Patty's Industrial Hygiene, Physical and Biological Agents. Группа авторов

Чтение книги онлайн.

СКАЧАТЬ irradiation is used to disinfect room air in institutions such as hospitals, prisons, and homeless shelters. The practice in designing upper room germicidal systems is to prevent irradiances in excess of 0.002 W m⁻² anywhere in the lowest 2 m (6.5 ft) of a room. A personal dosimetry study on workers in a hospital, a school, an office, and a shelter found that the eight hours UV‐C dose was a small fraction of the TLV even when some irradiances measured at eye level exceeded 0.002 W m⁻² by factors of 3–6 (45). The design criterion for the maximum allowable irradiance in the lower room thus appeared to be very conservative.

      Excimer lamps emitting radiation at 222 nm are increasingly being used as germicidal radiation sources. Because 222 nm radiation has lower penetration through the stratum corneum than 254 nm radiation, it is less damaging to skin (81). The TLV for 222 nm narrowband radiation, logarithmically interpolated from tabulated values (15), is 228 J m⁻². In a small pilot study, human volunteers radiated with a commercial 222 nm sterilizing lamp developed erythema at a threshold dose of 400–500 J m⁻² and DNA lesions at doses of 630–1010 J m⁻², well below the 3000 J m⁻² dose that can effectively kill pathogens (82). Secondary excimer emission peaks at 234 and 257 nm could have contributed to the adverse effects on the skin. These longer wavelengths can be removed with a bandpass filter (81). As with 254 nm radiation, UV‐absorbing eye protection is recommended to prevent photokeratitis from 222 nm germicidal radiation (81).

      6.5 Stage and Studio Lighting

      High‐powered lamps for stage or studio illumination can be a significant source of exposure to performers and production crew members. A study of 11 models of metal halide or halogen photoflood lights used in television studios and theaters found that, for several photofloods, the TLV for actinic UV, UV‐A, or blue‐light exposure could be exceeded in a few minutes. Exposures were higher in the television studios than in the theater stages (83).

      Blue LEDs used in stage lighting can cause blue‐light hazard overexposure in minutes (84). Stage luminaires that used a combination of blue, green, and red LEDs to produce white light were found to be similar to other white stage lighting tested in terms of the ratio of the blue‐light hazard‐weighted radiance to the illuminance (perceived brightness) of the source. Due to the low photopic response to blue light (around 450 nm), blue LED arrays used as blue stage lighting did not appear very bright; therefore viewing time might not be limited by aversion (84). Exposure to UV‐A from “blacklights” used for fluorescent effects during performances could exceed dose limits for protection of the lens in about an hour of viewing, and exposure duration would not be limited by behavioral aversion to bright light (85).

      Stage and studio lights should be equipped with UV filters, which are very effective at reducing actinic UV and UV‐A exposure (86). Protecting performers from blue light may pose a difficult challenge because these workers must often look toward the lights for extended periods and might not be able to wear protective eyeglasses for cosmetic reasons. The possibility of using contact lenses that absorb UV and blue light has been suggested (83).

      6.6 Dental Curing and Bleaching

      Both UV light and short‐wavelength visible light are used in dentistry for curing resins in composite fillings and for tooth whitening treatments. Light is used to activate photoinitiators, which initiate polymerization of the resin. Photoinitiators can be activated by radiation only in specific bands; for example, the commonly used photoinitiator camphoroquinine has an activity peak between 470 and 480 nm. Photocuring units use halogen lamps, LEDs, plasma‐arc lamps, or lasers, and produce irradiance levels that range from 3000 to over 10 000 W m⁻² (87). The duration of irradiation is typically just a few minutes for curing but may last up to an hour for bleaching. Dental personnel is at risk from exposure to radiation reflected from the patient's teeth. Calculations of the maximum permissible exposure time to blue‐light radiance from 26 models of dental lamps indicated that the blue‐light dose could be exceeded in several seconds or several minutes, depending on the type of lamp (88).

      In an evaluation of the spectral transmittance of 18 different filters used in protective eyeglasses, handheld filters, or stationary filters for dental curing or bleaching lights, it was found that nine of the filters had transmittance less than 0.1% in the blue‐light region and would provide adequate attenuation when used with any dental lamp on the market. Six of the filters were found to provide inadequate protection if used with the lamps for which they were recommended (88).

      6.7 Glassblowing and Foundries

Glassblowers and foundry workers can be exposed to excessive near‐IR irradiances to the eyes when working at open furnaces . Significant UV radiation may also be emitted from some types of glass in the molten state (91). Shielding, in the form of protective eyewear and possibly other barriers, is the most common means of controlling exposure. Exposure can also be reduced by increasing the distance from the hot source through the use of long handles on implements such as ladles, rods, or tongs (93).

      Glassblowers often wear didymium glass lenses to filter out intense yellow light at about 590 nm emitted by sodium in molten glass. Didymium glass has high transmittance in much of the IR region, however, and should, therefore, be combined with additional IR and UV filtering (91). Cobalt blue lenses are effective at filtering yellow light, UV, and IR. Filter lenses with shade number no less than 2.5 are recommended for work with soda lime or quartz glass (91), and higher shades may be appropriate (90).

      A guideline published by the American Foundry Society recommends shade numbers for eye protection during melting and pouring operations based on the metal being handled: iron (shade Nos. 3–5: green); steel (shade No. 8: green, or shade No. 6: cobalt blue); brass/bronze (shade Nos. 3–5: green, or shade No. 3: green with No. 3 aluminized face shield, or shade No. 6 cobalt blue half lenses); aluminum (clear, no‐tint) or magnesium (clear, no‐tint) (94).

Bibliography

      1 1. International Agency for Research on Cancer (IARC) (1997). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Vol. 55, Solar and Ultraviolet Radiation. Lyons: IARC.

      2 2. Reidenbach, H.‐D., Dollinger, K., and Hofmann, J. (2005). Results from two research projects concerning aversion responses including the blink reflex. Proc SPIE 5688: 429–439.

      3 3. Sliney, D.H., Bitran, M., and Murray, W. (2012). Infrared, visible and ultraviolet radiation. In: Patty's Toxicology, 6e, vol. 6 (ed. E. Bingham and B. Cohrssen), 169–209. New York: Wiley.

      4 4. Suess, M.J. (1989). Introduction to the second edition. In: Nonionizing Radiation Protection (ed. M. Suess and D. Benwell‐Morison), 2–3. Copenhagen: World Health Organization Regional Office for Europe.

      5 5. Diffey, B.L. (2002). Sources and measurement of ultraviolet radiation. Methods 28: 4–13.

      6 6. Commission Internationale de l'Éclairage (CIE) (1999). Standardization of the Terms UV‐A1, UV‐A2 and UV‐B, 134/1 CIE TC 6‐26 Report. Vienna: CIE.

      7 7. Hale, G. and Querry, M. (1973). Optical constants of water in the 200 nm to 200 μm wavelength region. Appl Opt 12: 555–563.

      8 8. Sliney, D. and Wohlbarsht, M. (1980). Safety with Lasers and Other Optical Sources. New York: Plenum Press.

      9 9. Wolfe, W.L. (1998). Introduction to Radiometry. Bellingham, Washington: SPIE Optical Engineering Press.

      10 10. Ryer, A.D. (1997). The Light Measurement Handbook. Peabody, Massachusetts: International Light Technologies.

      11 11. Seinfeld, J.H. and Pandis, S.N. (1998). СКАЧАТЬ