[X1ANNEX U.K. EXPOSURE LIMIT AND ACTION VALUES FOR ELECTROMAGNETIC FIELDS

The following physical quantities shall be used to describe the exposure to electromagnetic fields:

Of these quantities, magnetic flux density, contact current, electric and magnetic field strengths and power density can be measured directly.

A. EXPOSURE LIMIT VALUES U.K.

Depending on frequency, the following physical quantities are used to specify the exposure limit values of electromagnetic fields:

Table 1

Exposure limit values (Article 3(1)). All conditions to be satisfied

Frequency range Current density for head and trunk J (mA/m 2 ) (rms) Whole body average SAR (W/kg) Localised SAR (head and trunk) (W/kg) Localised SAR (limbs) (W/kg) Power density S (W/m 2 )
Up to 1 Hz 40
1 — 4 Hz 40/f
4 — 1 000 Hz 10
1 000 Hz — 100 kHz f/100
100 kHz — 10 MHz f/100 0,4 10 20
10 MHz — 10 GHz 0,4 10 20
10 — 300 GHz 50

Notes: U.K.

1.

f is the frequency in Hertz.

2.

The exposure limit values on the current density are intended to protect against acute exposure effects on central nervous system tissues in the head and trunk of the body. The exposure limit values in the frequency range 1 Hz to 10 MHz 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 exposure limit values for exposure of short duration. However, since the exposure limit values refer to adverse effects on the central nervous system, these exposure limit values may permit higher current densities in body tissues other than the central nervous system under the same exposure conditions.

3.

Because of the electrical inhomogeneity of the body, current densities should be calculated as averages 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 (2) .

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 exposure limit value. For pulses of duration t p , the equivalent frequency to apply for the exposure limit values should be calculated as f = 1/(2t p ).

6.

All SAR values are to be averaged over any six-minute period.

7.

Localised SAR averaging mass is any 10 g of contiguous tissue; the maximum SAR so obtained should be the value used for estimating 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 recognised 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 pulsed exposures in the frequency range 0,3 to 10 GHz and for localised exposure of the head, in order to limit and avoid auditory effects caused by thermoelastic expansion, an additional exposure limit value is recommended. This is that the SA should not exceed 10 mJ/kg averaged over 10 g of tissue.

9.

Power densities are to be averaged over any 20 cm 2 of exposed area and any 68/f 1,05 -minute period (where f is in GHz) to compensate for progressively shorter penetration depth as the frequency increases. Spatial maximum power densities averaged over 1 cm 2 should not exceed 20 times the value of 50 W/m 2 .

10.

With regard to pulsed or transient electromagnetic fields, or generally with regard to simultaneous exposure to multiple frequency fields, appropriate methods of assessment, measurement and/or calculation capable of analysing the characteristics of the waveforms and nature of biological interactions have to be applied, taking account of European harmonised standards developed by Cenelec.

B. ACTION VALUES U.K.

The action values referred to in Table 2 are obtained from the exposure limit values according to the rationale used by the International Commission on Non-ionising Radiation Protection (ICNIRP) in its guidelines on limiting exposure to non-ionising radiation (ICNIRP 7/99).

Table 2

Action values (Article 3(2)) (unperturbed rms values)

Frequency range Electric field strength, E (V/m) Magnetic field strength, H (A/m) Magnetic flux density, B (μT) Equivalent plane wave power density, S eq (W/m 2 ) Contact current, I C (mA) Limb induced current, I L (mA)
0 — 1Hz 1,63 x10 5 2x10 5 1,0
1 — 8 Hz 20 000 1,63 x10 5 /f 2 2x10 5 /f 2 1,0
8 — 25 Hz 20 000 2x10 4 /f 2,5 x10 4 /f 1,0
0,025 0,82 kHz 500/f 20/f 25/f 1,0
0,82 2,5 kHz 610 24,4 30,7 1,0
2,5 — 65 kHz 610 24,4 30,7 0,4 f
65 — 100 kHz 610 1 600 /f 2 000 /f 0,4 f
0,1 — 1 MHz 610 1,6 /f 2/f 40
1 — 10 MHz 610/f 1,6 /f 2/f 40
10 — 110 MHz 61 0,16 0,2 10 40 100
110 — 400 MHz 61 0,16 0,2 10
400 — 2 000 MHz 3f 0,008 f 0,01 f f/40
2 — 300 GHz 137 0,36 0,45 50

Notes: U.K.

1.

f is the frequency in the units indicated in the frequency range column.

2.

For frequencies between 100 kHz and 10 GHz, S eq , E, H, Band I L are to be averaged over any six-minute period.

3.

For frequencies exceeding 10 GHz, S eq , E, Hand Bare to be averaged over any 68/f 1.05 -minute period (f in GHz).

4.

For frequencies up to 100 kHz, peak action values for the field strengths can be obtained by multiplying the rms value by (2) . For pulses of duration t p , the equivalent frequency to apply for the action values should be calculated as f = 1/(2t p ).

For frequencies between 100 kHz and 10 MHz, peak action [X2values for the field strengths are calculated by multiplying the relevant rms by 10 a , where a = ] (0,665 log (f/10) + 0,176), f in Hz.

For frequencies between 10 MHz and 300 GHz, peak action values are calculated by multiplying the corresponding rms values by 32 for the field strengths and by 1 000 for the equivalent plane wave power density.

5.

With regard to pulsed or transient electromagnetic fields, or generally with regard to simultaneous exposure to multiple frequency fields, appropriate methods of assessment, measurement and/or calculation capable of analysing the characteristics of the waveforms and nature of biological interactions have to be applied, taking account of harmonised European standards developed by Cenelec.

6.

For peak values of pulsed modulated electromagnetic fields, it is also suggested that, for carrier frequencies exceeding 10 MHz, S eq as averaged over the pulse width should not exceed 1 000 times the S eq action values or that the field strength should not exceed 32 times the field strength action values for the carrier frequency.]