What Is Electromagnetic Protection?

The energy transfer, propagation, and absorption activities that occur in the form of particles or waves are called radiation, and are mainly divided into two categories: ionizing radiation and non-ionizing radiation. The radio frequency, microwave and other parts of non-ionizing radiation are collectively called electromagnetic radiation.

Chinese name: Electromagnetic protection

Foreign name: Electromagneticshielding

Introduction to electromagnetic protection

With the advancement of science and technology, electromagnetic radiation has been widely used in various workplaces. Typical applications include: TV and broadcast transmission systems, radio frequency induction and dielectric heating equipment, microwave medical equipment, communication transmitting stations, satellite earth communication stations, etc. In addition, some electrical facilities in contact with life have also become sources of electromagnetic radiation, such as: electrical transformation equipment, high-voltage and ultra-high-voltage power lines, and household appliances (such as induction cookers) near the place of residence ^[1] .
While the application of electrical technology brings human convenience and production efficiency improvement, the accompanying electromagnetic radiation is becoming a new source of pollution. Due to the increasing popularity of electromagnetic radiation in the environment of human life and work, countries around the world are paying more and more attention to the electromagnetic environment and the research on the harm of electromagnetic radiation to humans. The impact of electromagnetic radiation on human health and its protection has become a rapidly developing scientific new field. International cooperative research on electromagnetic radiation has also begun: The World Health Organization has launched the "International Electromagnetic Field Project" (The InternationalEMF Project), which aims to study the health effects of electromagnetic radiation from 0 to 300GHz on the human body. . Since its inception, the program has attracted scientists and occupational health and safety experts from around the world, and promoted human understanding of the dangers of electromagnetic radiation ^[1] .

The main influence forms of electromagnetic radiation on the human body

The main effects of electromagnetic fields on the human body can be summarized as follows: (1) Thermal effect: The electromagnetic field acts on the human body (cells and biological media), causing the tissue temperature to rise. (2) Non-thermal effect: The electromagnetic field changes the physiological and biochemical processes by means other than increasing the temperature of the human body. (3) Cumulative effect: After the thermal effect and non-thermal effect act on the human body, the human body suffers damage that does not heal itself (commonly known as human toleranceinternal resistance) before it is exposed to electromagnetic wave radiation again, and the damage will accumulate. People who have been exposed to electromagnetic radiation for a long time, even if the exposure power is very small and the frequency is low, may be affected by the cumulative effect and produce different degrees of health hazards ^[1] .

Damage to the human body from electromagnetic radiation

The body systems that are easily affected by electromagnetic radiation include the central nervous system, endocrine system, cardiovascular system, immune system, hematopoietic system, reproductive system, and visual system ^[1] .

Central nervous system: When exposed to high-frequency electromagnetic fields, the central nervous system of the human body is affected by the mid-wave and short-wave parts of it, and the following symptoms appear: central nervous system and autonomic nervous system dysfunction: headache, fatigue, insomnia, daytime sleepiness, memory Symptoms of mental weakness such as diminution ^[1] .

Endocrine system: In terms of its effects on the endocrine system, the electromagnetic waves of normal power can cause the hypothalamus, pituitary gland, and peripheral target gland hormone secretion disorders at an early stage. In the early stage of the impact, the levels of adrenal glucocorticoids and thyroid hormones increased, but in the later stages they showed a downward trend. At the same time, the pituitary, adrenal, and thyroid cells all showed malnutrition changes, increased apoptosis, and lasted for a long time ^[1] .

Cardiovascular system: The probability of cardiovascular disease in people who have been exposed to electromagnetic waves for a long time will greatly increase. Studies have shown that the influence of electromagnetic waves will change the transport of sodium and calcium channels on the surface of ventricular myometrium and affect ventricular muscle repolarization. Time, which affects myocardial contractility. In addition, the patient's ECG may also show abnormalities such as a decrease in RT wave voltage, prolongation of PQ wave, and widening of P wave ^[1] .

Immune system: As early as 1979, Shandala et al. Reported that microwave radiation can stimulate the electrophysiological activities of animal brains, cause changes in the central region of the cerebral cortex, and inhibit immune system functions, such as causing lymphocyte dysfunction in the blood and roses in the spleen. Reduction of rosette forming cells, etc. ^[1] .

Hematopoietic system: The human body is exposed to low- and medium-power electromagnetic waves, which can cause red blood cells, white blood cells, and platelets to be reduced to varying degrees. After the high-power irradiation, the above phenomenon is more obvious, which can cause continuous damage for more than one year and poor reconstruction of hematopoietic tissue.

Reproductive system: The effects of electromagnetic wave exposure on reproduction are mainly increased abortion rates, delayed embryonic development, and increased teratogenic rates. According to a survey, female physiotherapists who were engaged in microwave thermotherapy 6 months before and / or 3 months before pregnancy significantly increased the risk of early miscarriage. Men receive electromagnetic radiation and their offspring are affected. According to a Nordstorm epidemiological survey of Swedish power plant workers, males working near high-voltage installations have a 3.6-fold increase in perinatal mortality and a 3.2-fold increase in congenital malformations ^[1] .

Vision system: The damage caused by electromagnetic radiation to vision is mainly the long-term cumulative damage to the eyes, causing structural damage to the lens and cornea. Binocular cataracts occurred after one year of unprotected radar operators working under microwave radiation at 100 mW / cm2 for one year ^[1] .

Objects affected by electromagnetic radiation

Power transmission lines , Residents near Wireless Base Station <br /> With the increase of urban population density and the rise of urban residential construction, the distance between electromagnetic radiation sources such as power transmission equipment and high-voltage lines and residential areas cannot be completely controlled. Some residential buildings are too close to high-voltage transmission lines, threatening the health of residents. In addition, during the widening of the coverage of the wireless communication network, some wireless communication base stations may also affect the surrounding residents ^[1] .

Special workers <br /> The adverse effects of human exposure to high-intensity electromagnetic fields on human health have long been identified, and more and more studies have revealed that long-term exposure to low-frequency or low-intensity electromagnetic radiation can also harm human health. Workers in an electromagnetic radiation environment are threatened by two types of electromagnetic fields of different strengths at the same time: they are in a low-intensity radiation environment during normal operations, and in some special cases there is a danger of receiving high-frequency and high-intensity radiation. Strong electromagnetic source) ^[1] .
For these workers, the effects of electromagnetic radiation are more serious than ordinary people. Due to the invisibility of electromagnetic radiation, many operators are not aware of its harm to the human body, resulting in weak safety awareness, and the related special operators have the danger of lacking proper protection. With the deepening of human understanding of electromagnetic radiation and its negative physiological effects on the human body, the urgency and importance of workers' protection in electromagnetic environments should be given due attention ^[1] .

Electromagnetic radiation protection

The importance and necessity of electromagnetic radiation protection <br /> In the process of recognizing electromagnetic damage and studying the harm of electromagnetic radiation to humans, people are also actively thinking about the protection of electromagnetic radiation. As early as the 1950s, the former Soviet Union and the United States Many countries on behalf of them have carried out research on electromagnetic radiation protection standards. The main research objects are the protection of operators in electromagnetic radiation environments ^[1] .

Status of electromagnetic radiation protection standards at home and abroad <br /> The current representative international electromagnetic radiation protection standards are the American Institute of Electrical and Electronics Engineers (IEEE) C95.1 and the International Committee of Non-Ionizing Radiation Protection (ICNIRP) guidelines. IEEE C95.1 is adopted by the United States, Australia, Canada, and South Korea, while the European Union, Japan, and other countries adopt the ICNIRP guidelines. In the process of formulating relevant standards in China, we also borrowed and made reference to the upper protection standards and guidelines ^[1] .

China's electromagnetic radiation protection system includes a series of standards formulated by the Ministry of Health and the State Environmental Protection Administration, including GBZ-1-2002 "Design Sanitary Standards for Industrial Enterprises" and GB 18555-2001 "Occupational Exposure Limits for High Frequency Electromagnetic Fields in Workplaces" Et al. [8]. Both the IEEE C95.1 standard and the ICNIRP guidelines establish maximum allowable exposure levels or limits based on the thermal effects of electromagnetic fields. However, studies on the biological effects of electromagnetic fields have shown that electromagnetic radiation below these standard limits can affect human health through non-pyrogenic effects, and a large amount of epidemiological data also indicates the adverse effects of low-intensity long-term electromagnetic field exposure on human health. Therefore, the above-mentioned guidelines still have deficiencies and need to be improved. Ministry of Health Standards (including: GB18555-2001 Occupational Exposure Limits for High Frequency Electromagnetic Fields in Workplaces), GB 10437-1989 Workplace Ultraviolet Radiation Hygiene Standards, GB 10436-1989 Workplace Microwave Radiation Hygiene Standards (GB16203-1996 "Sanitary Standards for Power Frequency Electric Fields at Workplaces" and GB 9175-1988 "Sanitary Standards for Environmental Electromagnetic Waves") are characterized by:-formulas for calculating the field strength in various frequency bands are provided to provide predictions of electromagnetic radiation levels Basis; The electromagnetic radiation intensity and its frequency band characteristics may cause a potential adverse effect on the human body, and the environmental electromagnetic wave allowable radiation intensity standard is divided into two levels (exceeding the second level standard, which may cause harmful effects to the human body); Formulated radiation health standards for power frequency, high frequency, ultra high frequency, microwave and other frequency bands; The concept of maximum allowable exposure was adopted in the standard. "Environmental Protection Standards" formulated by the State Environmental Protection Administration (including GB 8702-88 "Electromagnetic Radiation Protection Regulations", HJ / T 10.3-1996 "Electromagnetic Radiation Environmental Impact Assessment Methods and Standards" and HJ / T 24 -1998 "500kV Ultra High Voltage Transmission Technical Specifications for Environmental Impact Assessment of Electromagnetic Radiation in Substation Projects) The characteristics are as follows: The concept of limit values is adopted, and the limit values are considered to be the upper limit of acceptable radiation levels, and include the total possible electromagnetic radiation pollution. Quantities; Specific Absorption Rate (SAR) is used as the basic limit unit; Applicable frequency range is 10 kHz to 300 GHz, excluding industrial frequencies; SAR is used as the basic limit unit within 10 kHz to 300 GHz, not considered Different frequencies and near-field and far-field electromagnetic radiation affect the human body in different forms and results ^[1] .

Electromagnetic radiation protection equipment

Domestic research on electromagnetic radiation protection has already begun, but the concept and application of electromagnetic radiation protection equipment have been widely accepted late ^[1] . To reduce the harm of electromagnetic radiation, we mainly start from two aspects:
(1) Reduce the radiation intensity of the radiation source. For example, if a special material is laid around a radiation source, the material generates an induced current by the electromagnetic field, and the radiant energy is converted into thermal energy by the current thermal effect ^[1] .

(2) Passive shielding method. When the radiation intensity of the radiation source cannot be effectively reduced, the passive shielding method is often adopted, that is, equipped with electromagnetic radiation protection equipment.
Due to the complexity of electromagnetic radiation characteristics, it is difficult to eliminate its harm simply by a reasonable design of shielding the radiation source. Equipped with protective equipment is very necessary to ensure the safety and health of the operator ^[1] .

Electromagnetic radiation protective clothing

Electromagnetic radiation protective clothing shields electromagnetic radiation and reduces its harm to the human body. It is the main protective equipment used in electromagnetic radiation workplaces. Electromagnetic radiation protective clothing is mainly divided into two types according to the principle: conductive type and magnetically conductive type. When the conductive protective clothing is subjected to an external magnetic field, an induced current is generated, and the induced current generates a magnetic field opposite to the external magnetic field to cancel the external magnetic field to achieve a protective effect. The magnetic conductive protective clothing has a large amount of hysteresis loss and ferromagnetic loss Absorb the energy of electromagnetic waves and convert them into other forms of energy to achieve the attenuation effect of electromagnetic radiation ^[1] .
According to shielding clothing materials, the main protective clothing on the market can be divided into 4 categories: (1) carbon fiber, stainless steel fiber and other textile materials made of textile fibers: the advantages are soft to the touch and good air permeability. The disadvantage is that the shielding efficiency of the manufactured radiation-proof fabric is low, which is generally about 15-30dB, and the difference in different frequency bands is large, which limits its use range, and is currently being gradually replaced. (2) Polyionic fabrics are made by a certain physical process (vacuum spray method, vacuum plating method, etc.) or chemical reactions (such as electrolytic method, etc.). The advantages are high shielding efficiency, wide use frequency band, stable performance, and the characteristics of soft and breathable blended fabric. (3) Fabrics made of electromagnetic radiation protection fibers mainly include intrinsic conductive polymer fibers and composite polymer conductive fibers. (4) The coating anti-radiation fabric uses coating formulations made by incorporating metal oxides or metal powders, polymer film-forming agents, etc., so that the fabric can obtain electromagnetic radiation protection capabilities ^[1] .
Performance evaluation and technical requirements < br At present, there are a large number of electromagnetic radiation protective clothing on the Chinese market, and the application range covers the general living environment (such as electromagnetic radiation protective clothing for pregnant women) to the workplace (such as anti-microwave radiation clothing) . To evaluate the effectiveness of electromagnetic shielding, commonly used shielding efficiency (SE), the unit is dB. It is defined as the ratio of the electric field strength E0 (or magnetic field strength H0, power W0) at a certain point in space to the electric field strength E1 (or voltage, magnetic field strength H1, power W1) at that point after shielding ^[1] .

Problems in electromagnetic radiation protection in China

Early electromagnetic radiation protective clothing was limited by the process, and had problems such as heavy weight, poor wearing comfort, and high cost, so it was only used in very few workplaces. With the development of electromagnetic radiation injury research and the advancement of textile science, the comfort and convenience of electromagnetic radiation protective clothing have increased, and the scope of application has continued to expand ^[1] . Although the popularity of the concept of electromagnetic radiation protection has gradually deepened, and electromagnetic radiation protection has received more and more attention, the related standards and protective equipment market for electromagnetic radiation protection still have the following problems:
(1) The theoretical basis for the establishment of electromagnetic radiation limit standards is the pyrogenic effect, which cannot fully reflect the impact of electromagnetic radiation on the human body; the evaluation method of the limit standard is not uniform, which affects its effective implementation and the effective evaluation of electromagnetic radiation in the workplace ^[1] .
(2) The current national standard for electromagnetic radiation protection equipment in China is GB6568.1 "Shielded Clothing for Live Working", which is mainly aimed at operators of high-voltage electrical equipment, and the protection standard for microwave radiation is GB / T 23463 "Protective Clothing for Microwave Radiation Protective Clothing" New standards for 2009 are yet to be implemented. Therefore, the protection of electromagnetic radiation components such as microwaves needs to be strengthened ^[1] .
(3) Inadequate research and application of civilian electromagnetic radiation protection equipment, lack of standards, lack of supervision, and exaggerated publicity of products. In foreign countries, electromagnetic radiation protective clothing has entered ordinary households, while workers in electromagnetic radiation places in China have not been equipped with sufficient protective equipment. As the understanding of the characteristics of electromagnetic radiation and its short-term and long-term physiological damage is deepened, China's emphasis on electromagnetic protection in the workplace will continue to increase ^[1] . In the light of existing results, further work should be done on the following issues:
(1) Improve and harmonize the electromagnetic radiation exposure limit standards. Further research on the mechanism of electromagnetic radiation damage, fully understand the harm of non-pyrogenic effects to human health, and use it as a reference to revise the electromagnetic radiation exposure limit standards. (2) Improve national standards for electromagnetic radiation protective clothing, increase coverage, and include civilian protective clothing in the scope of standard management ^[1] .