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People have a lot of questions about radio frequency emissions in general and those of TETRA in particular. Often the science is not easy to access or understand, and it is easy to be worried by claims made or media stories. These Qs and As aim to provide some factual information and to point to independent expert sources from which further information can be obtained. It is important that people think about the reliability and validity of the information sources they use and whether the information is being provided by acknowledged experts. TIG does not claim to be expert in this topic, and therefore does not promote its own opinions but points the way to expert advice so that there can be an informed debate. One useful general source of information on radio frequency emissions is the radiation section of the Health Protection Agency web site, click here.

If you want an explanation of any of the terms or abbreviations used in these questions and answers, please refer to our glossary of terms - click here.

1. Why can't scientists say categorically that TETRA is safe?
    
2. In the UK, the Stewart Report expressed concern about the potential health impact of RF emissions. What has happened since then?
    
3. Which countries use TETRA?
    
4. Do TETRA transmitters and handsets pulse at 17Hz?
    
5. How are ICNIRP standards set?
    
6. If TETRA is safe why is the Home Office sponsoring a major epidemiological study of police officers to be conducted by Imperial College? Why not put the use of TETRA on hold until a proper study has been completed?
    
7. Do TETRA terminals interfere with other electrical equipment and is there a risk that they could cause explosions in situations encountered by fire and rescue?
    
8. Could TETRA equipment inadvertently trigger bombs when used in anti-terrorism operations?
    
9. What recent scientific studies have there been on possible biological effects?
    
10. There have been claims that people who are hypersensitive to RF can be affected by TETRA signals.  What is the position on this?
     
11. People living near transmitters have no choice in the matter and there is growing opposition to mast siting.  Why is this, if the technology is safe?
     
12. Why does the industry take no notice of people living near proposed transmitter sites?

1    Why can't scientists say categorically that TETRA is safe?

Science cannot prove categorically that something is safe; the only certainty in science is that there is no certainty. It is not possible to prove a negative, so no-one can prove conclusively that a product or technology is not harmful. Scientific methodology is empirical. Knowledge develops from observation and measurement, producing theories that can be used to predict what might happen under certain conditions, testing those theories through experiments and studies, peer-reviewing the findings, methodology, and conclusions, and attempting to replicate the results. In this way a body of robust scientific evidence builds up. If, after many years, a number of studies find no harmful effects, scientists can say with growing confidence that a product is probably safe.

The World Health Organisation holds a database of hundreds of studies into the impact of radio frequency emissions, including some at the frequencies used by the TETRA standard. The balance of evidence has demonstrated no adverse impact on health. While uncertainties remain about the potential effects of long-term use of radio-based technologies, advisory bodies like the World Health Organisation advocate a precautionary approach. However, this does not mean that radio technologies should not be used and it reaffirms the importance of science-based standards.

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2    In the UK, the Stewart Report expressed concern about the potential health impact of RF emissions. What has happened since then?

The original Stewart committee report was published in 2001 and its terms of reference were to review the frequencies at which the mobile phone networks operated. The committee did not examine TETRA in detail and so did not make any specific recommendations about TETRA technology.

However it did mention scientific work, dating back to the 1970s, that implied that radio signals with modulations around 16Hz might have an impact on release of cellular calcium. the report acknowledged that this evidence was inconclusive but suggested that “ …as a precautionary measure, amplitude modulation around 16Hz should be avoided if possible in future development of signal coding”. Professor Lawrie Challis, who was the vice chairman of the Stewart Inquiry, has explained publicly that this recommendation was made not because of any worries about health, but merely to acknowledge the existence of unreplicated research dating back to the 1970s.

Since then, both industry and Government have responded to the recommendations made by the Stewart Committee, in particular:

-         The Government adopted the ICNIRP safety guidelines as recommended by the Stewart Inquiry. These ICNIRP standards were already being used for TETRA systems. (Click here to find out more about ICNIRP.)

-         Operators and carriers have established guidance to help them identify those potential transmitter sites which may be of concern to communities and have devised a communications and communications and consultation model to help ensure that the appropriate amount and nature of communications takes place.

-         The Mobile Telecommunications Health Research (MTHR) programme, co-funded by industry and Government but independently managed under the Chairmanship of Professor Lawrie Challis has been established, to make sure that further high quality independent studies into health aspects of mobile phone use take place. This programme includes a number of TETRA studies - click here to see the list of studies.

-   Studies on the release of cellular calcium, commissioned by the Home Office, have been completed by the Defence Science and Technology Laboratory. This study found that the TETRA signal had no effect on cellular calcium. See the answer to Question 9 below for more information.

The Stewart team conducted an update inquiry in 2004 and published a further report (Mobile Phones and Health, 2004), known as “Stewart 2”. This report included a section on TETRA which reaffirmed the conclusions of the 2001 report by the Advisory Group on Non-Ionising Radiation. AGNIR had said “it is notable that the signals from TETRA base stations are not pulsed, whereas those from mobile terminals and repeaters are. Although areas of uncertainty remain about the biological effects of low level RF radiation in general, including modulated signals, current evidence suggests that it is unlikely that the special features of the signals from TETRA terminals and repeaters pose a hazard to health."

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3    Which countries use TETRA?

The TETRA standard is well-established in a number of countries round the world, and has been deployed since 1997. TETRA systems are designed to provide the emergency services and other public safety organisations, public utilities, transport organisations and other users of mobile communications such as the oil and gas industry and distribution organisations with greatly improved communications relative to previous analogue technologies. There are some 788 TETRA contracts in existence in nearly 80 countries. The USA and Canada have their own digital systems similar to TETRA. More information can be found on our "TETRA around the World Page", click here.

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4    Do TETRA transmitters and handsets pulse at 17Hz?

The simple answer is that handsets do, and transmitters don’t.

TETRA base stations emit a continuous signal. This has been confirmed by independent review and a statement to this effect was included in the January 2004 AGNIR report, which referred back to the comprehensive report published by AGNIR in 2001. That report stated “It is notable that the signals from TETRA base stations are not pulsed whereas those from mobile terminals and repeaters are” and “The measurements confirm that, to within the limitations of the measurement technique (less than 1%), TETRA base station signals are continuous and not pulsed over time intervals that could cause amplitude and therefore power modulation at frequencies between 1 and 200Hz." Further information is available on the radio emission pages of the Health Protection Agency web site - click here.

TETRA portable radios do pulse at 17.65Hz, but they are very low powered – with most operating at only 1 Watt or less; they emit RF only while the equipment is in transmit mode, which tends to be for very brief periods; and they use a feature called adaptive power control, which means that the radio continually adjusts its power output to the lowest level needed to maintain communication with the base station.

In any event, there is no scientific evidence that radio frequency emissions pulsed at 17Hz have any biological effects. The 1970s experiments which suggested there was an effect on calcium efflux have not been replicated, despite many attempts. The most recent study, carried out recently by a team at the Defence Science and Technology Laboratories found no evidence of calcium efflux. The results of this study were published in the International Journal of Radiation Biology in December 2005 and a summary can also be found on the Home Office's web site - click here.

Professor Colin Blakemore, who was a member of Stewart Inquiry, has spoken and written extensively on this issue, and, talking about the 1970s calcium efflux studies, has said “…..there is a much greater danger to life associated with poor communications than that implied by a questionable investigation [some 30 years ago]……”

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5    How are ICNIRP standards set?

The ICNIRP standards are the de facto global safety standards for radio-frequency emissions. They are set by the International Commission for Non-Ionising Radiation Protection (ICNIRP) - an international expert body combining the scientific expertise of acknowledged experts in the field from around the world. In setting the standards, ICNIRP reviewed all the scientific evidence about the impact of RF, including both thermal effects and potential biological effects. In doing so they found that there was only evidence of a thermal effect. ICNIRP regularly reviews new scientific studies to look at whether changes to the guidelines are necessary.

The standard-setting methodology incorporates a precautionary approach. The standards are based on the threshold levels at which effects on body tissue from radio frequency emissions can be observed. This is the level which brings about, on average, a rise in overall body temperature of one degree Celsius within a six minute period. (Body temperature generally fluctuates by one degree during a typical day). Maximum emission levels are then set at one tenth of the threshold level for occupational use, and at one fiftieth for exposure of the general public. The difference takes account of the fact that occupational users are trained to use the equipment and that the occupational group excludes people like the elderly and children.

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6    If TETRA is safe why is the Home Office sponsoring a major epidemiological study of police officers to be conducted by Imperial College? Why not put the use of TETRA on hold until a proper study has been completed?

Following publication of the Stewart report, the Home Office asked AGNIR to produce a report about the use of TETRA in the UK. AGNIR published a report in July 2001, which can be found on the Home Office website, and this included 8 recommendations for a long-term research programme. The Imperial College long-term study, monitoring user health and patterns of usage, was established in response to one of these. The study involves a cohort of around 100,000 police users, and will go on for some fifteen years. For further details of this and the Home Office response to the other recommendations click here. For more information on the benefits and pitfalls of epidemiological studies, please see our Science and Standards leaflet (click here - pdf file).

The use of radio frequency emissions has been subject to a far greater number of scientific studies and risk assessments than many of the chemicals in our food. Advances in all technologies carry a small degree of risk, but no products or services reach the market without appropriate studies, testing and assessment having been conducted.

As TETRA equipment complies with all the relevant safety standards, there is no reason to stop using it. TETRA exposes officers to less RF than their old communications systems, and Prof Lawrie Challis says he makes this point when he talks to the police.

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7    Do TETRA terminals interfere with other electrical equipment and is there a risk that they could cause explosions in situations encountered by fire and rescue?

There are regulations that require all electrical equipment to work within a defined frequency band. Some equipment that pre-dates or does not comply with these regulations (electro-magnetic compatibility standards) might be affected – eg older televisions, some car alarms. But this is because that equipment does not comply with the standards and is therefore susceptible to interference. TETRA does comply and operates squarely within its allocated frequency band.

It is a requirement of most hospitals that equipment that transmits radio waves is switched off on hospital premises in case there is interference with sensitive medical equipment. TETRA handsets are no different in this respect from any other radio equipment except that they benefit from a transmit-inhibit feature that enables users to prevent transmission without turning off the equipment altogether.

Firefighters may have a requirement for special ‘intrinsically safe’ handsets, for example for use at incident scenes where there is danger of explosion or where the presence of inflammable gas or chemicals is suspected. Any TETRA equipment used in these circumstances would meet appropriate standards.

For more information, see our fact sheet on the subject – click here.

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8    Could TETRA equipment inadvertently trigger bombs when used in anti-terrorism operations?

TETRA equipment offers a number of features such as encryption, setting up of talk groups and direct mode operation, that have substantial operational benefits in emergency situations, from anti-terrorist operations to major road traffic accidents. These features can facilitate rapid and effective working within and between emergency services. This is invaluable in an emergency situation, such as was experienced in London on 7/7 (7 July 2005) or earlier in Madrid.

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9    What recent scientific studies have there been on possible biological effects?

The biomedical sciences department of the Defence Science and Technology Laboratories (DSTL) has completed an investigation of the effects of TETRA signals on cellular calcium. As well as reproducing the maximum exposure that can arise from TETRA handsets, the researchers used several lower power levels to see if there could be "power windows" where TETRA signals cause a reaction. No effects of TETRA on calcium efflux have been found at any of the power levels used in the measurement. Further information is available on the Home Office web site. To visit the Home Office programme of work on TETRA health and safety issues click here; to see the DSTL quarterly reports of its work ("An Investigation of the Effects of the Airwave TETRA Signal on Cellular Calcium and Brain Function") click here.

In June 2002 the Swedish Radiation Protection Authority (SSI) appointed an International Expert Team to analyse and evaluate the research on EME (electromagnetic emissions) and its potential effect on health, specifically biological effects. The first annual report was published at the end of 2003 - click to view the report for 2003, 2004, 2005 or 2006. 

Work by Dr Alan Preece at the University of Bristol, presented at the Bioelectromagnetics Society Conference in June 2002, based on a study of TETRA users, found no effect on cognitive brain function.

The United States Air Force reported at the Electromagnetic Fields and Human Health seminar in Russia in September 2002 an attempt to replicate the calcium efflux studies. Its studies failed to show any effect. It also conducted some very high pulse power tests looking at calcium channels that were reported at the Second International Workshop on Biological Effects of Electro Magnetic Emissions in Rhodes in October 2002, and again saw no effects.

The Expert Panel of the Royal Society of Canada (1999) and the subsequent Report from the French Ministry of Health (Zmirou Report, 2001) both backed the extensive research reported in a UNEP/WHO/IRPA Report of 1993, which concluded that there was no strong reason to believe that 16Hz modulation has special effects.

To obtain more detailed information on RF studies and reviews, click here for a list of independent reviews of various aspects of the scientific evidence.

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10    There have been claims that people who are hypersensitive to RF can be affected by TETRA signals. What is the position on this?

The HPA published a review of the literature on electro-sensitivity in November 2005 – to read the summary click here.

The review stated that the use of the term electrical sensitivity did not imply acceptance of a causal relationship between symptoms and attributed exposure.

The HPA conclusion is consistent with the WHO view as expressed following the Prague workshop in October 2004, which can be summarised as:

•            electrosensitivity is characterised by a variety of non-specific symptoms

•            while the symptoms are real, there is no scientific evidence of a causal link – more than 30 studies have failed to demonstrate a relationship and the evidence is that fields from base stations cannot affect molecules of biological tissue

•             there is no indication that making the international standards more stringent would reduce such symptoms

The HPA review suggests areas for further research and notes that the Mobile Telecommunications and Health Research Programme (MTHR) already includes some relevant studies. Click here to visit the research pages of the MTHR web site.

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11    People living near transmitters have no choice in the matter and there is growing opposition to mast siting.  Why is this, if the technology is safe?

The reasons for public concern about transmitter siting are complex and embrace both health issues and environmental concerns such as visual amenity and consequent concerns about potential effects on property prices.

Such concerns are often exacerbated by sensational media coverage and by the pronouncements of some theorists who claim to be experts. In addition, no-one likes dealing with uncertainty, and people often ask for categorical assurances of absolute safety, which, for good reason, cannot be given (see 1 above).

TETRA base station equipment is low powered and typically operates at tiny fractions of the emission levels allowed by the safety standards and all sites are designed to be safe and tested for compliance when the equipment is installed. Many measurements have been made, both in the laboratory and in situ, of the RF field strength around TETRA transmitters. The level of RF falls away rapidly with distance from the transmitter so that 10m away at ground level it is 1000 times below the ICNIRP standard, at 50m away it is 1300 times below, at 100m away (the levels are higher here as this is where a down-tilted beam would hit the ground) it is 365 times below, and at 300m it is 3500 times below the safety standard.

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12    Why does the industry take no notice of people living near proposed transmitter sites?

As with the siting of any telecommunications equipment, the siting of TETRA transmitters always complies fully with planning requirements, including certification of ICNIRP compliance and consultation with those immediately affected by a planning application. However, the planning regime was not designed to encompass effective and timely communication with the community at large. There is a broad range of stakeholders – mobile operators, site owners, local authorities, users of mobile services and members of the public. With that in mind, companies in the wireless industry signed up to a Code of Practice following the Stewart Inquiry. This provides for earlier and more transparent communications with a wider range of community interests when considering siting. While it is rarely possible to please everyone, through improved communication and consultation, the industry is attempting to strike a better balance of interests and the most recent MORI research into public concern showed only 5% of people are concerned about transmitter siting or other health issues.  The Code is available here.

A TETRA system for the emergency services has to provide coverage everywhere it is needed as well as adequate capacity. It is not acceptable to the emergency services to have gaps where professional users are unable to communicate. By comparison, mobile telephony networks cater for average capacity and it is not uncommon to find areas where there is no coverage.

TETRA also allows multiple professional users on a single network. This means that the network can be shared by emergency services such as the police, ambulance and fire and rescue, all of whom have signed up to use the TETRA-based service in the UK. This provides a considerable environmental advantage over three or more separate networks even though a few additional transmitters may need to be added to accommodate the coverage needs of new user communities.

It is also fair to say that the more transmitters or base stations there are, the lower the power of each needs to be, as the ability of radio signals to travel is dependent on distance and terrain.

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