Difference between electromagnetic radiation and power frequency electromagnetic field
2008- 1 1- 14
The inaccurate concept of using "electromagnetic radiation" to describe the power frequency electric field and magnetic field generated by power transmission and transformation facilities often spreads in society, which increases public misunderstanding and concern. Power transmission and transformation facilities produce power frequency electric field and power frequency magnetic field. The concept of electromagnetic radiation refers to the energy flow phenomenon that electromagnetic energy is emitted from a radiation source into space and propagates alternately in the form of electromagnetic waves between electric and magnetic fields through wave impedance. The energy of electromagnetic radiation is related to the frequency of wave source. The higher the frequency, the shorter the wavelength, the easier it is to produce electromagnetic radiation and form electromagnetic waves. In the field of electric power or electric power, the frequency of 50 or 60 Hz is usually called "power frequency" (abbreviated as "power frequency"). The surrounding environment near transmission lines or power facilities produces power frequency electric fields and power frequency magnetic fields, which belong to low frequency induction fields. Its wavelength is 6000 kilometers. According to the antenna theory, in order to be an effective radiation source, its antenna must have a length equivalent to the wavelength. Compared with such a long "wave", the length of the transmission line itself is far from enough to form an effective "transmitting antenna", so it cannot form effective radiation. Power frequency electric field and power frequency magnetic field exist and act respectively, and there is no fixed relationship between them along the propagation direction. Unlike high frequency field, electric field and magnetic field vectors are closely coupled with wave impedance to form "electromagnetic radiation", which penetrates organisms. Power frequency electricity and magnetic field cannot form effective electromagnetic energy radiation or energy absorption in the body in the form of electromagnetic waves. Compared with high frequency electromagnetic waves, power frequency electric fields and magnetic fields are quite different in their existing forms and biological functions. Power frequency electricity and magnetic field are induced fields, voltage-induced electric fields and current-induced magnetic fields. They can be regarded as two independent entities, which are characterized by exponential decay with the increase of distance. Household appliances used in our living environment, such as TV sets, vacuum cleaners, refrigerators, electric blankets, AC electric razors, etc. , generating power frequency electricity and magnetic field.
The internationally recommended guidelines for health exposure limits need to be evaluated through published scientific and pharmacological knowledge that may have harmful effects on health. This must be mainly based on science and has nothing to do with vested interests. As an independent scientific organization, ICNIRP has all basic scientific disciplines. Together with the World Health Organization, ICNIRP is qualified to evaluate factors that may be harmful to health. ICNIRP is a non-ionizing radiation protection NGO officially recognized by the World Health Organization, the International Labour Organization and the European Union. The assessment of the harmful effects of EMF (electric field, magnetic field and electromagnetic field) exposure and ICNIRP's guidelines for limiting EMF exposure based on health are based on scientific data and have nothing to do with vested interests. They don't consider political, social and economic factors. Guidelines for limiting the exposure of time-varying electric field, magnetic field and electromagnetic field (below 300GHz) are determined in the frequency range of 100kHz and below, and the "basic limit" physical quantity to prevent adverse effects on health is "current density". Laboratory experiments have confirmed that the current density of 100 mA/m2 is a healthy threshold. In order to further protect the health of the occupation and the public, ICNIRP gives the safety factors of 10 and 50 times for the occupation and the public exposure respectively, that is, the basic limits are 10 mA/m2 and 2 mA/m2 respectively, so as to determine the "reference level" for the occupation and the public exposure to electric and magnetic fields. In other words, the standard limit is that the safety margins of the occupation and the public are 10 times and 50 times, respectively, based on the threshold that is known to have an impact on health. Because the "basic limit" physical quantity "current density" is a physical quantity in the body, it is difficult to measure directly. Therefore, in order to facilitate the actual exposure assessment, ICNIRP guidelines introduce a physical quantity that is convenient for actual measurement, called "reference level". The physical quantities derived from this include: electric field intensity, magnetic field intensity, magnetic induction intensity and so on.
Can China's electromagnetic field standards effectively protect public health?
2008- 1 1- 14
After 10 years' research, the World Health Organization officially released the official document of electromagnetic field research results in 2006 (entitled "Formulating the Standard Framework of Health-based Electromagnetic Field"). In this document, the World Health Organization issued a request to member countries: "International standards (including exposure standards and emission standards) are strongly recommended". The exposure standard recommended by WHO in this official publication is the "ICNIRP (1998) Guide" officially approved by WHO. Among them, the exposure limits of electric field and magnetic field allowed by the public are: electric field intensity 5 kV/m, magnetic field intensity 100μT respectively. On the basis of determining the hazards, the safety margin of occupational exposure is 10 times, and that of public exposure is 50 times. This international standard has enough safety margin for human exposure, so it can ensure the safety of human health.
Comparing China's current electromagnetic field environmental assessment standards (electric field intensity is 4 kV/m and magnetic field intensity is 100μt) with the limits of the above two standards, it can be clearly seen that all the limits of China's current standards are stricter than or equal to the above international standards.