Safe mobile network
What is a safe radiation level for chronic exposure?
From the peer-reviewed literature (see: Neurotoxic effects
, particularly Hutter et al
. 2006, and also Navarro et al.
, 2003) it is concluded that chronic exposure levels of 100-500 microwatt/m2 (0.2-0.4 V/m) already lead to a (small) increased incidence of headaches and other complaints in residents living near mobile phone masts. The lower value of this interval (100 microwatt/m2) was proposed as the European limit for chronic exposure in a document of the Scientific and Technological Options Assessment (STOA) of the European Union (Hyland, 2001
) and was adopted by the car manufacturer BMW in 2004 (in an effort to reduce sick-leave) as the maximum permitted exposure in the workplace for its 105,000 employees.
The upper level of this interval (500 microwatt/m2) is close to the limit of 600 microwatt/m2 set for brief exposure to GSM and UMTS antennas in Tuscany. When we apply the customary safety factor of 100 to the results of Hutter et al. we end up with a limit of 1 microwatt/m2 (0.02 V/m). This value corresponds to the target formulated by the Governmental Health Department in Salzburg and achieved in large areas of the city (Dr Gerd Oberfeld, personal communication).
Our knowledge platform considers such a target value of 1 microwatt/m2 in combination with a statutory exposure limit in homes (chronic facade burden) of 100 microwatt/m2 (0.2 V/m) reasonable for all stakeholders involved: it can then be expected that in 99% of the homes the levels will be at least 5 fold lower. In these houses where this level of 100 microwatt/m2 is closely approached, residents may, if desired, further reduce the exposure indoors with a factor of 10-100 through a number of simple protective measures.
Furthermore, a chronical exposure (facade burden) limit of 100 microwatt/m2 is excellently workable for the telecom industry (see next section).
note: a conversion table from microwatt/m2 to V/m and vice versa is available as a pdf-file.
What signal strength is needed for mobile devices?
Most mobile devices will work with signal strengths of the order of 0.001 microwatt/m2 . Given a loss of 90% due to reflection and absorption by the building (the building penetration loss) an external signal strength of 0.01 microwatt/m2 is needed. Where the penetration loss is more like 99%, such as in deep basements or reinforced concrete structures with radiation reflecting windows, signal strengths of around 0.1 microwatt/m2 per provider may be needed. It is technically difficult to achieve uniform signal strengths of 0.01-0.1 microwatt/m2, but with today’s technology, a variation in signal strength at street level by a factor 100 should be feasible.
This would involve a maximum signal strength at street level (at the so-called hotspots) of 1 or 10 microwatt/m2 (assuming penetration losses of 90 or 99% respectively). In the case of buildings with high penetration losses or where the mast is relatively distant, it should be possible to install repeaters, which consist of external receivers that pick up the signal, boost it and send it to small transmitters inside. If this were done, there should be no need for any signal at street level to exceed 1 microwatt/m2 per provider.
What are the current continous exposure levels in the Netherlands (similar to the situation in many parts of Europe)?
Radiation levels of 10,000-20,000 microwatt/m2 are commonly found in homes around antennas on low masts
). Figure 1 gives the reason for these high radiation levels. The closest homes are in the main beam of the antenna, which has to be powerful enough (typically 20 watt per transmitter) to reach the basements of houses 10 blocks away. Only a very small proportion of the radiation will reach these basements because the masts are too low and much of the signal is lost by having to pass through the walls of many houses where it may be absorbed or reflected.
Fig. 1 (left) Antenna plan of many Dutch residential areas. Relatively powerful transmitters (often 10-20 watt) on low masts give nearby homes chronic high exposure levels (10,000-20,000 microwatt/m2, corresponding to 2-3 V/m) which lead to many neurological complaints such as migraine and headaches.
Fig. 2 (right) Alternative antenna plan (already standard practice in some places, e.g. Salzburg and parts of Switzerland). Tall masts with relatively weak transmitters give the radiation a much better spread and the upper exposure limits (10-100 microwatt/m2, corresponding to 0.06-0.2 V/m) are 100-1000-fold lower than in the Netherlands. Nevertheless, the network coverage is still excellent because most mobile devices will work with signal strengths as low as 0.001 microwatt/m2.
The alternative: tall phone masts with low power transmitters (the Salzburger antenna plan).
When much taller masts are used; e.g. 20-30 meter above roof level, there are two advantages. Firstly, the transmitters can be less powerful (0.6 watt rather than 10-20 watt) because the radiation now comes from above and can penetrate even to basement level without passing through too many walls. Secondly, the main beam (where the radiation level is highest) can be angled to miss the nearest homes. With this plan, the highest radiation levels are not in nearby houses but in homes 300 meter away, where the maximum signal strength is lower at 10-50 microwatt/m2. The radiation is also spread much more evenly (see Fig. 3, at the bottom of this page). The reach of this system (how far a useful signal will travel) is about the same as with high power transmitters on low masts. The penetration into basements and buildings with radiation-reflecting windows is broadly similar and, as before, boosters (repeaters) can be used in difficult cases where signal penetration is poor and the use of landlines is not an option (the provision of these is normally the responsibility of the buildings’ owners or tenants). This kind of antenna plan is already standard practice in several places; e.g. Salzburg, Austria.
In the short term, a hybrid system can be created using relatively simple measures:
- The power of all transmitters in residential areas (now mostly 10-20 watt) should be reduced to 1-2 watt. Existing masts in residential areas should be raised from 5 meter to 15 meter (permit unnecessary). This will reduce exposure levels in almost all nearby residences to under 500 microwatt/m2. Antennas should no longer be angled downwards if this causes exposures above 500 microwatt/m2 in any nearby home.
- Mast-sharing should be (temporarily) allowed in cases where the coverage level is endangered.
- Buildings with high penetration losses such as offices situated far away from a mast should be provided with repeaters.
- The agreement of telecom companies with each other on roaming (foreign visitors using the Dutch network) should be adjusted so that the provider with the nearest mast gets the call rather than the one with the strongest signal. The current situation rewards the telecom providers that set their transmitters to the highest level (often more than a million times higher than necessary) in tourist areas, airports and business centers.
ALARA is the correct approach
The formalities of EU guidelines pertaining to the application of preventive measures for environmental factors are so specific that there is very little room for discussion. These guidelines emphasize that the absence of a known mechanism for the occurrence of adverse health effects is no reason not to take preventive measures. Furthermore, the entire scientific community does not need to agree on these health effects.
Scientific proof (for which there is no stated definition) is not a requirement. It is required that the researchers who have demonstrated the health effects of a certain environmental factor should come from an “unsuspicious” source. The last requirement will be met for the most part. In the case of the radiation burden on people living near transmission masts and who may suffer neurological effects (see health effects) it is logical to follow the ALARA (As Low As Reasonably Achievable) principle. In practice, this means that the telecom industry is obliged to place their transmitters in such a way (and adjust them in such a manner) that there is just enough reach within their service areas, but at the same time the radiation burden on nearby residents is minimal. The use of the ALARA principle will have no detrimental effects on competition between telecom companies since they will all have to meet these requirements. Ultimately, they will all be better off since they will all be working with less powerful transmitters that use less energy. The costs of these changes to the antenna plan will be more than offset by the lower cost in health care and absence from work due to continual headaches and other neurological disturbances in people living near the masts. In addition, there will be significant energy savings as a result of the lower wattage of the transmitters.
The use of the Salzburg antenna plan, as described above, will comply with the ALARA principle. In combination with a compulsory legal exposure limit of 100 microwatt/m2, the current problem will be mostly solved.
Fig. 3. Model calculation of the radiation levels (at 15 meter height) around and between a threesome of GSM masts (45 meters high) each with three 0.6 watt transmitters. The yellow areas have exposure levels of 10-50 microwatt/m2 and the green areas have less than 10 microwatt/m2 (source: Dr Gerd Oberfeld, Salzburg).