[TheForge] Vision damage and welding shields pt 2

Sat Jan 11 20:35:00 2003

>
> Hey Folks,
>  A few years ago an ophthalmologist wrote a letter published in the
ANVIL'S
> RING about safety glasses. He said that didymium lenses are used because
> they filter out the certain color wave lengths  ( sodium-yellow) to give a
> truer assessment of color temperatures They are not designed for UVA or
UVB  ultraviolet light or infra red protection.
> There are special coatings that can be added to safety glass to protect
you  from UVA and UVB, but the only protection from IR is by using gold
coated
> glass or plastic shield like the space helmets or foundry workers use.
> Remember exposure to these wave lengths is cumulative and  is a
significant  factor in cataract formation.

I had a phone conversation with Jim Schell about 5 years ago, about the
didymium/gold
face shields we were in the process of  purchasing from his company, Schell
Glass.
Jim told me that  because of his concern from the number if serious
eye related medical problems that he observed in the glass blower community,
He helped to initiate the NIOSH study listed in his E-mail below.
He said that IR radiation is cumulative and can cause severe vision problems
and even blindness. If you have any specific questions about the NIOSH study
he suggests that you contact Gene Moss directly.
I asked him about the differences between the three types of shields he
stocked. He said:
The  plain gold shield,  looks transparent to the user and is
used if you need max light transmission or you wear the shield with shaded
didymium safety glasses.
The didymium/ gold shield, = a 3.5 grade shaded welding lens
and reduces sodium flare,
The cobalt blue/gold shield  is several shades darker, and he
says it's too dark for most of our forging requirements.

This was an e-mail I received from Jim several years ago addressing
the danger of light damage to the eyes from long term exposure.

Chuck... received and reviewed your four (4) e-mails.  My contact at NIOSH
is:  Mr. Gene Moss-NIOSH-MS-R-13, 4676 Columbia Drive, Cincinnati, OH, 45226
phone:  (513) 841-4374.
I do not have any way to address Doug Learn's comments about UV emissions
from gas or coal forges.  However, while at my studio here in Houston, NIOSH
did check for UV and IR emissions from my electric kilns, propane glory
holes and propane/oxygen torch.  Gene Moss can address each of these areas
for you or you can see his report:  HETA 95-0119-2554.  Doug Learn's
comments about genuine didymium being only in glass spectacles is correct.
The polycarbonate spectacles and face shields I have, incorporate a
"didymium-like" material that mimic's the effects of didymium glass.  The
goal of reducing the yellow sodium flare in didymium polycarbonate lenses is
almost the same as in genuine didymium glass.  The polycarbonate lenses are
much lighter, cost less and are less fragile.
JIM SCHELL

My final comments on this subject.

The intense visible light of the welding arc can be very dangerous to
your eyesight.  As with any bright light source, this high intensity
exposure can cause damage to the retina, especially the central area where
your vision is most acute (the fovea centralis).  Any shaded lens will help
here. There is also a growing body of evidence that the light can be a
significant causative factor in cataract formation.
While plastic UVA & UVB filters could be added to the protective plastic
lens covers on welding helmets, I would much rather see them coat the clear
shields with the vaporized gold coating that they used on Jims face shields.
I have been using one fore several years now for welding Damascus billets in
my forges,
 as well as plasma cutting and oxy-acetylene welding and really love it.

Jim Schell is no longer in business due to severe health problems, but an
internet search
should provide several current sources for  these shields.
Chuck

----- Original Message -----
From: "Bruce Freeman" <[email protected]>
To: <[email protected]>
Sent: Wednesday, January 08, 2003 4:07 PM
Subject: Re: [TheForge] Anyone own one of these? Opinions?

Chuck,

Is flash BURN really an issue here?  "Burn" implies actual damage due to UV
on the eye.  (SOME of this damage does heal, but you may be right about it
being cumulative.  I simply don't know.)  What I WOULD expect is flash
"dazzle", where the bright visible (non-UV) light dazzles you, causing your
pupils to shrink, leaving an intense after-image, and generally making it
difficult to see � but without doing permanent damage to your eyes.

I have virtually no experience with these helmets, not being a welder
myself. (I've worn one once or twice.)   But what I DO know is that ordinary
window glass is virtually opaque to UV.  I don't know the "% transmittance"
of glass to UV light, only that it's quite low.

(FYI, "% transmittance" is the percentage of the incident light that will
pass through a layer of glass of some standard thickness, usually 1 cm.   If
99% of the UV light is absorbed by a 1-cm glass plate, then 99.99% will be
absorbed by a 2-cm layer, but only about 40% will be absorbed by a 2-mm
glass plate.  Transmission it's highly dependent upon wavelength.  A glass
that's clear for white light can be "black" for UV light.)

Bottom line is that if your color-changing mask does pass too much UV light
in that brief interval before it darkens, then the fix would be to add an
additional filter of clear glass of sufficient thickness to filter out all
the UV, regardless of the color of the changeable filter.

Bruce
NJ
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