UV radiation exposure

Biological effects

Absorption by skin

Excessive doses of ultraviolet radiation cause photochemical damage of tissue: UV photons disrupting DNA structures directly, or indirectly from free radical formation. The skin can suffer mild effects such as erythema (redness) of the skin, to blistering and swelling; to severe effects, such as skin cancer. The eyes can suffer from corneal burns and cataract formation. A summary of the benefits and negative effects of UV radiation on the skin and eyes are summarized on the WHO website [1] as well as the Canadian Centre for Occupation Health and Safety [2].

The absorption depth of UV radiation by the skin changes with wavelength, as seen in Figure 1. The UV-C band – a far-ultraviolet band absorbed by our atmosphere but present in many industrial sources – is absorbed by the dead skin layers [3,4], but in the UV-A band, the radiation penetrates as deep as the dermis layer.

In response to the presence of UV radiation, the epidermis layer produces melanin to counteract the photochemical damage caused by ultraviolet radiation. The melanin is distributed in the stratum corneum as well as the epidermis layer of the skin [4]. The epidermis continually produces new skin cells, helping to mitigate the damage induced in this region.

Skin type

Skin type plays a role in an individual's responsivity to UV light [5]. A numerical classification system (Fitzpatrick scale) was developed to categorize skin types as follows:

References

[1] WHO. (Accessed 2013, May 23). Fact sheet No 305: Ultraviolet radiation and human health [Online]. (No longer available online).

[2] Canadian Centre for Occupational Health and Safety. (Accessed 2013, May 23). Ultraviolet Radiation : OSH Answers [Online]. Available: www.ccohs.ca/oshanswers/phys_agents/ ultravioletradiation.html

[3] Health Physics Society. (Accessed 2013, May 23). Ultraviolet Radiation [Online]. Available:www.hps.org/hpspublications/articles/uv.html

[4] R. Henderson, K. Schulmeister, Laser Safety. Bristol, UK: IoP Publishing, 2004

[5] R.L. McKenzie et al., "UV Radiation: Balancing Risks and Benefits," Photochem. and Photobiol. vol.85, pp.88-98, 2009, doi: 10.1111/j.1751-1097.2008.00400.x

Chemical photosensitivity

Photosensitivity is an enhanced skin response, like an exaggerated sunburn reaction, from the combined effect of a light source and a chemical agent. There are many medications and topical agents that can cause photosensitivity.

A list by class of medication is presented below with examples of the chemicals involved in causing enhanced UV photosensitivity. The references for this list follows the table. If you have any questions about the photosensitivity of your medications or topical solutions, consult your doctor or a pharmacist.

References

[1] D.E. Moore , “Drug-Induced Cutaneous Photosensitivity: Incidence, Mechanism, Prevention and Management”, Drug Safety. vol. 25, pp.345-372, 2002. doi: 10.2165/00002018-200225050-00004

[2] International Commission on Non-Ionizing Radiation Protection, “ICNIRP Statement on protection of workers against ultraviolet radiation”, Health Phys. vol. 99, pp.66-87, 2010. doi:10.1097/HP.0b013e3181d85908

Field work

Awareness of the Global Solar UV Index, the maximum daily UVI for the region you are working in, and the protection required for each UVI range as discussed on the Outdoor work page should be consulted. In addition, UVI variation occurs with these geological factors:

Altitude

UV radiation increases by 4 % for every 300 m of elevation and as much as 10 % to 12 % with every km of elevation.

Latitude

Daily UV maximums are highest in the tropics and are very low in the polar regions [1].

Elements

Snow can reflect up to 80 % of UV. Dry sand can reflect 15 % and sea foam reflects 25 % of the UV radiation.

References

[1] R.L. McKenzie et al., "UV Radiation: Balancing Risks and Benefits," Photochem. and Photobiol. vol.85, pp.88-98, 2009, doi: 10.1111/j.1751-1097.2008.00400.x

Outdoor grounds work

When working outdoors, awareness of the daily UV Index (UVI) maximum is recommended. The maximum daily UVI prescribes specific UV protection (WHO, CCOHS) to avoid excessive exposure to solar UV radiation. In many cases, the following prescriptions are necessary:

Shade

As the sun’s elevation changes throughout the day, periods of peak elevation increases the UVI. Nearly 60 % of the daily UV received on the surface occurs between 10 am and 2 pm and it is recommended that you seek shade during this time period.

Clothing

Wide-brimmed hats that cover the eyes, face and neck should be worn. Sunglasses that block 99 % - 100 % UV-A and UV-B are also recommended.

Sunscreen

Broad spectrum sunscreen with an SPF 30+ should be applied on areas of the skin that are not covered by clothing. Sunscreen should not be used to prolong the duration of exposure to the Sun.

The Global Solar UV Index (UVI) is a simple indication of UV radiation levels reaching the surface of the Earth. The threshold for using the above protection is a UVI of 3. Each range has the following prescriptions:

1-2: No extra UV protection required
3-7: Seek shade and apply clothing, hat and sunscreen
7+: Avoid midday sun by seeking shade at peak hours. Clothing, hat and sunscreen are a must.

There are two forms of ultraviolet radiation on campus: incoherent (plamas and lamps) and coherent (lasers). The term ‘industrial’ is used here to be distinguished these sources from our natural source: the Sun.

The UV exposure limits can be reached much more quickly than with a lamp; however, UV exposure limits with either source can be reached quite rapidly as discussed below.

Lasers

Excimer lasers (XeCl, KrF, ArF) and diode-pumped solid state lasers (mainly frequency-tripled (3ω) and quadrupled (4ω) Nd:YAG laser beams) are coherent, industrial sources of UV radiation.

Example of UV dosage: An unfocused krypton fluoride (KrF) excimer laser (248 nm) producing a 30 mJ pulse in an 8 mm by 3 mm beam generates a radiant exposure of 125 mJ/cm² in one pulse, which exceeds the threshold limit value by more than 10 times in that pulse. Note that these pulsed sources can operate at 10 Hz to 100 Hz, so the user would exceed the threshold exposure limit by 100 to 1000 times in one second.

Lamps

Mercury vapour lamps used as a germicidal lamp or spectral calibration source, or to induce fluorescence in chemical and mineral samples are an incoherent, industrial source of UV radiation on campus. These lamps typically convert about 33 % of the indicated electrical energy into 254 nm photons.

Example of UV dosage: A 15 W bulb produces about 5 W of UV light at 254 nm. If treated as a point source with a user standing 50 cm from that lamp, the user would experience an irradiance of 0.16 mW/cm² and it would take nearly a minute to reach the threshold limit for that wavelength. Note that a point source approach is a simplification since the lamp could also be treated as a line source; however, a point source approach is a reasonable back-of-the-envelope approximation [1].

References

[1] P.J. Meechan, C. Wilson, “Use of Ultraviolet Lights in Biological Safety Cabinets: A Contrarian View,” Appl. Biosafety, vol. 11, pp. 222-227, 2006. 

The Ontario Ministry of Labour has recommended engineering controls and personal protection to protect oneself from common sources of UV radiation in the workplace. Below are various controls that have been implemented wherever possible to minimize exposure and mitigate the risks associated with germicidal lamps inside Biological Safety Cabinets.

Engineering controls

• Containment/Location: Limit access to those working directly with the equipment by locating equipment in a separate room or a low traffic area.  Use UV-absorbing glass or plastic shields
• Interlocks: Some equipment has built-in interlock devices that prevent operation when safety may be compromised.  Never tamper with interlocks, and repair when damaged.
• Eliminate Reflection: Many surfaces, especially shiny ones, reflect UV rays.  If possible, paint such surfaces with non-UV-reflecting material
• Check safety equipment to ensure that it is rated for the wavelength in use.
• Close the sash hood completely if using UV lights in a BSC

Administrative controls

• Training: Personnel should be trained in correct and safe procedures of preparing, start-up, working inside and post-working inside Biological Safety Cabinets
• Warning Signs: All potentially dangerous areas should be conspicuously labelled with warning signs e.g. “UV HAZARD-PROTECT EYES AND SKIN”

Personal protection

• Limit time and distance when working with UV-producing equipment
• Wear lab coat and long pants
• Gloves: Nitrile gloves are recommended, but other hazards also need to be considered in choosing the correct glove.  Note that wrist areas are often left unprotected
• Glasses should wrap around and be ANSI-Z87 rated.  Normal eyeglasses/contacts offer very little protection!
• Face Shield: is preferred as it protects more skin area.  People commonly forget to protect their chin and neck

Maintenance

• Routine monitoring of the lamp’s output is necessary
• Bulbs should be wiped off on a monthly basis with a soft cloth dampened with ethanol
• The bulb must not be operating and must be cool to the touch prior to wiping
• Bulb replacement should proceed according to manufacturer’s instructions based on the amount of use

Don't forget to look at the additional information on biological effects of UV, exposure limits and photosensitivity is available on the OCRO webpage.

ALARA

In addition to engineering controls, recall the ALARA principle as it also applies to UV radiation to minimize exposure. Time, distance and shielding help mitigate the risk of over-exposure to UV radiation as outlined below. Except for shielding, most of these measures only apply to incoherent sources of UV radiation (lamps and bulbs). Only the shielding principle (i.e.: PPE) will protect a user from UV laser radiation.

Shielding

Clothing and windows offer the most shielding from UV sources. Lab coats can block transmission of UV radiation from 80 % (disposable lab coat) to over 99 % (typical lab coat) [1]. Although these data come from a single source, it suggests that the type of weave and fabric should be examined for its UV blocking abilities. Windows, for example on cabinets, can block more than 99 % of the UV light as well [1].

Eyewear also protects the eyes from UV exposure. Laser goggles can be selected to block UV light in excess of 5 orders of magnitude (OD 5+) and safety goggles can have UV inhibitors to specifically block UV [2].

Time and distance

Dosage limits can be reached by standing near a lamp too long (remember that power (W) is energy divided by time) and too close (as described in the lamp example above). Turn off lamps when not required, never look directly at a lamp, and keep the lamp as far away as possible to limit your exposure to UV radiation.

References

[1] The International Commission on Non-Ionizing Radiation Protection, “Guidelines on limits of exposure to ultraviolet radiation of wavelength between 100 nm and 400 nm (incoherent optical radiation),” Health Phys. vol. 87, pp.171-186, 2004. 

[2] UVEX. (Accessed 2013, May 24). Culture of Safety | What are UV ultraviolet light and VLT visual light transmission?