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  Ultraviolet
rays are electromagnetic waves whose wave length ranges between 400 and
200 nm and they represent the non-ionizing radiations of smallest wave
length. They are present in the solar spectrum and they can be
artificially produced by means of a voltaic arc with carbon electrodes or
by mercury-vapor lamp.
Ozone absorbes the energy of radiations of wave length smaller than 280
nm. This is why ultraviolet C radiations (harmful to the organism), whose
wave length ranges between 280 and 200 nm, are stopped by the ozone
barrier. Nowadays such barrier is progressively reducing itself and this
could represent, in the future, a further risk factor for workers that
carry out their job outdoor. Furthermore, the sensitization of the
population from a non-occupational point of view (aesthetical-purpose
exposure) might become necessary.
Ultraviolet radiations are employed in the health field for sterilization
procedures (germicide lamp) and for diagnostic and therapeutical
purposes.
Ultraviolet radiations of short wave length (mainly 254 nm) given out by
mercury-vapor lamp are widely employed in the sterilization of air in
confined spaces (such as operating theatres, etc), of liquids and
materials' surfaces.
The sterilization of air in confined spaces is the main application of
germicide lamp, in fact it allows the attainment of favourable results
also in those cases where the usual disinfectant methods do not satisy.
The sterilization of liquids depends on the nature of the liquid itself,
on its capacity of conveying the UV radiation at 250 nm and on the
absence of particles in suspension able to shield the infective agents.
The sterilization of surfaces requires high-intensity UV radiations of
short wave length. This is why an installation is placed close to the surface
to treat. Such installation should be as smooth as possible and without
shade zones.
In the diagnostic and therapeutical fields, UV radiations are mainly
employed for the treatment of dermatological pathologies, although their
use extends to other applications, such as phototherapy of icterus
neonatorum and other applications in dentistry. The dermatological
applications mainly involve phototherapy of skin disorders,
photochemotherapy of psoriasis and photodermatosis diagnosis. Odontological
applications mainly involve the employment of UV radiations for the
polymerization of resins to seal cavities or reconstruct missing portions
of the teeth.
Finally, UV radiations of specific wave length are employed in
laboratories for diagnostic equipment (fluorometers, spectrophotometers).
The biological effect on man is influenced by the fact that such
radiations, although of relatively small wave length, have a reduced
biological materials' penetration power (some tenths of millimetre). Therefore,
the effects deriving from exposure to UV radiations basically involve the
skin and the eyes with short and long term damage.
As far as the skin is involved these radiations can cause erythema and
they can influence cutaneous pigmentation. In the case of intense and prolonged
exposure, they can have tumorigenic activity and be responsible for the
appearance of basal cell carcinoma, squamous cell carcinoma and malignant
melanoma; the bands of UV rays responsible for such neoplastic effects
are those of wave length between 280 and 315 nm.
As far as the eyes are involved these radiations can cause conjunctivitis
and keratitis; some bands of UV radiations of wave length bigger than 295
nm can reach beyond the cornea, as far as the crystalline lens and
provoke cataract.
For additional information
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