Radiofrequency (RF) Radiation
Kelly Classic, Certified Medical Physicist
Probably the most important use for RF energy is in providing telecommunications services. Radio and television broadcasting, cellular telephones, radio communications for police and fire departments, amateur radio, microwave point-to-point links, and satellite communications are just a few of the many telecommunications applications. Microwave ovens are a good example of a noncommunication use of RF energy. Other important noncommunication uses of RF energy are radar and for industrial heating and sealing. Radar is a valuable tool used in many applications from traffic enforcement to air traffic control and military applications. Industrial heaters and sealers generate RF radiation that rapidly heats the material being processed in the same way that a microwave oven cooks food. These devices have many uses in industry, including molding plastic materials, gluing wood products, sealing items such as shoes and pocketbooks, and processing food products.
Radio and television broadcast stations transmit their signals via RF electromagnetic waves. Broadcast stations transmit at various RF frequencies, depending on the channel, ranging from about 550 kHz for AM radio 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 for some radio stations or up to millions of watts for certain television stations. Some of these signals can be a significant source of RF 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.
Ground-based antennas used for satellite-earth communications typically are parabolic "dish" antennas, some as large as 10 to 30 meters in diameter, that are used to transmit (uplinks) or receive (downlinks) microwave signals to or from satellites in orbit around the earth. The satellites receive the signals beamed up to them and, in turn, retransmit the signals back down to an earthbound receiving station. These signals allow delivery of a variety of communications services, including long-distance telephone service. Some satellite-earth station antennas are used only to receive RF signals (that is, just like a rooftop television antenna used at a residence) and, since they do not transmit, RF exposure is not an issue. Because of the longer distances involved, power levels used to transmit these signals are relatively large when compared, for example, to those used by the microwave point-to-point antennas discussed above. However, as with microwave antennas, the beams used for transmitting earth-to-satellite signals are concentrated and highly directional, similar to the beam from a flashlight. In addition, public access would normally be restricted at station sites where exposure levels could approach or exceed safe limits.
- Radar systems send electromagnetic waves in pulses and not continuously. This makes the average power emitted much lower than the peak pulse power.
- Radars are directional and the RF energy they generate is contained in beams that are very narrow and resemble the beam of a spotlight. RF levels away from the main beam fall off rapidly. In most cases, these levels are thousands of times lower than in the main beam.
- Many radars have antennas which are continuously rotating or varying their elevation by a nodding motion, thus constantly changing the direction of the beam.
- Areas where dangerous human exposure may occur are normally inaccessible to unauthorized personnel.
- Bioelectromagnetics Society
- US Department of Defense
- European BioElectromagnetics Association
- Federal Communications Commission
- US Food and Drug Administration
- ICNIRP (Europe)
- Microwave News
- J. Moulder, Medical College of Wisconsin
- National Council on Radiation Protection & Measurements
- National Radiation Protection Board (United Kingdom)
- US OSHA
- Wireless Industry (CTIA)
- Wireless Information Resource Centre (Canada)
- World Health Organization (WHO)
Radiofrequency (RF) Radiation - Dangers Of Exposure
- Roof maintenance
- Window cleaning
- Facade maintenance
RF radiation, also known as EME, EMR or EMF, is low frequency radiation (less than 300 GHz) which includes microwave transmissions. The major sources of RF radiation are radio, television, mobile telephone and paging transmission antennas.
RF radiation heats in the same way that microwave ovens heat food. Harmful heating of body tissue is a possibility where there is exposure to RF fields above the maximum recommended exposure levels. Shocks, similar to electric shocks, due to touching or receiving arcs from RF devices are also possible from over-exposure to RF radiation.
Employers must ensure that employees, independent contractors or the general public are not exposed to RF radiation above recommended maximum levels outlined in the radiation protection standard, Maximum Exposure Levels to Radiofrequency Fields -- 3 kHz to 300 GHz published by the Australian Radiation Protection and Nuclear Safety Agency, ARPANSA (see Further Information for more details).
- Identify radiation sources and list the contact numbers of all companies controlling transmissions from the roof or work location.
- Determine "NO GO" areas where maximum exposure levels may be exceeded. This may be by measurement, or on the advice of a competent person.
- Document information on No Go Areas.
- The preferred method of controlling exposure to RF radiation is to cease or power down transmissions. However, as control over the transmission signal is usually remote from the worksite, employers need to ensure that they are able to continually verify the strength of the signal during the works.
- Develop a Safe Work Procedure (SWP) giving consideration to all identified risks, including RF radiation.
- Induct and train all workers in the SWP.
- Make sure that NO GO areas are sign-posted, marked or provided with physical barricades in accordance with the SWP.
- Where workers have a need to enter a NO GO area, they should be directly supervised by a competent person who has undergone training in safely managing an RF radiation environment.