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 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, Ei,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.
Da notare che la maggior parte degli effetti avversi considerati nel DLgs.81/2008 compaiono immediatamente (es. aritmie, contrazioni muscolari, ustioni), ma alcuni, come la cataratta o la sterilità maschile, essendo la conseguenza di un meccanismo cumulativo, possono manifestarsi a distanza di tempo