[TheForge] Vision damage and welding shields pt 2

[theforge@mailman.qth.net]

The ANSI Z87.1-1989 standard referenced in the add, and to which OSHA 
applies to all eye protection devices, seems to require BOTH UV and IR 
protection to be in effect whether the device is energized or not.     I 
did a google search on auto darkening helmets and eye damage and came up 
with several articles that  indicate the same, including one on the 
Lincoln Electric site.    The real question I have for the Harbor 
Freight helmets is : Do they actually perform to the  spec?  It is real 
easy to print "ANSI Z87 compliant", in the add, quite another to 
actually build it in the product.   The add actually states only "UV/IR 
protection" and "Meets ANSI Z87.1-1989 standards"  both of these 
statements are far from conclusive.   Harbor Freight items are not know 
for their rigorous quality assurance process.   That being said, I have 
an older autodarkening cartridge from northern that I use, but need to 
replace now, since it has a major crack in the lense.  Still works, but 
I think some arc light is making it through now.   I will probably look 
at the referenced Harbor Freight unit.    I will probably blink when I 
strike the arc, but if you have a high end speedglass or somesuch hood, 
don't feel the need to blink.

Charles


> "Bruce Freeman" wrote:
>  
>
>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.
>
>  
>