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
isbn:
5.3.2 Visible and IR Shielding
Various absorptive filter media are available for eyewear to attenuate visible and IR radiation. Sunglasses marketed to airline pilots as protective against blue light exposure were found to provide sufficient protection against the solar blue‐light hazard at flying altitude as well as at ground level (49). Protective eyewear with known attenuation in the blue region should be used for protection against the blue‐light hazard from artificial sources.
Tinted eyewear that does not attenuate light uniformly across the visible spectrum may alter color perception, potentially inhibiting the ability to distinguish color‐coded safety signals and markings. Under the ANSI Z87.1‐2015 standard for eye and face protection (58), visible light filters that transmit 13.9% or more of visible light (and are thus suitable for wearing while driving a vehicle) must comply with the light transmittance requirements of the ANSI Z80.3‐2010 standard for nonprescription sunglasses, which include traffic signal recognition. However, brown‐tinted sunglasses that met the ANSI Z80.3 standard were found to distort color perception among railroad workers in Canada such that yellow railroad signals appeared red to some individuals (59). When color distortion could compromise safety or job performance, a neutral gray tint, which attenuates visible wavelengths uniformly, should be considered when selecting filtering eyewear, provided that adequate attenuation of any blue‐light hazards present can be achieved without excessive darkening of vision overall.
In some cases, extremely high radiant energy absorbed by a filter could potentially raise its temperature high enough for the filter to become a significant source of IR itself, or even to melt. A reflective coating of certain metals such as gold or copper can block some of the radiation from entering a filter, enhancing the filter's performance, though with some reduction in transmission of visible light. Alternatively, interference filters have recently been developed for use in near‐IR protective eyewear that may provide IR reflectance and visible light transmittance similar to that of reflective filters while showing more resistance to mechanical damage such as cracking, scratching and delamination (60, 61).
Reflective aluminized clothing, illustrated in Figure 10, is widely used for protection against radiant heat stress. Barrier creams with reflective flecks are available for application to skin that could be exposed to high levels of IR.
5.3.3 Filter Shade Numbers
The ANSI Z87.1‐2015 standard for eye and face protection established transmittance requirements for general‐purpose filter lenses, which are identified by shade numbers (58). Shade number is determined by the manufacturer of the lens using the following formula:
(29)
where TL is the luminous transmittance (the nominal fraction of photopic‐weighted visible light that is transmitted through the filter). A maximum effective transmittance in the “far‐UV” region (200–315 nm) and a maximum IR average transmittance (780–2000 nm) are specified by the standard for each shade number. The transmittance of blue‐light‐weighted radiation for a shade must be less than the luminous transmittance for that shade.
FIGURE 10 Firefighters on a field training exercise wear aluminized clothing for protection against radiant heat.
Source: Photo by Airman 1st Class Kathrine McDowell, U.S. Air Force.
6 BROADBAND OPTICAL RADIATION IN SPECIFIC PROCESSES
The nature and degree of hazards posed by optical radiation exposure in the workplace depend foremost on the spectral distribution of the radiation, which is a function of the radiation source(s) present. It is, therefore, sensible to approach occupational exposures by type of source, or by type of process that uses optical radiation sources. Quantitative assessment of optical radiation hazards can be difficult, requiring specialized instrumentation and complex mathematical manipulations. In practice, the industrial hygienist in the workplace must often rely upon guidelines developed by standards‐setting bodies or recommendations from manufacturers that specify control measures based on easily accessible information about the source and the exposure conditions (62). In this section, optical radiation hazards and recommended controls are discussed for specific processes and sources.
6.1 Solar Radiation Exposure to Outdoor Workers
Many occupational groups are exposed to solar radiation because the location of their work is outdoors. Occupations exposed to the sun year‐round and full‐time include farmworkers, groundskeepers, construction workers, and postal carriers. Occupations that are exposed either part‐time or seasonally may include maintenance workers, mechanics, beach lifeguards, ski instructors, and carnival and amusement park workers.
For most occupational exposures to solar radiation, the hazards – principally skin cancer, sunburn, and cataract due to solar UV – will not be different from those to the general public, except that workers may be exposed for longer times than the general public. Significant solar UV dose can be received at any time of the day between sunrise and sunset. Although the solar irradiance decreases when the sun is low in the sky, the direct rays will intercept a larger cross section of a standing person's body than when the sun is high overhead. Outdoor workers may receive actinic UV‐radiation doses several times higher than the TLV during a daytime work shift. Additionally, solar IR radiation can contribute to heat stress.
Unless direct measurements of erythemal effective radiation are made (see Section 4.2.2), the Global Solar UVI is often the most convenient means to assess solar UV risk. The UVI is often reported along with the weather forecast in the news media and is available online from meteorological services in many countries (63). The UVI is a dimensionless number that is computed from the erythemal effective irradiance from solar radiation between 250 and 400 nm, Esolar eff. Esolar eff may be measured using either a spectroradiometer or a broadband detector at a monitoring station, or it may be modeled based on atmospheric conditions (64). The UVI is equal to Esolar eff measured in W m−2, multiplied by 40 and rounded to the nearest integer. For example, if the erythemal effective solar irradiance is 0.16 W m−2, the UVI is 6. Because the solar irradiance changes throughout the day, the UVI reported in weather forecasts is usually the predicted maximum level for the day, occurring around solar noon (65). The UVI forecast can be presented together with simple messages to the public (66):
UVI 1 or UVI 2. Low risk. No sun protection is required.
UVI 3–7. Medium to high risk. Seek shade during midday hours. Wear shirt, hat, and sunscreen.
UVI 8–11+. Very high to extreme risk. Avoid being outside during midday hours. Seek shade. Be sure to wear shirt, hat, and sunscreen.
Although these risk level designations and messages may be appropriate for members of the general public engaged in part‐time outdoor leisure activities such as sunbathing, they do not adequately address the risk to workers who СКАЧАТЬ