Protecting Workers from Ultraviolet Radiation - icnirp

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Protecting Workers from Ultraviolet Radiation The ocular media partially transmit and refract UVR. The refraction may concentrate directly incident radiation to a higher irradiance. Therefore, ocular effects of the Sun are primarily located in the lower nasal part of the outer eye (Figure 5). Figure 5. Concentration of UVR in the eye by refraction (the Coroneo Effect) into the corneal limbus (A) and nasal area of the lens (B) The UVR reaching internal structures of the eye is attenuated depending upon the wavelength of incident radiation (Figure 6). Figure 6. Penetration of UVR into the eye (adapted from Sliney and Wolbarsht 1980) Radiation with wavelengths shorter than 290 nm is almost entirely absorbed by the cornea, Figure 6. Further, radiation in the range 300-370 nm is almost entirely attenuated in the lens. There is a strong increase of UVR attenuation by the lens with increasing age. If the lens is 26
Protecting Workers from Ultraviolet Radiation removed (cataract surgery) without implantation of an UVR absorbing lens or if there is no lens (i.e. aphakia, which is rare), a significant fraction of the incident UVR (290 - 400 nm) may reach the retina. The cornea does not adapt to repeated exposures like the skin (by thickening of the stratum corneum and epidermis). Therefore, the cornea is equally vulnerable day after day to the same exposure to UVR. The effects of UVR on the eyelids are equivalent to those described for the skin. For this reason only adverse effects of UVR to the eye will be considered here. Since the transparent media of the eye do not have any melanin pigment (as in the skin), there is no correlation between the UVR sensitivity of the eye and skin type. 3.3.2 Acute effects An unprotected eye exposed to UVR from the sunlight reflected from light sand or snow during one day may accumulate a sufficient dose to cause an adverse effect in the cornea of the eye. As with sunburn of the skin, the symptoms are delayed for several hours. Within six hours such an exposure gives rise to a gradual transition symptoms form a feeling of itchiness, “sand in the eye” sensation, increased tearing, to severe pain and photophobia (light sensitivity). This is caused by an inflammatory reaction in the cornea and conjunctiva known as photokeratoconjunctivitis, which leads to a swelling and loss of the superficial cells in the cornea and the conjunctiva. Within 24-48 hrs, the pain decreases and the light sensitivity disappears. This condition is popularly referred to as “snowblindness” or “welders flash.” In addition to corneal injury, laboratory studies have demonstrated acute cataract formation from UVR at wavelengths greater than 310 nm emitted by artificial or laser sources (Pitts et al 1977, Söderberg et al 2002, Ayala 2005, Hockwin et al 2002). In the unusual situation where the UVR absorbing lens or lens implant is not present, retinal injury is possible for wavelengths greater than approximately 300 nm (Zuclich 1989, Ham et al 1982) 3.3.3 Chronic effects Pterygium is a fibrous ingrowth of the cornea of tissue making the cornea opaque. Epidemiological data strongly support a correlation between chronic exposure to UVR and pterygium (Taylor 1992, Taylor 2000, Sliney 2000). A pingueculum is a non malignant connective tissue tumor in the conjunctiva. Droplet keratitis is a focal deposition of lipids in the cornea with an adverse effect on transparency. Both of these conditions have been epidemiologically associated with exposure to UVR (Lim et al 1998, Taylor 1992). Development of cataract, a clouding of the lens that disturbs vision, is part of the natural ageing process. Epidemiological data show an increased risk for cortical cataract with UVB exposure from the sun (Taylor 1988, McCarty et al 2002, Sasaki et al 2002). The prevalence of the blinding disease of cataract world-wide exceeds 50 million (Brian 2001, Thylefors 2001, WHO 1994). Animal experiments have clearly shown that UVR exposures produce cataracts, but experts disagree on the degree of importance played by environmental solar exposure (Sliney 2002). 27
Page 1 and 2: Protecting Workers from Ultraviolet
Page 3 and 4: International Commission on Non-Ion
Page 5: PREFACE The objective of this book
Page 11 and 12: 1. Introduction Protecting Workers
Page 17 and 18: 3. Biological and Health Effects Pr
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Page 33 and 34: 4.5.5 Shading Protecting Workers fr
Page 35 and 36: 5.3.1 Welding Protecting Workers fr
Page 37 and 38: 5.3.6 Materials inspection Protecti
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Page 43 and 44: 7.4 CIE Risk Groups for Lamps Prote
Page 47 and 48: 8.3.4 Personal dosimeters Protectin
Page 49 and 50: 8.4.2 Orientation of the detector P
Page 67 and 68: 10.3 Administrative Control Measure
Page 71 and 72: APPENDIX A RADIOMETRIC TERMS AND UN
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Protecting Workers from Ultraviolet
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APPENDIX C Protecting Workers from
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APPENDIX E Protecting Workers from
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APPENDIX F Protecting Workers from
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REFERENCES Part II: Additional Refe
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ISBN 978-3-934994-07-2
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