Solar UV Radiation Profile
RADIATION – KNOWN CARCINOGEN (IARC 1)
Solar UV Radiation Profile
- Radiation from the sun between wavelengths of 100 and 400 nanometres on the electromagnetic spectrum
- Associated cancers: Skin cancer (well known); eye cancers (limited evidence)
- Most important routes of exposure: Skin or eye contact
- Occupational exposures: Approx. 1.5 million Canadians are exposed at work, primarily in construction and farming industries
- Environmental exposures: Those closer to the equator and at higher altitudes experience higher exposure levels; maximum solar radiation levels occur during the summer when the sun is at its maximum elevation
- Fast fact: The southern prairies are the sunniest place in Canada, receiving approximately 2,400 hours of bright sunshine per year.
Solar ultraviolet radiation (UVR) includes wavelengths in the electromagnetic spectrum between 100-400 nm. It is used by plants for photosynthesis and by humans to synthesize Vitamin D. The three components of UVR are UV-A (315-400 nm), UV-B (280-315 nm) and UV-C (100-280 nm).[1,2]
UVR is produced by a variety of natural and artificial light sources. The main natural source of exposure to UVR is the sun. Approximately 95% of sunlight reaching the earth’s surface is UV-A and 5% is UV-B.[1,2] UV-C from the sun is removed by the atmosphere. Levels of solar UVR exposure for the general population vary depending on geography, seasonality, time of day, and meteorology, as well as time spent out of doors and amount of skin exposed.
Over the last century, artificial sources of UVR have increasingly contributed to exposure during certain occupational and recreational activities. For more information on these exposure sources, please see Artificial UV radiation.
Solar UVR has been classified by the International Agency for Research on Cancer (IARC) as Group 1, a known human carcinogen, with a well-established link to skin cancer (cutaneous malignant melanoma and non-melanocytic skin cancer). Additional studies show associations between solar radiation and melanoma of the eye, and non-Hodgkin lymphoma. Solar UVR is the most important cause of skin cancer, and skin cancer is the most common cancer in countries with large Caucasian populations.
Regulations and Guidelines
No occupational exposure limits for solar UVR specifically were identified in Canada. In general, occupational limits for UVR exposure are applied to artificial sources, although these limits can easily be exceeded by exposure to solar radiation outdoors during the spring and summer.
For artificial UVR exposure, many Canadian jurisdictions adhere to occupational UVR threshold limit values (TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH). The ACGIH TLVs for UVR with various wavelengths in air between 180 and 400 nanometres are shown in the graph below. Under these limits, a normally-sensitive lightly pigmented adult population is not expected to experience acute effects, such as erythema (sunburn) or photokeratitis (a.k.a. “welder’s flash” or “snow blindness”). However, almost all provinces and territories exclude solar UVR in occupational UVR exposure limits (except Nova Scotia and Newfoundland and Labrador, where occupational health and safety regulations do not explicitly exclude solar in UVR limits).
TLV = threshold limit value
J/m2 = joules per square metre
Occupational exposure to solar UVR can be reduced using administrative controls, engineering controls, and personal protective equipment (PPE).[8,9] Administrative controls include scheduling, education programs, restricted access, and warning signs. Shade covers or canopies are examples of engineering controls. Clothing, hats, sunscreen, and sunglasses are the recommended forms of PPE for solar radiation. Generally, engineering controls are preferable to administrative controls or PPE, however in some cases PPE is the only feasible option.
Environmental Exposures Overview
Latitudes closer to the equator experience higher UVR levels. At these latitudes, maximum UVR levels occur during the summer when the sun is at its maximum elevation (solar noon). Higher elevations also experience higher UVR levels, because the atmosphere is thinner and absorbs less radiation. In mountainous areas UVR levels can increase 10-12% per 1000 meter gain in elevation.[11,10]
In 1992, Environment Canada developed a UV Index to inform Canadians about the strength of solar UVR. The UV Index scale ranks the intensity of UV from 0-11+ (low to extreme). Levels as high as 11+ are rare in Canada, but the UV Index may reach up to 14 or 15 in the tropics.[13,14] Forecasts of UV index levels are accompanied by corresponding recommendations for sun protection measures.
The southern prairies are the sunniest places in Canada, receiving approximately 2,400 hours of bright sunshine per year. In contrast, St. John’s, NL receives the least sunshine, averaging approximately 1,500 hours per year.
Occupational Exposures Overview
Exposure to solar UVR may be dermal or ocular in occupational settings.
CAREX Canada estimates that approximately 1.5 million Canadians are likely exposed to solar ultraviolet radiation in their workplaces.
All outdoor occupations have a potential for exposure to solar radiation. The largest industrial groups exposed include the construction industry, farming, and services to buildings and dwellings. The largest occupational groups exposed are farmers and farm managers, construction trades helpers, and landscaping and ground maintenance labourers.
Other job categories with a potential for exposure to solar UVR include logging, fishing, open-pit mining, road building, and maintenance, as well as athletes, maintenance workers, pipeline workers, military personnel and police, ski instructors, lifeguards, oilfield workers, postal carriers, surveyors, sailors, and railway track workers.[5,13] Indoor workers receive only 10-20% of outdoor workers’ annual exposure to solar UVR.
According to the Burden of Occupational Cancer in Canada project, occupational exposure to solar radiation leads to approximately 4,600 non-melanoma skin cancers each year, based on past exposures (1961-2001).[16,17] This amounts to 6.3% of non-melanoma skin cancer cases diagnosed annually. Most occupational non-melanoma skin cancers associated with solar radiation occur among workers in the agricultural and construction sectors. Work-related solar radiation exposure resulted in approximately $34.2 million in costs for newly diagnosed non-melanoma skin cancer cases in 2011.
For detailed estimates of exposure to solar ultraviolet radiation, see the occupational exposures tab.
The Sun Safety at Work Canada project has developed a series of resources and tools that workplaces can use to identify, assess, and control occupational exposure to solar radiation.
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