Abgeschickt von Bob Lecardson am 11 Juni, 2004 um 22:45:36
Antwort auf: - von Viagra am 04 Dezember, 2003 um 07:01:42:
The announced and now in-process rollout of wireless network access in McHenry and Science & Engineering has raised concerns from Library staff about potential health effects of this technology. The following addresses these concerns in two parts. First is a discussion of the nature of the radio frequency waves used with wireless networks and what we know about health hazards related to exposure. (A list of links to useful source documents can be found at the end of this article.) Second is the results of our discussions with campus networking staff about where wireless access are to be installed and what can be done to reduce exposure of staff locations.
Wireless networks use radio frequency (RF) waves in the 2.4GHz frequency bandwidth to transmit and receive data between workstations and base stations (also called wireless access points). Eleven base stations are planned for McHenry Library and six are planned for Science & Engineering. The base stations, mounted on walls or ceilings, will be deployed in order to provide widest possible coverage in public areas.
Wireless networks RF waves similar to those used in microwave ovens, cell phones and cordless phones. The main difference -- and a critical one from the health perspective -- is the amount of energy used with each of these technologies. For instance, where a microwave oven's output is more than 1000 Watts, cell phones operate on less than 10 Watts and wireless access points are about the same. Even more important is the intensity of the waves, the Specific Absorbtion Rate (SAR), used in each technology. While the RF output allowed for cell phones is a SAR of 10 Watts/square meter (W/m2), wireless networks operate at a SAR of 0.05 to 0.1 W/m2. That's 100th to 200th less energy than found in cell phones.
The comparison to cell phone output is particularly important because most of the research and literature you will find about the health effects of RF waves talks about cell phones, not wireless networks. It is also worth noting that cell phones are often worn on the body or head against the head, while wireless access points are mounted on the ceiling. RF waves, like many other forms of radiation, diminish exponentially with distance; the further away you are, the less your exposure, squared. Another factor, RF waves in this frequency are blocked by a variety of common materials, particularly metals. Book stacks are a particularly good shield (or impediment, depending on how
you look at it) against
Now the good news. Cell phones have a fairly clean bill of health. Study after study has found no clinical or epidemiological connection between cell phone use or low level RF exposition and health problems. (See the American Cancer Society link below for a good summary of the evidence.) It is reasonable to expect as good or better results with wireless networks which operate at a much lower level of energy and at a significantly greater distance.
Still, it would be misleading to say that no one has expressed responsible concerns about the health effects of wireless networks. You will see from a couple of the links below that some reliable sources suggest that -- while still being clear that there is no evidence of health effects -- it is too soon to tell and recommend a cautionary approach. (See the Independent Expert Group report, linked below, for this view.)
Given concerns raised by staff and the reasonable recommendation of a cautionary approach, several of us met on 7/21 with campus network staff to see what could be done to reduce exposure to Library staff members. The networking folks were very open to doing whatever they could in this area, offering to locate access points away from staff work areas, to reduce power at selected access points to limit the reach of RF fields, and use directional antennas keep certain areas out of the RF fields. They also offered to conduct an RF assessment of the building after the wireless network installation and to advise us on measures we can take to protect staff areas.
After hearing this report at their 7/22 meeting, LMG charged a work group with reviewing the wireless distribution plans and recommending possible changes to limit staff exposures. Lee Jaffe, Mike Edmonds (S&E), and Vince Novoa (S&E) will work with campus networking staff to put these changes in place.
Independent Expert Group on Mobile Phones (Stewart
Commission, UK) http://www.iegmp.org.uk/
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