What is radio frequency (RF)?
Radio frequency (RF), also known as electromagnetic fields (EMF) are common in all facets of modern life. Such fields with frequencies between about 100 kiloHertz (kHz) and 100 GigaHertz (GHz) [100,000 and 100,000,000,000 cycles per second] are known as radio frequency fields, or simply “RF.” Microwave ovens operate in this range, as do cordless telephones, cellular telephones, CB radios, garage door openers, motion sensors, walkie-talkies, and numerous other devices.
RF should not be confused with extremely low frequency energy (ELF). ELF fields are typically associated with household electric devices, such as electric blankets, and with overhead power lines. These operate at a frequency of 60 Hertz – millions or billions of times lower in frequency than RF. Neither should RF be confused with ultra-violet (UV) or X-ray energy, which is at frequencies millions or billions of times higher than RF energy. Radiated energy near X-ray frequencies is called ionizing, because it has enough energy to remove electrons from individual atoms. RFradiation is non-ionizing; that is, it does not by its nature change matter at the atomic level.
What are typical RF exposure levels?
The antennas are designed to concentrate their energy toward the horizon, with very little energy wasted toward the sky or the ground. Along with the low power of such facilities, this means that it is generally not possible for exposure conditions to approach the maximum permissible exposure limits without being physically very near the antennas.
Have there been any studies looking at RF exposure over long time periods?
Yes. There have been studies of people exposed to RF energy over a long period of time. The epidemiological studies have not shown adverse health effects at exposure levels at or below the FCC standard.
The World Health Organization (WHO) maintains a comprehensive searchable database of research in the effects of electromagnetic fields on biological systems, available at http://www.who.int/peh-emf/en/.
Can base stations affect implantable devices, such as cardiac pacemakers?
The prevailing U.S. standard for the RF immunity of medical devices is the 2007 revision of the Association for the Advancement of Medical Instrumentation (AAMI) Standard 60601-1-2, which mirrors the International Electrotechnical Commission (IEC) Standard 601-1-2. Formally recognizing this standard, the Food and Drug Administration (FDA) says that it “will allow manufacturers to ensure that cardiac pacemakers and defibrillators are safe from cell phone EMI [electromagnetic interference].”
Medtronics, one of the principal manufacturers of pacemakers, provided this RF immunity information in 2009 for its devices, and other manufacturers should have incorporated similar resilience into their own products:
“Medtronic pacemakers/defibrillators are designed to operate normally in electric fields measuring 100 volts per meter” (V/m) and “to operate normally within RF levels that meet the government Maximum Permissible Exposure (MPE) limits” for electric fields at “150 kHz and up,” including “[s]ources such as: radio transmitter antennas, television transmitter antennas, cellular telephone antennas, RF welding equipment, dielectric heaters, radar.”
What are typical RF exposure levels from base stations?
The antennas used by wireless carriers are designed to concentrate their energy toward the horizon, with very little energy wasted toward the sky or the ground. Along with the low power of such facilities, this means that it is generally not possible for exposure conditions to approach the maximum permissible exposure limits without being physically very near the antennas. Typical levels can be hundreds – thousands of times below the standard.
What is Radiation?
Radiation is a term meaning, simply, that something is spreading out – something is being dispersed (sound waves are an example, as are heat and light from a regular light bulb, or the ripples in a pond, dispersing the energy from a rock dropped in the water). Radioactivity, as might be associated with nuclear weapons or power plants, refers to something else entirely: the radiation of atomic particles, some of which can cause severe health problems, including death, if absorbed in sufficient quantity. There is no radioactivity associated with wireless telecommunications base stations or with any other energy source at non-ionizing frequencies.
Your report says that the maximum RF level at my house will be 1% of the standard. Does that mean that there’s a 1 in a hundred chance I’ll get sick?
No, it doesn’t, and understanding the terminology is vital to understanding such results. An exposure level of 1% means that, calculated using several conservative factors, the level is 100 times lower than the standard allows and, to quote from the latest version in the U.S., “[N]o measurable risk is associated with exposure levels less than … this standard.” We express the results in percent to show how they compare with the standard; anything less than 100% is, by definition, less than the standard and so has “no measurable risk.” An exposure level of 1% means there’s an additional 100-times margin of safety on top of the 50-times factor already in the standard; that equals a total margin of 5,000 times.
Isn’t radiation dangerous?
The term radiation should not be frightening. It does not imply radioactivity, which is the radiation of atomic particles due to the spontaneous decay of an unstable substance. Light and heat from an incandescent bulb are radiation, the ripples in a pond from a dropped pebble are radiation, and the sounds of speech are radiation, these last two being examples of radiation that is not electromagnetic. Radiation simply means dispersal.
Isn’t radiation used to kill cancer cells? Won’t the radio tower emit radiation that could kill normal cells, too, and make me sick?
Radiation therapy is one method of treating cancer, and that medical procedure uses ionizing radiation, which is recognized to damage cell structure and so is targeted at cancerous cells. This radiation is distinct from radio frequency radiation, which is non-ionizing and does not interact with living cells in this way. Radio towers do not emit ionizing radiation.
They have found problems with studies. The National Institute of Health is doing another study.
The studies have been published in peer-reviewed journals, and the particularly valuable studies used in developing the standards have been replicated by other researchers.
The National Institute of Health published its study on cell phones in 2001 and summarizes its major finding as follows:
“There was no indication of higher brain tumor risk among persons who had used hand-held cellular phones compared to those who had not used them. More importantly, there was no evidence of increasing risk with increasing years of use or average minutes of use per day, nor did brain tumors among cellular phone users tend to occur more often than expected on the side of the head on which the person reported using their phone. Specifically, there was no indication of increased risk associated with use of a cell phone for one hour or more per day, for five or more years, or for cumulative use of more than 100 hours. These findings pertain to all three tumor types considered (glioma, meningioma, and acoustic neuroma).”
How can statements be made about health risks from this radioactivity if they are still studying the issue?
There is no radioactivity associated with wireless telecommunications base stations or with any other energy source at non-ionizing frequencies. There have been hundreds of published, peer-reviewed studies over several decades concerning health risks from RF exposure, and this body of work is the basis for today’s standards.
In Europe, they consider our studies so bad that they have a prohibition of having sites near schools.
The RF exposure standards in the majority of the developed countries in Europe are very similar to the US standards. Just like in the US, some local areas in Europe may have siting guidelines for wireless base stations, where preference is given to some sites and disfavor to others.
What are the health effects of the standards level? Is it cumulative over time like cigarettes?
There are reported no adverse health effects at exposure levels equal to or below the FCC standard. Unlike the toxic substances in cigarette smoke or other known carcinogens, RF energy at low levels is not considered to have a cumulative effect over time. Exposure to RF fields below the FCC public limit is allowed 24 hours a day, 7 days a week.
There are three schools in this area. How will the tower affect the health of the students? How does EMF radiation affect children?
The FCC public limits include a 50-times safety factor intended to ensure a safe environment for all persons, whether young or old, healthy or infirm, large or small, for continuous operation of radio sources. So long as the exposure levels are in compliance of the FCC limits, there is presumed to be no effect to children and students. Here is what the latest standard (IEEE 2005) says:
“[N]o measurable risk is associated with exposure levels less than … this standard.” We express the results in percent to show how they compare with the standard; anything less than 100% is, by definition, less than the standard and so has “no measurement risk.”
Are there any other studies of how this would affect the wildlife in the area like raccoons and birds?
Yes. In fact, most of the in vivo (live organism) studies were conducted on animals, with the intent to extrapolate data derived from animal studies to humans. These studies used by the standard-setting bodies have not shown any harmful effects at RF exposure levels below the FCC limits. Please refer to the WHO International EMF project database for more information on such studies.
What are the RF exposure limits for base stations?
As shown in the table, separate limits apply for occupational and public exposure conditions, with the latter limits up to five times more restrictive. The standards incorporate a 50-times safety factor, to provide a prudent margin of protection for all members of the public – old or young, large or small, healthy or inform – for continuous exposure: 24 hours a day, seven days a week.
What are wireless telecommunications base stations or cell sites?
Wireless telecommunications base stations (also called cell sites) consist of two distinct parts: the electronic transceivers (also called radios or channels) that are connected to the traditional wired telephone lines, and the passive antennas that send the wireless signals created by the radios out to be received by customer mobile units. Base stations and mobile phones communicate with each other using RF energy. The RF energy is highest at the antenna, and drops significantly with distance, according to the inverse square law. For example, if the distance from the antenna is doubled then the RF energy will reduce by four times, and if the distance from the antenna in increased fen-fold, then the RF energy will reduce by 100 times.
Is exposure to RF energy regulated?
Yes. The U.S. Congress required (1996 Telecom Act) the Federal Communications Commission (FCC) to adopt a nationwide human exposure standard to ensure that its licensees do not, cumulatively, have a significant impact on the environment. The FCC adopted the limits from Report No. 86, “Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields,” published in 1986 by the Congressionally chartered National Council on Radiation Protection and Measurements (NCRP). Separate limits apply for occupational and public exposure conditions, with the latter limits generally five times more restrictive. The more recent standard, developed by the Institute of Electrical and Electronics Engineers and approved as American National Standard ANSI/IEEE C95.1-2006, “Safety Levels with Respect to Human Exposure to Radio Frequency Electromagnetic Fields, 3 kHz to 300 GHz,” includes similar limits. These limits apply for continuous exposures from all sources and are intended to provide a prudent margin of safety for all persons, regardless of age, gender, size, or health.
Why do cell phone companies need so many base stations?
If there were enough frequencies for each cell phone to have its own frequency, only a few, centrally located base stations would be required. However, since there are only a limited number of frequencies available, and since there could be tens of thousands of cell phones in an urban area, the same frequencies must be used over and over again. This is accomplished by establishing small areas, called cells, that have a small enough number of callers on the system so that each can have one of the available frequencies. If too many callers want to use their phones within one cell, they will get busy signals, and the carrier will get complaints, leading them to squeeze in an additional cell, making all the ones around it just a little smaller.
If a wireless carrier hired you to do a report, how can you remain unbiased in your reporting?
We’re hired by carriers, by landlords, and occasionally by cities and private individuals. As engineers, we deal with the facts as we know them, and any registered Professional Engineer would provide the same factual information. Our job is to project or measure RF power density levels and to compare them with the standards. Our computers don’t know who the client is when we’re calculating projected levels, and our calibrated meters don’t know who the client is when we’re measuring RF levels. The numbers are what they are.
Where did our RF standards come from?
The American National Standards Institute (ANSI) sets voluntary safety standards for products and materials ranging from motorcycle helmets to buildings. One particular ANSI standard, ANSI C95.1, sets guidelines for human exposures to RF energy. In 1992, this standard was revised to reflect the latest in research findings. The limit for public exposure was set at a level 50 times below the observed threshold of physical effects. While the possibility exists that there may be some as yet unknown adverse effects caused by a long-term mechanism, there have been no definitive findings in this area and no standards have been proposed for such low exposure conditions.
The Federal Communications Commission (FCC), the regulatory body for radio transmitting stations, has adopted the RF exposure guidelines published in a 1986 report by the National Council on Radiation Protection and Measurements (“NCRP-86”). The NCRP-86 recommendations are similar to those adopted in ANSI C95.1-1992, and at PCS frequencies are even more restrictive. Though the effective date for applying the NCRP standard to FCC licenses is September 1, 1997, the most conservative approach is to use the most restrictive applicable limit of the NCRPstandard to evaluate cellular, PCS, and other transmitting facilities.
The standards in the U.S. are very similar to those in Europe, Canada, Australia, etc, since all the standard-setting bodies around the world are looking at the same set of data from hundreds of published research studies, spanning decades of inquiry in industry and academia. The standards incorporate a 50-times safety factor, judged by those independent bodies to be a prudent margin of protection for all members of the public – old or young, large or small, healthy or inform – for continuous exposure: 24 hours a day, seven days a week.
Our reports and measurements always express RF exposure levels as a percentage of the FCC limit. For example, a proposed site may be 1% of the most restrictive public limit. This does not mean that there is a 1% health risk. Rather, it means that it is only 1% of the FCC’s RF limit.
What do all of these acronyms mean?
- EMF – electromagnetic field
- RF – radio frequency
- NIER – non-ionizing electromagnetic radiation
- ELF – extremely low frequency
Is there a scientific basis for the RF exposure standard?
Yes. Research spanning several decades has resulted in a large number of peer-reviewed scientific publications on the potential biological effects of RF exposure. When scientists examine all the published literature, they have found that no biological effects had been consistently shown below a certain RF exposure level. This scientific consensus, with the addition of a 50-fold safety factor, established the limit for continuous RF exposure of the general public.
What are RF exposure standards like in other countries?
The standards in most other developed countries are very similar to those in the U.S., since all the standard-setting bodies around the world are looking at the same set of data from hundreds of published research studies, spanning decades of inquiry in industry and academia. The standard by the International Commission on Non-Ionization Radiation Protection (ICNIRP), adopted by several European countries, includes similar exposure limits, as does the more recent standard, developed by the Institute of Electrical and Electronics Engineers (IEEE) C95.1-2005; this standard continues to be updated periodically: 1982, 1992, 1999, 2005.