Solar radiation incorporates the majority of the electromagnetic spectrum, including ionizing radiation (cosmic, gamma and x-rays), optical radiation (ultraviolet, visible and infrared) and radio frequency radiation. Wavelengths between 100-400 nm in the optical band are known as broad spectrum ultraviolet radiation (UVR) and are used by plants for photosynthesis and by humans to synthesize Vitamin D. These wavelengths can also be the most damaging to living things. The three components of UVR are: UV-A (315-400 nm), UV-B (280-315 nm) and UV-C (100-280 nm).[2,3]
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.[2,3] UV-C from the sun is removed by the atmosphere. Levels of solar UVR exposure for the general population vary depending on conditions related to geography, seasonality, time of day and meteorology, as well as time spent out of doors and the amount of exposed skin surface.
Over the last century, artificial sources of UVR have provided an increasing contribution to exposure, during certain occupational and recreational activities. For more information on these exposure sources, please see Artificial UV radiation.
Solar radiation has been classified by IARC as a Group 1 carcinogen, known to be a human carcinogen (3), with a well-established link to skin cancer (cutaneous malignant melanoma and non-melanocytic skin cancer). Additional studies have found associations between solar radiation and melanoma of the eye and non-Hodgkin lymphoma. Solar UV is the most important cause of skin cancer, and skin cancer is the most common cancer worldwide.
No occupational exposure limits for solar radiation 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 UV radiation exposure, many Canadian jurisdictions adhere to occupational UV threshold limit values (TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH). The ACGIH TLVs for UV radiation with various wavelengths in air between 180 and 400 nanometres are shown in a table 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 radiation in occupational UVR exposure limits (except Nova Scotia and Newfoundland and Labrador, where occupational health and safety regulations do not explicitly exclude solar UV in UVR limits).
J/m2=Joules per square metre
Administrative controls, engineering controls and personal protective equipment (PPE) are methods which are used to control occupational exposure to solar UV radiation[9,10]. Administrative controls include scheduling, education programs, restricted access and warning signs. Shade covers or canopies are an example of the type of engineering controls which can be applied in workplaces. Clothing, 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.
Exposure to solar radiation may be dermal or ocular.
CAREX Canada estimates that approximately 1.5 million Canadians 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, followed by farming, and then 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 include: logging, fishing, open-pit mining, road building and maintenance, athletes, maintenance workers, pipeline workers, military personnel and police, ski instructors, lifeguards, oilfield workers, postal carriers, surveyors, sailors and railway track workers.[1,6,11] Indoor workers receive only 10-20% of outdoor workers’ annual exposure.
Latitudes closer to the equator experience higher UV levels. At higher latitudes, maximum UV levels occur during the summer when the sun is at its maximum elevation (solar noon).
Higher elevations have a thinner atmosphere to absorb solar UV radiation; in mountainous areas UV levels can increase 10-12% per 1000 meter gain in elevation.
In 1992, Environment Canada developed a UV Index to inform Canadians about the strength of solar UV rays. 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.[11,14] Forecasts of UV levels are accompanied by corresponding recommendations for sun protective measures.
The southern prairies are the sunniest place in Canada, receiving approximately2400 hours of bright sunshine per year. In contrast, St. John’s, NL is Canada’s city with the least sunshine per year, averaging approximately 1,512 hours per year.
Our team has performed a detailed scan of exposure control resources and assembled a compilation of key publications and resources. These are organized by type of exposure (environmental or occupational) and by specificity (general or carcinogen-specific). Please visit our Exposures Reduction Resources page to view.
We also recommend exploring the Prevention Policies Directory, a freely-accessible online tool offering information on policies related to cancer and chronic disease prevention. Providing summaries of the policies and direct access to the policy documents, the Directory allows users to search by carcinogen, risk factor, jurisdiction, geographical location, and document type. Click here to learn more about policies specific to solar radiation in the Directory. For questions about this resource, please contact a member of the Prevention Team at the Canadian Partnership Against Cancer at firstname.lastname@example.org.