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Base stations transmit and receive radio waves to connect the users of mobile phones and other devices to mobile communications networks. The strength of the radio waves from base-station antennas reduces rapidly with increasing distance and the levels at locations where the public can be exposed tend to be small.
The health effects of exposure to radio waves have been researched extensively over several decades, and very many publications can be found in scientific journals and elsewhere. Coordinated research around the world has addressed concerns about rapidly proliferating mobile communications technologies from around the year 2000.
Independent expert groups in the UK and at international level have examined the accumulated body of research evidence. Their conclusions support the view that health effects are unlikely to occur if exposures are below international guideline levels.
Control of exposures occurs through product safety legislation, health and safety legislation and planning policy. These regulatory areas all consider the international guidelines.
With some of the larger and more powerful base stations there can be regions around the antennas within which the guideline levels can be exceeded. Operators identify the extent of any such regions and prevent access to them by the public.
Many exposure measurements have been made at publicly accessible locations near to base stations, and these have consistently been well within guidelines.
Industry has voluntarily committed to comply with international guidelines and to provide certificates of compliance with planning applications for base stations.
Public Health England (PHE) continues to monitor the health-related evidence applicable to radio waves, including in relation to base stations, and is committed to updating its advice as required.
2. Mobile network technology
Mobile communications technology has developed through several generations (G), and there are now many 2G, 3G and 4G base stations installed throughout the environment, providing services to users of mobile phones and other devices. A fifth generation of the technology (5G) is being developed and reflects the latest evolution in mobile communications technology.
Base stations are stationary radio transmitters with antennas mounted on freestanding masts or on buildings. The largest base stations provide the main infrastructure for networks and may be up to several kilometres apart. Their antennas tend to be mounted at sufficient height to give them a clear view over the surrounding geographical area. Smaller base stations tend to be mounted nearer to ground level and provide additional radio capacity where there are a high number of users, such as in cities and towns.
The radio waves transmitted by base stations are a form of non-ionising radiation and have frequencies in the microwave region of the electromagnetic spectrum.
3. Exposure guidelines
PHE’s main advice about radio waves from base stations is that the guidelines of the International Commission on Non-Ionizing Radiation Protection (ICNIRP) should be adopted for limiting exposures. ICNIRP is formally recognised as an official collaborating non-governmental organisation by the World Health Organization (WHO) and the International Labour Organization (ILO). ICNIRP is also consulted by the European Commission.
After reviewing the evidence, ICNIRP set guidelines to avoid excessive heating of the body, an established impact of exposure which can have detrimental effects. The ICNIRP guidelines apply to frequencies up to 300 gigahertz and cover exposures arising from new 5G base stations as well as from older technologies.
ICNIRP’s radiofrequency guidelines were published in 1998. However, ICNIRP restated these in 2009 following its own updated review of the scientific evidence. ICNIRP concluded that the scientific literature published since the 1998 guidelines provided no evidence of any adverse health effects below the restrictions in the guidelines and did not necessitate an immediate revision of its guidelines.
Radio-wave exposure levels can be measured or calculated and are usually expressed in terms of their power density in watts per square metre, or as a fraction of the ICNIRP guideline level.
4. Health-related evidence and reviews
Radio waves have been transmitted into the environment for many years to deliver broadcast radio and television signals and to support professional radio communications, for example for the emergency services. There are also applications in industry and medicine, where the heating properties of radio waves are used. Against that background, the health effects of exposure to radio waves have been researched extensively over several decades.
A large amount of new scientific evidence has been produced in recent years through dedicated national and international research programmes, which have addressed concerns about rapidly proliferating modern communications technologies. Expert groups have examined the accumulated body of research evidence at national and international levels. Their conclusions support the view that health effects are unlikely to occur if exposures are below ICNIRP’s internationally agreed guideline levels.
Concerns about base stations and exposures to radio waves came to the fore in the late 1990s when the networks were expanding rapidly. In the UK, the Independent Expert Group on Mobile Phones (IEGMP) concluded in its 2000 report that the balance of evidence indicates that there is no general risk to the health of people living near base stations on the basis that exposures are expected to be small fractions of guidelines. Also in the UK, the independent Advisory Group on Non-ionising Radiation (AGNIR) concluded in a 2003 report that exposure levels from living near to base stations are extremely low, and the overall evidence indicates they are unlikely to pose a risk to health. While these conclusions were reached some years ago, they remain in line with conclusions reached by expert groups that have rigorously examined the more recent scientific evidence.
AGNIR undertook another comprehensive review of the accumulated evidence to consider whether there was evidence for health effects occurring in relation to exposures below the ICNIRP levels and published its report in 2012. The overall conclusion was that, although a substantial amount of research has been conducted in this area, there is no convincing evidence that radiofrequency field exposures below guideline levels cause health effects in either adults or children.
The World Health Organization (WHO) states that the main conclusion from its reviews is that EMF exposures below the limits recommended in the ICNIRP guidelines do not appear to have any known consequence on health. WHO is presently preparing a review covering the evidence in relation to radiofrequency exposures and health. Information from WHO about exposure guidelines can be found here.
The European Commission has scientific expert committees to provide it with advice on aspects of public health. The Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) has produced several reports, known as ‘opinions’, in which it expressed views broadly in line with those of PHE, ICNIRP and WHO. The most recent SCENIHR opinion was published in March 2015 and contains detailed conclusions on different aspects of the scientific evidence. A plain language summary, based on the opinion, explains that the results of current scientific research show that there are no evident adverse health effects if exposure remains below the levels set by current standards.
Research is ongoing and new studies continue to be published in the literature. In the UK, the Government continues to support research on this topic, including the ongoing Cohort Study of Mobile Phone Use and Health (COSMOS) and the Study of Cognition, Adolescents and Mobile Phone studies (SCAMP) at Imperial College London. PHE continues to monitor the health-related evidence applicable to radio-wave exposures and is committed to providing any advice that might be necessary.
5. Protection measures
The ICNIRP guidelines have been incorporated into the 1999 EU Council Recommendation on limiting exposure of the general public to radio waves (1999/519/EC), which the UK Government supported. Subsequently, European technical standards have been published that apply to base stations and other types of radio-emitting products and which limit their radio emissions such that exposure guidelines are not exceeded.
Measures are in place to reduce risks to employees of the companies and to the general public. The ICNIRP guidelines are applied through UK health and safety legislation whereby companies deploying and operating communication networks are required to carry out suitable and sufficient risk assessments, as well as put in place measures to reduce the identified risks so far as reasonably practicable. In controlling risks arising from EMF exposure, the HSE refer to compliance with the ICNIRP guidelines.
The ICNIRP guidelines are applied through the Government’s National Planning Policy Framework for England. The framework describes the information about local community consultation and compliance with the ICNIRP exposure guidelines that should accompany planning applications and also explains that local planning authorities should not seek to determine health safeguards if the proposal meets ICNIRP guidelines for public exposure.
Industry has voluntarily committed to comply with the ICNIRP guidelines and to provide certificates of compliance with planning applications for base stations.
6. Monitoring of exposures
The radio-wave exposure level produced by base stations depends on their output powers, the directional characteristics of their transmitting antennas and where people can be exposed in relation to the antennas. In general, being closer to an antenna results in higher exposures, but the most powerful antennas tend to be mounted high up on masts or buildings, and they are designed to direct most of their power towards the horizon, so exposure levels beneath antennas are small. Antennas located nearer to street level and inside buildings are designed to communicate over short distances and transmit with lower power levels than antennas mounted at height. People can access directly in front of these types of antennas, but the exposure levels are low due to the low output powers.
The maximum output power from each base station is set by operators to balance call/data traffic across the different sites that make up the network. The actual output power at any given time depends on the amount of calls and data being handled and use of excessive power at any given site reduces the capacity of the network for other users. So, optimising transmitted powers to be the minimum needed to carry out communications effectively is an important feature of efficient network design. It also tends to keep public exposures low.
The strength of the radio waves from base-station antennas falls off very quickly with increasing distance. So, radiofrequency fields at ground level and in places normally accessible to the public are many times below guideline levels. Where guidelines can be exceeded, normally within a few metres directly in front of the most powerful antennas, exclusion zones are implemented to restrict access.
Exposure measurements made by one of PHE’s predecessor organisations can be found in 2 technical reports. The first of these focused on larger 2G base stations with their antennas mounted high above the ground and was published in 2000. It included measurements taken at 118 locations at 17 different base station sites. Average exposures were found to be 50,000 times below the ICNIRP public exposure guidelines and the maximum found at any location was 500 times below the guidelines. The second report was published in 2004 and focused on a sample of smaller base stations with their antennas nearer to ground level. The results showed exposures generally between 50,000 and 50 times below the ICNIRP guideline levels at accessible locations within a few tens of metres of the antennas.
Subsequent to the publication of the above reports, and as part of the Government’s response to the IEGMP report, Ofcom has been carrying out an audit of the emissions from mobile phone base stations. AGNIR’s 2012 report contains a summary of over 3,000 measurements made at over 500 sites by Ofcom. The maximum exposure found at any location was hundreds of times below the ICNIRP guideline levels, and typical exposures were much lower still (see AGNIR Figure 2.6). Further information about base stations and the audit is available from Ofcom.
In summary, many exposure measurements have been made in the UK at publicly accessible locations near to base stations, and these have consistently been well within the ICNIRP guideline levels.