Wireless Local Area Networks (WLANs)
Wireless Local Area Networks (WLANs) are becoming a popular way of networking computer equipment in the home and office. The different items of equipment communicate with each other using radio signals. More information on using WLANs can be found on the British Educational Communications and Technology Agency (BECTA) website at
People using WLAN equipment will be exposed to the radio signals that are emitted; information about such exposures is provided here.
Advice on protection
The HPA has UK-wide responsibility for providing advice on protecting people from radiation hazards, including those arising from exposure to electromagnetic fields (EMFs) such as radio waves. The International Commission on Non-Ionizing Radiation Protection (ICNIRP) is also an independent scientific organisation with responsibility in this area. Both the HPA and ICNIRP are formally recognised by the World Health Organization in the field of EMF protection.
ICNIRP published guidelines on limiting human exposure to EMFs in 1998 and the HPA, as the successor to the National Radiological Protection Board (NRPB), recommends that that these should be adopted in the UK. These documents are available as follows.
Implementation of advice
There is no UK legislation specifically requiring compliance with any EMF protection guidelines. Within the context of general UK safety legislation (the Health and Safety at Work etc Act 1974 and the Management of Health and Safety at Work Regulations 1999), the Health and Safety Executive requirements are as follows.
The ICNIRP public exposure guidelines were incorporated into the EU Council Recommendation published in 1999 and this was supported by the UK Government, as follows.
Implementation of the Council Recommendation in the UK is a matter for the UK Government.
European Directives contain provisions relating to radiation (including EMFs) safety. The Radio and Telecommunications Terminal Equipment Directive (1999/5/EC) extends the objectives with respect to safety requirements contained in the Low Voltage Directive (73/23/EEC) in order to apply to all apparatus, with no voltage limit applying (see Article 3, Point 1a). In the Low Voltage Directive it is stated that measures of a technical nature should be prescribed in order to ensure that temperatures, arcs or radiation which would cause a danger are not produced (see Point 1 in Article 2 and Annex I, Part 2b). The text of these Directives can be accessed through the following.
The European Commission has issued a Standardisation Mandate to European electrical standards bodies for them to develop harmonised technical standards to enable a presumption of conformity of products with the above Directive Articles. The standards bodies are asked to take into account the basic restrictions and reference levels in the Council Recommendation. The text of the Mandate is accessible through the following.
To date, no harmonised technical standard has been published indicating how to assess the exposure of people in the vicinity of WLAN equipment. Nevertheless, the essential requirements of the applicable directives should be satisfied by equipment bearing the CE mark.
Exposure assessments
There are many different manufacturers producing WLAN equipment and there are several different technical standards to which equipment can be designed. The systems the HPA has seen operate in the 2.4-2.5 GHz frequency band. The output powers from the base stations and computer terminals were a few tens of milliwatts during data transmission and very much lower while on standby. There are also systems operating in bands between 5 and 6 GHz.
The HPA has made measurements of the power density of radio waves generally in and about the offices where WLANs are deployed and these have always been found to be very much below the guideline levels referred to above. The situation is rather more complicated for exposure within the first few centimetres of the transmitters, for example, for the situation where a laptop computer is placed on someone's lap with its transmitting antenna projecting on one side, or mounted inside the case. This is the situation where exposure would be highest and there is no practical assessment that can be rapidly performed to check levels with an installed system. Nevertheless, given the low powers, a problem with guideline compliance would not be expected.
When a radio terminal is used close to the body, some of the radio energy penetrates into the body and it is absorbed in the tissues. The pattern of this absorption and the total amount of energy absorbed depend on parameters such as the frequency, output power, position of use, antenna type, etc and it is not easy to predict without a detailed investigation. The exposure is characterised by the specific absorption rate of energy (SAR) in the tissues and this will generally have a spatial peak value near the surface of the body and close to the radiating antenna.
Guidelines expect SAR to be averaged over various different tissue-masses and time-periods before comparison with the basic restrictions. The most stringent basic restrictions for the situation where low power radio transmitters are used near to the body are those on localised SAR in the head, which involve an averaging mass of 10 g and an averaging time of six minutes. For this situation, the ICNIRP guidelines for workers advise that SAR should not exceed 10 W/kg. The ICNIRP guidelines and Council Recommendation basic restriction for the general public is that SAR averaged in this way should not exceed 2 W/kg.
Summary
On the basis of current evidence, the HPA does not consider there to be a problem with the safety of WLAN. If an explicit statement that exposures are within the ICNIRP guidelines is required, this would have to be obtained from the manufacturers; however, it could be argued that this is implicit in the CE marking.
Last reviewed: 29 April 2008