Ultraviolet Radiation

Ultraviolet (UV) radiation is defined as that portion of the electromagnetic spectrum between X-rays and visible light, with wavelengths that range between 40 and 400 nanometers (nm). This wavelength interval falls in the energy range of 3 to 30 electron volts (eV). The UV spectrum is divided into the following five categories:

• Vacuum UV with wavelength of 40 to 190 nm
• Far UV with wavelength of 190 to 220 nm
• UVC with wavelength of 220 to 290 nm
• UVB with wavelength of 290 to 320 nm
• UVA with wavelength of 320 to 400 nm

The sun is our primary natural source of UV radiation. Artificial sources include germicidal lamps, mercury vapor lamps, tanning booths, black lights, curing lamps, halogen lights, high-intensity discharge lamps, fluorescent and incandescent sources, and some types of lasers (excimer lasers, nitrogen lasers, and third harmonic Nd:YAG lasers). Different sources of UV radiation might have different effects and hazards depending on their wavelength range.

The biological effects of UV radiation involve the following:

• UVC, far UV, and vacuum UV are almost never observed in nature because they are absorbed completely in the atmosphere. Therefore, any changes in ozone layer will cause a big change in UV shielding of the atmosphere.
• Germicidal lamps are designed to emit UVC radiation because of its ability to kill bacteria. In humans, UVC is absorbed in the outer dead layers of the epidermis. Accidental overexposure to UVC can cause corneal burns, commonly termed welders’ flash, and snow blindness, a severe sunburn to the face. While UVC injury usually clears up in a day or two, it can be extremely painful.
• UVB is typically the most destructive form of UV radiation because it has enough energy to cause photochemical damage to cellular DNA, yet not enough to be completely absorbed by the atmosphere.
• UV plays an important role in the synthesis of vitamin D. Therefore, humans need UVB for metabolism. However, harmful effects can cause erythema (sunburn), cataracts, and [Page 476]development of skin cancer. Individuals working outdoors are at the greatest risk of UVB effects. Most solar UVB is blocked by ozone in the atmosphere, and there is concern that reductions in atmospheric ozone could increase the prevalence of skin cancer, since the shielding effect is reduced as result of atmospheric ozone reduction.

UVA is the most commonly encountered type of the UV light in nature. UVA exposure has an initial pigment-darkening effect or tanning followed by erythema if the exposure is more excessive than normal exposure. As the photon energy increases, the chance of its absorption decreases. Therefore, since the energy of UVA falls in 320 to 400 nm, atmospheric ozone can absorb very little of this part of the UV spectrum.

The photochemical effects of UV radiation can be exacerbated by chemical agents. There are some chemical agents that make the human body more sensitive to UV radiation. Any accidental UV overexposure can injure the victims due to the fact the UV is invisible and does not produce an immediate reaction after absorption. Labeling on UV sources usually consists of a caution or warning label on the product or the bulb packaging cover or a warning sign on the entryway. Actually, the intensity of the UV source and length of exposure influence the level of the accidental damage. Hazard communication training is especially important to help prevent accidental exposures in the workplace.

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