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?
6.1 What are the sources of intermediate frequency fields (IF fields)?
The SCENIHR opinion states:
3.4. Intermediate Frequency Fields (IF fields)
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 and will likely continue to do so. 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. For most systems, exposure is well below the recommended limits. However, under worst case conditions, the so-called reference levels can be exceeded when in close proximity to some systems. 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. Visual display units containing cathode ray tubes are still common sources of exposure and emit in the ELF range and the IF range, in the order of 1 nT up to 50 nT. The emissions from new types of lighting bulbs (compact fluorescence lamps, CFLs) have been investigated recently (see also BFE 2004, SCENIHR 2008). Available results showed compliance with existing limits; i.e. the levels measured in the near vicinity (30 cm) were for IF fields (typically 30-60 kHz in this case) from single nT levels up to 30 nT and ELF fields (50 Hz) in the order of 10 nT. Even these levels decrease rapidly beyond 30 cm. This means that in normal domestic use for room illumination, the exposure of CFL users to IF fields is almost negligible. Radio transmitters operated in the long-wave range (30 kHz to 300 kHz) can cause exposure in the intermediate frequency range 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, and 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 common example is electrosurgery. 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.
6.2 What possible health effects of intermediate frequency fields have been studied?
The SCENIHR opinion states:
3.4.2. Health effects and conclusions about IF fields
The previous opinion expressed its concern that very little useful epidemiologic data on intermediate fields and health risks are available. Furthermore, it was noted that in vivo and in vitro data are very sparse. Well established acute effects occur and these are explained by extrapolation from ELF and RF field mechanisms. Thus it was concluded that there was no basis for an appropriate assessment of long term effects.
Occupational exposure to IF fields in certain areas is considerably higher than exposure to the general public. However, very little research on IF and health risks in occupational settings or for the general public have been presented since the previous opinion, and no epidemiological studies have appeared. Consequently, the data are still too limited for an appropriate risk assessment.
In view of the increasing occupational exposure to IF among workers in e.g. security, shops, and certain industries it is important that research in this area is given priority.