Patty's Industrial Hygiene, Physical and Biological Agents. Группа авторов
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Название: Patty's Industrial Hygiene, Physical and Biological Agents
Автор: Группа авторов
Издательство: John Wiley & Sons Limited
Жанр: Химия
isbn: 9781119816225
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6.1.1 Controls for Solar Radiation Hazards
To the extent possible, job tasks should be located indoors or under shade when exposure to solar radiation presents a risk. Work that must be conducted outdoors should be scheduled to avoid sun exposure during the period of highest solar irradiance, two hours before to two hours after solar noon.
In many occupations, however, outdoor work is unavoidable, and the only practical means of controlling exposure is the use of skin and eye protection. Protective clothing should be chosen to provide an adequate protection factor and the best coverage possible. Acceptance of protective clothing by the workers is also an important consideration (67), however, and may need to be balanced against the level of protection offered by different styles and fabrics. Sunscreens should be used on those parts of the body that are not protected by clothing but not as a substitute for wide‐brimmed hats and protective clothing. According to the American Academy of Dermatologists, sunscreens should have a minimum SPF of 30, and provide protection from UV‐A as well as UV‐B radiations (68).
6.2 Welding, Cutting, and Brazing
Arc welding produces intense radiation across the optical spectrum, from near‐IR to UV‐B and UV‐C. Erythema (similar to sunburn) and photokeratoconjunctivitis (“welder's flash”), a painful inflammation of the cornea and the lining of the eyelid, are common acute effects of overexposure to UV‐B and UV‐C from welding arcs (69). Arc welders could be at increased risk of skin and ocular cancers due to their high UV‐B and UV‐C exposure (70). Thermal burns from hot metal during welding could contribute to this risk (71). Repeated eye burns among welders have been found to be associated with the risk of ocular melanoma (72). High levels of ozone may also be generated during gas shielded arc welding (73).
Requirements for eye and face protection and protective clothing for welders were established by the American Welding Society (AWS) in the ANSI Z49.1:2012 standard, Safety in Welding, Cutting, and Allied Processes (74). The UV output of the welding process depends upon the type of welding, the material being welded, and the arc current. The appropriate eye protection filter for the welder is specified in the ANSI Z49.1 standard by shade number based on characteristics of the welding process. Welding helmets with autodarkening filters enable welders to see through the filter under ambient light while they position their work and strike the arc. A light sensor then detects the arc flash and activates an electronic device that causes a liquid crystal filter to switch from light to dark. This eliminates the old practice by some welders, who left their welding helmets flipped up until the arc was struck (62). Practitioners should ensure that equipment in use meets the requirements of the table titled “Switching Index Requirements for Automatic Darkening Welding Filter Lenses” that was provided in ANSI/ISEA standard Z87.1‐2015 (75).
FIGURE 11 A welder wears helmet, gloves, heavy jacket, and cap with neck drape.
Source: Photo by OSHA.
Protective clothing is required to protect the skin from radiation as well as other hazards of welding, including ignition, sparks, and electric shock. An example of good coverage by protective clothing is illustrated in Figure 11. Workers such as maintenance and repair personnel, whose main job function is not welding, sometimes neglect to use adequate skin protection during welding tasks. Care should be taken to ensure that workers who do not routinely perform welding are aware of the need for skin protection. Full‐time welders, too, might occasionally put themselves at risk by forgoing some protective clothing, as illustrated in Figure 12 (76).
FIGURE 12 A welding technician neglects to wear UV‐absorptive gloves while repairing an aluminum‐lithium weld.
Source: Photo by NASA (76).
In addition to the exposure to the welding operator, the arc and reflections from the arc present a hazard to assistants and bystanders. Guidance on the safe viewing distance for bystanders to control UV hazards to the skin and eye is available from AWS (77, 78). Another control measure for the protection of bystanders is to surround the welding operation with curtains. Transparent plastic welding curtains containing suitable dyes can attenuate both UV and hazardous blue‐light radiation to acceptable levels while still providing sufficient visibility of the welding process to allow visual supervision by a bystander (79).
6.3 Photocuring of Coatings in Manufacturing
Several regions of the optical radiation spectrum have been used in manufacturing for drying and curing coatings and other materials.
In the powder coating process, an alternative to solvent‐based painting or finishing, pigment in a resin powder matrix is deposited on the substrate by electrostatic attraction and heat is then used to melt the powder so that it forms a smooth, solid layer. IR lamps or ovens are often used as the heat source for the melting process.
Photocuring processes that produce cross‐linking in polymers require higher quantum energies and thus a much shorter wavelength, typically in the UV region. UV‐A is the most commonly used wavelength band for photocuring. However, xenon lamps, mercury‐vapor lamps, and metal halide lamps used for high‐powered photocuring may also emit UV‐B and UV‐C radiation. High‐power lamps for photocuring are typically enclosed in opaque housings, but stray radiation may still exceed exposure limits for UV radiation (80). There is also a potential blue‐light hazard if the source is viewed. In the case of pulsed xenon photocuring systems, the risk of retinal thermal damage should also be evaluated. Enclosures should be designed with minimal openings. Direct light from the source should not be visible to the operator or other personnel. Reflected light should be minimized by painting surfaces with black matte paint. Because ozone may be generated by UV‐C radiation, source enclosures should be ventilated to the outside. Workers should wear eye and skin protection for UV. Electrical safety and excess heat are additional concerns due to the power requirements of these photocuring systems.
Photocuring systems that use ultraviolet light‐emitting diode (ULED) technology are also available. ULEDs emit radiation in a relatively narrow band, for instance 380–420 nm, eliminating the risk of ozone generation and exposure to UV‐B and UV‐C radiation. ULED photocuring sources might still produce high UV‐A irradiances of about 1 W cm−2, sufficient to cause overexposure in a few seconds or minutes. Blue‐light exposure could also be a hazard if the source is viewed. Potentially exposed skin and eyes should be protected.
6.4 Germicidal Lamps
Low‐pressure mercury‐vapor lamps for germicidal use emit radiation primarily in a narrow peak at 254 nm. The TLV for radiant exposure to the eye or skin at this wavelength is 60 J m−2 (15), which is equivalent to a continuous irradiance of 0.002 W m−2 in an eight hours period or 60 W m−2 in one second. Some germicidal lamps also emit a small amount of radiation at 185 nm, which generates ozone. The high irradiances needed to inactivate pathogens could present a hazard to exposed personnel within a few seconds (69). Therefore, germicidal UV СКАЧАТЬ