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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 might be in the sun for eight hours or more a day. On the other hand, since the solar irradiance is determined for a horizontal surface, the noontime UVI based on solar irradiance could tend to overestimate the risk to workers in a vertical posture.
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