Limites de radiação não ionizante

Limites de radiação não ionizante

(Parte 6 de 13)

Si 5the power density at frequency i.

For practical application of the basic restrictions, the following criteria regarding reference levels of field strengths should be applied.

Table 8. Reference levels for time varying contact currents from conductive objects.a

Exposure characteristics Frequency range

Maximum contact current (mA)

Occupational exposure up to 2.5 kHz 1.0 2.5–100 kHz 0.4f 100 kHz–110 MHz 40

General public exposure up to 2.5 kHz 0.5 2.5–100 kHz 0.2f 100 kHz–110 MHz 20 a f is the frequency in kHz.

Table 9. Reference levels for current induced in any limb at frequencies between 10 and 110 MHz.a

Exposure characteristics Current (mA)

Occupational exposure 100 General public 45 a Note: 1. The public reference level is equal to the occupational reference level divided by u5. 2. For compliance with the basic restriction on localized SAR, the square root of the time-averaged value of the square of the induced current over any 6-min period forms the basis of the reference levels.

513Guidelines for limiting exposure to time-varying electric, magnetic, and electromagnetic fields c ICNIRP GUIDELINES

For induced current density and electrical stimulation effects, relevant up to 10 MHz, the following two requirements should be applied to the field levels:

O i51H z

1 MHz Ei and

O j51H z where

Ei 5the electric field strength at frequency i;

EL, i 5the electric field reference level from Tables 6 and 7;

Hj 5the magnetic field strength at frequency j;

HL, j 5the magnetic field reference level from Tables 6 and 7; a 5610Vm 21 for occupational exposure and 87Vm 21 for general public exposure; and b 524.4 A m21 (30.7mT) for occupationalexposureand5Am 21 (6.25mT) forgeneralpublic exposure.

The constant values a and b are used above 1 MHz for the electric field and above 65 kHz for the magnetic field because the summation is based on induced current densities and should not be mixed with thermal consider- ations. The latter forms the basis for EL,i and HL,j above 1 MHz and 65 kHz, respectively,found in Tables 6 and 7.

For thermal considerations, relevant above 100 kHz, the following two requirements should be applied to the field levels:

300 GHzS Ei

EL,i and

300 GHzS Hj

HL,j where

Ei 5the electric field strength at frequency i;

EL, i 5the electric field reference level from Tables 6 and 7;

Hj 5the magnetic field strength at frequency j;

HL, i 5the magnetic field reference level from Tables 6 and 7; c 5610/f Vm 21 (f in MHz) for occupational exposure and 87/f 1/2 Vm 21 for general public exposure; and d 51.6/f Am 21 (f in MHz) for occupational exposure and 0.73/f for general public exposure.

For limb current and contact current, respectively, the following requirements should be applied:

110 MHz S Ik

IL,k n51H z

110 MHz In where

Ik 5the limb current component at frequency k;

IL, k 5the reference level of limb current (see Table 9);

In 5the contact current component at frequency n; and

IC, n 5the reference level of contact current at frequency n (see Table 8).

The above summation formulae assume worst-case conditions among the fields from the multiple sources. As a result, typical exposure situations may in practice require less restrictive exposure levels than indicated by the above formulae for the reference levels.

ICNIRP notes that the industries causing exposure to electric and magnetic fields are responsible for ensuring compliance with all aspects of the guidelines.

Measures for the protection of workers include engineering and administrative controls, personal protection programs, and medical surveillance (ILO 1994). Appropriate protective measures must be implemented when exposure in the workplace results in the basic restrictions being exceeded. As a first step, engineering controls should be undertaken wherever possible to reduce device emissions of fields to acceptable levels. Such controls include good safety design and, where necessary, the use of interlocks or similar health protection mechanisms.

Administrative controls, such as limitations on access and the use of audible and visible warnings, should be used in conjunction with engineering controls. Personal protection measures, such as protective clothing, though useful in certain circumstances, should be regarded as a last resort to ensure the safety of the worker; priority should be given to engineering and administrative controls wherever possible. Furthermore, when such items as insulated gloves are used to protect individuals from high-frequency shock and burns, the basic restrictions must not be exceeded, since the insulation protects only against indirect effects of the fields.

With the exception of protective clothing and other personal protection, the same measures can be applied to the general public whenever there is a possibility that the general public reference levels might be exceeded. It is also essential to establish and implement rules that will prevent:

● interference with medical electronic equipment and devices (including cardiac pacemakers);

514 Health Physics April 1998, Volume 74, Number 4

● detonation of electro-explosive devices (detonators); and c fires and explosions resulting from ignition of flammable materials by sparks caused by induced fields, contact currents, or spark discharges.

Acknowledgments—The support received by ICNIRP from the International Radiation Protection Association, the World Health Organization, the United Nations Environment Programme, the International Labour Office, the European Commission, and the German Government is gratefully acknowledged.

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Adair, E. R.; Adams, B. W. Microwaves modify thermoregulatory behavior in squirrel monkey. Bioelectromagnetics 1:1–20; 1980.

Albert, E. N.; Slaby, F.; Roche, J.; Loftus, J. Effect of amplitude modulated 147 MHz radiofrequency radiation on calcium ion efflux from avian brain tissue. Radiat. Res. 109:19–27; 1987.

Allen, S. G.; Bernhardt, J. H.; Driscoll, C. M. H.; Grandolfo,

(Parte 6 de 13)

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