Radiation is the emission (sending out) of energy from any source. The main source of UV radiation (rays) is the sun, although it can also come from man-made sources such as tanning beds and welding torches. The wavelength of UV lights from 400 nm to 100 nm shorter than that of visible light but longer than X-rays.
Types of UV Radiation
Scientists classify UV radiation into three types or bands—UVA, UVB, and UVC. The ozone layer absorbs some, but not all, of these types of UV radiation:
Wavelength: 320-400 nm. Not absorbed by the ozone layer. UVA rays are the weakest of the UV rays. They can cause skin cells to age and can Cause some indirect damage to cells’ DNA. UVA rays are mainly linked to long-term Skin damage such as wrinkles, but are also thought to play a role in some skin Cancers.
Wavelength: 290-320 nm mostly absorbed by the ozone layer, but some does reach the Earth’s surface. UVB rays are slightly stronger. They are mainly responsible for direct damage to the DNA, and are the rays that cause sunburns. They are also thought to cause most skin cancers.
Wavelength: 100-290 nm. Completely absorbed by the ozone layer and atmosphere. UVC rays are the strongest UV rays. Fortunately, because of this, they react with ozone high in our atmosphere and do not reach the ground. Therefore UVC rays are not present in sunlight are not normally a risk factor for skin cancer. But they can be found in some man-made sources, such as arc welding torches and mercury lamps. In the past, sun beds were also a source of UVC rays.
UVA and UVB radiation that reaches the Earth’s surface contributes to the serious health effects .It also contributes to environmental impacts. Levels of UVA radiation are more constant than UVB, reaching the Earth’s surface without variations due to the time of day or year. In addition, UVA radiation is not filtered by glass.
How UV Rays comes to earth from the sun?
Ultraviolet radiation (UV) comes naturally from the sun. The Ozone layer protected from the UV light now a days due to pollution it makes a big hole in the ozone layer from this hole the UV lights comes directly to earth.
How Ozone Layer protect us from UV Rays?
Ozone is a molecule made of three oxygen atom or O3. When ultraviolet light in the range 240 and 320 nm strikes an ozone molecule, it absorbs the energy and the O3 changes to O2 and O. The O atom soon combines with another O2 molecule to form O3 and is ready to absorb ultra violet light. The ozone layer is situated at the highest level of our atmosphere and by absorbing the harmful ultra violet radiation from the Sun, serves a very important purpose. Chlorofluorocarbons or CFCs damage the ozone layer by not allowing O3 to form again once it has split to O and O2 molecules.
Sources of UV Rays
There are two main sources of UV rays:-
Sunlight is the main source of UV radiation, even though UV rays make up only a small portion of the sun’s rays. About 95% of the UV radiation from the sun that reaches the earth is UVA, with the remaining 5% being UVB. The amount of UV radiation you may be exposed to at any point depends on a number of factors, such as:-
Man made sources of UV rays
Man-made sources of UV rays can also be important. These include:-
Sunlamps and sun beds (tanning beds and booths)
The amount and type of UV radiation someone is exposed to from a tanning bed (or booth) depends on the specific lamps used in the bed, how long a person stays in the bed, and how many times the person uses it. Most modern UV tanning beds emit mostly (more than 95%) UVA rays, with the rest being UVB.
Phototherapy (UV therapy)
Some skin problems (psoriasis, for example) can be treated with UV light. For a treatment known as PUVA, a drug called a psoralen is given first. The drug collects in the skin and makes it more sensitive to UV. Then the patient is treated with UVA radiation. Another treatment option is the use of UVB alone (without a drug).
These lamps use bulbs that emit UV. The bulb may also make some visible light, but it is made with a filter that blocks most of that out, letting through UV rays (mostly UVA). They have a purple glow and are used to view fluorescent material. Bug zapping insect traps also uses “black light,” but the bulbs use a different filter that causes them to glow blue.
Mercury vapor lamps can be used to light large public areas such as streets or gyms. They do not expose people to UV rays if they are working properly. They are actually made up of 2 bulbs an inner bulb that emits light and UV rays, and an outer bulb that filters out the UV. UV exposure can only occur if the outer bulb is broken. Some mercury vapor lamps are designed to turn themselves off when the outer bulb breaks. The ones that don’t have this feature are only supposed to be installed behind a protective layer or in areas where people wouldn’t be exposed if part of the bulb breaks.
High-pressure xenon and xenon-mercury arc lamps, plasma torches, and Welding arcs
Xenon and xenon-mercury arc lamps are used as sources of light and UV rays for many things, such as UV “curing” (of inks, coatings, etc), video projection, fiber optics, disinfection, to simulate sunlight (to test solar panels, for example), and even in some car headlights. Most of these, along with plasma torches and welding arcs, are mainly of concern in terms of workplace UV exposure.
Harmful Effects of UV rays
UV radiation can initiate a photochemical reaction called erythema within exposed skin. This “sunburn” can be quite severe and can occur as a result of only a few seconds exposure. Effects are exaggerated for skin photosensitized by agents such as coal tar products, certain foods (e.g., celery root), certain medications and photo allergens. Chronic skin exposure to UV radiation has been linked to premature skin aging, wrinkles and skin cancer.
UV radiation exposure can injure the cornea, the outer protective coating of the eye. Photokeratitis is a painful inflammation of the eye caused by UV radiation-induced lesions on the cornea. Symptoms include a sensation of sand in the eye that may last up to two days. Chronic exposures to acute high-energy UV radiation can lead to the formation of cataracts
Safety against the UV radiation
There are number of measures than can reduce the risk at the workplace:-
For outdoor workers this would include the provision of shade cover or canopies. In the context of non-solar sources of UV radiation, suitable engineering controls measures would include opaque barriers, UV radiation blocking filters and door interlocking power supplies.
For outdoor workers this would include rescheduling outdoor work programs where possible to be performed outside the peak UV radiation period (2 hours either side of solar noon), moving where possible the jobs indoors or to shady areas or rotating workers between indoor and outdoor tasks to lessen each employees total UV exposure. In the context of non-solar sources of UV radiation, administrative controls would include warning signs, keeping staff at a safe distance and limiting the time during which UV radiation sources are switched on. Training of supervisors and employees should be undertaken for workers exposed to solar and non-solar sources of radiation
Personal protective equipment (PPE)
If necessary, outdoor workers should be provided with protective clothing that is loose fitting, made of close weave fabric and provides protection to the neck and preferably to the lower arms and legs. Hats should shade the face, neck and ears and have a wide brim (8-10cm). If hard hats have to be worn, they should have attached neck flaps. Sunscreen should be a minimum SPF 15, and be broad-spectrum, that is blocking UVA and UVB, and be applied regularly and liberally to exposed skin. Sunglasses should be close fitting, of a wrap-round design and block at least 99% UV radiation. In the context of non-solar sources of UV radiation, arc welders in particular need to be provided with purpose-specific protective equipment.
Training should be offered to all employees exposed to medium to very high levels (see table 1) of UV radiation at work so that they understand the risks and what is expected of them while at the workplace.