FAQ on RF

  1. WHAT IS NON-IONIZING RADIATION?

“Ionization” is a process by which electrons are stripped from atoms and molecules.  This process can produce molecular changes that can lead to damage in biological tissue, including effects on DNA, the genetic material of living organisms.  This process requires interaction with high levels of electromagnetic energy.  Those types of electromagnetic radiation with enough energy to ionize biological material include X-radiation and gamma radiation.  Therefore, X-rays and gamma rays are examples of ionizing radiation. gamma radiation.  Therefore, X-rays and gamma rays are examples of ionizing radiation.

 

  1. IS RF RADIATION SOMETHING NEW TO US?

No, it is not. RF emission have been used for many other purposes, such as radio and television broadcasting. They have been around us for a very long time. We have been living with them for years without realizing that they are everywhere.

 

  1. WHAT ARE “RADIOFREQUENCY” AND MICROWAVE RADIATION?

Electromagnetic radiation consists of waves of electric and magnetic energy moving together (i.e., radiating) through space at the speed of light.  Taken together, all forms of electromagnetic energy are referred to as the electromagnetic “spectrum.”  Radio waves and microwaves emitted by transmitting antennas are one form of electromagnetic energy.  The RF part of the electromagnetic spectrum is generally defined as that part of the spectrum where electromagnetic waves have frequencies in the range of about 3 kilohertz (3 kHz) to 300 gigahertz (300 GHz).

They are collectively referred to as “radiofrequency” or “RF” energy or radiation.  Note that the term “radiation” does not mean “radioactive.”  Often, the terms “electromagnetic field” or “radiofrequency field” are used to indicate the presence of electromagnetic or RF energy.

 

  1. CAN RADIOFREQUENCY RADIATION CAUSE CANCER?

 Some studies have also examined the possibility of a link between RF exposure and cancer.  Results to date have been inconclusive.  While some experimental data have suggested a possible link between exposure and tumor formation in animals exposed under certain specific conditions, the results have not been independently replicated.  Many other studies have failed to find evidence for a link to cancer or any related condition.

 

5.    WHAT BIOLOGICAL EFFECTS ARE ASSOCIATED WITH EXPOSURE TO RADIOFREQUENCY (RF) ENERGY?

The biological effects from laboratory studies reported in scientific peer-reviewed literature include those related to changes in temperature, blood brain barrier, melatonin, calcium efflux, DNA damage and gene expression. However, not all these biological effects have been established or are considered to be health effects. For example, blood brain barrier and melatonin effects have not been consistently replicated. Studies on DNA strand breaks have also failed numerous independent attempts at confirmation and calcium efflux changes are considered to be more of a biological response than an adverse health effect.

Several laboratory studies have looked into whether RF energy can initiate and promote cancer. The overwhelming majority of these studies have found no evidence that RF energy damages DNA or that it is likely to act as an initiator or a promoter of carcinogenesis.

 

  1. WHAT LEVELS ARE SAFE FOR EXPOSURE TO RF ENERGY?

Exposure standards for radiofrequency energy have been developed by various organizations and governments.  Most modern standards recommend safe levels of exposure separately for the general public and for workers.  In the United States, the FCC has adopted and used recognized safety guidelines for evaluating RF environmental exposure since 1985.  Federal health and safety agencies, such as the EPA, FDA, the National Institute for Occupational Safety and Health (NIOSH) and the Occupational Safety and Health Administration (OSHA) have also been involved in monitoring and investigating issues related to RF exposure.

The FCC guidelines for human exposure to RF electromagnetic 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).  Both the NCRP exposure criteria and the IEEE standard were developed by expert scientists and engineers after extensive reviews of the scientific literature related to RF biological effects.  The exposure guidelines are based on thresholds for known adverse effects, and they incorporate prudent margins of safety.  In adopting the current RF exposure guidelines, the FCC consulted with the EPA, FDA, OSHA and NIOSH, and obtained their support for the guidelines that the FCC is using.

Many countries in Europe and elsewhere use exposure guidelines developed by the International Commission on Non-Ionizing Radiation Protection (ICNIRP).  The ICNIRP safety limits are generally similar to those of the NCRP and IEEE, with a few exceptions.  For example, ICNIRP recommends somewhat different exposure levels in the lower and upper frequency ranges and for localized exposure due to such devices as hand-held cellular telephones.  One of the goals of the WHO EMF Project (see above) is to provide a framework for international harmonization of RF safety standards.  The NCRP, IEEE and ICNIRP exposure guidelines identify the same threshold level at which harmful biological effects may occur, and the values for Maximum Permissible Exposure (MPE) recommended for electric and magnetic field strength and power density in both documents are based on this level.  The threshold level is a Specific Absorption Rate (SAR) value for the whole body of 4 watts per kilogram (4 W/kg).

In addition, the NCRP, IEEE and ICNIRP guidelines for maximum permissible exposure are different for different transmitting frequencies.  This is due to the finding (discussed above) that whole-body human absorption of RF energy varies with the frequency of the RF signal.  The most restrictive limits on whole-body exposure are in the frequency range of 30-300 MHz where the human body absorbs RF energy most efficiently when the whole body is exposed.  For devices that expose only part of the body, such as mobile phones, different exposure limits are specified (see below), but these limits are based on the same underlying threshold level.

The exposure limits used by the FCC are expressed in terms of SAR, electric and magnetic field strength and power density for transmitters operating at frequencies from 100 kHz to 100 GHz.  The applicable limits depend upon the type of sources (e.g, whether a cellphone or a broadcast transmitting antenna).

 

  1. HOW SAFE ARE MOBILE AND PORTABLE PHONES?

In recent years, publicity, speculation, and concern over claims of possible health effects due to RF emissions from hand-held wireless telephones prompted various research programs to investigate whether there is any risk to users of these devices  There is no scientific evidence to date that proves that wireless phone usage can lead to cancer or a variety of other health effects, including headaches, dizziness or memory loss.  However, studies are ongoing and key government agencies, such as the Food and Drug Administration (FDA) continue to monitor the results of the latest scientific research on these topics.  Also, as noted above, the World Health Organization has established an ongoing program to monitor research in this area and make recommendations related to the safety of mobile phones.

The FDA, which has primary jurisdiction for investigating mobile phone safety, has stated that it cannot rule out the possibility of risk, but if such a risk exists, “it is probably small.”  Further, it has stated that, while there is no proof that cellular telephones can be harmful, concerned individuals can take various precautionary actions, including limiting conversations on hand-held cellular telephones and making greater use of telephones with hands-free kits where there is a greater separation distance between the user and the radiating antenna.

The Government Accountability Office (GAO) prepared a report of its investigation into safety concerns related to mobile phones.  The report concluded that further research is needed to confirm whether mobile phones are completely safe for the user, and the report recommended that the FDA take the lead in monitoring the latest research results.

The FCC’s exposure guidelines specify limits for human exposure to RF emissions from hand-held mobile phones in terms of Specific Absorption Rate (SAR), a measure of the rate of absorption of RF energy by the body.  The safe limit for a mobile phone user is an SAR of 1.6 watts per kg (1.6 W/kg), averaged over one gram of tissue, and compliance with this limit must be demonstrated before FCC approval is granted for marketing of a phone in the United States.  Somewhat less restrictive limits, e.g., 2 W/kg averaged over 10 grams of tissue, are specified by the ICNIRP guidelines used in Europe and most other countries.

 

  1. DO “HANDS-FREE” EAR PIECES FOR MOBILE PHONES REDUCE EXPOSURE TO RF EMISSIONS?  WHAT ABOUT MOBILE PHONE ACCESSORIES THAT CLAIM TO SHIELD THE HEAD FROM RF RADIATION?

“Hands-free” kits with ear pieces can be used with cell phones for convenience and comfort.  In addition, because the phone, which is the source of the RF emissions, will not be placed against the head, absorption of RF energy in the head will be reduced.  Therefore, it is true that use of an ear piece connected to a mobile phone will significantly reduce the rate of energy absorption (or “SAR”) in the user’s head.  On the other hand, if the phone is mounted against the waist or other part of the body during use, then that part of the body will absorb RF energy.  Even so, mobile phones marketed in the U.S. are required to meet safety limit requirements regardless of whether they are used against the head or against the body.  So either configuration should result in compliance with the safety limit.  Note that hands-free devices using Bluetooth technology also include a wireless transmitter; however, the Bluetooth transmitter operates at a much lower power than the cell phone.

A number of devices have been marketed that claim to “shield” or otherwise reduce RF absorption in the body of the user.  Some of these devices incorporate shielded phone cases, while others involve nothing more than a metallic accessory attached to the phone.  Studies have shown that these devices generally do not work as advertised.  In fact, they may actually increase RF absorption in the head due to their potential to interfere with proper operation of the phone, thus forcing it to increase power to compensate.  The Federal Trade Commission has published a Consumer Alert regarding these shields on its website at: FTC Consumer Information.

 

  1. CAN MOBILE PHONES BE USED SAFELY IN HOSPITALS AND NEAR MEDICAL TELEMETRY EQUIPMENT?

The FCC does not normally investigate problems of electromagnetic interference from RF transmitters to medical devices.  Some hospitals have policies, which limit the use of cell phones, due to concerns that sensitive medical equipment could be affected.  The FDA’s Center for Devices and Radiological Health (CDRH) has primary jurisdiction for medical device regulation.

 

  1. ARE WIRELESS CELLULAR AND PCS TOWERS AND ANTENNAS SAFE?

Cellular wireless radio services transmit using frequencies between 824 and 894 megahertz (MHz).  Transmitters in the Personal Communications Service (PCS) use frequencies in the range of 1850-1990 MHz.  More recently, advanced wireless services have been or are being introduced that transmit at frequencies in the 600, 700, 800, 1695-1780, 1915-1920, 1995-2020, 2110-2200 MHz spectrum ranges. Antennas used for cellular and PCS transmissions are typically located on towers, water tanks or other elevated structures including rooftops and the sides of buildings.  The combination of antennas and associated electronic equipment is referred to as a cellular or PCS “base station” or “cell site.”  Typical heights for free-standing base station towers or structures are 50-200 feet.  A cellular base station may utilize several “omni-directional” antennas that look like poles, 10 to 15 feet in length, although these types of antennas are less common in urbanized areas.

In urban and suburban areas, cellular and PCS service providers commonly use “sector” antennas for their base stations.  These antennas are rectangular panels, e.g., about 1 by 4 feet in size, typically mounted on a rooftop or other structure, but they are also mounted on towers or poles.  Panel antennas are usually arranged in three groups of three each.  It is common that not all antennas are used for the transmission of RF energy; some antennas may be receive-only.

At a given cell site, the total RF power that could be radiated by the antennas depends on the number of radio channels (transmitters) installed, the power of each transmitter, and the type of antenna.  While it is theoretically possible for cell sites to radiate at very high power levels, the maximum power radiated in any direction usually does not exceed 500 watts.

The RF emissions from cellular or PCS base station antennas are generally directed toward the horizon in a relatively narrow pattern in the vertical plane.  In the case of sector (panel) antennas, the pattern is fan-shaped, like a wedge cut from a pie.  As with all forms of electromagnetic energy, the power density from the antenna decreases rapidly as one moves away from the antenna.  Consequently, ground-level exposures are much less than exposures if one were at the same height and directly in front of the antenna.

Measurements made near typical cellular and PCS installations, especially those with tower-mounted antennas, have shown that ground-level power densities are hundreds to thousands of times less than the FCC’s limits for safe exposure.   This makes it extremely unlikely that a member of the general public could be exposed to RF levels in excess of FCC guidelines due solely to cellular or PCS base station antennas located on towers or monopoles.

When cellular and PCS antennas are mounted at rooftop locations it is possible that a person could encounter RF levels greater than those typically encountered on the ground.  However, once again, exposures approaching or exceeding the safety guidelines are only likely to be encountered very close to and directly in front of the antennas.  For sector-type antennas, RF levels to rear are usually very low.

 

  1. ARE CELLULAR AND OTHER RADIO TOWERS LOCATED NEAR HOMES OR SCHOOLS SAFE FOR RESIDENTS AND STUDENTS?

As discussed above, radiofrequency emissions from antennas used for cellular and PCS transmissions result in exposure levels on the ground that are typically thousands of times below safety limits.  These safety limits were adopted by the FCC based on the recommendations of expert organizations and endorsed by agencies of the Federal Government responsible for health and safety.  Therefore, there is no reason to believe that such towers could constitute a potential health hazard to nearby residents or students.

Other antennas, such as those used for radio and television broadcast transmissions, use power levels that are generally much higher than those used for cellular and PCS antennas.  Therefore, in some cases there could be a potential for higher levels of exposure to persons on the ground.  However, all broadcast stations are required to demonstrate compliance with FCC safety guidelines, and ambient exposures to nearby persons from such stations are typically well below FCC safety limit.