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2011, Sep-12

Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

The following document compares the Radio Frequency Radiation (RFR) exposure limits specified by the Federal Communications Commission (FCC) and the International Council on Non-Ionizing Radiation Protection (ICNIRP) agencies who have conducted studies in this field. The comparison is done using field strength in terms of equivalent power density in mW/cm2 of the Electric (E) and Magnetic (H) fields for occupational (controlled) and public (uncontrolled) exposure, as well as the Specific Absorption Rate (SAR) in W/Kg as defined by both organizations.

ICNIRP Radiation Limits

The International Council on Non-Ionizing Radiation Protection (ICNIRP) standard provides a two-tier set of RF exposure limits. The ICNIRP standard is used in most European countries and is gaining acceptance in many other countries throughout the world outside of North America. The higher tier is referred to as Occupational while the more restrictive tier is referred to as General Population.

The ICNIRP standard has exposure limits for electric fields and magnetic fields that are whole-body and time averaged over a 6 minutes period. Exposure limits are given from DC to 300 GHz. Exposure limits for the magnetic (H) field are relaxed below 100 MHz since the exposure limits at lower frequencies are based more on electro-stimulation than body heating and both induced and contact currents are related to the strength of the electric field. There are also limits for induced currents and contact currents.

FCC MPE Limits

The FCC adopted new regulations in 1997. They became fully effective on September 1, 2000. It is a two-tier standard with frequency-dependent exposure limits, referred to as Maximum Permissible Exposure (MPE) limits. Time averaging over 6 minutes for Occupation/Controlled exposure below 15 GHz is specifically called out. Unlike other standards and regulations, the FCC does not allow time averaging for General Population/Uncontrolled exposure. The exception is if the environment is “controlled”, which means time averaging rarely applies for general population areas. Although spatial averaging is not specified, the FCC is on record as fully accepting and supporting spatial averaging. There is, however, no specific spatial-averaging method specified. There are currently no limits for induced currents or contact currents.

ICNIRP vs. FCC

Tables 1 and 2 which were derived from the graphs shown in Appendix I, show that the ICNIRP exposure limits in the range of 400 to 2000MHz are slightly more restrictive when compared with the US FCC limits, in that the former specifies f/400 and f/2000 for calculating the equivalent power density for occupational and public exposure, compared with f/300 and f/1500 for the US FCC.

Table1

Table2

However as the following sample calculation illustrates the difference in the limits for a measurement of frequency of 850 MHz is extremely small; and even smaller for the 1900 MHz band.

Table2a

This indicates that for exposure to an emission of 850 MHz the US FCC MPE limit would allow 0.566 – 0.425 = 0.141 mW/cm2 more exposure (for the general population) when compared with the ICNIRP MPE limit.

However it should be noted that the ICNIRP MPE limit for localized Specific Absorption Rate (SAR) for head and trunk exposure in the range 10 MHz to 10 GHz is 2 W/kg while the FCC limit in this range is 1.6 W/kg (This will be further discussed in the next section).

SAR Limits

ICNIRP SAR limits

The independent scientific organization ICNIRP investigates potential health effects of NIR and develops international guidelines on exposure limits. These guidelines form the basis of many national standards and regulations. The ICNIRP guidelines are based on consensus of all the existing scientific results and provide protection against all established health effects of NIR exposure.

In the frequency range from 10 MHz to 10 GHz, the fundamental exposure limits, which are called basic restrictions, are expressed as SAR limits. SAR is a measure of the rate of absorption of electromagnetic energy in tissue during exposure. There are two sets of limits, one for general public exposure and another for occupational exposure. Furthermore, there are three different SAR limits; whole-body averaged SAR, localized SAR in the head and trunk, and localized SAR in the limbs. The averaging mass for the latter two limits is 10 g of tissue and these are primarily applied for partial-body and near-field exposure situations.

Table 3 below shows the ICNIRP general public SAR restrictions. The localized SAR limits are those applicable to low-power mobile communication terminals that are used close to the body by the general public. Most important is the limit for the head and trunk, 2 W/kg in a 10 g of tissue, since most devices are held close to these parts of the body. The whole-body averaged SAR limit can never be exceeded by this type of devices.

The averaging time is 6 minutes, which means that higher exposure levels are accepted for shorter exposure times than six minutes.

Table3

FCC SAR limits - ANSI / IEEE

The FCC has adopted the SAR limits from the U.S. standard ANSI/IEEE C95.1-1992 in its RF exposure rules. The SAR limits are the same as the ICNIRP levels except for the limit for the head and trunk, which is slightly lower, 1.6 W/kg. The averaging mass and time are also different, 1 g and 30 minutes, respectively. The current FCC rules were published in 1996 and SAR testing is required for all mobile telephones to be used in the United States.

Table4

ICNIRP vs. ANSI/IEEE

According to Tables 3 and 4, the SAR limits of ICNIRP and ANSI/IEEE are generally the same except for the limits for head and trunk. However, the localized averaging SAR values for the two standards cannot be directly inter-converted as the two sets of limits use different averaging mass and averaging time. It is worth noting that both the ICNIRP and ANSI/IEEE have applied large safety margins in establishing the SAR limits.

Appendix 1

Graph1

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Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

Table2a

Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

Table3

Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

Table4

Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

Table2

Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

Table1

Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

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Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

Graph1

Comparison of Radio Frequency Radiation MPE Limits, FCC and ICNIRP

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