6. Intermediate frequency fields like those from computer screens and anti theft devices
- 6.1 What are the sources of intermediate frequency fields (IF fields)?
- 6.2 What possible health effects of intermediate frequency fields have been studied?
- 6.3 What can be concluded about intermediate frequency fields?
6.1 What are the sources of intermediate frequency fields (IF fields)?
The source document for this Digest states:
3.4.IntermediateFrequency Fields (IFfields)
Intermediate frequencies are, in the frame of this report, defined as frequencies between 300 Hz and 100 kHz. They involve two different mechanisms, namely induced currents and dielectric absorption. The frequency limit when one predominates over the other is not precisely defined. Existence of effects depends upon two superimposed phenomena: absorption of the external field in the organism at the macroscopic level and the stimulation of biological effects by the penetrating fields. Those two phenomena depend on the kind of field, electric or magnetic, and on the frequency. Well-known biological effects are nerve stimulation at low frequencies and heating at high frequencies.
3.4.1. Sources and distribution of exposure in the population
The number of applications in this frequency range has been increasing in recent years. Examples are anti-theft devices operated, e.g., at the exits of shops. Depending on the type of system, they are operated at very different frequencies ranging from some tens of Hz to a few GHz. The majority of these applications are operated in the intermediate frequency range. Close to some systems the so called reference levels can be exceeded under worst case conditions, but for most of the systems the exposure is well below the recommended limits. Other applications are induction hobs and hotplates typically operated at frequencies between 20 to 50 kHz, electric engines, and badge readers (typical frequency about 100 kHz). Information on the exposure due to such applications is scarce. Still common sources are visual display units containing cathode ray tubes which are causing emissions in the ELF range and the IF range, in the order of 1 nT up to 50 nT. Radio transmitters operated in the long wave range (30 kHz to 300 kHz) can cause exposure in the intermediate frequencies with levels above the recommended limits. Therefore, safety precautions need to be implemented both for the general public and workers. Some industrial applications like induction heating and welding need to be mentioned. Welding devices can cause considerable exposure up to a few hundred kHz. Induction heaters are operated in a frequency band from typically some tens of Hz to some tens of kHz, the exposure levels can reach values of about 100 µT or more. Welding is a complex process that can cause emissions up to a few 100 kHz. The sparse information on IF field exposure due to welding devices available so far indicates that safety measures need to be implemented in some cases.
Some medical applications exist in the IF range. One example is electrosurgery used very commonly in hospitals. These systems are operated at some hundred kHz. In addition, the IF fields of typically up to 10 kHz arising from MRI applications need to be mentioned.
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Section 3.4 Intermediate Frequency Fields, 3.4.1 Sources and distribution of exposure in the population, p.29
6.2 What possible health effects of intermediate frequency fields have been studied?
The source document for this Digest states:
3.4.2. Health Effects
Epidemiological studies on IF fields were reviewed at a workshop organized by the WHO and by ICNIRP in 1999 (Hietanen 1999). It seems that very few useful data are available for health risk assessment. The few studies that do exist are relatively old occupational studies using occupations or job titles but no actual exposure estimation. Groups that have been studied include VDU (video display units) users and radio and telegraph operators. One study looked at radio amateurs. The studied outcomes include ocular effects, cardiovascular effects, cancer, and reproductive effects.
The available in vivo and in vitro evidence was reviewed in articles published in the proceedings of the WHO/ICNIRP seminar on IF fields (Juutilainen and Eskelinen 1999, Glaser 1999, Litvak and Repacholi 1999). In contrast to the active experimental and epidemiological research onELF and RF fields, only a very limited number of studies have addressed the biological effects of IF fields. While there is limited evidence for effects on reproduction and development (Juutilainen 2005, Huuskonen et al. 1998), studies on other effects (such as carcinogenicity, genotoxicity, nervous system effects and general toxicity) are almost totally lacking.
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Section 3.4 Intermediate Frequency Fields, 3.4.2 Health effects, p.29-30
6.3 What can be concluded about intermediate frequency fields?
The source document for this Digest states:
3.4.3. Conclusions about IF fields
It is considered that the well established hazard mechanisms in the IF range are associated with a limited number of phenomena and apply to acute exposures. However, the extension to long term effects is based on weak grounds and on possibly unjustified assumptions about frequency dependence of effects (Litvak et al. 2002). In addition to established mechanisms, comprehensive risk assessment should consider also other information, such as well-conducted epidemiological and laboratory studies. Studies on possible effects associated with chronic exposure at low exposure levels (below exposure limits) are particularly relevant for assessing risks to human health and for confirming adequacy of current exposure limits.
Proper evaluation and assessment of possible health effects from exposure to IF fields is essential because human exposure to such fields increases due to new and emerging technologies.
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Section 3.4 Intermediate Frequency Fields, 3.4.3 Conclusions about IF fields, p.30
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