7 Shade Planning for America’s Schools Chapter 1 How Is UV Radiation Measured? In the past, different countries measured and reported solar UV radiation intensity in different ways. One common way of reporting UV radiation intensity was in the form of estimated “burn time” or “time to burn,” expressed as the number of minutes of solar exposure required for the reddening of a fairskinned person’s exposed skin, assuming a clear sky. Although there may be some advantages to this method of reporting UV radiation intensity, there are a number of disadvantages. In 1994, international agreement was reached on standardizing the measure of UV radiation intensity. Revised by the World Health Organization in 2002 and adopted by the Environmental Protection Agency and the National Oceanic and Atmospheric Administration’s National Weather Service in 2004, the UV Index is the internationally accepted system for reporting the intensity of UV radiation. Although the mathematical model developed to determine the UV Index might be complicated, the measurement is easy to understand. The UV Index is a measure of the amount of damaging UV radiation that reaches the earth’s surface at noon on a given day and at a given location, expressed as a risk scale. It is predicted daily on a scale of 0 to 11+, where 0 represents a minimal risk of overexposure to UV radiation and any number higher than 11 represents an extreme risk of overexposure to UV radiation. Q: Where do I find the UV Index for tomorrow? A: In most communities, the UV Index is reported in newspapers and on television with the daily weather forecast. Every day at approximately 1:30 PM Eastern, the National Oceanic and Atmospheric Administration (NOAA) and the Environmental Protection Agency (EPA) post the UV Index for the next day at the EPA’s Website, http://www.epa.gov/sunwise/ uvindex.html. Shade Planning Toolbox What Are the Health Effects of Exposure to UV Radiation? Few people would dispute the beneficial effects of solar radiation. The sun warms the earth, fuels photosynthesis, and ensures the continued existence of life on earth. Many of us enjoy the warmth of the sun on our skin. But at some point in our lives, most of us have experienced the painful effect of too much sun exposure in the form of sunburn. Having experienced sunburn, many would agree that there must be some negative health effect to exposure to the sun. Although many different conditions occur as a normal response to exposure to UV radiation, they all fall into one of two classifications, acute or chronic. Acute effects of UV radiation exposure usually have a rapid onset and are of short duration, such as sunburn, tanning, and synthesis of vitamin D3 . Chronic effects of UV radiation exposure usually have a gradual onset and are of long duration, such as skin cancer and photoaging. Sunburn Sunburn is an acute injury resulting from excessive exposure to the sun. The redness associated with sunburn results from the dilation of superficial blood vessels in the skin. Redness usually appears within 4 hours of exposure, reaches a maximum within 12 hours, and fades after a few days. High doses of UV radiation can result in blistering and peeling. Skin color, hair color, eye color, and freckles all are characteristics that help predict an individual’s susceptibility to sunburn. Individuals are typically grouped into one of six
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