In 1801, I. Ritter (Germany) and W. Walaston (England), using a photographic plate, proved the presence of ultraviolet rays. Beyond the violet end of the spectrum, it turns black faster than under the influence of visible rays. Since the blackening of the plate occurs as a result of a photochemical reaction, scientists have concluded that ultraviolet rays are very active.
Ultraviolet rays cover a wide range of radiation: 400...20 nm. The radiation region of 180... 127 nm is called vacuum. Through artificial sources (mercury-quartz, hydrogen and arc lamps), giving both a line and a continuous spectrum, produces ultraviolet rays with a wavelength of up to 180 nm. In 1914, Lyman explored the range up to 50 nm.
Researchers have discovered the fact that the spectrum of ultraviolet rays from the Sun reaching the earth's surface is very narrow - 400...290 nm. Doesn't the sun emit light with a wavelength shorter than 290 nm?
The answer to this question was found by A. Cornu (France). He found that ozone absorbs ultraviolet rays shorter than 295 nm, after which he put forward a hypothesis: the Sun emits short-wave ultraviolet radiation, under its influence oxygen molecules break down into individual atoms, forming ozone molecules, therefore, in the upper layers of the atmosphere, ozone should cover the earth with a protective screen. Cornu's hypothesis was confirmed when people rose to the upper atmosphere. Thus, under terrestrial conditions, the spectrum of the sun is limited by the transmission of the ozone layer.
The amount of ultraviolet rays reaching the earth's surface depends on the height of the Sun above the horizon. During the period of normal illumination, the illumination changes by 20%, while the amount of ultraviolet rays reaching the earth's surface decreases by 20 times.
Special experiments have established that when rising upward for every 100 m, the intensity of ultraviolet radiation increases by 3...4%. The share of scattered ultraviolet radiation at summer noon accounts for 45...70% of the radiation, and that reaching the earth's surface - 30...55%. On cloudy days, when the solar disk is covered with clouds, mainly scattered radiation reaches the Earth's surface. Therefore, you can tan well not only in direct sunlight, but also in the shade and on cloudy days.
When the Sun is at its zenith, rays with a length of 290...289 nm reach the earth's surface in the equatorial region. In mid-latitudes, the short-wave limit, during the summer months, is approximately 297 nm. During the period of effective lighting upper limit spectrum is about 300 nm. Beyond the Arctic Circle, rays with a wavelength of 350...380 nm reach the earth's surface.
The influence of ultraviolet radiation on the biosphere
Above the range of vacuum radiation, ultraviolet rays are easily absorbed by water, air, glass, quartz and do not reach the Earth's biosphere. In the range of 400... 180 nm, the effect on living organisms of rays of different wavelengths is not the same. The most energy-rich short-wave rays played a significant role in the formation of the first complex organic compounds on Earth. However, these rays contribute not only to the formation, but also to the decay organic matter. Therefore, the progress of life forms on Earth occurred only after, thanks to the activity of green plants, the atmosphere was enriched with oxygen and, under the influence of ultraviolet rays, a protective ozone layer was formed.Of interest to us are ultraviolet radiation from the Sun and artificial sources of ultraviolet radiation in the range of 400...180 nm. Within this range there are three areas:
A - 400...320 nm;
B - 320...275 nm;
C - 275...180 nm.
There are significant differences in the effect of each of these ranges on a living organism. Ultraviolet rays act on matter, including living matter, according to the same laws as visible light. Some of the absorbed energy is converted into heat, but thermal effect ultraviolet rays have no noticeable effect on the body. Another way of transmitting energy is luminescence.
Photochemical reactions under the influence of ultraviolet rays are most intense. The energy of ultraviolet light photons is very high, so when they are absorbed, the molecule ionizes and breaks into pieces. Sometimes a photon knocks an electron out of the atom. Most often, atoms and molecules are excited. When absorbing one quantum of light with a wavelength of 254 nm, the energy of the molecule increases to a level corresponding to the energy of thermal motion at a temperature of 38000°C.
The bulk of solar energy reaches the earth in the form of visible light and infrared radiation, and only a small part in the form of ultraviolet radiation. The UV flux reaches its maximum values in midsummer in the Southern Hemisphere (the Earth is 5% closer to the Sun) and 50% of the daily amount of UV arrives within 4 midday hours. Diffey found that for latitudes with temperatures of 20-60°, a person sunbathing from 10:30 to 11:30 and then from 16:30 to sunset will receive only 19% of the daily dose UV. At noon, the UV intensity (300 nm) is 10 times higher than three hours earlier or later: an untanned person needs 25 minutes to get a light tan at noon, but to achieve the same effect after 15:00, he will need to lie in the sun not less than 2 hours.
The ultraviolet spectrum, in turn, is divided into ultraviolet-A (UV-A) with a wavelength of 315-400 nm, ultraviolet-B (UV-B) -280-315 nm and ultraviolet-C (UV-C) - 100-280 nm which differ in penetrating ability and biological effects on the body.
UV-A is not retained by the ozone layer and passes through glass and the stratum corneum of the skin. The UV-A flux (mean value at noon) is twice as high at the Arctic Circle as at the equator, so its absolute value is greater at high latitudes. There are no significant fluctuations in UV-A intensity in different times of the year. Due to absorption, reflection and scattering when passing through the epidermis, only 20-30% of UV-A penetrates into the dermis and about 1% of its total energy reaches the subcutaneous tissue.
Most UV-B is absorbed by the ozone layer, which is "transparent" to UV-A. So the share of UV-B in all ultraviolet radiation energy on a summer afternoon is only about 3%. It practically does not penetrate through glass, 70% is reflected by the stratum corneum, and is weakened by 20% when passing through the epidermis - less than 10% penetrates into the dermis.
However long time It was believed that the share of UV-B in the damaging effects of ultraviolet radiation is 80%, since it is this spectrum that is responsible for the occurrence of sunburn erythema.
It is also necessary to take into account the fact that UV-B is scattered more strongly (shorter wavelength) than UV-A when passing through the atmosphere, which leads to a change in the ratio between these fractions with increasing geographical latitude(in northern countries) and time of day.
UV-C (200-280 nm) is absorbed by the ozone layer. If an artificial ultraviolet source is used, it is retained by the epidermis and does not penetrate the dermis.
The effect of ultraviolet radiation on the cell
In the effect of short-wave radiation on a living organism, the greatest interest is the effect of ultraviolet rays on biopolymers - proteins and nucleic acids. Biopolymer molecules contain ring groups of molecules containing carbon and nitrogen, which intensively absorb radiation with a wavelength of 260...280 nm. Absorbed energy can migrate along a chain of atoms within a molecule without significant loss until it reaches weak bonds between atoms and breaks the bond. During this process, called photolysis, fragments of molecules are formed that have a strong effect on the body. For example, histamine is formed from the amino acid histidine, a substance that dilates blood capillaries and increases their permeability. In addition to photolysis, denaturation occurs in biopolymers under the influence of ultraviolet rays. When irradiated with light of a certain wavelength, the electrical charge of molecules decreases, they stick together and lose their activity - enzymatic, hormonal, antigenic, etc.The processes of photolysis and denaturation of proteins occur in parallel and independently of each other. They are caused by different radiation ranges: rays of 280...302 nm cause mainly photolysis, and 250...265 nm - mainly denaturation. The combination of these processes determines the pattern of action of ultraviolet rays on the cell.
The most sensitive cell function to ultraviolet rays is division. Irradiation at a dose of 10(-19) J/m2 causes the division of about 90% of bacterial cells to stop. But the growth and vital activity of cells does not stop. Over time, their division is restored. To cause the death of 90% of cells, suppression of the synthesis of nucleic acids and proteins, and the formation of mutations, it is necessary to increase the radiation dose to 10 (-18) J/m2. Ultraviolet rays cause changes in nucleic acids that affect the growth, division, and heredity of cells, i.e. on the main manifestations of life.
The importance of the mechanism of action on nucleic acid is explained by the fact that each DNA (deoxyribonucleic acid) molecule is unique. DNA is the cell's hereditary memory. Its structure encrypts information about the structure and properties of all cellular proteins. If any protein is present in a living cell in the form of tens or hundreds of identical molecules, then DNA stores information about the structure of the cell as a whole, about the nature and direction of metabolic processes in it. Therefore, disturbances in the DNA structure may be irreparable or lead to serious disruption of life.
The effect of ultraviolet radiation on the skin
Exposure to ultraviolet radiation on the skin significantly affects our body's metabolism. It is well known that it is UV rays that initiate the process of formation of ergocalciferol (vitamin D), which is necessary for the absorption of calcium in the intestine and ensuring the normal development of the bone skeleton. In addition, ultraviolet radiation actively affects the synthesis of melatonin and serotonin - hormones responsible for the circadian (daily) biological rhythm. Research by German scientists has shown that when blood serum is irradiated with UV rays, the content of serotonin, the “hormone of vigor”, which is involved in the regulation of the emotional state, increases by 7%. Its deficiency can lead to depression, mood swings, and seasonal functional disorders. At the same time, the amount of melatonin, which has an inhibitory effect on the endocrine and central nervous systems, decreased by 28%. It is this double effect that explains the invigorating effect of the spring sun, which lifts your mood and vitality.The effect of radiation on the epidermis - the outer surface layer of the skin of vertebrates and humans, consisting of human stratified squamous epithelium, is an inflammatory reaction called erythema. The first scientific description of erythema was given in 1889 by A.N. Maklanov (Russia), who also studied the effect of ultraviolet rays on the eye (photoophthalmia) and found that they are based on common causes.
There are caloric and ultraviolet erythema. Caloric erythema is caused by the effect of visible and infrared rays on the skin and the flow of blood to it. It disappears almost immediately after the irradiation ceases.
After the cessation of exposure to UV radiation, after 2..8 hours, redness of the skin (ultraviolet erythema) appears simultaneously with a burning sensation. Erythema appears after a latent period, within the irradiated area of the skin, and is replaced by tanning and peeling. The duration of erythema ranges from 10...12 hours to 3...4 days. The reddened skin is hot to the touch, slightly painful and appears swollen and slightly swollen.
Essentially, erythema is an inflammatory reaction, a burn of the skin. This is a special, aseptic (Aseptic - putrefactive) inflammation. If the radiation dose is too high or the skin is especially sensitive to it, the edematous fluid accumulates, peels off the outer layer of the skin in places, and forms blisters. In severe cases, areas of necrosis (death) of the epidermis appear. A few days after the erythema disappears, the skin darkens and begins to peel. As peeling occurs, some of the cells containing melanin are exfoliated (Melanin is the main pigment of the human body; it gives color to the skin, hair, and iris of the eye. It is also contained in the pigment layer of the retina and is involved in the perception of light), the tan fades. The thickness of human skin varies depending on gender, age (in children and the elderly - thinner) and location - on average 1..2 mm. Its purpose is to protect the body from damage, temperature fluctuations, and pressure.
The main layer of the epidermis is adjacent to the skin itself (dermis), which contains blood vessels and nerves. In the main layer there is a continuous process of cell division; older ones are forced out by young cells and die. Layers of dead and dying cells form the outer stratum corneum of the epidermis with a thickness of 0.07...2.5 mm (On the palms and soles, mainly due to the stratum corneum, the epidermis is thicker than in other parts of the body), which is continuously exfoliated from the outside and restored from the inside.
If the rays falling on the skin are absorbed by dead cells of the stratum corneum, they have no effect on the body. The effect of irradiation depends on the penetrating ability of the rays and the thickness of the stratum corneum. The shorter the radiation wavelength, the lower their penetrating ability. Rays shorter than 310 nm do not penetrate deeper than the epidermis. Rays with a longer wavelength reach the papillary layer of the dermis, in which blood vessels pass. Thus, the interaction of ultraviolet rays with the substance occurs exclusively in the skin, mainly in the epidermis.
The main amount of ultraviolet rays is absorbed in the germinal (basic) layer of the epidermis. The processes of photolysis and denaturation lead to the death of styloid cells of the germ layer. Active products of protein photolysis cause vasodilation, skin swelling, release of leukocytes, and others. typical signs erythema.
Photolysis products, spreading through the bloodstream, also irritate nerve endings skin and through the central nervous system reflexively affect all organs. It has been established that in the nerve extending from the irradiated area of the skin, the frequency of electrical impulses increases.
Erythema is considered as a complex reflex, the occurrence of which involves active products of photolysis. The severity of erythema and the possibility of its formation depend on the state of the nervous system. On affected areas of the skin, with frostbite, or inflammation of the nerves, erythema either does not appear at all or is very weakly expressed, despite the action of ultraviolet rays. The formation of erythema is inhibited by sleep, alcohol, physical and mental fatigue.
N. Finsen (Denmark) first used ultraviolet radiation to treat a number of diseases in 1899. Currently, the manifestations of the effects of different areas of ultraviolet radiation on the body have been studied in detail. Of the ultraviolet rays contained in sunlight, erythema is caused by rays with a wavelength of 297 nm. To rays with longer or shorter wavelengths, the erythemal sensitivity of the skin decreases.
With the help of artificial radiation sources, erythema was caused by rays in the range of 250...255 nm. Rays with a wavelength of 255 nm are produced by the resonant emission line of mercury vapor used in mercury-quartz lamps.
Thus, the curve of erythemal sensitivity of the skin has two maxima. The depression between the two maxima is provided by the shielding effect of the stratum corneum of the skin.
Protective functions of the body
IN natural conditions Following erythema, skin pigmentation develops - tanning. The spectral maximum of pigmentation (340 nm) does not coincide with any of the peaks of erythemal sensitivity. Therefore, by selecting a radiation source, you can cause pigmentation without erythema and vice versa.Erythema and pigmentation are not stages of the same process, although they follow one another. This is a manifestation of different processes related to each other. The skin pigment melanin is formed in the cells of the lowest layer of the epidermis - melanoblasts. The starting material for the formation of melanin are amino acids and adrenaline breakdown products.
Melanin is not just a pigment or a passive protective screen that fences off living tissue. Melanin molecules are huge molecules with a network structure. The links of these molecules bind and neutralize fragments of molecules destroyed by ultraviolet radiation, preventing them from entering the blood and the internal environment of the body.
The function of tanning is to protect the cells of the dermis, the vessels and nerves located in it from long-wave ultraviolet, visible and infrared rays, which cause overheating and heat stroke. Near-infrared rays and visible light, especially its long-wave, “red” part, can penetrate tissue much deeper than ultraviolet rays - to a depth of 3...4 mm. Melanin granules - a dark brown, almost black pigment - absorb radiation in a wide range of the spectrum, protecting delicate internal organs, accustomed to a constant temperature, from overheating.
The body's operational mechanism to protect itself from overheating is a rush of blood to the skin and expansion blood vessels. This leads to an increase in heat transfer through radiation and convection (The total surface of the skin of an adult is 1.6 m2). If the air and surrounding objects have high temperature, another cooling mechanism comes into play - evaporation due to sweating. These thermoregulatory mechanisms are designed to protect against exposure to visible and infrared rays from the Sun.
Sweating, along with the function of thermoregulation, prevents the effects of ultraviolet radiation on humans. Sweat contains urocanic acid, which absorbs short-wave radiation due to the presence of a benzene ring in its molecules.
Light starvation (deficiency of natural UV radiation)
Ultraviolet radiation supplies energy for photography chemical reactions in organism. IN normal conditions sunlight causes the formation of small amounts of active photolysis products, which have a beneficial effect on the body. Ultraviolet rays in doses that cause the formation of erythema, enhance the work of the hematopoietic organs, the reticuloendothelial system (Physiological system connective tissue, producing antibodies that destroy bodies and microbes foreign to the body), barrier properties of the skin, eliminate allergies.Under the influence of ultraviolet radiation in human skin, fat-soluble vitamin D is formed from steroid substances. Unlike other vitamins, it can enter the body not only with food, but also be formed in it from provitamins. Under the influence of ultraviolet rays with a wavelength of 280...313 nm, provitamins contained in the skin lubricant secreted by the sebaceous glands are converted into vitamin D and absorbed into the body.
The physiological role of vitamin D is that it promotes the absorption of calcium. Calcium is part of bones, participates in blood clotting, compacts cell and tissue membranes, and regulates enzyme activity. A disease that occurs due to a lack of vitamin D in children in the first years of life, whom caring parents hide from the Sun, is called rickets.
In addition to natural sources of vitamin D, artificial ones are also used, irradiating provitamins with ultraviolet rays. When using artificial sources of ultraviolet radiation, it should be remembered that rays shorter than 270 nm destroy vitamin D. Therefore, using filters in the light flux of ultraviolet lamps, the short-wave part of the spectrum is suppressed. Solar starvation manifests itself in irritability, insomnia, fatigue person. In large cities, where the air is polluted with dust, ultraviolet rays that cause erythema almost do not reach the surface of the Earth. Long-term work in mines, engine rooms and closed factory workshops, work at night, and sleep during the daytime lead to light starvation. Light starvation is facilitated by window glass, which absorbs 90...95% of ultraviolet rays and does not transmit rays in the range of 310...340 nm. The color of the walls is also significant. For example, yellow color completely absorbs ultraviolet rays. The lack of light, especially ultraviolet radiation, is felt by people, pets, birds and houseplants during the autumn, winter and spring periods.
Lamps that, along with visible light, emit ultraviolet rays in the wavelength range 300...340 nm can compensate for the lack of ultraviolet rays. It should be borne in mind that errors in prescribing the radiation dose, inattention to such issues as the spectral composition of ultraviolet lamps, the direction of radiation and the height of the lamps, the duration of lamp burning, can cause harm instead of benefit.
Bactericidal effect of ultraviolet radiation
It is impossible not to note the bactericidal function of UV rays. In medical institutions, this property is actively used to prevent nosocomial infections and ensure the sterility of surgical units and dressing rooms. The impact of ultraviolet radiation on bacterial cells, namely DNA molecules, and the development of further chemical reactions in them leads to the death of microorganisms.Air pollution with dust, gases, and water vapor has bad influence on the body. The ultraviolet rays of the Sun enhance the process of natural self-purification of the atmosphere from pollution, promoting the rapid oxidation of dust, smoke particles and soot, destroying microorganisms on dust particles. Natural ability self-cleaning has limits and with very severe air pollution it turns out to be insufficient.
Ultraviolet radiation with a wavelength of 253...267 nm most effectively destroys microorganisms. If we take the maximum effect as 100%, then the activity of rays with a wavelength of 290 nm will be 30%, 300 nm - 6%, and rays lying on the border of visible light 400 nm - 0.01% of the maximum.
Microorganisms have varying sensitivity to ultraviolet rays. Yeasts, molds and bacterial spores are much more resistant to their action than vegetative forms of bacteria. Spores of individual fungi, surrounded by a thick and dense shell, thrive in high layers of the atmosphere and it is possible that they can travel even in space.
The sensitivity of microorganisms to ultraviolet rays is especially great during the period of division and immediately before it. The curves of the bactericidal effect, inhibition and cell growth practically coincide with the absorption curve of nucleic acids. Consequently, denaturation and photolysis of nucleic acids leads to the cessation of division and growth of microorganism cells, and in large doses to their death.
The bactericidal properties of ultraviolet rays are used to disinfect air, tools, and utensils; with their help, they increase the shelf life of food products, disinfect drinking water, and inactivate viruses when preparing vaccines.
Negative effects of ultraviolet radiation
Well known and a number negative effects, which arise when exposed to UV radiation on the human body, which can lead to a number of serious structural and functional damage to the skin. As is known, these damages can be divided into:The role of UV-A rays in the etiology of photoaging has been proven by the work of many foreign and Russian scientists, but nevertheless, the mechanisms of photoaging continue to be studied using modern scientific and technical base, cell engineering, biochemistry and methods of cellular functional diagnostics.
The mucous membrane of the eye - the conjunctiva - does not have a protective stratum corneum, so it is more sensitive to UV radiation than the skin. Pain in the eye, redness, lacrimation, and partial blindness appear as a result of degeneration and death of cells of the conjunctiva and cornea. The cells become opaque. Long-wave ultraviolet rays, reaching the lens in large doses, can cause clouding - cataracts.
Artificial sources of UV radiation in medicine
Germicidal lampsDischarge lamps are used as sources of UV radiation, in which, during the process of electrical discharge, radiation is generated containing a wavelength range of 205-315 nm (the rest of the radiation spectrum plays a secondary role). These lamps include low and low mercury lamps. high pressure, as well as xenon flash lamps.
Mercury vapor lamps low pressure constructively and electrical parameters practically no different from conventional fluorescent lighting lamps, except that their bulb is made of special quartz or uviol glass with a high transmittance of UV radiation, on the inner surface of which there is no layer of phosphor applied. These lamps are available in a wide range of wattages from 8 to 60 W. The main advantage of low-pressure mercury lamps is that more than 60% of the radiation falls on the line with a wavelength of 254 nm, which lies in the spectral region of maximum bactericidal action. They have a long service life of 5,000-10,000 hours and instantaneous ability to work after they are ignited.
The bulb of high-pressure mercury-quartz lamps is made of quartz glass. The advantage of these lamps is that, despite their small dimensions, they have a large unit power from 100 to 1,000 W, which makes it possible to reduce the number of lamps in the room, but they have low bactericidal efficiency and a short service life of 500-1,000 hours. In addition, normal combustion mode occurs 5-10 minutes after they are ignited.
A significant disadvantage of continuous radiant lamps is the risk of contamination of the environment with mercury vapor if the lamp is destroyed. If the integrity of bactericidal lamps is damaged and mercury enters the room, thorough demercurization of the contaminated room must be carried out.
IN last years A new generation of emitters has appeared - short-pulse ones, which have much greater biocidal activity. The principle of their operation is based on high-intensity pulsed irradiation of air and surfaces with continuous-spectrum UV radiation. Pulsed radiation is produced using xenon lamps, as well as lasers. There is currently no data on the difference between the biocidal effect of pulsed UV radiation and that of traditional UV radiation.
The advantage of xenon flash lamps is due to their higher bactericidal activity and shorter exposure time. Another advantage of xenon lamps is that if they accidentally break, environment not contaminated by mercury vapor. The main disadvantages of these lamps, which hinder their widespread use, are the need to use high-voltage, complex and expensive equipment for their operation, as well as the limited life of the emitter (on average 1-1.5 years).
Germicidal lamps are divided into ozone and non-ozone.
Ozone lamps have a spectral line with a wavelength of 185 nm in their emission spectrum, which, as a result of interaction with oxygen molecules, forms ozone in the air. High concentrations of ozone can have adverse effects on human health. The use of these lamps requires monitoring of the ozone content in the air and careful ventilation of the room.
To eliminate the possibility of ozone generation, so-called bactericidal “ozone-free” lamps have been developed. For such lamps, due to the manufacture of the bulb from a special material (coated quartz glass) or its design, the output of the 185 nm line radiation is eliminated.
Germicidal lamps that have reached the end of their service life or are out of order must be stored packed in a separate room and require special disposal in accordance with the requirements of the relevant regulatory documents.
Bactericidal irradiators.
A bactericidal irradiator is an electrical device that contains: a bactericidal lamp, a reflector and other auxiliary elements, as well as devices for its fastening. Germicidal irradiators redistribute the radiation flux into the surrounding space in a given direction and are divided into two groups - open and closed.
Open irradiators use a direct germicidal flow from lamps and a reflector (or without it), which covers a wide area of \u200b\u200bthe space around them. Installed on the ceiling or wall. Irradiators installed in doorways, are called barrier irradiators or ultraviolet curtains, in which the bactericidal flow is limited to a small solid angle.
A special place is occupied by open combined irradiators. In these irradiators, due to the rotating screen, the bactericidal flow from the lamps can be directed to the upper or lower zone of the space. However, the efficiency of such devices is much lower due to changes in wavelength upon reflection and some other factors. When using combined irradiators, the bactericidal flow from shielded lamps must be directed to the upper zone of the room in such a way as to prevent direct flow from the lamp or reflector from escaping into the lower zone. In this case, the irradiance from reflected fluxes from the ceiling and walls on a conventional surface at a height of 1.5 m from the floor should not exceed 0.001 W/m2.
In closed irradiators (recirculators), the bactericidal flow from the lamps is distributed in a limited, small enclosed space and has no outlet to the outside, while air disinfection is carried out in the process of pumping it through the ventilation holes of the recirculator. When using supply and exhaust ventilation, bactericidal lamps are placed in the exit chamber. The air flow speed is provided either by natural convection or forced by a fan. Closed-type irradiators (recirculators) must be placed indoors on the walls along the main air flows (in particular, near heating devices) at a height of at least 2 m from the floor.
According to the list of typical premises divided into categories (GOST), it is recommended that rooms of categories I and II be equipped with both closed irradiators (or supply and exhaust ventilation) and open or combined ones - when they are turned on in the absence of people.
In rooms for children and pulmonary patients, it is recommended to use irradiators with ozone-free lamps. Artificial ultraviolet irradiation, even indirect, is contraindicated for children with an active form of tuberculosis, nephroso-nephritis, a febrile state and severe exhaustion.
The use of ultraviolet bactericidal installations requires strict implementation of safety measures that exclude possible harmful effects on humans of ultraviolet bactericidal radiation, ozone and mercury vapor.
Basic safety precautions and contraindications for the use of therapeutic UV irradiation.
Before using UV irradiation from artificial sources, it is necessary to visit a doctor in order to select and establish the minimum erythemal dose (MED), which is a purely individual parameter for each person.Since individual sensitivity varies widely, it is recommended that the duration of the first session be reduced to half the recommended time in order to establish the user's skin reaction. If any adverse reaction is detected after the first session, further use of UV irradiation is not recommended.
Regular irradiation over a long period of time (a year or more) should not exceed 2 sessions per week, and there can be no more than 30 sessions or 30 minimum erythemal doses (MED) per year, no matter how small the erythemal-effective irradiation may be. It is recommended to occasionally interrupt regular radiation sessions.
Therapeutic irradiation must be carried out with the mandatory use of reliable protective eye glasses.
The skin and eyes of any person can become a “target” for ultraviolet radiation. It is believed that people with fair skin are more susceptible to damage, but dark-skinned people may not feel completely safe either.
Very careful with natural and artificial UV exposure of the whole body should be the following categories of people:
The influence of sun light on a person is difficult to overestimate - under its influence, the most important physiological and biochemical processes are launched in the body. The solar spectrum is divided into infrared and visible parts, as well as the most biologically active ultraviolet part, which has a great influence on all living organisms on our planet. Ultraviolet radiation is invisible by the human eye the short-wave part of the solar spectrum, which has an electromagnetic character and photochemical activity.
Due to its properties, ultraviolet light is successfully used in various areas of human life. UV radiation is widely used in medicine because it can change the chemical structure of cells and tissues, having different effects on humans.
Ultraviolet wavelength range
The main source of UV radiation is the sun. The share of ultraviolet radiation in the total flux of sunlight is not constant. It depends on:
- time of day;
- time of year;
- solar activity;
- geographical latitude;
- state of the atmosphere.
Despite the fact that the celestial body is far from us and its activity is not always the same, a sufficient amount of ultraviolet radiation reaches the Earth's surface. But this is only its small long-wavelength part. Short waves are absorbed by the atmosphere at a distance of about 50 km from the surface of our planet.
The ultraviolet range of the spectrum, which reaches the earth's surface, is conventionally divided by wavelength into:
- far (400 – 315 nm) – UV – A rays;
- medium (315 – 280 nm) – UV – B rays;
- near (280 – 100 nm) – UV – C rays.
The effect of each UV range on human body varies: the shorter the wavelength, the deeper it penetrates through the skin. This law determines the positive or Negative influence ultraviolet radiation on the human body.
Near-range UV radiation has the most adverse effect on health and carries the threat of serious diseases.
UV-C rays must be scattered into ozone layer, but due to poor ecology they reach the surface of the earth. Ultraviolet rays of the A and B ranges are less dangerous; with strict dosage, far- and mid-range radiation has a beneficial effect on the human body.
Artificial sources of ultraviolet radiation
The most significant sources of UV waves affecting the human body are: 
- bactericidal lamps - sources of UV - C waves, used to disinfect water, air or other objects external environment;
- industrial welding arc – sources of all waves in the range of the solar spectrum;
- erythemal fluorescent lamps - sources of UV waves in the A and B ranges, used for therapeutic purposes and in solariums;
- industrial lamps are powerful sources of ultraviolet waves used in manufacturing processes to cure paints, inks, or cure polymers.
The characteristics of any UV lamp are its radiation power, wavelength range, type of glass, and service life. These parameters determine how useful or harmful the lamp will be to humans.
Before irradiation with ultraviolet waves from artificial sources for the treatment or prevention of diseases, you should consult with a specialist to select the necessary and sufficient erythema dose, which is individual for each person, taking into account his skin type, age, and existing diseases.
It should be understood that ultraviolet is electromagnetic radiation, which not only has a positive effect on the human body.
A germicidal ultraviolet lamp used for tanning will cause significant harm rather than benefit to the body. Only a professional who is well versed in all the nuances of such devices should use artificial sources of UV radiation.
Positive effects of UV radiation on the human body
Ultraviolet radiation is widely used in the field modern medicine. And this is not surprising, because UV rays produce analgesic, sedative, antirachitic and antispastic effects. Under their influence occurs: 
- formation of vitamin D, necessary for the absorption of calcium, development and strengthening of bone tissue;
- decreased excitability of nerve endings;
- increased metabolism, as it causes activation of enzymes;
- dilation of blood vessels and improvement of blood circulation;
- stimulating the production of endorphins - “hormones of happiness”;
- increasing the speed of regenerative processes.
The beneficial effect of ultraviolet waves on the human body is also expressed in a change in its immunobiological reactivity - the body’s ability to exhibit protective functions against pathogens various diseases. Strictly dosed ultraviolet irradiation stimulates the production of antibodies, thereby increasing the human body's resistance to infections.
Exposure of the skin to UV rays causes a reaction called erythema (redness). Vasodilation occurs, expressed by hyperemia and swelling. The breakdown products formed in the skin (histamine and vitamin D) enter the blood, which causes general changes in the body when irradiated with UV waves.
The degree of development of erythema depends on:
- ultraviolet dose values;
- range of ultraviolet rays;
- individual sensitivity.
With excessive UV irradiation, the affected area of the skin is very painful and swollen, a burn occurs with the appearance of a blister and further convergence of the epithelium.
But skin burns are far from the most serious consequences of prolonged exposure to ultraviolet radiation on humans. Unwise use of UV rays causes pathological changes in organism.
Negative effects of UV radiation on humans
Despite important role in medicine, The harm of ultraviolet radiation on health outweighs the benefits. Most people are not able to accurately control the therapeutic dose of ultraviolet radiation and resort to protection methods in a timely manner, so an overdose often occurs, which causes the following phenomena:
- headaches appear;
- body temperature rises;
- fatigue, apathy;
- memory impairment;
- cardiopalmus;
- decreased appetite and nausea.
Excessive tanning affects the skin, eyes and immune (defense) system. Perceptible and visible consequences of excessive UV irradiation (burns of the skin and mucous membranes of the eyes, dermatitis and allergic reactions) pass within a few days. Ultraviolet radiation accumulates over a long period of time and causes very serious diseases.
The effect of ultraviolet radiation on the skin
A beautiful, even tan is the dream of every person, especially the fairer sex. But it should be understood that skin cells darken under the influence of the coloring pigment released in them - melanin in order to protect against further ultraviolet irradiation. That's why tanning is a protective reaction of our skin to damage to its cells by ultraviolet rays. But it does not protect the skin from the more serious effects of UV radiation: 
- Photosensitivity – increased sensitivity to ultraviolet radiation. Even a small dose of it causes severe burning, itching and sunburn of the skin. This is often associated with the use medications or consumption of cosmetics or certain foods.
- Photoaging. UV rays of spectrum A penetrate into the deep layers of the skin, damaging the structure of connective tissue, which leads to the destruction of collagen, loss of elasticity, and early wrinkles.
- Melanoma - skin cancer. The disease develops after frequent and prolonged exposure to the sun. Under the influence of an excessive dose of ultraviolet radiation, malignant formations appear on the skin or old moles degenerate into a cancerous tumor.
- Basal cell and squamous cell carcinoma are non-melanoma skin cancers that do not lead to fatal outcome, but requires removal of the affected areas surgically. It has been noticed that the disease occurs much more often in people who work in the open sun for a long time.
Any dermatitis or phenomena of skin sensitization under the influence of ultraviolet radiation are provoking factors for the development of skin cancer.
Effect of UV waves on the eyes
Ultraviolet rays, depending on the depth of penetration, can also negatively affect the condition of a person’s eyes: 
- Photoophthalmia and electroophthalmia. Expressed in redness and swelling of the mucous membrane of the eyes, lacrimation, photophobia. Occurs when safety rules are not followed when working with welding equipment or in people who are in bright sunlight in a snow-covered area (snow blindness).
- Growth of the conjunctiva of the eye (pterygium).
- Cataract (clouding of the lens of the eye) is a disease that occurs to varying degrees in the vast majority of people in old age. Its development is associated with exposure to ultraviolet radiation on the eyes, which accumulates throughout life.
Excess UV rays can cause various forms cancer of the eyes and eyelids.
The effect of ultraviolet radiation on the immune system
If the dosed use of UV radiation helps to increase the body’s defenses, then Excessive exposure to ultraviolet radiation depresses immune system . This was proven in scientific research US scientists on the herpes virus. Ultraviolet radiation changes the activity of cells responsible for immunity in the body; they cannot restrain the proliferation of viruses or bacteria, cancer cells.
Basic safety precautions and protection against exposure to ultraviolet radiation
To avoid negative consequences Because of the influence of UV rays on the skin, eyes and health, every person needs protection from ultraviolet radiation. When forced to spend long periods of time in the sun or in a workplace exposed to high doses ultraviolet rays, you definitely need to find out whether the UV radiation index is normal. In enterprises, a device called a radiometer is used for this.
When calculating the index at meteorological stations, the following are taken into account: 
- ultraviolet wavelength;
- ozone layer concentration;
- solar activity and other indicators.
The UV index is an indicator of the potential risk to the human body as a result of the influence of ultraviolet radiation on it. The index value is assessed on a scale from 1 to 11+. The norm for the UV index is considered to be no more than 2 units.
At high values index (6 – 11+) increases the risk of adverse effects on human eyes and skin, so protective measures must be taken.
- Use Sunglasses(special masks for welders).
- In the open sun, you should definitely wear a hat (if the index is very high, a wide-brimmed hat).
- Wear clothing that covers your arms and legs.
- On areas of the body not covered by clothing Apply sunscreen with a protection factor of at least 30.
- Avoid being in an open, unprotected area sun rays, space between noon and 4 p.m.
Following simple safety rules will reduce the harmfulness of UV radiation to humans and avoid the occurrence of diseases associated with the adverse effects of ultraviolet radiation on the body.
For whom ultraviolet irradiation is contraindicated?
The following categories of people should be careful with exposure to ultraviolet radiation: 
- with very light and sensitive skin and albinos;
- children and teenagers;
- those who have many birthmarks or nevi;
- suffering from systemic or gynecological diseases;
- those who have had skin cancer among their close relatives;
- taking certain medications for a long time (consult a doctor).
UV radiation is contraindicated for such people even in small doses; the degree of protection from sunlight should be maximum.
The effect of ultraviolet radiation on the human body and its health cannot be clearly called positive or negative. Too many factors must be taken into account when it affects humans under different environmental conditions and with radiation from different sources. The main thing to remember is the rule: any exposure to ultraviolet radiation on a person should be minimal before consulting a specialist and strictly dosed according to the doctor’s recommendations after examination and examination.
Ultraviolet radiation (UVR) - electromagnetic radiation of the optical range, which is conventionally divided into short-wave (UVI S - with a wavelength of 200-280 nm), medium-wave (UVI B - with a wavelength of 280-320 nm) and long-wave (UVI A - with a wavelength of 320-400 nm ).
UVR is generated by both natural and artificial sources. The main natural source of UVR is the Sun. UVR reaches the Earth's surface in the range of 280-400 nm, since shorter waves are absorbed in the upper layers of the stratosphere.
Artificial UVR sources are widely used in industry, medicine, etc.
Virtually any material heated to a temperature exceeding 2500 eK generates UVR. UVI sources are welding with oxygen-acetylene, oxygen-hydrogen, and plasma torches.
Sources of biologically effective UVR can be divided into gas-discharge and fluorescent. Gas-discharge lamps include low-pressure mercury lamps with a maximum emission at a wavelength of 253.7 nm, i.e. corresponding to maximum bactericidal efficiency, and high pressure with wavelengths of 254, 297, 303, 313 nm. The latter are widely used in photochemical reactors, in printing business, for phototherapy of skin diseases. Xenon lamps are used for the same purposes as mercury lamps. The optical spectra of flash lamps depend on the gas used in them - xenon, krypton, argon, neon, etc.
In fluorescent lamps, the spectrum depends on the mercury phosphor used.
Workers may be exposed to excess UV radiation industrial enterprises and medical institutions where the above sources are used, as well as people working outdoors due to solar radiation (agricultural, construction, railway workers, fishermen, etc.).
It has been established that both a deficiency and an excess of UVR negatively affect human health. If UVR is insufficient, children develop rickets due to a lack of vitamin D and impaired phosphorus-calcium metabolism, the activity of the body's defense systems, primarily the immune system, decreases, which makes it more vulnerable to the effects of adverse factors.
The critical organs for UVR perception are the skin and eyes. Acute eye lesions, so-called electroophthalmia (photoophthalmia), are acute conjunctivitis. The disease is preceded by a latent period, which lasts about 12 hours. Chronic eye lesions are associated with chronic conjunctivitis, blepharitis, and lens cataracts.
Skin lesions occur in the form of acute dermatitis with erythema, sometimes swelling, up to the formation of blisters. Along with the local reaction, general toxic phenomena may be observed. Subsequently, hyperpigmentation and peeling are observed. Chronic changes in the skin caused by ultraviolet radiation are expressed in skin aging, the development of keratosis, atrophy of the epidermis, and malignant neoplasms are possible.
IN Lately interest in improving public health through preventive ultraviolet irradiation increased significantly. Indeed, ultraviolet starvation, usually observed in the winter season and especially among residents of the North of Russia, leads to a significant decrease in the body's defenses and an increase in the incidence rate. Children are the first to suffer.
Our country is the founder of the movement to compensate for ultraviolet deficiency in the population using artificial sources of ultraviolet radiation, the spectrum of which is close to natural. Experience with the use of artificial sources of ultraviolet radiation requires appropriate adjustment in terms of dose and methods of use.
The territory of Russia from south to north extends from 40 to 80? north latitude and is conventionally divided into five climatic regions of the country. Let us evaluate the natural ultraviolet climate of two extreme and one middle geographical regions. These are the regions of the North (70°N - Murmansk, Norilsk, Dudinka, etc.), the Middle Zone (55°N - Moscow, etc.) and the South (40°N - Sochi, etc. ) our country.
Let us recall that according to the biological effect, the spectrum of ultraviolet radiation from the Sun is divided into two regions: “A” - radiation with a wavelength of 400-315 nm, and “B” - radiation with a wavelength of less than 315 nm (up to 280 nm). However, rays shorter than 290 nm practically do not reach the earth’s surface. Ultraviolet radiation with a wavelength of less than 280 nm, which is found only in the spectrum of artificial sources, belongs to the “C” region of ultraviolet radiation. Humans do not have receptors that urgently (with a short latent period) respond to ultraviolet radiation. A feature of natural UV radiation is its ability to cause (with a relatively long latent period) erythema, which is a specific reaction of the body to the action of UV radiation in the solar spectrum. UV radiation with a maximum wavelength of 296.7 nm is capable of forming erythema to the greatest extent. (Table 10.1).
Table 10.1.Erythemal efficiency of monochromatic UV radiation
As can be seen from table 10.1, radiation with a wavelength of 285 nm is 10 times less active, and rays with a wavelength of 290 nm and 310 nm are 3 times less active in forming erythema than radiation with a wavelength of 297 nm.
Arrival of daily UV radiation from the sun for the above regions of the country in summer (Table 10.2) relatively high 35-52 er-h/m -2 (1 er-h/m -2 = 6000 μW-min/cm 2).
However, in other periods of the year there is a significant difference, and in winter, especially in the North, there is no natural radiation from the sun.Table 10.2.
Average distribution of erythemal radiation of the area (er-h/m -2) | northern latitude |
|||
Month | III | VI | IX |
|
18,2 | ||||
26,7 | 46,5 | |||
XII
The amount of total radiation at different latitudes reflects the daily arrival of radiation. However, when taking into account the amount of radiation arriving on average not in 24, but only in 1 hour, the following picture emerges. So, in June at latitude 70? north latitude 35 er-h/m -2 are received per day. At the same time, the sun does not leave the sky for 24 hours, therefore, per hour the erythemal radiation will be 1.5 er-h/m -2. During the same period of the year at latitude 40? The sun emits 77 er-h/m -2 and shines for 15 hours, therefore, the hourly erythemal irradiance will be 5.13 er-h/m -2 , i.e. a value 3 times greater than at latitude 70?. To determine the irradiation regime, it is advisable to assess the arrival of total UV solar radiation not over 24, but over 15 hours, i.e. during a person’s waking period, since ultimately we are interested in the amount of natural radiation affecting a person, and not in the amount of solar energy falling on the surface of the Earth in general.
An important feature of the effect of natural UV radiation on humans is the ability to prevent so-called D-vitamin deficiency. Unlike regular vitamins, vitamin D is not actually found in natural foods (exceptions include the liver of some fish, especially cod and halibut, as well as egg yolk and milk). This vitamin is synthesized in the skin under the influence of UV radiation.
In the process of D-vitamin deficiency, trophism of the central nervous system and cellular respiration, as a substrate of nervous trophism, are primarily disrupted. This disorder, leading to a weakening of redox processes, should obviously be considered the main one, while all other diverse manifestations will be secondary. The most sensitive to the lack of UV radiation are young children, who, as a result of vitamin D deficiency, can develop rickets and, as a consequence of rickets, myopia.
UVB radiation has the greatest ability to prevent and cure rickets.
The process of vitamin D synthesis under the influence of UV radiation is quite complex.
In our country, vitamin D was obtained synthetically in 1952. The starting material for the synthesis was cholesterol. During the conversion of cholesterol to provitamin, a double bond was formed in the B ring of the sterol through successive bromination. The resulting 7-dehydrocholesterol benzoate is saponified into G-dehydrocholesterol, which, under the influence of UV radiation, is converted into a vitamin. The complex processes of the transition of provitamin into vitamin depend on the spectral composition of UV radiation. Thus, rays with a wavelength of a maximum of 310 nm are capable of converting ergosterol into lumisterol, which turns into techisterol, and, finally, under the influence of rays with a wavelength of 280-313 nm, techisterol is converted into vitamin D.
Vitamin D in the body regulates the content of calcium and phosphorus in the blood. If this vitamin is insufficient, phosphorus-calcium metabolism is disrupted, which is closely related to the processes of skeletal ossification, acid-base balance, blood clotting, etc.
With rickets, conditioned reflex activity is disrupted, while the formation conditioned reflexes occurs more slowly than in healthy people, and they quickly disappear, i.e. The excitability of the cerebral cortex in children suffering from rickets is significantly reduced. In this case, the cortex cells function poorly and are easily depleted. In addition, there is a disorder of the inhibitory function of the cerebral hemispheres.
Inhibition over a long period of time can spread widely throughout the cerebral cortex.
It is absolutely clear that it is necessary to carry out appropriate preventive measures, i.e. use a full UV climate.
Source type | Power, W | Irradiance in energy units at a distance of 1 m |
|||||
UV radiation area A | UV radiation area B | UV radiation region C |
|||||
µW/cm 2 | % | µW/cm 2 | % | µW/cm 2 | % |
||
PRK-7 (DRK-7) | 1000 | ||||||
LER-40 | 28,6 | 22,6 | |||||
However, it should be noted that the spectral composition of the artificial radiation climate, which takes place under the conditions of a fotaria with a PRK-type lamp, differs significantly from natural presence shortwave UV radiation.
With the release of low-power erythemal fluorescent lamps in our country, it became possible to use artificial sources of UV radiation in fotarium conditions and in general lighting systems.
Dose of preventive UV irradiation. A few words from history. Preventive irradiation of miners began in the 30s of the twentieth century. At that time there was no relevant experience and the necessary theoretical basis regarding the choice of dose specifically
preventive radiation. It was decided to use the therapeutic experience used in physiotherapeutic practice in the treatment of various diseases. Not only the sources of UV radiation were borrowed, but also the irradiation scheme. The biological effect of irradiation with PRK lamps, the spectrum of which contains bactericidal radiation, was very doubtful. Thus, we have established that the ratio of the biological activity of areas “B” and “C” involved in the formation of erythema is 1:8. The first guidelines for using photaria were developed primarily by physiotherapists. Subsequently, hygienists and biologists dealt with issues of preventive radiation. In the 50s of the last century, the problem of preventive radiation acquired a hygienic focus. Numerous studies were carried out in different cities and climatic regions of Russia, which made it possible to take a new approach to the dose of preventive UV irradiation.
Establishment prophylactic dose UV radiation is a very difficult problem, because a number of interrelated factors must be addressed and taken into account, such as:
UV radiation source;
How to use it;
Irradiated surface area;
Season of the beginning of irradiation;
Skin photosensitivity (biodose);
Irradiation intensity (irradiation);
Irradiation time.
The work used erythema lamps, the spectrum of which does not contain bactericidal UV radiation. Erythema biodose
Table 10.4.Relationship between physical and reduced units for
Expressions for the dose of UV radiation in region B (280-350 nm)
µW/cm 2 | mER-h/m2 | μEr-h/cm 2 | mER-min/m 2 |
|
µW/cm 2 | 0,0314 | |||
mER-h/m2 | ||||
μEr-h/m 2 | 0,157 | |||
mER-min/m 2 | 0,0157 |
expressed in physical (μW/cm 2) or reduced (μEr/cm 2) quantities, the ratios of which are presented in table 10.4.
It should be especially emphasized that the irradiance of the erythemal flux of UV radiation can be assessed in effective (or reduced) units - eras (Er - erythemal flux of radiation with a wavelength of 296.7 nm and a power of 1 W) only when emitting in the “B” region.
To express the irradiance of section “B” of the UV spectrum in eras, its irradiance, expressed in physical units (W), should be multiplied by the coefficient of erythemal sensitivity of the skin. The coefficient of erythemal sensitivity of the skin for rays with a wavelength of 296.7 nm was adopted in 1935 by the International Commission on Illumination as a unit.
Using LER lamps, we began to find the optimal prophylactic dose of UV radiation and evaluate the “irradiation method,” which basically refers to the duration of daily exposure, lasting from a minute to several hours.
In turn, the duration of preventive irradiation depends on the method of using artificial emitters (the use of emitters in a general lighting system or in a fotarium) and on the photosensitivity of the skin (on the value of the erythemal biodose).
Of course, when in different ways When artificial emitters are used, body surfaces of different sizes are exposed to irradiation. Thus, when using fluorescent lamps in a general lighting system, only open parts of the body are irradiated - the face, hands, neck, scalp, and in a photolight - almost the entire body.
UV irradiation in a room when using erythema lamps is small, hence the duration of irradiation is 6-8 hours, while in a fotaria, where irradiation reaches a significant value, the effect of radiation does not exceed 5-6 minutes.
When finding the optimal dose of preventive radiation, one should be guided by the fact that the initial dose of preventive radiation should be lower than the biodose, i.e. suberythemal. Otherwise, skin burns may occur. The prophylactic dose of the UV component should be expressed in absolute values.
Raising the question of expressing a prophylactic dose in absolute physical (reduced) values is by no means
means eliminating the need to determine individual skin sensitivity to UV radiation. Determining the biodose before starting irradiation is necessary, but only to find out whether it is less than the recommended prophylactic dose. In practice, when determining the biodose (according to Gorbachev), you can use a biodisimeter that has not 8 or 10 holes, as is the case in medical practice, but much less or even one, which can be irradiated with a dose equal to the prophylactic one. If the irradiated area of the skin turns red, i.e. biodose is less than prophylactic, then the initial dose of radiation should be reduced, and radiation is carried out in increasing doses with an initial dose equal to the biodose.
Comparative analysis of such physiological indicators, as erythemal biodose, phagocytic activity of blood leukocytes, capillary fragility, alkaline phosphatase activity indicated that additional artificial irradiation with UV radiation by erythemal lamps, carried out in winter, causing a very positive effect, does not contribute to to the fullest maintaining the studied physiological reactions at the level observed in the fall after prolonged exposure to natural UV radiation.
Analysis of the levels of physiological indicators irradiated with a dose of UV radiation during different methods exposure due to the method of using artificial emitters, led to the conclusion that the biological effect of exposure to UV radiation does not depend on the irradiation methods used.
The dynamics of skin sensitivity to UV radiation in a known way reflects the processes occurring in the body as a result of a long absence of natural UV radiation.
During preventive UV irradiation, it is necessary to take into account the climatic features of the area where the irradiated people live (to determine the timing of irradiation), the average value of their erythemal biodose (to select the initial radiation dose) and the fact that the preventive radiation dose, normalized in absolute values, should not be lower 2000 μW-min/cm 2 (60-62 mEr-h/m 2).
Preventive measures to prevent acute conjunctivitis when exposed to ultraviolet radiation are reduced to the use of light-protective glasses or shields during electric welding and other work with ultraviolet radiation sources. To protect the skin from UV rays are used
protective clothing, sun screens (canopies), special creams.
The main role in preventing the adverse effects of ultraviolet radiation on the body belongs to hygiene standards. Are the “Sanitary Standards for Ultraviolet Radiation in Industrial Premises” SN currently in effect? 4557-88. The normalized value is irradiance, W/m1. These standards regulate the permissible UVR values for the skin, taking into account the duration of exposure during the work shift and the area of the irradiated skin surface.
Ultraviolet radiation (ultraviolet, UV, UV) is electromagnetic radiation occupying the range between the violet boundary of visible radiation and X-ray radiation (380 - 10 nm, 7.9 1014 - 3 1016 Hertz).
The concept of ultraviolet rays first found by a 13th century Indian philosopher in his work. The atmosphere of the Bhootakasha area he described contained violet rays that cannot be seen with the naked eye.
Soon after infrared radiation was discovered, the German physicist Johann Wilhelm Ritter began searching for radiation at the opposite end of the spectrum, with a wavelength shorter than that of violet. In 1801, he discovered that silver chloride, which decomposes faster when exposed to light decomposes under the influence of invisible radiation outside the violet region of the spectrum. Silver chloride white within a few minutes it darkens in the light. Different parts of the spectrum have different effects on the rate of darkening. This happens most quickly in front of the violet region of the spectrum. Many scientists, including Ritter, then agreed that light consists of three distinct components: an oxidative or thermal (infrared) component, an illuminant (visible light) component, and a reducing (ultraviolet) component. At that time, ultraviolet radiation was also called actinic radiation. Ideas about unity three different parts of the spectrum were first voiced only in 1842 in the works of Alexander Becquerel, Macedonio Melloni and others.
The electromagnetic spectrum of ultraviolet radiation can be divided into subgroups in various ways. The ISO standard for the definition of solar radiation (ISO-DIS-21348) gives the following definitions:
|
Name |
Abbreviation |
Wavelength in nanometers |
Amount of energy per photon |
|
Near |
400 nm - 300 nm |
3.10 - 4.13 eV |
|
|
Average |
300 nm - 200 nm |
4.13 - 6.20 eV |
|
|
Further |
200 nm - 122 nm |
6.20 - 10.2 eV |
|
|
Extreme |
121 nm - 10 nm |
10.2 - 124 eV |
|
|
Ultraviolet A, long wave range |
400 nm - 315 nm |
3.10 - 3.94 eV |
|
|
Ultraviolet B, midwave |
315 nm - 280 nm |
3.94 - 4.43 eV |
|
|
Ultraviolet C, shortwave |
280 nm - 100 nm |
4.43 - 12.4 eV |
The near ultraviolet range is often called “black light” because it is not recognized by the human eye, but when reflected from some materials, the spectrum moves into the visible region.
For the far and extreme range, the term "vacuum" (VUV) is often used, due to the fact that waves in this range are strongly absorbed by the Earth's atmosphere.
The biological effects of ultraviolet radiation in the three spectral regions are significantly different, so biologists sometimes identify the following ranges as the most important in their work:
Near ultraviolet, UV-A rays (UVA, 315-400 nm)
UV-B rays (UVB, 280-315 nm)
Far ultraviolet, UV-C rays (UVC, 100-280 nm)
Almost all UVC and approximately 90% of UVB are absorbed by ozone, as well as water vapor, oxygen and carbon dioxide when sunlight passes through the earth's atmosphere. Radiation from the UVA range is rather weakly absorbed by the atmosphere. Therefore, the radiation reaching the Earth's surface largely contains near-ultraviolet UVA and a small proportion - UVB.
Somewhat later, in the works of (O. G. Gazenko, Yu. E. Nefedov, E. A. Shepelev, S. N. Zaloguev, N. E. Panferova, I. V. Anisimova), this specific effect of radiation was confirmed in space medicine . Preventive UV irradiation was introduced into space flight practice along with the 1989 Methodological Instructions (MU) “Preventive ultraviolet irradiation of people (using artificial sources of UV radiation).” Both documents are a reliable basis for further improvement of UV prevention.
Exposure of skin to ultraviolet radiation in excess of the skin's natural protective ability to tan results in burns.
Long-term exposure to ultraviolet radiation can contribute to the development of melanoma and premature aging.
Ultraviolet radiation is imperceptible to the human eye, but with intense irradiation it typically causes radiation damage(retinal burn).
Natural springs
The main source of ultraviolet radiation on Earth is the Sun. The ratio of UV-A to UV-B radiation intensity, the total amount of ultraviolet rays reaching the Earth's surface, depends on the following factors:
on the concentration of atmospheric ozone above earth's surface(see ozone holes)
from the height of the Sun above the horizon
from altitude above sea level
from atmospheric dispersion
on the state of the cloud cover
on the degree of reflection of UV rays from the surface (water, soil)
Thanks to the creation and improvement of artificial sources of UV radiation, which went in parallel with the development of electrical sources of visible light, today specialists working with UV radiation in medicine, preventive, sanitary and hygienic institutions, agriculture, etc., are provided with significantly greater opportunities than with using natural UV radiation.
There are a number of lasers operating in the ultraviolet region. The laser produces high-intensity coherent radiation. However, the ultraviolet region is difficult for laser generation, so there are no sources as powerful here as in the visible and infrared ranges. Ultraviolet lasers find their application in mass spectrometry, laser microdissection, biotechnology and other scientific research.
Many polymers used in consumer products degrade when exposed to UV light. To prevent degradation, special substances that can absorb UV are added to such polymers, which is especially important in cases where the product is directly exposed to sunlight. The problem manifests itself as color fading, surface dulling, cracking, and sometimes complete destruction the product itself. The rate of destruction increases with increasing exposure time and intensity of sunlight.
The described effect is known as UV aging and is one of the types of aging of polymers. Sensitive polymers include thermoplastics such as polypropylene, polyethylene, polymethyl methacrylate (plexiglass), as well as special fibers such as aramid fiber. UV absorption leads to destruction of the polymer chain and loss of strength at a number of points in the structure. The effect of UV on polymers is used in nanotechnology, transplantology, X-ray lithography and other fields to modify the properties (roughness, hydrophobicity) of the polymer surface. For example, the smoothing effect of vacuum ultraviolet (VUV) on the surface of polymethyl methacrylate is known.
Application: Ultraviolet (UV) radiation disinfection, Sterilization of air and hard surfaces, Disinfection of drinking water, Chemical analysis, UV spectrometry, Mineral analysis, Qualitative chromatographic analysis, Insect fishing, Artificial tanning and “Mountain sun”, restoration.
Degradable when exposed to light, degrades more quickly when exposed to invisible radiation outside the violet region of the spectrum. Silver chloride, which is white in color, darkens in the light within a few minutes. Different parts of the spectrum have different effects on the rate of darkening. This happens most quickly in front of the violet region of the spectrum. Many scientists, including Ritter, then agreed that light consists of three distinct components: an oxidative or thermal (infrared) component, an illuminant (visible light) component, and a reducing (ultraviolet) component.
Ideas about the unity of three various parts spectrum first appeared only in 1842 in the works of Alexander Becquerel, Macedonio Melloni and others.
Subtypes
The active medium in ultraviolet lasers can be either gases (for example, argon laser, nitrogen laser, excimer laser, etc.), condensed inert gases, special crystals, organic scintillators, or free electrons propagating in an undulator.
There are also ultraviolet lasers that use the effects of nonlinear optics to generate second or third harmonics in the ultraviolet region.
Impact
Degradation of polymers and dyes
On human health
In the most common low-pressure lamps, almost the entire radiation spectrum falls at a wavelength of 253.7 nm, which is in good agreement with the peak of the bactericidal efficiency curve (that is, the efficiency of ultraviolet absorption by DNA molecules). This peak is located around the wavelength of radiation equal to 253.7 nm, which has the greatest effect on DNA, but natural substances (for example, water) delay the penetration of UV.
Relative spectral bactericidal effectiveness of ultraviolet radiation - the relative dependence of the action of bactericidal ultraviolet radiation on the wavelength in the spectral range 205 - 315 nm. At wavelength 265 nm maximum value spectral bactericidal efficiency is equal to unity.
Germicidal UV radiation at these wavelengths causes dimerization of thymine in DNA molecules. The accumulation of such changes in the DNA of microorganisms leads to a slowdown in the rate of their reproduction and extinction. Ultraviolet lamps with a bactericidal effect are mainly used in devices such as bactericidal irradiators and bactericidal recirculators.
Air and surface disinfection
Ultraviolet treatment of water, air and surfaces does not have a prolonged effect. The advantage of this feature is that it eliminates harmful effects on humans and animals. In the case of UV treatment of wastewater, the flora of reservoirs does not suffer from discharges, as, for example, when discharging water treated with chlorine, which continues to destroy life long after use in wastewater treatment plants.
Ultraviolet lamps with a bactericidal effect are often called simply bactericidal lamps in everyday life. Quartz lamps also have a bactericidal effect, but their name is not due to the effect of action, as in bactericidal lamps, but is associated with the material of the lamp bulb -
