FCC Regulations

Synopsis of FCC guidelines for evaluating the environmental effects of radio frequency radiation. This report and order were adopted and released on August 1, 1996.

Introduction

With the increased demand for wireless communication technology in the past decade, the FCC has had to amend its standard on radiation emissions from radio frequency transmitters operating at a frequency range of 300KHz - 100GHz. Its new guideline has been based on the ANSI/IEEE C95.1-1992 standards for evaluating effects of RF radiation on the environment, which is a more restrictive version of the ANSI/IEEE 1982 report. This new guideline includes Maximum Permissible Exposure (MPE) limits for the power density and magnetic and electric field strength from FCC regulated RF transmitters. The guideline also contains limits for the partial body absorption from portable transmitting devices.

The MPE limits were evaluated in terms of specific absorption rate (SAR), which is the mass-averaged , time averaged rate of energy absorption of a substance or tissue. The SAR is equal to the power dissipated per unit mass. It is calculated as the product of electrical conductivity and the square of the electric field divided by two times the mass density of tissue. The MPE limits originally were solely based on the SAR limit of 4 watts per kilogram and were later derived by incorporating safety factors resulting in at times more restrictive limits than the previous ones.

What is the history behind the establishment of RFEM exposure criteria?

Exposure criteria for RFEM radiation were first established in the early 1950's in an attempt to provide a margin of safety for industrial workers exposed to RFEM fields. At that time, little biological data was available for establishing exposure limits, except for the studies on energy absorption and transfer conducted by Schwan and students (Schwan and Piersol, 1954,1955; Schwan and Li, 1953, 1956). These studies concluded that the dangers from RFEM fields arose from the heating of tissue through the absorption of RFEM energy. Thus exposure criterion were based on the tolerable thermal loading of tissue.

In 1957, the first Tri Service Conference on the Biological Hazards of Microwave Radiation (Pattishell, 1975) established an occupational power density limit of 10mW/cm^2 at all microwave frequencies for industrial and military personnel. Many private corporations followed suit and established their own exposure guidelines for their workers. It was not until 1966 that the American Standards Institute (ANSI) created a subcommittee (Subcommittee C95-IV) that developed an exposure criteria similar to that of the Tri Service Conference for microwave frequencies from 10MHz to 100GHz. The ANSI standards remained unchanged, except for slight revisions, until 1982 when ANSI incorporated into their standards, the fact that the rate of energy absorption from RFEM fields was frequency dependent. Thus the ANSI C95.1-1982 protection guideline for radiofrequency electromagnetic radiation was established.

What is the FCC stance on low power devices?

In 1996, the FCC adopted the 1992 ANSI/IEEE standards in their RF emission regulations. The 1992 ANSI/IEEE standards report, however, did not exclude low power devices such as hand-held radios, cellular telephones, and radiating structures that were 2.5 cm from the body, due to their increased usage and therefore increased RF human exposure. This prompted the FCC to amend their exclusion clause permitting the exclusion of instruments with radiated power levels less than 7 watts at frequencies between 100KHz and 450MHz. At frequencies between 450MHz and 1500MHz, the radiated power limit is 7*(450/f) watts where f is frequency in MHz. The new standard was more restrictive on permissible environmental RF exposure, extended the range of frequency evaluated from 3KHz to 300GHz, established an exposure criteria for occupational (controlled ) and general public (uncontrolled) environments, and limits to RF field induced currents associated with shock and burns in the human body. The permissible SAR limit for the low power devices was reduced to 1.6W/kg for uncontrolled environments and was maintained at 8W/kg for controlled environments.

What other guideline did the FCC consult?

Besides the ANSI/IEEE report, the FCC also had available the NCRP (National Council on Radiation Protection and Measurement) criteria for RF radiation. Like ANSI/IEEE, NCRP established a threshold for the biological effects of radiation upon which the power density was based. The NCRP 1986 report had similar MPE limits for electric and magnetic field strength. Also, RF exposure was measured as a function of frequency for a "whole body average human", and the standards were established according to controlled ( occupational exposure) and uncontrolled environments (general population exposure).

The differences between the two guidelines were that the NCRP had more stringent standards for magnetic field strengths below 3MHz, which covered the radio frequency range of amateur, short wave, AM broadcasting , and marine and submarine communications. Limits were also stringent at power density levels at frequencies above 1500MHz which covered radar, space telemetry, microwave relay, and fixed and mobile radio. The NCRP had provisions (which were not used by the FCC) to reduce the exposure limit for workers around modulated RF carrier frequencies. They also suggested that the general population MPE limits for higher frequencies should be averaged over longer periods of time. The NCRP had specified limits for frequencies up to 100GHz, and the NCRP has the same limits as the ANSI/IEEE for low power density devices, but it doesn't recommend exclusions based on radiated power.

Hence the conclusion was that both guidelines had different standards at lower and higher frequencies, however, they concurred at the radio frequencies the FCC regulated.

What are the evaluations of other organizations on the ANSI/IEEE C95.1- 1992 report?

The guidelines of the ANSI/IEEE had been evaluated by other organizations such as the EPA (Environmental Protection Agency), the FDA (Food and Drug Administration), NIOSH (National Institute for Occupational Safety and Health), and OSHA (Occupational Safety and Health Administration).

The EPA agreed that the 1992 ANSI/IEEE was an improvement from the 1982 one, yet it found these subsequent provisions unacceptable: 1) MPE limits for power density at higher microwave frequencies . 2) Exposure limits for uncontrolled and controlled environments at the frequency range of 15GHz - 300GHz on the terms of a too low safety margin. 3) The terms for controlled and uncontrolled environments were not well defined and were not applicable to a specific population group.

The EPA recommended that the FCC adopt the NCRP MPE limits with the section of the 1992 ANSI/IEEE guidelines for localized exposure and induced and contact body currents. The EPA concluded that the NCRP MPE limits for power density and field strength was better for long term effects of RF exposure at higher microwave frequencies. Yet the EPA supported the ANSI/IEEE for induced and contact currents and protection for shocks and burns which was not included in the NCRP report because it was the result of research conducted after 1986. The EPA also supported the ANSI/IEEE standard for low power devices which was the same as the NCRP.

NIOSH, an organization that performs research for the health and safety of workers found the ANSI/IEEE MPE limits at higher frequencies unacceptable and recommend those of the NCRP, yet they supported ANSI/IEEE limits on reduced RF currents. The FDA had concerns about the radiated power exclusion in the ANSI/IEEE applied to hand held devices.

OSHA, an organization that has jurisdiction over federal regulations dealing with workers safety and health genuinely supported the ANSI/IEEE RF exposure guidelines. They wanted to include a worker protection program which offered training, medical monitoring, protective procedure, and engineering controls and signs for those working in a high radiation environment . OSHA however, objected to the ANSI/IEEE establishing two categories of standards, which OSHA argued, allowed a higher level of risk to the worker than the general public, because they are aware of the potential dangers of exposure.

What are the FCC emissions standards?

(A) Limits for Occupational/Controlled Exposure

Frequency
Range
(MHz) 		Electric Field
Strength
(V/m) 		Magnetic Field
Strength
(A/m)
Power Density
(mW/cm )
Averaging Time
(minutes)
0.3-3.0 614 1.63 (100)* 6
3.0-30 1842/f 4.89/f (900/f)* 6
30-300 61.4 0.163 1.0 6
300-1500 -- -- f/300 6
1500-100,000 -- -- 5 6

f = frequency in MHz
* = Plane-wave equivalent power density

(B) Limits for General Population/Uncontrolled Exposure

Frequency
Range
(MHz) 		Electric Field
Strength
(V/m) 		Magnetic Field
Strength
(A/m)
Power Density
(mW/cm )
Averaging Time
(minutes)
0.3-1.34 614 1.63 (100)* 30
1.34-30 824/f 2.19/f (180/f)* 30
30-300 27.5 0.073 0.2 30
300-1500 -- -- f/150 30
1500-100,000 -- -- 1.0 30

f = frequency in MHz
* = Plane-wave equivalent power density

NOTE 1 TO TABLE 1: Occupational/controlled limits apply in situations in which persons are exposed as a consequence of their employment provided those persons are fully aware of the potential for exposure and can exercise control over their exposure. Limits for occupational/controlled exposure also apply in situations when an individual is transient through a location where occupational/controlled limits apply provided he or she is made aware of the potential for exposure.

NOTE 2 TO TABLE 1: General population/uncontrolled exposures apply in situations in which the general public may be exposed, or in which persons that are exposed as a consequence of their employment may not be fully aware of the potential for exposure or can not exercise control over their exposure.

(Taken from FCC 96-326 Guidelines for Evaluating the Environmental Effects of Radiofrequency Radiation ET Docket No. 93-62)

What is averaging time?

Information from the NCRP no.86 report gives a reason as to why averaging time is part of the radiation criteria. Due to the wide variety of radiation source, in addition to varying frequency where the duty cycle of the generators varied from continuous to pulse waves with large and small duty cycles, one needed to differentiate the effects of continuous wave and pulse wave sources, the decision was to account for this uncertainty through the practice of time averaging. Hence the average of the power density of a period of (6 minutes for occupational and 30 minutes for the general public) was taken. The purpose of time averaging was to limit the mass normalized quantity of energy absorbed by the body to an SA of 144J/kg. The 30 minute time average period for the general public restricts the maximal SA to the population during the 30 minute time averaging period to no value larger than that experienced during the 6 minute time averaging period of occupational exposure.

Does the FCC have any antenna area and rooftop access restrictions?

FCC regulations for transmitter construction and installation require that the antennae area be protected from and be inaccessible to unauthorized personnel. The FCC does not have specific rules regarding fencing, and signs, and leaves the responsibility of reasonably protecting the antennae area to the licensee. Once the owner of the antennae has FCC certified transmitter equipment, and has complied with FCC limits on antennae radiation pattern, the FCC allows protection from attractive nuisances i.e. vandals, unsupervised children etc... The owner has no obligation to put up signs around the antennae area.

What are the FCC regulations on construction, marking, and lighting?

Antennae that are to be 200 feet above ground level or near airports must be reported to the FAA (federal aviation administration) so as to acquire the proper markings and painting so as to not interfere with the safety of air navigation. Thus in order to comply with FAA regulations, these towers must be painted with aviation surface white and orange, and both the top and bottom must be painted orange. The width of these bands will be constant and be calculated to be one seventh of the height of the tower. Antennae structures that are up to 150 feet off the ground shall have two 116 or 125 watt bulbs in a red aviation light globes at the top of the tower. The intensity of the bulbs should be at least 32.5 candelas. For towers above 150 feet, a 300m/m electric code beacon with two 620 or 700 watt bulbs with red aviation filters resulting in an intensity that should be no less than 2000 candelas in red is required.

References:

FCC , Guidelines for Evaluating the Environmental Effects of Radiofrequency Radiation ET Docket No. 93-62, 1996.

FCC, Rules and Regulations, Volume VII, Part 21, September 1982.

FCC, Rules and Regulations, Part 17, October 1982.

NCRP Report No. 86, Biological Effects and Exposure Criteria for Radiofrequency Electromagnetic Fields. National Council on Radiation Protection and Measurements, 1986.