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Electromagnetic Fields

Viimati uuendatud: 11.10.2019


Electromagnetic Fields

Electromagnetic fields are characterized by the following:

  • they are invisible;
  • people do not have suitable organs for sensing them;
  • they appear in the vicinity of electricity;
  • they spread at the speed of light;
  • they are both electric and magnetic.

Electric and magnetic fields are interconnected, but are two different aspects of the same phenomenon. Wherever there is electricity, both appear – both electric field and magnetic field. The two must both be separated in the working environment as their influential mechanism differs and distinct maximum tolerances have been established for both.

Table. The differences and similarities of electric and magnetic fields.   

Electric Field

Magnetic Field

unit of   measurement: volt per meter (V/m)

unit of   measurement: Tesla (T)

relatively easy   to screen

penetrates   almost everything; hard to screen

spreads in rooms   via magnetic field

spreads in rooms   via electric field

field strength   decreases when moving away from the source

field strength   decreases when moving away from the source

emerges when the   device is energized (the device must not be switched on)

emerges when current   is consumed (when a device is switched on)

spread   characteristics

spread   characteristics

                                                                          

       

 

Differently from the static electric and magnetic fields, most electromagnetic fields in the working environment change in time (make several vibrations per minute).

Electromagnetic fields that change in time are generally divided into three zones:

1. low frequency;

2. medium frequency; and

3. high frequency.

The change in time is measured with the frequency unit Hertz (Hz), 1Hz = 1 vibration per second. It is important to be aware of the electromagnetic frequency that a device emits because different maximum tolerances apply for different frequencies (certain frequencies have a more serious effect on people than others).

Static

0 Hz

Low Frequency

0 - 300 Hz

Medium Frequency

300 Hz - 100 kHz

High Frequency

100 kHz - 300   GHz

electrochemical   processes (electrolysis), MRT-devices, electric transport, arc welding

power network   supply: systems with electric motors, transport, welding, energy   manufacturing and distribution (substations), furnaces

dielectric   fusers, pulse power suppliers, monitors and screens, induction ovens and   heaters, welding units, electrosurgical equipment

radio and   television transmitters, mobile communication (incl. radio transmitters),   radars, induction ovens, glue driers, microwave heaters, diathermy

 

Health Influences

Official maximum tolerances protect employees mostly against two main health influences:

  • thermal effect, in the case of which body tissues become too heated, expressed as the heat stress of the entire body or a body part;
  • stimulation of the nervous system.

Also other biological effects have been detected, but as scientists do not have a clear and uniform understanding about their functioning mechanism today, then these have not been calculated into the maximum tolerances yet.

Maximum tolerances regulating professional exposure apply only in the case of acute, short-term influences (up to one workday). Emanating from the limited scientific understanding about the long-term and repetitive exposition, such influence is not covered in the regulation.

Stimulation of the Nervous System

Alternating electromagnetic field generates weak currents in human organism, which gives rise to the ability to have harmful biological effects. Currents appearing in human bodies can have an irritating effect on nerves or muscles.

Thermal Effect

High-power radiation at the radio frequency is a source of heat energy and contact with it brings about all consequences related to the heating of biological organisms: burns, temporary or permanent changes in the reproductive ability, cataract and death. Even though humans can feel warmth with the skin, it is not sufficient for sensing dangerous situations – thermal receptors are located in the skin and cannot sense if the internal organs heat up due to radio frequency. The strength of the electrical current generated inside the body also depends on the body placement in relation to the source of radiation (the angle of penetration).   

The effect of the electromagnetic field on the body mostly depends on the strength of the electromagnetic field, the distance of the radiation source and the length of exposure. When it comes to contact with electromagnetic fields, the main risk groups are people with an active or passive medical implants and pregnant women. The people in the risk group are advised to choose such positions and tasks that do not come into contact with large electromagnetic fields (such as welding).

Induction ovens

 

Electrically conductive material is heated with the   strong magnetic current; used for blacksmithing, hardening, welding.   Operating frequencies from 50Hz – several million Hz.

Dielectric heating  

Radio frequency (3-50MHz) energy is used for   heating. Fields of use: closing and coinage of plastics, glue drying,   processing textiles, timber processing. In manufacturing: tarpaulins, plastic   lining, shoes, etc.

Communication and transmitting systems

Communication systems’ staff do not mostly come into   contact with high-power radio frequencies. Exposure is greater in the case of   pole technicians and other employees who must work in the vicinity of the   transmitting antennas.

Medical  contact

Medical diathermy applies radio frequency energy to   warm tissues. Unshielded electrodes create leakage-electromagnetic fields on   high levels.

In the case of MRT (magnetic resonance tomography),   the staff’s contact with radio frequency fields is not notable as the radio   frequency energy has a low power and spreads mostly inside the magnet.

Even though industrial devices sold in Europe must comply with European safety standards, including regulations about electromagnetic fields, then practice has shown that certain devices could emit so-called leakage-electromagnetic fields, which can influence the human bodies either in certain areas or as a whole. Thus, it is important to periodically monitor and maintain devices applying high electromagnetic currents. Special attention must be paid if pregnant or young women work in the vicinity.

Prevention

By adjusting the factors which influence the employee’s exposure to electromagnetic fields, the dose can be considerably decreased. It is important to protect employees in areas where they spend much time. As people do not sense electromagnetic fields, employees could receive a large share of contact from sources and in places that are irrelevant for the work process. Thus, it is necessary to perform measurements in order to detect the “hot spots” of the workplace and to train employees to apply safe tricks of work. The unnecessary exposure to electromagnetic fields must be immediately stopped. Devices and places with great radiation must be marked with corresponding hazard signs.

Means to Decrease Contact with Electromagnetic Fields

  • Eliminate the source of radiation – switch it off or replace with      an alternative and safer solution.
  • Bring employees away from the radiation source – the strength of      the electromagnetic field decreases with distance (squared); sources of      greater radiation should be placed away from employees. When planning      workplaces, the great radiation in the vicinity of devices or cables with      greater current should be considered. Devices emanating great leakage      radiation (e.g. induction and dielectric heaters) must be operated from a      distance, if possible.
  • Screen the radiation source – build a screen from reflecting or      absorbing material to protect the employees. Shield cables and other      radiant parts of the device. Leakage radiation could occur in the case of      radio or medium frequency electromagnetic fields, which must also be paid      attention to.
  • Protect the employees – choose shielding clothing (does not protect      against low frequency electromagnetic fields). For example, special aprons      are available for pregnant women that protect the foetus against radio      frequency radiations.

Emanating from the fast increase of electromagnetic fields in living and working environments, and taking into account the limited scientific evidence about their safety, it is not possible to make final conclusions about their safety. Therefore, European Union recommends to apply the principle of caution and, where possible, decrease the electromagnetic fields to the minimum.

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