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Electromagnetic fields of radio frequencies

Sources of electromagnetic fields of radio frequencies

Sources of electromagnetic fields of radio frequencies include: radio broadcasting, TV, radar-location, radio-management, tempering and melting of metals, welding of nonmetals, electro-investigation in geology (radio-frequency survey, methods of induction, etc.), radio communication, etc.

Electromagnetic energy of low frequency 1-12 kHz is widely used in the industry for induction heating with the purpose of tempering, melting and heating of metals.

Energy of an impulsive electromagnetic field of low frequencies is used for punching, pressing, for connection of various materials, casting, etc.

In case of dielectric heating (drying of damp materials, gluing of wood, heating, thermal fixation, melting of plastic) installations in the range of frequencies from 3 up to 150 MHz are used.

Ultrahigh frequencies are used in radio communication, medicine, radio broadcasting, TV, etc. Works with sources of ultrahigh frequency are carried out in radar-location, radio-navigation, radio astronomy, etc.

Biological effect of electromagnetic fields of radio frequencies

Subjective sensations and objective reactions of a human body during exposure to all range of radio waves of high-frequency, ultra-high frequency and extra-high frequency, and microwave frequencies do not differ, but consequences and effect of microwave-frequency of electromagnetic waves exposure are the most typical and the most adverse.

The most typical consequence of radio magnetic waves exposure of all ranges is deviation from a normal condition of the central nervous system and cardiovascular system of an individual. The general in character of biological action of electromagnetic fields of radio frequencies of the big intensity is the heating effect which is expressed in heating of separate tissues or organs of the body. The crystalline lens of an eye, a bilious bubble, a bladder and some other organs are especially sensitive to this heating effect.

Subjective sensations of the irradiated personnel include complaints of frequent headaches, drowsiness or sleepiness, fatigue, slackness, the weakness, perspiration, absent-mindedness, dizziness, decrease in memory, causeless feeling of alarm, fear, etc.

To the above- listed adverse effects on a man it is necessary to add mutagenic action as well as temporary sterilization in case of radiation exposure with strengths above a thermal threshold.

Maximum acceptable power characteristics of electromagnetic field for a various range of frequencies - electric and magnetic strength, density of a stream of energy - are approved to evaluate potential adverse consequences of electromagnetic waves of radio frequencies

Protection against electromagnetic fields of radio frequencies

Work safety when exposed to sources of electromagnetic waves is ensured by regular control of actual values of controlled parameters at workplaces and in places of possible location of personnel. If operating conditions do not meet the requirements of norms the following protection facilities are used:

1. Shielding of workplace or source of radiation.

2. Increase of the distance from a workplace up to the source of radiation.

3. Rational accommodation of the equipment in a working premise.

4. Use of means of warning protection.

5. Application of special absorbers of energy for reduction of radiation in the source.

6. Use of opportunities of remote control and automatic control, etc.

Workplaces are usually situated in a zone of the minimal intensity of the electromagnetic field. The final link in a circuit of engineering protection facilities is individual protection means. Individual means of protection of eyes from action of the microwave radiation include special goggles that are covered by a thin layer of metal (gold, tin dioxide).

Protective outfit is produced from the metallized fabric and is used in the form of overalls, dressing gowns, jackets with hoods, with the built-in goggles . Application of special fabrics in protective clothes allows lowering radiation by 100-1000 times, that is by 20-30 decibels (dB). Goggles reduce intensity of radiation by 20-25 дБ.

With a view of prevention of occupational diseases it is necessary to carry out preliminary and periodic medical surveys. Women during pregnancy and lactation periods should be transferred to other positions. Persons under 18-years age are prohibited to work with generators of radio frequencies. Persons having contact with sources of microwave and extra-high radiation are offered privileges (a reduced length of a working day, additional holiday).

Influence of electromagnetic fields (EMF) on health

In the USSR numerous researches of electromagnetic fields have been started in the 60s. The big clinical material about adverse action of magnetic filed has been accumulated and a proposal to introduce a new nozological disease “Radiowave illness” or “Chronic defeat by microwaves” was made. Subsequently it was established, that, first of all, a nervous system of the person, especially the higher nervous activity, is sensitive to electromagnetic fields, and, secondly, that electromagnetic fields possess the so-called information action during the exposure at strengths below the threshold value of a calorific effect. Results of these works were used at development of normative documents in Russia. As a result, specifications that were established in Russia are very strict and differ greatly from American and European ones by some thousand times (for example, in Russia MPL for professionals 0,01 mW/cm2; in the USA - 10 mW/cm 2).

Biological action of electromagnetic fields

Experimental data both of Russian and foreign researchers testify to high biological activity of electromagnetic fields in all frequency ranges. At relatively high levels of irradiating electromagnetic fields the modern theory recognizes the thermal mechanism of influence. At rather low level of electromagnetic fields (for example, for radio frequencies above 300 MHz it is less than 1 mV/cm2) the matter at issue is not-thermal or information character of influence on the body. Mechanisms of action of the electromagnetic fields in this case are still poorly studied. Numerous researches in the field of biological action of electromagnetic fields allow defining the most susceptible systems of the human body: nervous, immune, endocrine and sexual. These systems of the human body are critical.

Biological effect of electromagnetic fields in conditions of long long-term influence is accumulated, as a result, development of remote consequences, including degenerate processes of the central nervous system, blood cancer (leucosis), tumors of brain, hormonal diseases are possible. Electromagnetic fields can be especially dangerous for children, pregnant (embryo) women, people affected by diseases of central nervous, hormonal, cardiovascular system, highly allergic persons, and people with weakened immunity.

Influence on nervous system.

A large number of the researches conducted in Russia and monographic generalizations give the basis to consider the nervous system as one of the most sensitive systems in a human body to influence of electromagnetic fields. Low-strength electromagnetic field exposure can produce deviations at the level of a nervous cell, structural formations on transfer of nervous impulses (synapse), at the level of the isolated nervous structures. The higher nervous activity, memory of people exposed to electromagnetic fields changes. These persons can have a propensity to development of stressor reactions.

Influence on immune system

Now there’s abundant information on negative influence of electromagnetic fields on the immunology reaction of the human body. Results of researches undertaken by scientists of Russia give the reason to believe that electromagnetic field exposure disturbs the process of immunogenesis, more often to decrease of it. It has been established that in the animals irradiated with electromagnetic fields the character of infectious process changes – a course of the infectious process gets worse. Influence of electromagnetic fields of high strength on the immune system of the human body has proved its oppressing effect on a system of cellular immunity.

Other medical and biologic effects

From the beginning of 60s numerous researches have been carried out in the USSR on studying health of people having contact with electromagnetic fields in their vocation. Results of clinical researches have shown that a long contact with the electromagnetic fields in the microwave range can lead to development of diseases the clinical manifestation of which are characterized, first of all, by changes of a functional condition of nervous and cardiovascular systems. A proposal was made to identify a separate disease - radio-wave illness.

The earliest clinical manifestations of consequences of influence of electromagnetic radiation on the person are functional disorders of the nervous system, shown first of all in the form of vegetative dysfunctions of a neurotic and asthenic syndrome. Persons who are exposed to electromagnetic radiation complain of weakness, irritability, fast fatigability, lost of memory, sleeping disorders. Changes of marrow are characterized as reactive compensatory regeneration pressure. Usually these changes arise at persons who are exposed electromagnetic radiation of high intensity for a long time. People working with magnetic and electromagnetic equipment as well as population living in operative range of electromagnetic fields complain of irritability and impatience. In 1-3 years the some people have feeling of internal intensity, fussiness. The attention and memory are worsening. There are complaints of sleeping disorders and fatigue. It is possible to expect that long repeated influence of maximum permissible (especially in a decimeter wave band) radiation can lead to mental frustration.

How to protect oneself from electromagnetic fields

Organizational measures for protection from electromagnetic fields. Organizational measures for protection against electromagnetic fields include: a choice of operating modes of the radiating equipment providing a level of radiation, not exceeding the maximum permissible level, restriction of a place and time of a hold-up in the operative range of electromagnetic field (protection at a distance and by time limitation), designation and protection of zones with raised level of electromagnetic radiation.

Protection by time is applied when there is no opportunity to lower intensity of radiation in the given point up to the maximum permissible level. In Maximum Permissible Levels dependence between intensity of the density of a stream of energy and the time of an irradiation is provided.

Protection by distance is based on reduction of intensity of radiation that is in inverse proportion to the square of distance and is applied if it is impossible to weaken electromagnetic fields by other measures including protection by time. Protection in distance is approved as the basis for zones of rate setting of radiation for definition of necessary distance between sources of electromagnetic fields and apartment houses, office accommodations, etc. According to GOST a zone of radiation is fenced or warning signs with inscriptions are installed on them, reading as: “Danger, Do not enter!”.

Technical ways of protection

A metallic grid, a metallic sheet or any other conductive covering can be used to protect population from the effect of electromagnetic radiation in building structures as kind of protective shields, including specially developed building materials. In some cases it is sufficient to use grounded metal grid placed under a lining or a plaster layer. Various films and fabrics with metallized covering can be used as kind of schields. In the recent years radio-shielding materials on the basis of synthetic fibers have become very popular. Shielding textile materials are of small thickness, are light in weight and flexible; they can be backed up by other materials (fabrics, leather, and films) and are well combined with resins and latex.

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