field occupational reference level and the 2013 EU low AL are both lower than the SC23 limit value for occupational exposure by a factor 3.6; o between 50 Hz and 820 Hz the 2013 EU electric-field high AL is higher than the SC23 limit value for occupational exposure by a factor 2; o between 25 Hz and 100 khz the 2010 ICNIRP magnetic-field general-public reference level is higher than the SC23 action value by factors of 1 16; o between 25 Hz and 100 khz the 2010 ICNIRP magnetic-field occupational reference level is higher than the SC23 limit value for occupational exposure by factors of 1 12; and o between 8 Hz and 820 Hz the 2013 EU magnetic-field high AL is higher than the SC23 limit value for occupational exposure by a factor of 12. How should SC23 be amended to take account of the 2010 ICNIRP Guidelines and the 2013 EU Directive? In view of the uncertainty inherent in the scientific data 16, the following could be suggested: o it may be simplest not to change the SC23 electric-field action values, since at STFC most electrical equipment runs at frequencies 50 Hz, and below 25 Hz a factor of only 2 is involved; o it would probably be worthwhile increasing the SC23 magnetic-field action values between 25 Hz and 100 khz since factors of up to ~10 are involved; o it would probably be worthwhile increasing the SC23 electric-field limit value for occupational exposure between 25 and 1640 Hz to the 2013 EU high AL since STFC staff working on high-power electrical, magnetic and RF equipment should be expected to fully understand the issues involved; and o it would probably be worthwhile increasing the SC23 magnetic-field limit value for occupational exposure below 100 khz for the same reason. D J S Findlay 27 June 2016 16 2010 ICNIRP, page 819. considerations-she-sc23 Page 3 of 6
Fig. 1. Comparison of 1998 and 2010 ICNIRP reference levels (the 2010 ICNIRP reference levels do not cover the higher frequencies). In the 100 khz 10 MHz region the two sets of reference levels do not completely overlap; this is due essentially to differences between restrictions on current density to prevent effects on nervous system functions and restrictions on energy absorption to prevent heating of tissue. (The 1998 curves have been moved vertically by a few per cent in the interests of visibility.) considerations-she-sc23 Page 4 of 6
Fig. 2. Comparison between the 2004 and 2013 EU Directives. (The 2004 curve has been moved vertically by a few per cent in the interests of visibility.) considerations-she-sc23 Page 5 of 6
Fig. 3. Comparison of current SC23 action levels with EU 2013 action levels and ICNIRP 2010 reference levels. (One or two of the curves have been moved vertically by a few per cent in the interests of visibility.) considerations-she-sc23 Page 6 of 6