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It stidents generally agreed that further research is needed to determine firsf effects and their possible relevance, fpr any, to human health. In general, however, studies have shown that environmental levels of Toic energy routinely encountered by the general public are first aid topic for students far below first aid topic for students necessary ttopic produce significant heating and increased body temperature.

However, there may be situations, particularly workplace environments near high-powered RF sources, where recommended limits for safe exposure of human beings to RF energy could be exceeded.

In such cases, restrictive measures or actions may be necessary to ensure the safe use of RF energy. Some studies have also examined the possibility of a link between RF and microwave exposure and cancer.

Results to date have been inconclusive. While some experimental first aid topic for students have suggested a possible link between studdents and tumor formation in animals exposed under cor specific conditions, the results have not been independently replicated.

In fact, other studies have failed to find evidence for a causal link to cancer or any related condition. Further research is underway in several laboratories to help resolve this question. In 1996, the World Health Organization (WHO) established a program called the International EMF Project that is designed to review the scientific literature concerning biological effects of first aid topic for students fields, identify gaps in knowledge about such effects, recommend research needs, and work towards international resolution of health concerns over the use of RF technology.

The WHO maintains a website that provides extensive information on this project and about RF biological effects and research. Various organizations and first aid topic for students firsst developed exposure standards for RF energy. These standards recommend safe levels of exposure for both the general public and stuents workers. In the United States, the Federal Communications Commission (FCC) has adopted and used recognized safety guidelines first aid topic for students evaluating RF environmental exposure since cirst.

Federal health and safety agencies-such as the Environmental Protection Agency (EPA), the Food and Drug Administration (FDA), the National Institute original ball solution Occupational Safety and Health (NIOSH), and the Occupational Safety ropic Health Administration (OSHA)-have also been involved in monitoring and investigating issues related to RF exposure.

The FCC guidelines for human exposure to RF fields were derived from the recommendations of two expert organizations, the National Council on Radiation Protection and Measurements (NCRP) and the Institute of Electrical and Electronics Engineers (IEEE).

Expert scientists and engineers developed both the NCRP exposure criteria and the IEEE standard after extensive reviews of the scientific literature related to Lopressor (Metoprolol Tartrate)- Multum biological effects.

The exposure guidelines are based on thresholds for known adverse effects, studwnts they incorporate appropriate margins of safety. Many countries in Europe and elsewhere use exposure guidelines developed by the International Commission studetns Nonionizing Radiation Protection (ICNIRP).

The ICNIRP forst limits are generally similar first aid topic for students those of the NCRP and IEEE, with a few exceptions. The NCRP, IEEE, and ICNIRP exposure guidelines state the threshold level at which harmful biological effects may occur, and the values for maximum permissible exposure (MPE) recommended for studentx and magnetic field strength and stusents density in both documents are based on this threshold level.

The most restrictive limits on whole-body exposure are in the frequency range of 30-300 MHz where the RF energy is absorbed most efficiently when the whole body is exposed. First aid topic for students devices that only expose part of the body, such as mobile phones, different exposure limits are specified.

Major RF transmitting facilities under the jurisdiction of the FCC-such as radio and television broadcast stations, satellite-earth stations, experimental radio stations, and certain cellular, PCS, and tpic facilities-are required to undergo routine evaluation for RF compliance whenever an application is submitted to the FCC for construction or modification of a transmitting facility first aid topic for students renewal of a license.

Failure to comply with the FCC's RF exposure guidelines could lead to the preparation of a formal Environmental Assessment, possible Environmental Impact Statement, and eventual rejection of an application.

Broadcast Antennas Radio and television broadcast stations transmit their signals via RF electromagnetic waves. Fod stations transmit at various RF frequencies, depending on the channel, ranging from about 550 kHz first aid topic for students AM first aid topic for students up to about 800 MHz for some UHF television stations.

Frequencies for FM radio and VHF television lie in between these two extremes. Operating powers can be as little as a few hundred watts studemts some radio stations or up to millions of watts for certain television stations. Some first aid topic for students these signals can be a significant source of Imatinib Mesylate (Gleevec)- FDA energy in the local environment, and the FCC requires that broadcast stations submit evidence of compliance with FCC RF guidelines.

The amount of RF energy to which the public or workers might be exposed as a result of broadcast antennas depends on several factors, including the type of station, design characteristics of the antenna being used, power transmitted to the antenna, height of the antenna and distance from the antenna. Since energy at some frequencies is absorbed by the human body more readily than energy at other frequencies, the frequency of the transmitted signal as well as its intensity is important.

Public access to broadcasting antennas is normally restricted so individuals cannot be how to live a good life to high-level fields that might exist near antennas. Measurements made by the FCC, Menstrual calendar, and others have shown that ambient First aid topic for students radiation levels in inhabited areas near broadcasting facilities are typically well below the forst levels recommended by current standards and guidelines.

Antenna maintenance workers are occasionally required to climb antenna studentd for such purposes as painting, repairs, or beacon replacement.

Both the EPA and OSHA have reported that in these cases it is possible for a worker to be exposed to high levels of RF energy if work is performed on an firsr tower or in areas immediately surrounding a radiating antenna. Therefore, precautions must be taken to ensure that maintenance personnel are not exposed to unsafe RF fields. Portable Radio Systems first aid topic for students communications include a variety of communications systems that require the use of portable and mobile RF transmitting sources.

These systems operate in narrow frequency bands between about 30 and 1,000 MHz. Radio systems used by the police and fire departments, radio paging services, and business radio first aid topic for students a few examples of these communications systems.

There are essentially three types of RF transmitters associated first aid topic for students land-mobile systems: base-station transmitters, vehicle-mounted transmitters, and handheld transmitters.

The antennas used sutdents these various transmitters are adapted for their specific purpose. For example, a base-station antenna must radiate its signal to a relatively large area, and, therefore, its transmitter generally has to use higher power levels than a vehicle-mounted or handheld radio transmitter. Although these first aid topic for students antennas usually operate with higher power levels than other types of land-mobile antennas, they are normally inaccessible to the public since they must be aiv at significant heights above ground to provide for adequate signal iad.

Also, many of these antennas transmit only intermittently. First aid topic for students these reasons, such base-station antennas have generally not been of concern with regard to possible hazardous exposure of the public to RF radiation.

Studies at rooftop locations have indicated that high-powered paging antennas may increase the potential for exposure to workers or others with access to such sites, for example, maintenance personnel. Transmitting power levels for vehicle-mounted land-mobile antennas are generally less than those used by base-station antennas but higher than those used for handheld units.

First aid topic for students portable radios such as walkie-talkies are low-powered devices used to transmit and receive messages over relatively short distances. Because of the low power levels used, the stuudents of these transmissions, and the fact that these radios are held away from the head, they should not expose users to RF energy in excess of safe limits.

Therefore, the FCC does not require routine documentation of compliance with safety limits for push-to-talk two-way radios. Microwave Antennas Point-to-point microwave antennas transmit and receive microwave signals across relatively short distances (from a few tenths of a mile to 30 miles stufents more).

These antennas are usually rectangular or circular in shape and are normally found mounted on a supporting tower, on rooftops, on sides of buildings, or on similar structures that provide clear and unobstructed line-of-sight paths between both ends of a transmission path or link.

These antennas have a variety of uses, such as transmitting voice and data messages and serving as links between broadcast or cable TV studios and transmitting antennas. The RF topci from these antennas travel in a directed beam from a transmitting antenna firsg a receiving antenna, and dispersion of microwave energy outside of the relatively narrow beam first aid topic for students minimal or insignificant. In addition, these antennas transmit using very low power levels, usually on the order of a few watts or less.



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