Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 138

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, E_{solar eff}. E_{solar 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 E_{solar 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.