Steve Dillingham and Nick Cobb

A look at the exposure-limit requirements for the United States and Europe can help ensure that products will meet the testing requirements for both.

Even with a mutual recognition agreement in place between the United States and Europe, manufacturers must still meet individual country limits for human exposure to electromagnetic fields. This article compares the limits for Europe and the United States. Such a comparison should enable the test results of specific absorption rate (SAR) and maximum permissible exposure (MPE) to be evaluated against the compliance requirements for different countries. This discussion does not cover the practical aspects of SAR and MPE testing.

Europe

The requirements for Europe are rather vague. One document, "Council Recommendation of 12 July 1999 on the Limitation of Exposure of the General Public to Electromagnetic Fields (0 Hz to 300 GHz)" [1999/519/EC], gives recommendations on appropriate physical quantities.¹ These recommendations provide for a high level of health protection against exposure to electromagnetic fields. The Council also recommends that member states adopt a framework of basic restrictions and reference levels as contained in the document. Although this document presents only recommendations, Article 3.1 of the Radio and Telecommunications Terminal Equipment (R&TTE) Directive (1999/5/EC) states, "the following essential requirements are applicable to all apparatus:

• The protection of the health and safety of the user and any other person, including the objectives with respect to safety requirements contained in Directive 73/23/EEC [LV Directive], but with no voltage limit applying.
• The protection requirements with respect to electromagnetic compatibility contained in Directive 89/336/EEC."²

The requirements of the Low Voltage Directive effectively cover all safety issues, which includes exposure to radio frequencies.³ Compliance with the appropriate harmonized standard gives a legal presumption of conformity with the requirements. However, only one harmonized standard currently addresses the electromagnetic radiation issue: EN 60215:1989/A2:1994, "Safety Requirements for Radio Transmitting Equipment."⁴ The absence of harmonized standards does not preclude the obligation to comply with the basic safety requirement, and manufacturers must adhere to any other standards currently in preparation and close to publication.

Part 22.1 of EN 60215 requires measurement of non- ionizing radiation levels over the frequency range of 30 MHz to 30 GHz. In addition to setting levels, the standard notes the following:

• "The limits given in this sub-clause relate to the performance of the equipment. In certain cases lower limits and/or a maximum exposure time should be observed for personnel in order to comply with the national exposure standards of the country in which the transmitter is operating."
• This clause allows for Recommendation 1999/519/EC to be used over the 30 MHz to 30 GHz frequency range. The recommendation is based on the advice of the International Commission on Non-Ionising Radiation Protection (ICNIRP), and has been endorsed by the European Commission's Scientific Steering Committee.

Standards Under Development. A mandate has been issued by the European Commission M/305 to develop standards to cover the MPE and SAR aspects of Article 3.1(a) of the R&TTE Directive.⁵ The following standards are currently under development:

• Final Draft prEN 50371. "Generic standard to demonstrate the compliance of low-power electronic and electrical apparatus with the basic restrictions related to human exposure to electromagnetic fields (10 MHz–300 GHz)—General public." (Expected date of adoption April 2002.)
• Draft prEN 50xYY-2. "Product standard to demonstrate the compliance of radio base stations and fixed terminal stations for wireless telecommunication systems with the reference levels or the basic restrictions related to human exposure to radio-frequency electromagnetic fields (110 MHz–40 GHz)."
• prEN 50360. Basic standard that (in conjunction with the product-family standard prEN 50361) covers devices that: (a) transmit in the frequency range 300 MHz to 3 GHz, and (b) are intended to be used with the radiating antenna close to the human ear.
• prEN 50364. Basic standard that (in conjunction with the product-family standard prEN 50357) covers devices that: (a) transmit in the frequency range 0 Hz to 10 GHz, and (b) are intended for electronic article surveillance (EAS), radio-frequency identification (RFID), and similar applications.
• prEN 50xxx. This will be a generic standard that can be used to demonstrate compliance for low-power devices, which, due to the power level (<20 mW), are deemed to comply with the basic restrictions of the ICNIRP guideline.

Once the standards above have been harmonized, published in the Official Journal of the European Communities (OJEC), manufacturers can self-declare compliance with the safety requirements of the R&TTE Directive. Until then, a technical construction file must be generated and submitted to a notified body for review. Most of the standards described above are in initial-draft form, so publication is not expected in the near future.

An ETSI technical report (TR), Draft TR 101 870, "Fixed radio transmitter sites; Exposure to Non-Ionising Electromagnetic Fields; Guidelines for Working Conditions," is being produced to offer guidance to limit the exposure of installers and maintenance engineers to RF fields while working on base stations. However, there are no guidelines similar to those produced by the FCC detailed below in "Application of the FCC rules."

United States

The situation in the United States is more straightforward than in Europe in that licensed and unlicensed transmitters are subject to FCC certification requirements. These requirements include the evaluation of a product against FCC's radio-frequency radiation exposure limits. These requirements are found in Rule Parts 1.1310, 2.1091, and 2.1093.⁶

The FCC requirements are generally based on recommended exposure guidelines published by the National Council on Radiation Protection and Measurements (NCRP) in "Biological Effects and Exposure Criteria for Radio-Frequency Electromagnetic Fields." In the frequency range from 100 to 1500 MHz, exposure limits for field strength and power density are also generally based on guidelines recommended by the American National Standards Institute (ANSI) in Section 4.1 of "IEEE Standard for Safety Levels with Respect to Human Exposure to Radio-Frequency Electromagnetic Fields, 3 kHz to 300 GHz."⁷

On June 29, 2001, FCC issued FCC Public Notice DA 01-1557 announcing a revised Supplement C to OET Bulletin 65, which updates FCC guidelines for MPE and SAR measurements and evaluation of RF exposure on mobile and portable devices.⁸ The revision provides manufacturers requiring equipment authorization with the latest guidance on complying with the FCC MPE and SAR requirements, including test procedures. However, the test procedures are not mandatory provided the method used by the manufacturer can be technically justified. Additionally, the revised supplement is to provide the basis for training telecommunications certification bodies (TCBs) in MPE and SAR requirements to enable their scopes to be increased. TCB training is planned for August 27–29, 2001, with TCBs to begin processing applications October 1, 2001.

Application of European Recommendation 1999/519/EC

The Recommendation 1999/519/EC approach breaks the requirements into two restrictions for the assessment of possible health effects of electromagnetic fields.

Basic Restrictions. The restrictions on exposure to time-varying electric, magnetic, and electromagnetic fields that are based directly on established health effects and biological considerations are termed basic restrictions. Depending upon the frequency of the field, the physical quantities used to specify these restrictions are magnetic flux density (B), current density (J), specific energy absorption rate (SAR), and power density (S). Magnetic flux density and power density can be readily measured in exposed individuals.

Depending on frequency, the following physical quantities (dosimetric quantities) are used to specify the basic restrictions on electromagnetic fields:

• Between 0 and 1 Hz, basic restrictions are provided for magnetic flux density for static magnetic fields (0 Hz) and for current density for time-varying fields up to 1 Hz. These restrictions prevent effects on the cardiovascular and central nervous systems.
• Between 1 Hz and 10 MHz, basic restrictions are provided for current density to prevent effects on nervous-system functions.
• Between 100 kHz and 10 GHz, basic restrictions on SAR are provided to prevent whole-body heat stress and excessive localized heating of tissues.
• Between 100 kHz and 10 MHz, restrictions on both current density and SAR are provided.
• Between 10 and 300 GHz, basic restrictions on power density are provided to prevent heating in tissue at or near the body surface.

The basic restrictions, given in Table I, are set so that they account for uncertainties related to individual sensitivities, environmental conditions, and variations due to age and health.

 

Frequency Range	Magnetic Flux Density (mT)	Current Density (mA/m2) (rms)	Whole Body Average SAR (W/kg)	Localized SAR (Head and Trunk) (W/kg)	Localized SAR (limbs) (W/kg)	Power Density, S (W/m2)
0 Hz	40	—	—	—	—	—
0–>1 Hz	—	8	—	—	—	—
1–4 Hz	—	8/f	—	—	—	—
4–1000 Hz	—	2	—	—	—	—
1.0–100 kHz	—	f/500	—	—	—	—
0.1–10 MHz	—	f/500	0.08	2	4	—
0.01–10 GHz	—	—	0.08	2	4	—
10–300 GHz	—	—	—	—	—	10
Notes: 1. f is the frequency in Hz. 2. The basic restriction on the current density is intended to protect against acute exposure effects on central-nervous-system tissues in the head and trunk of the body and includes a safety factor. The basic restrictions for ELF fields are based on established adverse effects on the central nervous system. Such acute effects are essentially instantaneous and there is no scientific justification to modify the basic restrictions for exposure of short duration. However, since the basic restriction refers to adverse effects on the central nervous system, this basic restriction may permit higher current densities in body tissues other than the central nervous system under the same exposure conditions. 3. Because of electrical inhomogeneity of the body, current densities should be averaged over a cross section of 1 cm 2 perpendicular to the current direction. 4. For frequencies up to 100 kHz, peak current density values can be obtained by multiplying the rms value by (check) 2 (~1.414). For pulses of duration t, the equivalent frequency to apply in the basic restrictions should be calculated as f = 1/(2t p). 5. For frequencies up to 100 kHz and for pulsed magnetic fields, the maximum current density associated with the pulses can be calculated from the rise/fall times and the maximum rate of change of magnetic flux density. The induced current density can then be compared with the appropriate basic restriction. 6. All SAR values are to be averaged over any 6-minute period. 7. Localized SAR averaging mass is any 10 g of contiguous tissue; the maximum SAR so obtained should be the value used for the estimation of exposure. These 10 g of tissue are intended to be a mass of contiguous tissue with nearly homogeneous electrical properties. In specifying a contiguous mass of tissue, it is recognized that this concept can be used in computational dosimetry but may present difficulties for direct physical measurements. A simple geometry such as cubic tissue mass can be used provided that the calculated dosimetric quantities have conservative values relative to the exposure guidelines. 8. For pulses of duration tp, the equivalent frequency to apply in the basic restrictions should be calculated as f = 1/(2tp). Additionally, for pulsed exposures, in the frequency range 0.3 to 10 GHz and for localized exposure of the head, in order to limit and avoid auditory effects caused by thermoelastic expansion, an additional basic restriction is recommended. This is that the SA should not exceed 2 mJ kg–1 averaged over 10 g of tissue.

Table I. Basic restrictions for electric, magnetic, and electromagnetic fields (0 Hz to 300 GHz).

Reference Levels. These levels (shown in Table II) are provided for practical exposure-assessment purposes to determine whether the basic restrictions are likely to be exceeded. Some reference levels are derived from relevant basic restrictions using measurements or computational techniques. Some reference levels address perception and adverse indirect effects of exposure to electromagnetic fields.

 

E-field Strength (V/m)	H-field Strength (A/m)	B-field (µT)	Frequency Range	Equivalent Plane-Wave Power Density Seq(W/m2)
0–1 Hz	—	3.2 x 104	4 x 104	—
1–8 Hz	10,000	3.2 x 104/f2	4 x 104/f2	—
8–25 Hz	10,000	4000/f	5000/f	—
25–800 Hz	250/f	4/f	5/f	—
0.8–3 kHz	250/f	5	6.25	—
3–150 kHz	87	5	6.25	—
0.15–1 MHz	87	0.73/f	0.92/f	—
1–10 MHz	87/f1/2	0.73/f	0.92/f	—
10–400 MHz	28	0.073	0.092	2
0.4–2 GHz	1375 f1/2	0.0037 f1/2	0.0046 f1/2	f/200
2–300 GHz	61	0.16	0.20	10
Notes: 1. f as indicated in the frequency range column. 2. For frequencies between 100 kHz and 10 GHz, Seq, E2, H2, and B2 are to be averaged over any 6-minute period. 3. For frequencies exceeding 10 GHz, Seq, E2, H2, and B2 are to be averaged over any 68/f1.05-minute period (f in GHz). 4. No E-field value is provided for frequencies <1 Hz, which are effectively static-electric fields.

Table II. Reference levels for electric, magnetic, and electromagnetic fields (0 Hz to 300 GHz, unperturbed rms values).

The derived quantities are electric field strength (E), magnetic field strength (H), magnetic flux density (B), power density (S), and limb current (IL). Quantities that address perception and other indirect effects are (contact) current (IC) and, for pulsed fields, specific energy absorption (SA).

In any particular exposure situation, measured or calculated values of any of these quantities can be compared with the appropriate reference level. A respect of the reference level will ensure respect of the relevant basic restriction. If the measured value exceeds the reference level, it does not necessarily follow that the basic restriction will be exceeded. Under such circumstances, however, it is critical to establish whether the basic restriction has been respected.

Application of FCC Rules

FCC exposure limits (limits for maximum permissible exposure) are divided into two main categories: "Limits for Occupational/Controlled Exposures" and "Limits for General Population/Uncontrolled Exposure."⁹ FCC rule parts also address the issue based on the type of transmitter, either mobile or portable. Before an evaluation can proceed, the category the equipment falls into must be determined.

Occupational and Controlled Exposures. Occupational and controlled limits apply in situations in which persons are exposed as a consequence of employment, provided those persons are fully aware of the potential for exposure and can exercise control over their exposure. Limits for occupational and controlled exposure also apply in situations in which individuals are transient through a location where occupational and controlled limits apply, provided they are aware of the potential for exposure (see Table III).

 

Frequency Range (MHz)	Electric-Field Strength (V/m)	Magnetic-Field Strength (A/m)	Power Density (mW/cm2)	Averaging Time (min)
0.3–3.0	614	1.63	*(100)	6
3.0–30	1842/f	4.89/f	*(900/f2)	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.

Table III. Limits for occupational and controlled exposures.

General Population and Uncontrolled Exposure. General population and uncontrolled exposures apply in situations in which either the general public could be exposed or in which persons exposed as a consequence of employment may not be fully aware of the potential for exposure or cannot exercise control over exposure (see Table IV).

 

Frequency Range (MHz)	Electric-Field Strength (V/m)	Magnetic-Field Strength (A/m)	Power Density (mW/cm2)	Averaging Time (min)
0.3–3.0	614	1.63	*(100)	30
3.0–30	842/f	2.19/f	*(180/f2)	30
30–300	27.5	0.073	0.2	30
300–1500	—	—	f/1500	30
1500–100,000	—	—	1.0	30
f = frequency in MHz. * = Plane-wave equivalent power density.

Table IV. Limits for general population and uncontrolled exposure.

Mobile Devices. FCC Rule Part 2.1091 defines a mobile device as a "transmitting device designed to be used in other than 'fixed locations' and to generally be used in such a way that a separation distance of at least 20 cm is normally maintained between the transmitter's radiating structure(s) and the body of the user or nearby persons." The definition of fixed location is a device that is physically secured at one location and is not easily movable to another location.

Transmitting devices designed to be used by consumers or workers that can be easily relocated, such as wireless devices associated with a personal computer, are considered to be mobile devices if they meet the 20-cm separation requirement. Part 2.1091(c) details the various services and the specific power output and exposure requirements.

Portable Devices. Part 2.1093 defines a portable device as a transmitting device designed to be used while the radiating structures of the device are within 20 cm of the body of the user. They must meet the requirements of the radio-frequency radiation exposure limits in Part 1.1310 if applicable.

Exposure Limits Comparison. Tables V and VI allow a rough comparison to be made of the European and U.S. requirements for maximum exposure levels. Table V provides a comparison between the European reference levels and the FCC occupational and controlled-exposure levels. Both exposure tables use an averaging time of 6 minutes.

 

Frequency Range	European Reference Levels			FCC Occupational and Controlled-Exposure Levels
	E-field Strength (V/m)	H-field Strength (A/m)	Equivalent Plane-Wave Power Density Seq(W/m2)	E-field Strength (V/m)	H-field Strength (A/m)	Density (mW/cm2)
0–1 Hz	—	3.2 x 104	—	614	1.63	*(100)
1–8 Hz	10,000	3.2 x 104/f2	—	614	1.63	*(100)
8–25 Hz	10,000	4000/f	—	614	1.63	*(100)
25–800 Hz	250/f	4/f	—	614	1.63	*(100)
0.8–3 kHz	250/f	5	—	614	1.63	*(100)
3–150 kHz	87	5	—	614	1.63	*(100)
0.15–1 MHz	87	0.73/f	—	614	1.63	*(100)
1–3 MHz	87/f1/2	0.73/f	—	614	1.63	*(100)
3–10 MHz	87/f1/2	0.73/f	—	1842/f	4.89/f	*(900f2)
10–30 MHz	28	0.073	2 [0.2 mW/cm2]	1842/f	4.89/f	*(900f2)
30–300 MHz	28	0.073	2 [0.2 mW/cm2]	61.4	0.163	1.0 [10 W/m2]
300–400 MHz	28	0.073	2 [0.2 mW/cm2]	—	—	f/300
0.4–1.5 GHz	1375 f1/2	0.0037 f1/2	f/200	—	—	f/300
1.5–2.0 GHz	1375 f1/2	0.0037 f1/2	f/200	—	—	5 [50 W/m2]
2–100 GHz	61	0.16	10 [1 mW/cm2]	—	—	5 [50 W/m2]
100–300 GHz	61	0.16	10 [1 mW/cm2]	—	—	—
* = Equivalent plane-wave power. f = frequency as indicated in the frequency column.

Table V. A comparison of European reference levels and FCC occupational levels.

Table VI compares the European reference levels and the FCC general-population and uncontrolled-exposure levels. The European reference levels are averaged over 6 minutes, and the FCC general-population and uncontrolled-exposure levels are averaged over 30 minutes. It should be noted that European reference levels use W/m² for Equivalent plane wave power density whereas FCC uses mW/cm². The conversion from one to the other (10,000 cm² = 1 m²) should be carried out after the frequency component of the formula has been applied.

Frequency Range	European Reference Levels			FCC General-Population/Uncontrolled-Exposure Levels
	E-field Strength (V/m)	H-field Strength (A/m)	Equivalent Plane-Wave Power Density Seq(W/m2)	E-field Strength (V/m)	H-field Strength (A/m)	Density (mW/cm2)
0–1 Hz	—	3.2 x 104	—	614	1.63	*(100)
1–8 Hz	10,000	3.2 x 104/f2	—	614	1.63	*(100)
8–25 Hz	10,000	4000/f	—	614	1.63	*(100)
25–800 Hz	250/f	4/f	—	614	1.63	*(100)
0.8–3 kHz	250/f	5	—	614	1.63	*(100)
3–150 kHz	87	5	—	614	1.63	*(100)
0.15–1 MHz	87	0.73/f	—	614	1.63	*(100)
1–1.34 MHz	87/f1/2	0.73/f	—	614	1.63	*(100)
1.34–10 MHz	87/f1/2	0.73/f	—	842/f	2.19/f	*(180f2)
10–30 MHz	28	0.073	2 [0.2 mW/cm2]	842/f	2.19/f	*(180f2)
30–300 MHz	28	0.073	2 [0.2 mW/cm2]	27.5	0.073	0.2 [2 W/m2]
300–400 MHz	28	0.073	2 [0.2 mW/cm2]	—	—	f/1500
0.4–1.5 GHz	1375 f1/2	0.0037 f1/2	f/200	—	—	f/1500
1.5–2 GHz	1375 f1/2	0.0037 f1/2	f/200	—	—	1 [10 W/m2]
2–100 GHz	61	0.16	10 [1 mW/cm2]	—	—	1 [10 W/m2]
100–300 GHz	61	0.16	10 [1 mW/cm2]	—	—	—
* = Equivalent plane-wave power. f = frequency as indicated in the frequency column.

Table VI. A comparison of European reference levels and FCC general population and uncontrolled exposure levels.

Tables V and VI allow the reader to determine a worst-case FCC–EU combined limit, which, if met, may allow one set of tests to cover both the U.S. and European requirments.

Conclusion

Comparing the exposure measurement requirements for the United States and Europe helps determine whether a device that has met one set of requirements will meet the other set. Such a comparison is not meant to justify not testing for a particular market, but rather to provide an indication as to whether problems will arise when testing is carried out.

In the short term, the worst-case combined FCC–EU limit should provide for authorization in the United States (provided the appropriate test methods are used) and for approval in Europe. This may also be the case in the longer term, depending on the test methods described in the European harmonized standards still under development. However, Europe and the United States have a history of developing standards that are similar yet sufficiently different that both sets of testing are required to ensure compliance in each market.

Although knowledge of RF exposure effects on humans has been around for a number of years, detailed test methodologies are in their infancy. It is highly probable that test procedures will undergo a number of revisions before they become stable. One of the major problems with testing today is the high degree of measurement uncertainty, which will be one of the driving forces behind some of the anticipated revisions. Addressing MPE and SAR has become an important consumer and governmental issue that is not likely to diminish.

References

1.Council Recommendation of 12 July 1999 on the limitation of exposure of the general public to electromagnetic fields (0 Hz to 300 GHz) [1999/519/EC]; http://europa.eu.int/
eur-lex/en/lif/dat/1999/ en_399H0519.html.

2.R&TTE Directive (1999/5/EC); http://europa.eu.int/eur-lex/en/lif/ dat/1999/en_399L0005.html.

3.Directive 73/23/EEC [LV Directive]; http://europa.eu.int/eur-lex/ en/lif/dat/1973/en_373L0023.html.

4.EN 60215:1989/A2:1994, "Safety Requirements for Radio Transmitting Equipment," CENELEC, Brussels.

5.M/305, "Harmonized standards covering protection from electromagnetic fields (0 Hz to 300 GHz) generated by apparatus included in the scope of either the Low Voltage Directive 73/23/EEC, (LVD) or the Radio Equipment and Telecommunications Terminal Equipment (R&TTE) Directive 1999/5/EC," CENELEC, Brussels.

6.Rules of the Federal Communications Commission (Title 47, CFR), http://www.access.gpo.gov/nara/cfr/cfr-table-search.html.

7.ANSI/IEEE C95.1-1992, "IEEE Standard for Safety Levels with Respect to Human Exposure to Radio-Frequency Electromagnetic Fields, 3 kHz to 300 GHz, Section 4.1," American National Standards Institute (ANSI) and the Institute of Electrical and Electronics Engineers (IEEE), New York, 1992.

8.OET Bulletin 65 Supplement C (Ed. 01-01), June 2001, "Evaluating Compliance with FCC Guidelines for Human Exposure to Radio-Frequency Electromagnetic Fields, Additional Information for Evaluating Compliance of Mobile and Portable Devices with FCC Limits of Human Exposure to Radio-Frequency Emissions," http://www.fcc.gov/Bureaus/Engineering_Technology/
Documents/bulletins/oet65/oet65c.pdf.

9."Biological Effects and Exposure Criteria for Radio-Frequency Electromagnetic Fields," (NCRP Report No. 86, Sections 17.4.1, 17.4.1.1, 17.4.2, and 17.4.3. Copyright NCRP, 1986, Bethesda, MD).

Steve Dillingham, BEng, CEng, MIEE, (operations manager) and Nick Cobb, BSc, (principal engineer) work for the Regulatory and Technical Support Group of Radio-Frequency Investigation Ltd. (RFI; Basingstoke, Hants, UK). Nick Cobb is a principal engineer for RFI. Further information on SAR and MPE testing requirements can be obtained from RFI's SAR Web page at http://www. rfi-
wireless.com/services/sar/default.htm.

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