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Ultraviolet _UV_ Radiation Hazards

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					                       Ultraviolet (UV) Radiation Hazards

Ultraviolet light (UV) is non-ionizing electromagnetic radiation in the 180 – 400
nanometer wavelength region of the electromagnetic spectrum.




The ultraviolet spectrum is divided into the following three main regions:

          Region                  Wavelength (nm)              Hazard Potential
           UV-A                      315-400                       Lowest
           UV-B                      280-315                      Mid – high
           UV-C                      100-280                       Highest



For most people the main source of UV exposure is sunlight in the UV-A and UV-
B range. There are also many artificial sources of UV light that are a potential for
occupational exposure as well. Because of the limited penetration of UV
radiation, the main organs likely to be adversely affected as a result of excessive
exposure are the skin and the eyes. Some individuals may have abnormal skin
photosensitivity responses because of genetic or metabolic disorders. There are
also some drugs and chemicals which can increase one’s photosensitivity to UV
radiation.

Some UV exposure is essential for good health. It stimulates vitamin D
production in the body. Medically it is used for treating jaundice in new born
babies as well as psoriasis at all ages. It is excessive exposure that can damage
the skin and eyes.
Skin Effects:

UV-C exposure poses the maximum risk. Though the sun emits UV-C radiation it
is absorbed in the ozone layer of the atmosphere before it reaches earth so
poses no risk. But, there are artificial sources of UV-C that are common in many
research laboratories such as:

                 i)     germicidal lamps in containment hoods
                 ii)    transilluminators
                 iii)   crosslinkers

UV-B exposure causes erythema and darkening of the skin. Prolonged
exposures do cause premature skin aging and increase the risk of skin cancer.




Basal Cell carcinoma          Squamous Cell carcinoma   Malignant Melanoma

UV-A exposure is relatively harmless usually causing just darkening of the skin,
though certain chemicals and medications act as photosensitizers and can
enhance the effects of all UV exposures (UV-A, UV-B, UV-C)
Eye Effects:

The eyes are very sensitive to UV radiation and even a very short (seconds) of
exposure can cause a painful but temporary condition known as photokeratitis
and conjunctivitis.

Photokeratitis is an inflammation of the cornea where the eye waters and vision
blurs.

Conjunctivitis is an inflammation of the membrane that covers the inside of the
eyelid and the white of the eye. Swelling and a watery discharge are typical
symptoms. There may be some discomfort and vision is not normally affected.

Some examples of eye disorders resulting from UV exposure are:

        i)        flash burn
        ii)       ground-glass eye ball
        iii)      welders flash
        iv)       snow blindness

Eyes are most sensitive to UV radiation in the UV-C and UV-B range, though
absorption of UV-A in the lens of the eye may play a factor in producing
cataracts.


Sources of occupational UV exposure for Dalhousie workers:

   1.          Sunlight
   2.          Welding arcs
   3.          Certain lasers
   4.          Germicidal lamps in containment hoods
   5.          Transilluminators
   6.          Crosslinkers
   7.          Black lights

   Sources of non-occupational exposure for Dalhousie workers:

   1. Sunlight
   2. Artificial tanning beds
   3. Black lights

How do we protect ourselves from overexposure to UV radiation:

   1.          Engineering controls – enclosures and interlocks
   2.          Administrative controls – limit exposure time, increase distance from
               source, limiting access to authorized personnel only.
   3.    Personal protective equipment (PPE) – goggles, UV face shields, long-
         sleeved tightly woven clothing (including gloves) to cover exposed
         areas of skin.
   4.    Appropriate warning signs to alert personnel of a UV hazard.
   5.    Staff training
   6.    Sun protective measures to include:

         i)        Use of sunscreen with an SPF of 15 or higher
         ii)       Avoid outdoor work, where possible, between the hours of
                   11:00am – 4:00 pm
         iii)      Use wide brimmed hats and long tightly woven clothing to cover
                   the skin
         iv)       Use of UV blocking sunglasses

Occupational exposure limits:

Canadian occupational exposure limits follow those limits recommended by the
American Conference of Governmental Industrial Hygienists (ACGIH).

For UV-A exposure to the eye should not exceed 1 milliwatt/cm 2 for periods
greater than 1000 seconds ( ~ 16 minutes)

For UV-B and UV-C exposure to the unprotected skin and eye should not exceed
values in the following table within an 8 hour period:
                                                                  2
               Wavelength (nm)                          TLV (mJ/cm )
                     200                                     100
                     210                                      40
                     220                                      25
                     230                                      16
                     240                                      10
                     250                                       7
                     254                                       6
                     260                                     4.6
                     270                                       3
                     280                                     3.4
                     290                                     4.7
                     300                                      10
                     305                                      50
                     310                                     200
                     315                                    1000
Recommended reading:

  1.   Protecting Workers from Ultraviolet Radiation – ICNIRP 14/2007

          http://www.icnirp.org/documents/UVWorkers.pdf

  2.   Advice on Protection Against Ultraviolet Radiation - NRPB

         http://www.hpa.org.uk/radiation/publications/documents_of_nrpb/abstracts/absd13-1.htm

				
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