Electromagnetic fields [0 Hz - 300 GHz] : risk description

The term Non-Ionizing Radiation (NIR) generically indicates all radiations and fields of the electromagnetic spectrum that do not normally have sufficient energy to produce ionization in matter. Indeed, the electromagnetic spectrum is traditionally classified in Ionizing Radiation (IR), including gamma and X rays provided with an amount of energy capable of directly ionizing atoms and molecules, and in Non-Ionizing Radiation (NIR). The last is, in turn, classified depending on the frequency in Optical Radiation (300 GHz - 3x10⁴ THz) and a Non Optical Radiation (0 Hz – 300 GHz).

The Optical Radiation includes ultraviolet, visible and infrared radiations.

The Non-optical Radiation, which is the subject of this section, includes microwave (MV), radiofrequency (RF), electric and magnetic fields at extremely low frequency (ELF), up to static electric and magnetic fields.

The mechanisms of interaction of the electromagnetic fields with the biological matter that have been ascertained consist essentially in two basic effects: induction of currents in electrically excitable tissues and energy absorption with thermal increase. These effects are defined direct effects as they are the result of direct interaction of fields with the human body. At lower frequencies and up to around 1 MHz, the induction of electric currents in the electrically excitable tissues, such as nerves and muscles, prevails. With the increase of frequency, the absorption of energy in tissues through rapid oscillatory movement of ions and water molecules and the subsequent development of heat and heating, becomes more and more significant. At frequencies higher than around 10 MHz, this last effect is the only one still active and above 10 GHz, the only tissue where absorption takes place is skin.

These mechanisms are able to determine the acute effects, that can be observed above a given induction threshold. In relation to these effects it exists a broad scientific consensus and the pattern of the knowledge allows to dispose of a "rational" (i.e. a logical scientific base) to define the exposure limit values that include wide safety margins between the last and the actual danger thresholds.

In addition to the direct effects, indirect effects can be observed too. There are two mechanisms of indirect coupling with the exposed subjects: contact current that take place when the human body comes in contact with an object at a different electric potential and that can induce effects such as painful perceptions, muscle contractions, burns; and electromagnetic field coupling with electro-medical devices (including pacemakers) and other implantable or transportable devices carried by the exposed subject. Other indirect effects consist in the projectile risk from ferromagnetic objects in intense static magnetic fields; initiation of electro-explosive devices (detonators) and in fires and explosions resulting from ignition of flammable materials by sparks caused by the presence of EMF in the environment.

The main international protection organisations have developed a systematic and well established system for EMF protection. The most authoritative reference is represented by documents drawn by International Commission on Non Ionising Radiation Protection (ICNIRP). Concerning time-varying fields, ICNIRP published in 1998 some guidelines for limiting exposure to electromagnetic fields having a frequency up to 300 GHz. In 2010 ICNIRP published some new guidelines for varying fields (1 Hz to 100 kHz) and confirmed by a statement the validity of the contents of the guidelines of 1998 for radiofrequencies and microwaves (frequency higher than 100 kHz). The guidelines released in 2009 for limiting exposure to static magnetic fields, updating those previously published in 1994, are also relevant.

The philosophy behind all documents consists in defining at first the physical "dosimetric" quantities and units related to interaction between fields and living matter, in the two basic direct mechanisms previously described.

In the case of thermal effects, this basic quantity is represented by the extent of energy absorption from the tissues per unit mass and time, i.e. the (Specific Absorption Rate, SAR), expressed in watt/kilogram (W/kg).

Concerning current induction, in the 1998 guidelines, the basic quantity is the induced current density, J, defined for the purposes of Central Nervous System (CNS) protection in head and trunk, expressed as ampere per square meter (A/m²), i.e. the extent of the current that flows through a unitary tissue section. The new 2010 guidelines have introduced a new dosimetric quantity, the induced electric field in situ, E_i,expressed in V/m, that is considered more representative of the effects, as it is the direct responsible for the electrostimulation mechanism at a cellular level.

However, in the practice, the basic quantities can not be measured directly in the exposed subject. In order to verify that the basic restrictions are respected it is necessary to consider the values of the physical quantities specific for the electromagnetic fields, that can be measured directly in the environment. These quantities are represented by the electric field and magnetic field intensities. At those frequencies which are significant for thermal effects (over 10 MHz the power density, expressed as W/m² can be used. On the basis of the theoretical models of bioelectromagnetic interaction, subsequently validated by experimental analysis, the so called reference levels for the measurable quantities are calculated in conditions of maximum coupling between the fields and the exposed body, in order to guarantee that basic restrictions are respected in all exposure circumstances for SAR and electric field in situ. The reference levels are different for professionally exposed workers and for the general public, as in the last case 'stronger cautionary factors have been applied.

The 'ICNIRP guidelines have been assumed as the technical-scientific reference by Directive 2004/40/EC, establishing the minimum health and safety requirements regarding the exposure of workers to the risks arising from electromagnetic fields in the frequency range between 0 Hz and 300 GHz. Directive 2004/40/EC expresses exposure limit values and action values, whose numerical values are identical, respectively, to basic restrictions and to reference levels recommended by ICNIRP in the 1998 guidelines.

A livello nazionale, il riferimento normativo per la sicurezza nei luoghi di lavoro è il decreto legislativo 9 aprile 2008 n.81 “Testo Unico sulla salute e sicurezza sul lavoro”. Le disposizioni specifiche in materia di protezione dei lavoratori dalle esposizioni ai campi elettromagnetici sono contenute nel Capo IV del Titolo VIII - Agenti fisici – e derivano dal recepimento della direttiva 2004/40/CE, fissato inizialmente al 30 aprile 2008, e successivamente posticipato dalle direttive 2008/46/CE e 2012/11/CE.

On June 26 2013 the new DIRECTIVE 2013/35/EU OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL on minimum health and safety requirements regarding the exposure of workers to the risks arising from physical agents (electromagnetic fields) and repealing Directive 2004/40/EC has been approved. The member states must comply to the directive before July first 2016.