The effective irradiance changes with distance. If the effective irradiance is known at a certain distance but not known at the position of exposure it can be calculated with information from Appendix A. If there are any doubts about the application of these limits, please contact the University of Toronto’s Radiation Protection Service (RPS).

For high-power UV radiation sources, overexposure can occur in a few seconds. As mentioned above there are no immediate warning symptoms to indicate a UV radiation overexposure. Symptoms of overexposure including varying degrees of erythema (sunburn) or photokeratitis (welder’s flash) typically appear hours after exposure has occurred.

The limit for occupational exposure to non-coherent artificial UV radiation incident upon the skin or eyes is 30 J/m2 (or 3 mJ/cm2) [2; 3; 4; 5].

All persons with access to open UV radiation must receive training covering: UV radiation hazards identification, health effects, signs, engineering control measures, and operating procedures.

UVA penetrates the most in the eye and the skin and is absorbed in the lens and the subcutaneous layer of the skin. Having less energy per photon than UVB and UVC radiation, UVA radiation cannot cause direct DNA damage but can create free radicals and oxidative stress which can cause indirect DNA damage. UVB and UVC are absorbed in the cornea and the dermis and epidermis. These types of UV radiations carry a higher amount of energy per photon and can cause direct DNA damage.

UV lightwavelength

For how long may a person be irradiated by a lamp with effective irradiance at 1 m of  91.3 μW/cm2 without reaching the UV limit if the distance from the lamp is 50 cm?

The workplace supervisor is required to identify all potential UV radiation hazards associated with the workplace and equipment and then restrict all unauthorized workers and people from proximity to the equipment or work area. The workers operating the equipment need adequate training to understand the hazards involved and to carry out their work safely.

Coherent and non-coherent ultraviolet (UV) light sources are used in a variety of situations. The safe use of coherent UV light is covered in the University of Toronto Laser Safety Program. The safe use of non-coherent artificial UV radiation sources in buildings under the authority of the University of Toronto is covered by the Ultraviolet Radiation Safety Program.

Warning signs are available from commercial suppliers or may be available from the manufacturer of the ultraviolet light product. Examples of commercially available UV warning signs are:

UV lightuses

When enclosures with fail-safe interlocks, curtains or barriers cannot be installed, the distance from which workers operate the equipment must be assessed as well as the duration of any exposure.

ArtificialsourcesofUV light

Short over-exposure of the eyes to UV radiation can injure the cornea. Photokeratitis is a painful inflammation of the eye caused by UV radiation-induced lesions on the cornea. Symptoms include a sensation of sand in the eye that may last a few days.

For some of the described sources, the user may not be fully protected from UV light exposure by any inherent shielding around the source, or the user may not be aware of the hazards of UV light. The purpose of the UV Radiation Safety Program is to ensure that the safeguards necessary to limit exposure have been implemented.

The intensity of UV radiation decreases with the distance. UV rays are predominantly emitted perpendicular to the surface of the lamp. To determine the intensity of UV radiation on a surface at different distances from a UV lamp, multiply the effective irradiance of the lamp rating at 1 meter (in μW/cm2) by the correction intensity factor for the distance selected as in Table 4. This table provides an approximate simplified method for quickly calculating UV radiation Eeff at different distances when Eeff at a certain distance is known and when air absorption is neglected.

RPS does not routinely measure the intensity of UV radiation or determine the duration of an individual’s permitted use time. RPS will survey a source for light intensity upon request or if an accidental exposure is suspected and it is necessary to determine the potential extent of the injury. Sources may also be surveyed at the discretion of RPS.

For broadband sources emitting a range of wavelengths in the UV region (i.e., most UV unfiltered radiation sources), determination of the effective irradiance of such a broadband source is done by weighting all wavelengths present in the emission with their corresponding spectral effectiveness by using the following weighting formula:

When unprotected UV lights are used in the room, access to the room must be restricted to persons with training and wearing personal protective equipment (PPE). A warning light indicating that the UV light is on must be visible from outside the room.

UV light sourcesin home

When the exposure is from artificial sources, engineering control measures are preferable to protective clothing, goggles, and procedural safety measures. Light-tight cabinets and enclosures (including dedicated rooms) enclosed with opaque materials or UV radiation-absorbing glass and plastic shielding and fail-safe interlocks are the key engineering control measures used to prevent human exposure to UV radiation. For applications where cabinets are not practical, shields, curtains, barriers, and a suitable separation distance are used to protect individuals against the UV radiation emitted by open sources.

The exposure limit is based on a normal 24-hour cycle of light and dark where cellular repair takes place mainly when the exposure is discontinued. The exposure limit is intended to be used as a guideline only for Solar UV Radiation exposure.

Every device that can produce UV radiation above the exposure limit must have a warning sign with the following (or similar) content:

Ultravioletlightexamples

All supervisors of workplaces where the potential for exposure to artificial UV radiation exists must register the equipment with the University’s Radiation Protection Service.

UV lightsource spectrophotometer

Naturaluv light sources

NOTE: When using UV radiation as a germicidal control the following factors can influence the efficiency of the UV lamp:

A high-power UV radiation source must have failsafe interlock access so that it is shut off when the protective enclosure is open.

UV radiation can initiate a photochemical reaction called erythema in exposed skin. This “sunburn” can be quite severe and can occur as a result of only a few seconds of exposure. Effects are exacerbated for skin photosensitized by agents such as coal tar products, certain foods (e.g., celery root), certain medications and photo allergens.

Warning signs, lights and labelling of potential equipment that emits UV radiation are additional measures that may be used to aid the protection of workers (see Appendix B).

A Radiation Safety Officer (RSO) will perform an annual inspection of all existing areas where UV radiation is used and where the possibility of UV radiation exposure above the acceptable limit may be present. In addition, all new equipment or devices that can produce high levels of UV radiation will be inspected by the RSO before the equipment or device is used.

Good sources of information about your UV lamp will be the manufacturer’s webpage. Usually, the effective irradiance of the UV lamps is given at 1 m.

UV radiation is easily absorbed by clothing, plastic, or glass. In case of working with open UV radiation during maintenance, service, or other situations, particularly if safety shielding is removed, all personnel will be provided with personal protective equipment covering all areas of skin, eyes, and face. Long-sleeve lab coats, gloves, eyeglasses, and face shields must be used.

UV exposure induces the production of vitamin D in the skin. Vitamin D has regulatory roles in calcium metabolism (which is vital for the normal functioning of the nervous system, as well as for bone growth and maintenance of bone density), immunity, cell proliferation, insulin secretion, and blood pressure. Too little UV radiation may lead to a lack of vitamin D. An appropriate amount of UV (which varies according to skin colour) leads to a limited amount of direct DNA damage. This DNA damage is recognized and repaired by the body, and then melanin production is increased, which leads to a long-lasting tan. This tan occurs with a 2-day lag phase after irradiation.

If the effective irradiance is a superposition of different wavelengths, it can be determined by using the formula and information from Appendix A.

5 uses of ultraviolet rays

In humans, prolonged exposure to UV radiation may result in acute and chronic health effects on the skin, eyes, and immune system. An unfortunate property of UV radiation is that there are no immediate warning symptoms to indicate overexposure. Symptoms of overexposure including varying degrees of erythema (sunburn) or photokeratitis (welder’s flash) typically appear hours after exposure has occurred.

Permissible exposure time (measured in seconds) for exposure to UV radiation incident upon unprotected skin or eyes may be computed by dividing the 30 J/m2 (or 3 mJ/cm2) exposure limit by the effective irradiance measured in W/m2 (or mW/cm2). The maximum exposure duration may also be determined using Table 1 which provides representative exposure durations corresponding to effective irradiances in W/m2 (and mW/cm2).

Overexposure to UV radiation can cause sunburn and some forms of skin cancer. However, the deadliest form – malignant melanoma – is mostly caused by indirect DNA damage. UVC rays are the highest energy, most dangerous type of ultraviolet light. Chronic skin exposure to UV radiation has also been linked to premature skin ageing, skin darkening, and wrinkles. Chronic eye exposure to UV radiation can create cataracts.

The UV part of the electromagnetic radiation spectrum extends from 3.1 eV (400 nm) to 124 eV (10 nm). Most of the UV radiation is absorbed in the air and does not pose a health risk. However, UV radiation in the range from 400 nm to 180 nm is less absorbed in the air and can cause harm to the eyes and the skin. This portion of the UV spectrum is separated into three parts: UVA from 400 nm to 315 nm, UVB from 315 nm to 280 nm, and UVC from 280 nm to 180 nm. Most of the UVC from the Sun is absorbed by the atmosphere. The UVC radiation produced by artificial sources can pose a health risk to a person in the vicinity.

When the possibility of producing ozone is high, the ozone concentrations can increase over the limits. Most people can naturally detect about 0.01 ppm of ozone in the air where it has a very sharp, specific odour, somewhat resembling chlorine bleach. Exposures of 0.1 to 1 ppm produce headaches, burning eyes, and irritation to the respiratory passages.

The current UV radiation safety program does not cover exposure to solar UV light. Exposure to solar UV radiation is the predominant cause of skin cancer, particularly when the sun is highest in the sky, such as in summer during the middle of the day. Limiting UV light exposures at these times has the greatest potential for reducing skin cancer incidence. The best approach to implementing successful strategies in reducing skin cancer will be to encourage sun protection policies and practices that reduce sun exposure in both occupational and recreational activities. Solar UV radiation also affects the eyes by increasing the risk of photokeratitis, photo conjunctivitis and cataracts. Wearing sunglasses and a broad-brimmed hat can prevent most of the UV light from reaching the eyes.

The University of Toronto is committed to ensuring that the use of UV radiation sources is carried out safely with due regard for employees, students, the public and the environment. The University of Toronto Radiation Protection Authority (UTRPA) is the executive body charged with ensuring that effective radiation safety programs exist for all sources of radiation. The Radiation Protection Service (RPS) is responsible for the development and administration of radiation safety programs.