26 March 2009
Author: Charalambos SivridisTo WiFi or not to WiFi
In the following article we will discuss the affect of the wireless networks to the public health. The core of my article is official researches for the wireless networks and the use of microwave bands for communications.
Finally I don?t want to jump to any conclusion but point the facts that are available about the subject. Recommended is also that you search for yourself based on the links that are provided.
Wireless networks and frequency
Microwaves actually are just a part of the very well known electromagnetic spectrum between common radio waves and infrared frequencies. Microwave bands are in use for communications for many decades and for almost every need of wireless communication also used by cellular phones and Dect (Digital Enhanced Cordless Telecommunications) type phones.
From the UHF to the EHF band (wavelength from 1m to 1mm) we will focus around the 2,4 GHz frequency because it is commonly used for the wireless networks.
Microwave radiation is classified as Non-ionizing radiation that means a type of electromagnetic radiation that does not carry enough energy per quantum to ionize atoms or molecules. On the other hand Ionizing radiation (for example Xrays) can completely remove an electron from an atom or molecule and in simple words will create genetic mutation in the DNA (cancer...).
Microwave radiation is as I have explained a Non-ionizing radiation but it is capable of charging ions when passing through matter. Many molecules (for example water) are actually electric dipoles, and therefore rotate as they try to align themselves with the alternating electric field of the microwaves. The molecular movement creates heat as the rotating molecules hit other molecules and put them into motion.
This is exactly the way a microwave oven works, (keep in mind that ovens work with about 900Watts max power). Because we want the radiation to stay inside the oven, the cooking chamber is actually a Faraday cage which eliminates the radiation from escaping. The door is made form a conductive wire mesh with perforations less than the microwave wavelength.
It is easy to understand that the main ?officially? identified problem with the microwave radiation is the fact that it can heat up matter (dielectric heating effect). The human body can also be heated from microwave radiation and a temperature increase is the problem that we have to deal with. Many different organizations have issued standards and measuring methods to calculate the amount of energy absorbed by the human body during the use of wireless communication appliances.
Microwave radiation is not supposed to be dangerous but at the same time there are many safety limits issued by both FCC and EU identifying a ?potential danger? or doing if you like a precautionary approach.Distances
The first thing that was made was to separate the devices in two categories with different safety limits and measuring methods.Portable devices: A portable device is defined as a transmitting device designed to be used so that the radiating structure(s) of the device is/are within 20 centimeters of the body of the user.
Mobile devices: A mobile device is defined as a transmitting device designed to be used in other than fixed locations and to generally be used in such a way that a separation distance of at least 20 centimeters is normally maintained between the transmitter?s radiating structure(s) and the body of the user or nearby persons for example Routers, AP etc
Measuring and safety limits
SAR (Specific Absorption Rate) is a value to understand the rate at which radio frequency (RF) energy is absorbed by the body when exposed to radio-frequency electromagnetic field from portable devices. In simple words higher SAR is more power absorbed by the human body producing more heat. Due to the concern especially for the mobile phone users there have been defined safety limits for exposure to RF energy. At the moment there are two different, one for the US (FCC 2.1993) 1,6 W/kg and one for EU (IEC standard) 2W/kg.MPE
MPE is the Maximum Permissible Exposure limit from mobile devices, these limits are generally based on recommended exposure guidelines published by the National Council on Radiation Protection and Measurements (NCRP) in "Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields," NCRP Report No. 86, Sections 17.4.1, 188.8.131.52, 17.4.2 and 17.4.3. Copyright NCRP, 1986, Bethesda, Maryland 20814. In the frequency range from 100 MHz to 1500 MHz, exposure limits for field strength and power density are also generally based on guidelines recommended by the American National Standards Institute (ANSI) in Section 4.1 of "IEEE Standard for Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz," ANSI/IEEE C95.1-1992, Copyright 1992 by the Institute of Electrical and Electronics Engineers, Inc., New York, New York 10017.
The criteria listed in table 1 shall be used to evaluate the environmental impact of human exposure to radiofrequency (RF) radiation as specified in Sec. 1.1307(b), except in the case of portable devices which shall be evaluated according to the provisions of Sec. 2.1093 of this chapter. Further information on evaluating compliance with these limits can be found in the FCC's OST/OET Bulletin Number 65, "Evaluating Compliance with FCC-Specified Guidelines for Human Exposure to Radiofrequency Radiation."
Bottom line is the FCC specifies a maximum power density of 1.0 mW/cm2 (equal to 10W/m2) for general population/uncontrolled exposure.
The European Telecommunications Standards Institute (ETSI) is an independent, non-profit organization with worldwide projection. ETSI is recognized as an official European Standards Organization by the European Commission (EC). ETSI produces globally applicable standards for Information & Communications Technologies including fixed, mobile, radio, broadcast, internet and several other areas. According to ETSI EN 300 328 standard the equivalent isotropic radiated power (e.i.r.p.) of a device operating in the 2,4 GHz ISM band shall be equal to or less than -10 dBW (100 mW). This limit shall apply for any combination of power level and intended antenna assembly.
Now lets make some theoretical calculations...
According to the power density (S) for far field approximation equation, in 20 cm from a WiFi transmitter with e.i.r.p. 0,1Watt the power density is 0,19W/m2 and if you increase the distance to lets say 1meter the power density will drop to 0,0079W/m2.
It is easy to understand that a ETSI EN 300 328 certified WiFi device is far below the 10W/m2 MPE limit.
Concluded is also that power density decreases at a rate inversely proportional to the square of the distance.
Scientific researches and international agencies
Bellow you can find the official position of major international agencies about the electromagnetic radiation subject.Health protection agency (www.hpa.org.uk)
There is no consistent evidence to date that WiFi and WLANs adversely affect the health of the general population. The signals are very low power, typically 0.1 watt (100 milliwatts) in both the computer and the router (access point) and the results so far show exposures are well within internationally accepted (ICNIRP) guidelines. Based on current knowledge and experience, radio frequency (RF) exposures from WiFi are likely to be lower than those from mobile phones. Also, the frequencies used in WiFi are broadly the same as those from traditional RF applications.
On the basis of the studies so far carried out in house, the Agency sees no reason why WiFi should not continue to be used in schools. However with any new technology it is a sensible precautionary approach, as happened with mobile phones, to keep the situation under ongoing review so that parents and others can have as much reassurance as possible. That is why our Chairman, Sir William Stewart, has stated it would be timely to carry out further studies as this new technology is rolled out. The Health Protection Agency is discussing this with relevant parties.
Verum foundation ? Reflex project (www.verum-foundation.de/reflex)
A project funded by the EU under the programme "Quality of Life and Management of Living Resources", Key Action 4 "Environment and Health": QLK4-CT-1999-01574General position
Electromagnetic field (EMF) exposure, a topic of world-wide discussion, has created uncertainty regarding possible adverse health effects for both the population and the industry. Current research is characterized by conflicting data from epidemiological and animal studies, especially with respect to possible risk of cancer in different sites and neurodegenerative disorders, such as Alzheimer's disease. Clearly, mere continuation or replication of research, without introducing innovative concepts, will prolong the uncertainty as to whether EMF do, or do not, represent a health risk. The main goal of the REFLEX project was to investigate the effects of EMF on single cells in vitro at the molecular level below the energy density reflected by the present safety levels. Most, if not all chronic diseases are of diverse and heterogeneous origins. This variability is to a great extent generated by a relatively small number of critical events, such as gene mutations, deregulated cell proliferation and suppressed or exaggerated programmed cell death (apoptosis). Gene mutations, cell proliferation and apoptosis are caused by or result in altered gene and protein expression profiles. The REFLEX project was, therefore, designed to answer the question whether or not any of these disease-causing critical events could occur in living cells after EMF exposure. Failure to observe such events in living cells in vitro after EMF exposure would have suggested that further research efforts in this field could be suspended and financial resources should be reallocated for the investigation of more important issues. The now available scientific evidence of such critical events, however, demonstrates the need for intensifying research. Although in vitro data can never prove EMF as a cause of disease, they do support such an assumption. Precautionary measures seem to be warranted.
World health organization (www.who.int)
A common concern about base station and local wireless network antennas relates to the possible long-term health effects that whole-body exposure to the RF signals may have. To date, the only health effect from RF fields identified in scientific reviews has been related to an increase in body temperature (> 1 °C) from exposure at very high field intensity found only in certain industrial facilities, such as RF heaters. The levels of RF exposure from base stations and wireless networks are so low that the temperature increases are insignificant and do not affect human health.
The strength of RF fields is greatest at its source, and diminishes quickly with distance. Access near base station antennas is restricted where RF signals may exceed international exposure limits. Recent surveys have indicated that RF exposures from base stations and wireless technologies in publicly accessible areas (including schools and hospitals) are normally thousands of times below international standards.
In fact, due to their lower frequency, at similar RF exposure levels, the body absorbs up to five times more of the signal from FM radio and television than from base stations. This is because the frequencies used in FM radio (around 100 MHz) and in TV broadcasting (around 300 to 400 MHz) are lower than those employed in mobile telephony (900 MHz and 1800 MHz) and because a person's height makes the body an efficient receiving antenna. Further, radio and television broadcast stations have been in operation for the past 50 or more years without any adverse health consequence being established.
While most radio technologies have used analog signals, modern wireless telecommunications are using digital transmissions. Detailed reviews conducted so far have not revealed any hazard specific to different RF modulations.
Cancer: Media or anecdotal reports of cancer clusters around mobile phone base stations have heightened public concern. It should be noted that geographically, cancers are unevenly distributed among any population. Given the widespread presence of base stations in the environment, it is expected that possible cancer clusters will occur near base stations merely by chance. Moreover, the reported cancers in these clusters are often a collection of different types of cancer with no common characteristics and hence unlikely to have a common cause.
Scientific evidence on the distribution of cancer in the population can be obtained through carefully planned and executed epidemiological studies. Over the past 15 years, studies examining a potential relationship between RF transmitters and cancer have been published. These studies have not provided evidence that RF exposure from the transmitters increases the risk of cancer. Likewise, long-term animal studies have not established an increased risk of cancer from exposure to RF fields, even at levels that are much higher than produced by base stations and wireless networks.
Other effects: Few studies have investigated general health effects in individuals exposed to RF fields from base stations. This is because of the difficulty in distinguishing possible health effects from the very low signals emitted by base stations from other higher strength RF signals in the environment. Most studies have focused on the RF exposures of mobile phone users. Human and animal studies examining brain wave patterns, cognition and behaviour after exposure to RF fields, such as those generated by mobile phones, have not identified adverse effects. RF exposures used in these studies were about 1000 times higher than those associated with general public exposure from base stations or wireless networks. No consistent evidence of altered sleep or cardiovascular function has been reported.
Some individuals have reported that they experience non-specific symptoms upon exposure to RF fields emitted from base stations and other EMF devices. As recognized in a recent WHO fact sheet "Electromagnetic Hypersensitivity", EMF has not been shown to cause such symptoms. Nonetheless, it is important to recognize the plight of people suffering from these symptoms.
From all evidence accumulated so far, no adverse short- or long-term health effects have been shown to occur from the RF signals produced by base stations. Since wireless networks produce generally lower RF signals than base stations, no adverse health effects are expected from exposure to them.
According to the specifications a GSM phone has a 2 Watt peak output transmitted, a Dect type wireless phone 250mWatt and a wireless Access point router 100 mWatt. Now imagine that a GSM phone when in use is probably very close to the brain of the user and the output is 20 times more than a WiFi router and it is considered safe. Why should we worry for the WiFi microwave exposure if all organizations tell us ?it is safe??
Officially you don?t have to worry a lot, on the other hand if you want to reduce the radiation exposure the easiest way is to increase the distance between yourself and the transmitter. A more radical reaction would be to through away your wireless devices (Dect phone, Wifi router) and replace them with cabled. You can even paint your house with special conductive paint (CuPro-Cote, Y-shield etc) and create a huge Faraday cage eliminating all the exposure from the outside. As I wrote before it depends how radical you are...