Environmental Engineering Reference
In-Depth Information
Several types of badges that measure total effective irradiance on the badge surface
have been developed and can match the geometry of the skin, but not the eye.
15. Polysulfone film badge dosimeters
To date, the most widely used UV film-badge dosimeter has been the
thermoplastic film, polysulphone. When polysulfone is exposed to UVR (particularly
UVB), its UV absorption (generally calibrated at 330 nm) increases. This increase in
absorbance has a useful linear-response range. Most typically, a 40-µm thick piece of
polysulphone film is mounted in a cardboard or plastic mount, and these are worn by the
experimental subjects on anatomic sites of interest. Sydehham constructed contact lenses
of polysulfone and was able to corroborate the low UV exposure compared to that of the
skin.
16. Direct clinical measurement of UVR exposure
The action spectrum and threshold for photokeratitis (snow-blindness) has been
carefully studied, and was the basis of the action spectrum S UV (Ȝ), hence, where
individuals develop a threshold, just-detectable photokeratitis, the cornea itself is acting
as a dosimeter. Sliney used this approach to estimate UV exposure to the crystalline lens
or intra-ocular lens implant, and showed it to be an extremely small dose compared to
that of the skin 49 . Erythema has long been used as a measure of individual, acute
exposure of the skin to UVR, and dermatologists routinely examine benign markers of
sun damage of skin on the face and on the back of the hands to judge the accelerated
aging of the skin, and thereby estimate the risk for non-melanoma skin cancer.
However, previous attempts to correlate the incidence of cataract with the skin-exposure
estimates have been unsuccessful, presumably because of the lack of any direct relation
between skin exposure and direct ocular exposure with the lids open. Another factor of
interest is the impact of hats. Hats (particularly with wide brims) and other headwear
greatly affect exposure to the face; however, hats which shade the eyes, may actually lead
to greater lid opening, rendering the eye more vulnerable to ground reflections 50 .
17. Ocular exposure dosimetry
Very pertinent data could be given by UV-sensitive contact lens dosimeters 48 ,
but most of the pertinent data will come from studies of lid opening conditions
combined with directional field measurements and different environmental conditions.
Also the ground reflection will enter in these evaluations. Tables 2 and 3 from Sliney 3
provide information on the reflectance of ACGIH/ICNIRP-weighted solar UVB and the
measured ACGIH/ICNIRP effective UVR from the sky with a 40° cone field-of-view.
He effectively measured the UV radiance over a 40° averaging (acceptance) angle. This
was later used to calculate ocular dose. Note that the relative effective UV irradiance
near the horizon (i.e., within the eye's field of view) did not show big variations if the
sky was visible and could increase with haze. Indeed, on an overcast day with the
eyelids more open, the actual UV-B dose rate to the eye from the sky scatter can
increase.
Search WWH ::




Custom Search