Champs électromagnétiques

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)?

Cathode ray tube screens generate intermediate frequency fields
Credit: Anissa Thompson

In this assessment, intermediate frequency (IF) fields designate electromagnetic fields with frequencies ranging from 300 Hz to 100 kHz, roughly the frequencies that are lower than radio frequencies (RF) and higher than extremely low frequencies (ELF).

The term covers frequencies of the electromagnetic spectrum that are usually referred to as very low frequency (VLF) and low frequency (LF).

Applications generating intermediate frequency fields are still relatively limited, but have been increasing in recent years. Examples are some anti-theft devices operated at the exits of shops, induction hotplates, computer and television screens which use cathode ray tubes, as well as some radio transmitters. Such fields are also generated by some industrial uses such as welding. In most cases exposure is limited, but for radio transmitters and welding, exposure can be above the recommended limits, so safety precautions should be taken.

Some medical applications lead to exposures in this frequency range, like electrosurgery that uses an electric current to cut or remove tissues and magnetic resonance imaging (MRI) that provides three-dimensional images of internal structures such as the brain. More...

Typical frequencies for devices generating intermediate frequency fields 

6.2 What possible health effects of intermediate frequency fields have been studied?

Well-known biological effects at the intermediate frequency (IF) range are nerve stimulation at the lower end of the range and heating at the upper end of the range. (taken from 6.1)

Little data is available on the exposure of individuals to intermediate frequency (IF) fields and on possible health effects. The few studies conducted have focused on potential effects on the eyes, on the cardiovascular system, on cancer and on reproduction.

Very few studies have addressed the biological effects of intermediate frequency fields. While there is limited evidence regarding potential effects on reproduction and development, studies on other effects are virtually non-existent. More...

6.3 What can be concluded about intermediate frequency fields?

Because, experimental and epidemiological data for the intermediate frequency (IF) range are very sparse, the assessment of health risks of short-term exposure to high levels of intermediate frequency fields is currently based on known biological effects at lower and higher frequencies.

The well-established effects in the intermediate frequency range are a small number of phenomena following short, high exposures; however, there is much uncertainty in extrapolating from such conditions to possible effects of long-term, lower exposures.

Drawing conclusions regarding possible long term effects would be based on weak grounds. Proper evaluation and assessment of possible health effects from long term exposure to intermediate frequency fields are important because human exposure to such fields is increasing due to new and emerging technologies.

Epidemiological and long-term exposure studies are needed in order to correctly evaluate the risks to human health and to confirm the current exposure limits. More...