In order to guarantee that mobile phones, smartphones or tablet PCs can be used all the time without adverse health effects, legislation has prescribed protection limits. These exposure limits are based on current research and establish the maximum limit for transmitted power.

Compliance with these exposure limits guarantees that the electromagnetic fields used by mobile communications do not pose any health risk for the public. There are restrictions determining the safe distance around each antenna, guaranteeing that the electromagnetic field strength outside this safe distance is always below the limit. This ensures the safety of anyone in the surrounding area, even if they remain there permanently.

Effect thresholds

The exposure limits that are in force in Germany were not established arbitrarily. They were determined by scientific research on the basis of the so-called biological effect threshold. This threshold is the limit below which there is no biological effect. In order to be verifiable, thresholds must be measurable in units, for example, the level of concentration in a substance. In mobile communications, the effect threshold defines the amount of energy that is expected to cause biological change.

The International Commission on Non-Ionizing Radiation Protection (ICNIRP) regularly reviews new scientific results and evaluates findings about the biological effect threshold. They then determine threshold values which form the basis of exposure guidelines. These guidelines concentrate on scientifically proven effects (for example, the heat effect) but also consider findings from research into all other possible effects not caused by an increase in tissue temperature – the so-called non-thermal effects.

Basic limits

The heat effect is measured in watts per kilogram body weight. Based on the effectthresholds, the ICNIRP has defined the corresponding basic limits. Both the effect thresholds and the basic limits are expressed as the so-called specific energy absorption rate (SAR) in watts per kilogram (body weight). This value measures the electromagnetic power transformed into body heat.

For mobile communications, a difference is made between the absorption rates of the whole body and parts of the body. Whole-body limits apply to base stations because the station’s electromagnetic fields reach the entire body. In contrast, the fields primarily have an effect on the head when a call is made, so limits for parts of the body apply.

The ICNIRP has defined a value of 4 watts per kilogram body weight as the effect threshold for the whole body. This amount of absorbed energy corresponds to an increase in body temperature of about 1° C over 30 minutes. In the opinion of the ICNIRP experts, there are no adverse health effects below this threshold.

The basic limits recommended by the ICNIRP and codified in German law are 50 times lower than the effect threshold. According to the ICNIRP this guarantees that even vulnerable individuals such as sick people, pregnant women, children and senior citizens are fully protected. The maximum increase in body temperature possible within these limits is about the same as the increase in body heat that occurs during a walk.

Derived limits

Since measuring basic limits is difficult in practice, researchers have developed what they term ‘derived limits’ for electric and magnetic fields. These limits guarantee that the biologically important SAR values remain below the basic limits at all times. In Germany, the derived limit for the electric field is 42 volts per metre for the GSM900 and 57 volts per metre for GSM1800, LTE1800. The limit for UMTS and  LTE2600 is 61 volts per metre.