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Safety and Electromagnetic Field Guidelines

(IEEE, 2019). Te unrestricted tier exposure (unrestricted environment) limit applies to the general

public. Te general public includes, but is not limited to, children, pregnant women, individuals with

impaired thermoregulatory systems, and persons using medications that can result in poor thermo-

regulatory system performance.

Unrestricted environment for general public is an environment in which exposure does not result in

exceeding the DRL that marks the safety program initiation level, and which serves as an exposure limit

for the general public. Here, (1) the exposures can occur in living quarters or workplaces where there are

no expectations that the DRL or ERL for unrestricted environments would be exceeded and where the

induced currents or contact currents do not exceed the limits for unrestricted environments. (2) In some

documents, the unrestricted environment is referred to as a “lower tier” or an “uncontrolled environ­

ment” or a “general public exposure.”

7.5 Basic Restrictions and Reference Levels

In the safety guidelines for low-frequency and high-frequency electromagnetic felds, two types of

parameters are given to limit exposure. In the INCIRP guidelines, they are named basic restrictions and

reference levels (ICNIRP, 2010; ICNIRP, 2020).

Basic restrictions are defned based on the physical quantities directly related to the established

health efects. Depending on frequency, the physical quantities are used to specify the basic restrictions.

For low frequencies up to 10 MHz, the physical quantity is the internal electric feld strength (or in situ

electric feld in the IEEE standard) induced by electric and magnetic felds, which afects nerve cells and

other electrically sensitive cells. On the other hand, for high frequencies from 100 kHz to 6 GHz, the

physical quantity is the specifc energy absorption rate (SAR), which is the power absorbed per unit mass

and largely responsible for the heating efects of biological tissues. In addition, for frequencies above

6 GHz where electromagnetic felds are absorbed more superfcially, the physical quantity is the density

of absorbed power over the area and referred to as the absorbed power density.

Reference levels are provided as the strength of the environmental electric or magnetic feld for practi­

cal exposure assessment purposes since the internal electric quantities are practically difcult to assess.

Te reference levels are derived from the corresponding basic restrictions assuming a human equivalent

model and using measurement or computational techniques.

In the practical exposure situation examined, the measured or calculated values of electric or mag­

netic felds are frst compared with the relevant reference level. Compliance with the reference level

ensures compliance with the relevant basic restrictions. Even the value exceeds the reference level, it

does not necessarily mean that the basic restriction will be exceeded. However, it is necessary to test

compliance with the relevant basic restrictions.

It is noted that, in the IEEE standard (IEEE, 2019), the terms “dosimetric reference limit (DRL)” and

“exposure reference level (ERL)” are used for the counterparts of the basic restriction and the reference

level as in ICNIRP guidelines, respectively.

7.6 Guidelines for Static Magnetic Fields

According to the WHO Environmental Health Criteria for direct current electric and magnetic felds,

in order to limit the exposure of workers and the general public, (1) international exposure limits based

on science should be applied (general public: 40 mT for continuous exposure, occupational exposure:

200 mT for weighted average of all working hours a day, extremities (upper limit): 5 T, non-extremities

(upper limit): 2 T); (2) maintain a distance from magnetic felds, enclose it, and provide protective mea­

sures for industrial and scientifc use of magnetic felds; (3) consider a licensing system for MRI equip­

ment exceeding 2 T; (4) provide research grants to compensate for the lack of knowledge on safety; and

(5) collect health information on worker and patient exposure and make it available in a database.