At my job, I sit at a desk. The office opens onto a fab shop; welding
and machining. So, there's a weldor right outside my office window
(yeah - weird - the windows in my office looks into the shop), and
I'm wondering - Obviously, looking at the arc will hurt my eyes, so
I don't do that. But I'm wondering - when the light from the arc
is reflected off the walls, other areas of the weldment, his hood,
etc - is there any danger from looking at the light that's reflected
off those surfaces? Or is most of the UV gone by then. It's not
uncomfortably bright, but UV is invisible, after all. (sometimes
when I walk by, I can smell the ozone.)
Rich Grise wrote:
i would be looking at some form of protection, the glass might knock out
of the residual UV that is bouncing around but i wouldnt count on it. as
understanding UV really isnt the issue as much as IR is, which again if i
understand correctly takes more than just glass to knock out much (hence
reason for the special welding shades). ive had a friend standing in our
shop while some was welding with a wire welder behind us and the
the walls and all caused her eyes to become very very sore after just a
(she does have very sensitive eyes though)
if it was me i would get blinds for the office or wear a welding shade all
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Yeah, it could be dangerous if you are exposed to those reflections for the
long term. It all depends on how much reflection and exposure you are
getting. If the arc from welder is shining right in your window (he's
using nothing to block his arc from you - then you are in danger). If the
only light is the reflections off the work area around the welder, then the
risk is not as great, but is still not good for the long term. You should
probably do something to protect yourself.
What type of glass is in the windows? It might already be protecting you.
Polycarbonate plastic (used in many types of glasses and safety products
and used as the protective cover plate in welding helmets) is a great UV
block and if your shop windows are already made of polycarbonate, you are
probably safe. If you wear glasses with plastic lenses they are likely to
be polycarbonate as well, which would also give you even greater UV
protection. Real glass doesn't block much UV I don't believe, but if you
have real glass windows, you could just put a sheet of polycarbonate
plastic over it and that would likely cut down the radiation to a safe
level while still allowing you to watch what was happening in the shop.
You can also put protective window film on the glass to block the UV (from
places like Lowes to block heat).
If you don't need to see the shop, you might consider just blocking the
If the flash you can actually see is distracting, you could try and find
some shaded material to cover the window with but it would of course reduce
what you could see in the shop as well. Lowes I see has shaded window film
for cheap, but the shaded stuff only blocks 95% of the UV instead of 99% of
Just wearing clear safety classes as well (almost always made out of
polycarbonate) would greatly help protect you from UV reflections as well.
Thanks to you, Curt, and also Matt and Iggy.
They do have canvas curtains, so there's no danger from the direct arc,
and I have plastic-lensed old-guy glasses that I need for the computer,
(and the newspaper, the microwave oven display, the dial on the toaster
oven, etc, etc, etc. ;-) ) still, I'll do my best to minimize watching
It's like the army. If the enemy is in range, so are you. That is an
unsafe workplace. Both the workplace, and the place (desk) you work at.
I'm not up on OSHA any more, but if you can see the arc, or the bright light
it produces, I'd say you're being exposed to something you shouldn't.
Now, will you go blind next Tuesday? Probably not, but there are a lot of
times in my life that I was exposed to stuff when I was young and stupid and
ten feet tall and bulletproof that now I wish I had been more careful about.
Don't know about where you work, but where I worked, if you went blind, you
had to go home.
There should be an orange curtain on his side in front of the glass.
This could cost you eyesight or anyone that comes in.
If OSHA visited - heads would roll.
Until the curtain is installed - wear a auto welding helmet.
Glass attenuates UVB but does not attenuate UVA to any great extent.
Polycarbonate attenuates both. Talk to you safety rep about it. If
your windows are glass, adding some polycarbonate will also add
protection to keep the windows from being broken.
Apart from the chemical, electrical, thermal and mechanical hazards, a
welding arc emits IR, visible and UV light. All are potentially harmful,
in different ways.
IR: For a welder, IR can heat the skin, and the layers under the skin,
and cause burns. This only happens up-close, and isn't a factor in your
IR can also cause eye damage including partial or full blindness; apart
from causing cataracts, if focussed on the back of the eye IR damages
the receptors and nerves by heating them up, but it takes a lot of hot,
near-visible IR to do that (long wavelength IR is absorbed by the cornea
and lens, causing cataracts instead).
However a welding arc can put out a lot of short wavelength IR, and this
focussing may be a problem if you can see the arc directly.
This can cause damage over a considerable distance if the IR is focussed
on the retina.
Visible: Eyes adapt to with cope with brightness by shrinking the
pupils, changing the sensitivity of the retinal layer, partly closing
the eyelids, and by squinching up the area around the eyes - but up
close a welding arc is just too bright for the human eye, which can't
adapt enough to cope, and the bright visible light from an arc can
bleach and/or burn the retina.
Even at a distance the visible light from an arc can be very damaging,
similar to the second IR danger above, especially if the light is
focussed on the macula (the macula is the central part of the retina,
where you see best).
This is because the amount of adaptation the eye does is dependent on
the total illumination, not the brightness of the spot, and if only one
spot is very bright when most of the rest of the visual field is at
normal levels then the adaptation of the eye will be small, allowing
lots of light from the bright bit to pass through the pupil and be
focussed in a spot on the retina. It's worse when the ambient light
level is low.
In the case of an arc, this is a mixture of visible and IR light, and
the effect is similar to when someone goes partially blind from looking
at the sun, only it can be quicker.
Imagine focussing the sun into a spot with a lens - now imagine doing
the same with an arc, and the bright spot is in the sensitive part of
your eye where you see best ...
Even if the damage is temporary, just a black spot for a few minutes,
it's still damage, and it will come back to haunt you in the long term.
For this reason, no-one should *EVER* look directly at an arc without
eye protection, even from a distance.
MIG is apparently more dangerous than stick or TIG for this, and oxy
cutting is worst of all. Reflected arc light can be just as bad too, or
even worse. Usually of course it's less dangerous, but you won't always
be able to tell ...
UV: UV causes the reddening of the skin/sunburn associated with an arc,
tanning, arc-eye, conjunctivitis, skin aging, and skin cancer.
Distance will attenuate the effects of UV quite rapidly - the
long-distance focussing effect mentioned above doesn't happen with UV,
which is mostly stopped by the conjunctiva and cornea of the eye before
reaching the retina.
It was once thought that UV was absorbed in the lens too, leading to
welder's cataracts - however nowadays many people think that UV is
absorbed in the conjunctiva and cornea only, and that welder's cataracts
are caused by IR rather than UV. I'm not really up-to-date on this point
though, and afaik there are still arguments about it. I suppose it could
be both ...
(That's how you can get arc-eye without going blind btw, the UV is
absorbed by the cornea and inflames it, If the UV reached the retina and
was in focus, it would blind you very quickly indeed)
UV is usually divided into four bands, only three of which are found in
arc light - UVA, UVB and UVC (the fourth is called vacuum UV).
A bit over half the UV from an arc is UVA, the rest is mostly UVB with a
little UVC. The latter two are a lot more damaging than the UVA.
However a 4mm sheet of ordinary soda float window glass will cut out
around 98%-99% of the UVB, and all of the most damaging (but sparse) UVC.
Like UVB/UVC, UVA also causes damage, but not as much - it's the kind of
UV in a sunbed, it doesn't cause sunburn nearly as much as UVB/UVC, but
it can still cause arc-eye.
Also UVA is probably as carcinogenic as UVB/UVC, indeed there is recent
evidence to suggest that UVA actually causes more melanomas than UVB+UVC.
A sheet of glass will cut out from 10% to 90% of UVA, depending on exact
frequency etc - but on average, say half of it gets through. You can get
UV glass or films to stick to ordinary glass which cut out almost all of
the UVA (most glass is already almost entirely opaque to UVB and UVC).
If you are a reasonable distance away from the arc, especially through a
sheet of glass, the UV isn't going to cause much direct trouble in terms
of blindness, itchy eye or sunburn - though it may increase the chances
of skin cancer, especially if exposure is long-term and continuous.
1) Don't ever look directly at an arc. or a reflected arc, even from a
distance, without eye protection.
2) Avoid getting to close to an arc unless necessary, and if you do get
close, cover the skin and protect the eyes from IR, UV and brightness.
3) Avoid any sort of unprotected long-term and continuous exposure.
-- Peter Fairbrother
Forgot to add the notes, sorry.
[a] An arc can damage the retina quicker than the sun in this way for
three main reasons.
First, an arc is, or can be, brighter than the sun, and our eyes are
only adapted by evolution to cope with the brightness of the sun, as
nothing brighter exists in nature. Even the sun is too bright for
extended direct viewing, one reason for brows and eyebrows is protect
the eyes from the sun.
Second, the atmosphere reduces the light and the near-visible IR from
the sun, but this doesn't happen with an arc as there isn't miles of air
in the way.
Third, when you look at the sun it's usually against a bright sky and
your pupils will be small - however when looking at an arc the
background may be fairly dark, and the pupil will consequently be large,
allowing more light, both visible and near-IR, to enter.
[b] This is because UVA is absorbed in just the right, or wrong, place
to cause cancers, and especially the most life-threatening melanomas, at
the dermis and basal layers beneath the surface where the skin is
growing and the skin cells are dividing.
UVB tends to get absorbed more in the outer, dead or non-reproducing
keratinising (where the cells are changing to keratin) layers of the
skin, and doesn't reach the reproducing basal layer or dermal cells as
much as UVA does.
UVB can and will cause sunburn, and some other skin problems including
cancers, but 92% of melanomas are definitely not caused by UVB, and
we're not sure how many, if any, of the remaining 8% are.
UVC from the sun is mostly absorbed by the atmosphere, and isn't found
in quantity in nature. Consequently we have little evolutionary defense
against UVC in an arc, but fortunately it seems UVC also tends to be
absorbed in the outer, dead, layers of the skin.
I had never heard the term "float glass" before. After some Goggle
research I now know a little more. That's cool. I thought window
glass had been made basically the same way for the past few hundred years,
never had a clue there was a major technology change only 50 years ago.
Trying to find the transmission properties of typical glass proved
difficult however. The only graph I did find:
Seemed to indicate that about 80% of UVA (320nm-400nm) and maybe 50% UVB
(280-320) rays would make it through, and not hit near bottom until around
250 nm which is in the UVC band (100nm-280nm).
I have no clue how accurate the graph is (or how accurate my reading is
since it's not well graduated down at that level of the scale.
All very interesting stuff however.
Not very accurate at all, I'm afraid, though the graph is mostly to
blame. Here's a somewhat more accurate graph:
There's also a much more accurate graph here, with graduations in
approximately the right region, from the Tate museum:
The 98-99% figure I gave for blocking of UVB is a working average - it
actually varies between about 97% at 320 nm, and 100% at 280 nm.
I think so, though it may be getting a little off-topic here :)
-- Peter Fairbrother
Yeah, both those graphs are more likely to be trusted since they are scaled
and crated for the purpose of showing UV transmission - and both seem to
indicate 85% or above blocking of UVB for "standard window glass".
And I'm skeptical, since there were "acceptable levels of asbestos exposure"
and those were published by the government. Just like the troops they
marched out to watch the A bombs in the desert. "Acceptable levels of