Ultraviolet Radiation

Characteristics of UV Radiation

Fate and Transport of UV Radiation

Monitoring UV Radiation

Exposure Pathways

Methods of Measurement of Human Exposure

Prevention of Exposure

Harmful Effects

Dose Response

Absorption, Distribution, Metabolism

Sites of Toxicity

Biomarkers of Disease

Molecular Mechanism of Action

Risk Assessment and Risk Management

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Methods for Measuring Human Exposure to Ultraviolet Radiation

Health effects and environmental concerns have initiated the monitoring of UV radiation. Human exposure is detected through the use of Broad- band instruments. The National Weather Service has designed a computer model to calculate the next day’s UV levels. The calculation takes into account; ozone, overhead cloud cover, latitude, elevation, and time of year.

To determine the UV index, the dose rate, or the amount of UV radiation a person will be exposed to at noon under a clear sky is calculated. The dose rate is then adjusted for the effects of elevation and cloud cover. At a high elevation, the dose rate will increase due to less atmosphere to absorb and scatter UV rays. More clouds will reduce the UV dose rate because clouds screen out some UV rays.

The UV index is a scale for measuring the amount of UV radiation reaching the ground and posing danger to humans. On a scale of 0-10, 0 is minimal exposure, 10 is very high exposure.

  • 0-2 indicates little danger. Most people can stay outside one hour without burning.
  • 3-4 is low risk. An average person can withstand a half hour without burning.
  • 5-6 is a moderate risk. Twenty to Thirty minutes is the limit in noon sun.
  • 7-8 is high risk. The sun should be avoided from 10am to 4pm. Thirteen to twenty minutes of exposure can lead to burning.
  • 9-10 is very high risk. Burning can occur in less than thirteen minutes.

Using the UV Index

The UV Index can help the public be aware of the level of UV radiation exposure expected on a given day. As a result, people can use simple sun protective behaviors to reduce their lifetime risk of developing skin cancer and other sun-related illnesses. What follows is a description of each UV Index level and tips you can give to help people prepare.

0 to 2: Minimal A UV Index reading of 0 to 2 means minimal danger from the sun's UV rays for the average person: Most people can stay in the sun for up to 1 hour during the hours of peak sun strength, 10 a.m. to 4 p.m., without burning. People with very sensitive skin and infants should always be protected from prolonged sun exposure. Look Out Below Snow and water can reflect the sun's rays. Skiers and swimmers should take special care. Wear sunglasses or goggles, and apply sunscreen with an SPF of at least 15. Remember to protect areas that could be exposed to UV rays by the sun's reflection, including under the chin and nose.

3 to 4: Low A UV Index reading of 3 to 4 means low risk of harm from unprotected sun exposure. Fair-skinned people, however, might burn in less than 20 minutes: Wear a hat with a wide brim and sunglasses to protect your eyes. Use a sunscreen with an SPF of at least 15 and wear long-sleeved shirts and long pants when outdoors. Me and My Shadow An easy way to tell how much UV exposure you are getting is to look for your shadow: If your shadow is taller than you are (in the early morning and late afternoon), your UV exposure is likely to be low. If your shadow is shorter than you are (around midday), you are being exposed to high levels of UV radiation. Seek shade and protect your skin and eyes.

5 to 6: Moderate A UV Index reading of 5 to 6 means moderate risk of harm from unprotected sun exposure. Fair-skinned people might burn in less than 15 minutes. Apply a sunscreen with an SPF of at least 15. Wear a wide-brim hat and sunglasses to protect your eyes: Use sunscreen if you work outdoors and remember to protect sensitive areas like the nose and the rims of the ears. Sunscreen prevents sunburn and some of the sun's damaging effects on the immune system. Use a lip balm or lip cream containing a sunscreen. Lip balms can help protect some people from getting cold sores. Made in the Shades Wearing sunglasses protects the lids of your eyes as well as the lens.

7 to 9: High A UV Index reading of 7 to 9 means high risk of harm from unprotected sun exposure. Fair-skinned people might burn in less than 10 minutes. Minimize sun exposure during midday hours, from 10 a.m. to 4 p.m. Protect yourself by liberally applying a sunscreen with an SPF of at least 15. Wear protective clothing and sunglasses to protect the eyes: When outside, seek shade. Don't forget that water, sand, pavement, and grass reflect UV rays even under a tree, near a building, or beneath a shady umbrella. Wear long-sleeved shirts and trousers made from tightly woven fabrics. UV rays can pass through the holes and spaces of loosely knit fabrics. Stay in the Game Be careful during routine outdoor activities such as gardening or playing sports. Remember that UV exposure is especially strong if you are working or playing between the peak hours of 10 a.m. and 4 p.m. Don't forget that spectators, as well as participants, need to wear sunscreen and eye protection to avoid too much sun.

10+ Very High A UV Index reading of 10+ means very high risk of harm from unprotected sun exposure. Fair-skinned people might burn in less than 5 minutes. Outdoor workers are especially at risk as are vacationers who can receive very intense sun exposure. Minimize sun exposure during midday hours, from 10 a.m. to 4 p.m. Apply sunscreen with an SPF of at least 15 liberally every 2 hours: Avoid being in the sun as much as possible. Wear sunglasses that block 99 to 100 percent of all UV rays (both UVA and UVB). Some reduction in blue light also might be beneficial but colors should not be severely distorted. Wear a cap or hat with a wide brim, which will block roughly 50 percent of UV radiation from reaching the eyes. Wearing sunglasses as well can block the remainder of UV rays. Beat the Heat If possible, stay indoors on days when the UV Index is very high. Take the opportunity to relax with a good book rather than risk dangerous levels of sun exposure. Try not to pursue outdoor activities, whether at work or at play, unless protected with sunscreen, hat, and sunglasses.