Health and Safety
You might have heard the claim that cell phone use can lead to cancer or other illnesses. This claim has caused many users to be leery of using any radio devices, including WLAN systems. Because RF can be hazardous to the human body, there have been studies to try to analyze exactly what levels of RF are safe and acceptable. The FCC and other regulatory bodies around the world have done studies on this and provide some guidelines on the subject. In the U.S., the American National Standards Institute (ANSI), the Institute of Institute of Electrical and Electronics Engineers (IEEE), and the National Council on Radiation Protection and Measurements (NCRPM) offer guidelines on specific absorption rate (SAR), which is the rate at which a body absorbs RF energy. Based on the input from these organizations, the FCC has identified what is the maximum SAR for portable RF devices, including 802.11 radio transmitters. This limit for the workplace is 400 mW/kg when the entire body is exposed, and 1.6 W/kg for partial exposure. Devices such as cell phones, cordless phones, two-way pagers, and 802.11 devices fall into the partial-exposure category. Because of the limited transmitter power of a typical 802.11 transmitter, the levels are well below those of either limitation. Add to this the fact that the transmitter of an 802.11 device is typically in transmit mode a very limited amount of time (it is normally in receive mode), and the overall exposure is even less. The bottom line is that although users should be concerned about the health and safety considerations of any radio device, they should also be aware that years of research has been conducted in this area and the findings of this research have been incorporated into the applicable regulations. Everyone is familiar with a cellular phone, and when comparing them to an 802.11 device, the 802.11 device delivers a fraction of the transmit power of a typical cellular telephone. The energy exposure of the body is also a fraction of that delivered by the cellular device, and the differing usage patterns of a 802.11 device leads to far less exposure time than would be typical for a cellular telephone. Even with the preceding health and safety information, keep in mind that high-gain antennas do intensify the energy levels to a very narrow beam. Therefore, it is always wise to not stand in front of, or near, high-gain antennas any longer than absolutely necessary if you are not fully cognizant of the operational parameters of the antenna.
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