Answer to Question #90 Submitted to "Ask the Experts"

Q

My neighbors might have a radio transmitter tower put onto their property. What is the possibility of radiation, how could it affect them, and how much it could affect them?

A

The Federal Communications Commission (FCC) regulates radiofrequency (RF) broadcasting installations, including radio and television stations, cellular radio, paging, amateur radio, microwave point-to-point antennas, police and fire radio, and others. The potential hazards associated with any particular installation depend on the frequency and power of the transmitted radio signals and the height and broadcast characteristics of the antenna(s).

The FCC requires all radio installations to demonstrate that their radio frequency emissions will not cause exposure of the public in excess of acceptable RF safety standards. The American National Standards Institute (ANSI) sets safety standards for human exposure to radiofrequency (RF) electromagnetic energy in the United States. Exposure standards for RF energy are threshold standards. Unlike ionizing radiation, which many people believe to act cumulatively even at low exposure levels, RF exposure at low levels is not considered a cumulative hazard. Threshold standards define the level of RF energy above which there may be health hazards and below which there have been no reported harmful effects. ANSI conservatively set its maximum permissible exposure levels for RF energy at one-tenth (or less) of the threshold for human health effects. The maximum permissible exposure levels for protection against RF energy recommended by ANSI are comparable to those set in other countries. Government agencies recognize and generally accept the ANSI RF safety standard (ANSI/IEEE C95.1).

For more detailed information on RF safety, the FCC has published its Bulletin 56 titled Questions and Answers about Biological Effects and Potential Hazards of Radiofrequency Electromagnetic Fields.

The following question and answer is an exerpt from Bulletin 56: HOW SAFE IS THE RADIOFREQUENCY RADIATION EMITTED BY RADIO AND TELEVISION BROADCASTING ANTENNAS? "Radio and television broadcast stations transmit their signals via RF electromagnetic waves. These signals can be a significant source of RF energy in the environment since there are currently over 11,000 radio and TV stations on the air in the United States. 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. "Ground-level intensities of the RF electromagnetic fields resulting from broadcast transmissions depend 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. Calculations can be performed to predict what field intensity levels would exist at various distances from an antenna. Since energy at some frequencies is absorbed by the human body more readily than energy at other frequencies, the existence of a possible hazard would depend on the frequency of the transmitted signal as well as the intensity. "Public access to broadcasting antennas is normally restricted so that individuals cannot be exposed to high-level fields that might exist near an antenna. Measurements made by EPA and others (References 15 and 19) have shown that RF radiation levels in inhabited areas near broadcasting facilities are generally well below levels believed to be hazardous. There have been a few situations around the country where exposure levels have been found to be higher than those recommended by applicable safety standards (e.g., Reference 20). But such cases are relatively rare, and few members of the general public are likely to be routinely exposed to excessive levels of RF radiation from broadcast towers. "In unusual cases where exposure levels pose a problem, there are various steps a broadcast station can take to ensure compliance with safety standards. For example, high-intensity areas could be posted and access to them could be restricted by fencing or other appropriate means. In some cases more drastic measures might have to be considered, such as redesigning an antenna, reducing power, or station relocation. "Maintenance workers are occasionally required to climb antenna structures 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 hazardous levels of RF radiation if work is performed on an active tower or in areas immediately surrounding a radiating antenna (References 21 and 22). Therefore, precautions should be taken to ensure that maintenance personnel are not exposed to hazardous field intensities. Such precautions could include temporarily lowering power levels while work is being performed, having work performed only when the station is not broadcasting, using auxiliary antennas while work is performed on the main antenna, and establishing work procedures that would specify the minimum distance that a worker should maintain from an energized antenna."

Gary H. Zeman, ScD, CHP