Researchers study the effect of electromagnetic radiation on the body and establish exposure limits for every type of electromagnetic radiation. An exposure limit indicates what the maximum radiation intensity can be to prevent harmful effects on the health.
How are exposure limits determined?
An exposure limit tells us what the maximum radiation (or another factor) can be to avoid harmful effects on our health.
The first step in determining an exposure limit is to establish a threshold value for the occurrence of a harmful effect on our health. Multiple threshold values are determined if multiple effects are possible.
In order to obtain an exposure limit, a safety margin (safety factor) is applied on the threshold values. The safety margin is used to compensate for uncertainties. Uncertainties can include: experimental errors, rendering from animal tests to humans, the possible higher sensitivity in certain population groups (elderly, children and sick people). The use of safety margins generally applies for the protection of public health.
Different quantities of exposure limits are used depending on the environmental factor and the health effect. The exposure to chemical substances is for instance described with the quantity "concentration", expressed in milligram of substance per cubic metre. Electromagnetic radiation from radio frequencies is converted into heat in the body. This process is described with the quantity "Specific Absorption Rate" (SAR).
Some quantities in which the exposure limits are expressed are difficult to measure. In that case, other quantities that are easier to measure must be used for verification purposes. Such a quantity is called a reference quantity, and the threshold value for this quantity is called a reference value.
Revision of exposure limits
Exposure limits are formulated (and re-examined) by scientific committees of experts under the supervision of competent organisations such as the World Health Organisation, the European Commission or by independent organisations of scientific experts such as the International Commission on Non-Ionizing Radiation Protection (ICNIRP).
The website of the ICNIRP contains scientific reports and evaluations regarding the exposure limits for optical radiation (light, infrared light, ultraviolet light), radio waves and other forms of electromagnetism.
For radio waves
Radio waves are known to be absorbed by the body. This means that the electromagnetic energy of radio waves is converted into heat in the body. This is called the thermal effect. Our body initiates its internal cooling mechanism as a reaction to this warming up so that the body temperature remains constant. This thermal effect only results in damage to our health when the intensity is too high. There is no risk of this happening because telecommunication and radio equipment have to meet the standards (SAR value of 2 W/kg or 4 W/kg) as described in the technical standards under the R&TTE directive.
What is an SAR value?
The quantity that is used to assess the heat absorption is the Specific Absorption Rate (SAR) which is expressed in watt per kilogram (W/kg). In fact, the SAR value describes the speed at which the energy of radio waves is absorbed in the body. The producer must measure the SAR value for every product. Only wireless devices with a low average power (less than 20 mW) are exempted from the SAR measurements (such as a Bluetooth device).
You can read more about exposure limits for radio waves in our brochure “Electromagnetic fields and health: your guide to the electromagnetic landscape” (note: this is only available in Dutch, French and German).
For electromagnetic fields of low frequencies
Alternating fields with extremely low frequencies generate an electric current in the body. If the field is strong enough, the current generated in the body can disturb the working of nerves and muscles or cause flashes of light to be seen. A threshold value has been imposed on the generated (induced) current density in the body to prevent these effects. The threshold value (exposure limit) is 2 mA/m2, which corresponds to a magnetic field of 100 µT (at 50 Hz) or an electric field of 5 kV.
You can read more about exposure limits for electromagnetic fields of low frequencies in our brochure “Electromagnetic fields and health: your guide to the electromagnetic landscape” (note: this is only available in Dutch, French and German).
The exposure limits are mostly based on scientifically proven effects and these are mostly short-term effects. The long-term effects, for example high-voltage lines and childhood leukaemia, mobile telephone and brain cancer, electromagnetic hypersensitivity, have been insufficiently studied for the most part to be able to make reliable statements.
If you are wondering if living next to a high-voltage line implies a risk of childhood leukaemia, or the use of a mobile telephone would be associated with brain cancer, please read the pages under the section “Electromagnetic radiation”. We clarify in that section (per product, technology) which are the proven health effects and when precautionary measures are necessary.