Is there any rule of thumb on how close I can be and still safely watch
(not a casual glance) arc welding without any eye protection? Does
this distance vary by amperage or type (stick, wire, TIG, etc.)?

- les

A good rule of thumb would be: if you can see it at all, you are too close
for anything but a quick glance.

Carmine Castiglia
ISOFits! - ISO 286 on your PalmOS handheld
InfosystemsPro LLC
PalmOS apps for engineers and machinists
http://www.infosystemspro.com


"Les" wrote in message
oups.com...
Is there any rule of thumb on how close I can be and still safely watch
(not a casual glance) arc welding without any eye protection? Does
this distance vary by amperage or type (stick, wire, TIG, etc.)?

- les

I would suggest just around the corner, behind a wall, without eye
protection. Even a semi-safe distance would be so far away as to make
observation useless. Why would one want to risk optic damage when a lens is
so simple a solution?
Respectfully,
Ron Moore

"Les" wrote in message
oups.com...
Is there any rule of thumb on how close I can be and still safely watch
(not a casual glance) arc welding without any eye protection? Does
this distance vary by amperage or type (stick, wire, TIG, etc.)?

- les

"Les" wrote in message
oups.com...
Is there any rule of thumb on how close I can be and still safely watch
(not a casual glance) arc welding without any eye protection? Does
this distance vary by amperage or type (stick, wire, TIG, etc.)?

- les


You have to be close enough to see what's happening in the puddle to "watch"
arc welding. At that distance, you need eye protection. Any further away,
it is only a pretty blue arc, as you can't see what's being melted.

The sun is 93 million miles away, and looking at it directly for a few
seconds can damage your eyes. I would say that a couple of hundred yards
would tone down the intensity of an arc to the point where it won't make a
permanent white spot in your optical system.

Why mess with it? If you are interested, get a hood and get right in there.
Otherwise, look away.

A good work rule to remember is:

If you go blind, they send you home.

Steve

Carmine Castiglia wrote:
A good rule of thumb would be: if you can see it at all, you are too close
for anything but a quick glance.

So how do they get away with welding outdoors where the public may be
exposed?

I've detoured to walk down alternate streets, blocked the view with my
hand, etc - but I know it's generally not something I should be looking
at. Joe Average, (or worse Joey Average, jr) doesn't.

"Les" wrote : Is there any rule of thumb on how close I can be and still
safely watch (not a casual glance) arc welding without any eye protection?
(clip)
^^^^^^^^^^^^^^^^
The eye is just like a camera--the farther away the smaller the image, but
the brightness stays the same. By standing farther away, you are damaging a
smaller area on the retina. How large an image are you willing to damage?

Les wrote:

Is there any rule of thumb on how close I can be and still safely watch
(not a casual glance) arc welding without any eye protection? Does
this distance vary by amperage or type (stick, wire, TIG, etc.)?

Seattle is a town with lots of shipyards. When you go by in a car or ferryboat
you see welding arcs, lots of 'em. The intensity of the light drops off as the
cube of the distance to the arc. Think about it this way: the arc puts off a
certain number of high energy photons, and the light heads off in a sphere whose
surface area is 4/3PI*r^3, and the light intensity at any radius is proportional
to the subtended entry aperture of the viewer, in this case your pupils.

My guess is you're completely safe at 100 feet, but I personally wouldn't stare
at an arc at that distance. From a mile, I'd stare at it a lot, like a star.

Leo Lichtman wrote:

The eye is just like a camera--the farther away the smaller the image, but
the brightness stays the same. By standing farther away, you are damaging a
smaller area on the retina. How large an image are you willing to damage?

The above statement is rubbish. Perhaps Leo has never looked at the stars, which
would indeed destroy retinal tissue if he were close enough, but to my knowledge
throughout human history nobody's eyes have been hurt looking at the stars,
except for the sun, which is too close. The sun is a bit more energetic than a
welding arc, though ..

GWE

"Grant Erwin" wrote: (clip) The intensity of the light drops off as the
cube of the distance to the arc.
^^^^^^^^^^^^^^^^^^^^^^
Come on, Grant. You don't know the inverse square law? You had to derive
your own, and then get it wrong?
^^^^^^^^^^^^^^^^^^^^^^
Grant wrote: The above statement is rubbish. Perhaps Leo has never looked
at the stars, (clip) [Referring to Leo's statement that the intensity of an
image doesn't drop off with distance.]
^^^^^^^^^^^^^^^^
The inverse square law (not inverse cube) does mean that the amount of light
per unit area decreases with distance, but that is not the end of the story.
The light reaching a lens is collected and focused on the image plane. If
you do the math, you find out that the brightness of the image is
proportional to the brightness of the source. That is why exposure control
on a camera works. If you take a picture of an outdoor scene, for example,
the foreground and the background receive the same exposure. In fact, if
you take a picture of a full moon, it needs the same exposure as a picture
taken on a sunny day.

I do not know off the top of my head why stars don't burn your eyes. I
think it has to do with the fact that the images are so small that there is
not enough energy to heat up the retinal cells. Are there any astronomical
photographers in the group?

Leo Lichtman wrote:

The inverse square law (not inverse cube) does mean that the amount of light
per unit area decreases with distance, but that is not the end of the story.
The light reaching a lens is collected and focused on the image plane.

A lens can't collect and focus more energy than is intercepted by it's
total area.

The further out you go from a spherically radiationing source, the less
the incident power density, and so the less total energy incident on a
lens of fixed diameter.

However I could see the energy density of a welding arc at substantial
distance, multiplied by the area of the lens, and then concentrated
onto a small area of the retina still being dangerous.

wrote in message
ups.com...
Leo Lichtman wrote:

The inverse square law (not inverse cube) does mean that the amount of
light
per unit area decreases with distance, but that is not the end of the
story.
The light reaching a lens is collected and focused on the image plane.

A lens can't collect and focus more energy than is intercepted by it's
total area.

The further out you go from a spherically radiationing source, the less
the incident power density, and so the less total energy incident on a
lens of fixed diameter.

However I could see the energy density of a welding arc at substantial
distance, multiplied by the area of the lens, and then concentrated
onto a small area of the retina still being dangerous.


Ask OSHA. They have probably calculated it to a knats whisker. At any less
distance and it must be shielded from public view...

They fingered everything else...

--

Clif

wrote: A lens can't collect and focus more energy
than is intercepted by it's total area. (clip)
^^^^^^^^^^^^^^^^^^
That is true. However, a given light source at a greater distance produces
a proportionately smaller image. so the brightness of the image remains the
same. I'm not making this up. Lay out a diagram of a lens and do the ray
tracing, and you'll see.

Or, as experimental evidence, think about what i said about taking a
photograph. Let's say you take a picture of two billboards. One is 100
feet from you, and the other is 1000 feet. They are in the same picture,
and they are both correctly exposed. The more distant billboard has the
same illumination falling on it, but, being 10x farther away, the lens will
receive 1/100 as much light. Inside the camera, the image of the more
distant billboard will be 1/10 as large, so it will have 1/100 as much area.
So the brightness of the image will come out the SAME.

Leo Lichtman wrote:
wrote:

A lens can't collect and focus more energy
than is intercepted by it's total area. (clip)
^^^^^^^^^^^^^^^^^^
That is true. However, a given light source at a greater distance produces
a proportionately smaller image. so the brightness of the image remains the
same. I'm not making this up. Lay out a diagram of a lens and do the ray
tracing, and you'll see.

Yes, and I allowed for the possibility of that in the part of the post
you clipped (though without the certainty).

However the power of the lens is limited. At some point the number of
incident photons becomes small enough and the ability of the lens to
focus them to a point limited enough, that the power density of the
image on the retina can no longer exceed the threshold of damage. This
is clearly the case when looking at stars other than our sun; at what
point it becomes true for a welding arc I don't know.

It's also going to depend on the size of the pupil, which is going to
depend on what impression of light levels the eye has adjusted to -
being suddenly flashed at night is presumably worse than the same arc
at the same distance on a sunny day.

Les. here's my free advice(& you know what that's worth )-

The problem ain't how bright the visible light is. If the visible
light is too bright you'll naturally move back to a distance where it
doesn't bother you. The problem is the UV that's generated, your eye
has no way of detecting dangerous levels so you can get a "burn level"
dose & not know about it until the pain starts up hours later. IIRC
the UV is actuually burning the cornea, not the retina, which is why
people get the "gritty eye" pain instead of just going blind. Also
IIRC prolonged exposure leads to cataracts.

UV does , above & beyond cubed root losses, attenuate with distance
through air but I have no idea what the factor is .

My recommendations a

a. If your going to watch anyhow wear a pair of good quality UV
blocker sunglasses. If you get a sunburn you're too close (don't ask
me how I know )

b. Ask this question on sci.engr.joining.welding, I can absoulutely
guarentee you'll get the real skinny there.

H.



On 28 Oct 2005 08:18:04 -0700, "Les"
wrote:

Is there any rule of thumb on how close I can be and still safely watch
(not a casual glance) arc welding without any eye protection? Does
this distance vary by amperage or type (stick, wire, TIG, etc.)?

- les

Leo Lichtman wrote:

wrote: A lens can't collect and focus more energy
than is intercepted by it's total area. (clip)
^^^^^^^^^^^^^^^^^^
That is true. However, a given light source at a greater distance produces
a proportionately smaller image. so the brightness of the image remains the
same. I'm not making this up. Lay out a diagram of a lens and do the ray
tracing, and you'll see.

Or, as experimental evidence, think about what i said about taking a
photograph. Let's say you take a picture of two billboards. One is 100
feet from you, and the other is 1000 feet. They are in the same picture,
and they are both correctly exposed. The more distant billboard has the
same illumination falling on it, but, being 10x farther away, the lens will
receive 1/100 as much light. Inside the camera, the image of the more
distant billboard will be 1/10 as large, so it will have 1/100 as much area.
So the brightness of the image will come out the SAME.



Brightness is a slightly misleading term here, what we need to worry
about is energy absorbed by tissue.

Consider a match and a nice big wood bonfire, both will burn at the same
temperature and be emitting the same infra red wavelengths, if you look
at them they will have the same brightness, but one will be much bigger
than the other.

Now hold your hand an inch from the burning match, then try the same
thing with the bonfire. Obviously the match won't be a problem and the
bonfire will burn you - to put it another way, the energy absorbed from
the match isn't enough to damage the skin, the energy absorbed from the
bonfire is enough to blister it, keep it there long enough and the
tissue will be destroyed.

It all comes down to how much energy, how long ?.



--
scruttocks
k12rs r80g/s

"Howard Eisenhauer" (clip) the UV is actuually burning the cornea, not the
retina, which is why people get the "gritty eye" pain instead of just going
blind. (clip)
^^^^^^^^^^^^^^^^^^
Howard, thanks for flushing the toilet on all my fancy optical reasoning. I
believe you are correct, and it doesn't matter about the focused image on
the retina. So, since the inverse square law is in effect, the OP's
original question is valid, and unanswered.

Training texts for welders in British Columbia Canada say 40 feet. That was
when I took welder training and wire feed was some high tech thing.
There is more radiation from wire feed because there is so little smoke
to diffuse the light.
Randy


"Les" wrote in message
oups.com...
Is there any rule of thumb on how close I can be and still safely watch
(not a casual glance) arc welding without any eye protection? Does
this distance vary by amperage or type (stick, wire, TIG, etc.)?

- les

After watching a mob of people flog a dead equine, let me toss this in:

I have welded since 1974.

I DO NOT

REPEAT

DO NOT

watch arc welding FROM ANY DISTANCE unless I have a hood on.

I have seen it at night from 1/2 mile away, and it sure is pretty, but
there's always that tinge that comes from being flashed or flash burned.

This stuff is dangerous, and there is very very little margin for error.

Intellectual masturbation aside on the inverse square therories versus
statistical correlaries, if you are watching arc welding, it is always a
good idea to have a hood on.

Do as you like.

Steve

Brightness at the source is the same - but light falls off by the square of the
distance. It is fainter and fainter.
So there is a safe distance - but it is dependent on so many variables.

Martin
Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder



Leo Lichtman wrote:
"Les" wrote : Is there any rule of thumb on how close I can be and still
safely watch (not a casual glance) arc welding without any eye protection?
(clip)
^^^^^^^^^^^^^^^^
The eye is just like a camera--the farther away the smaller the image, but
the brightness stays the same. By standing farther away, you are damaging a
smaller area on the retina. How large an image are you willing to damage?



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Doing a tracing of lenses doesn't show you much but direction of the image
and compression or expansion.

You say you can read a news paper in pitch darkness with a candle 200 yards
away just as well as having it over the shoulder. We don't buy the concept
or the fact. It isn't rocket science.

Martin
Martin Eastburn
@ home at Lions' Lair with our computer lionslair at consolidated dot net
NRA LOH, NRA Life
NRA Second Amendment Task Force Charter Founder



Leo Lichtman wrote:
wrote: A lens can't collect and focus more energy
than is intercepted by it's total area. (clip)
^^^^^^^^^^^^^^^^^^
That is true. However, a given light source at a greater distance produces
a proportionately smaller image.**I DON'T See the SO** so the brightness of the image remains the
same. I'm not making this up. Lay out a diagram of a lens and do the ray
tracing, and you'll see.

Or, as experimental evidence, think about what i said about taking a
photograph. Let's say you take a picture of two billboards. One is 100
feet from you, and the other is 1000 feet. They are in the same picture,
and they are both correctly exposed. The more distant billboard has the
same illumination falling on it, but, being 10x farther away, the lens will
receive 1/100 as much light. Inside the camera, the image of the more
distant billboard will be 1/10 as large, so it will have 1/100 as much area.
So the brightness of the image will come out the SAME.



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http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups
----= East and West-Coast Server Farms - Total Privacy via Encryption =----

"SteveB" wrote in
news:0FA8f.30901$fE5.30430@fed1read06:

After watching a mob of people flog a dead equine, let me toss this in:

I have welded since 1974.

I DO NOT

REPEAT

DO NOT

watch arc welding FROM ANY DISTANCE unless I have a hood on.

I have seen it at night from 1/2 mile away, and it sure is pretty, but
there's always that tinge that comes from being flashed or flash burned.

This stuff is dangerous, and there is very very little margin for error.

Intellectual masturbation aside on the inverse square therories versus
statistical correlaries, if you are watching arc welding, it is always a
good idea to have a hood on.

Do as you like.

Steve




Agree fully here and would add, You need not look directly at the arc to
get yourself a bad flash burn. Shop walls have been the cause of quite a
few incidents of flash burn inasmuch as almost any surface will reflect the
harmful rays..Including the inner surface of your hood, many burns in the
shipyard back in the 70s this way for me.

Related question for comments;
My wife is blind and often sits on our back porch (outside) while I am
welding in the shop about 50 yards away with the doors open. I wonder if
the arc is dangerous to her at that distance, I know it would be up close
but at that distance??

Just wonderin'
granpaw

wrote:
Carmine Castiglia wrote:
A good rule of thumb would be: if you can see it at all, you are too close
for anything but a quick glance.

So how do they get away with welding outdoors where the public may be
exposed?

I've detoured to walk down alternate streets, blocked the view with my
hand, etc - but I know it's generally not something I should be looking
at. Joe Average, (or worse Joey Average, jr) doesn't.

Where I live if you are welding in a public area you are required to
screen the work area. This prevents people passing by from watching the
welding without eye protection and limits the area which may be
affected by spatter.

I did some welding today. About six inches of wirefeed to make a fence
bracket. I normally wear a long sleeve khaki Wrangler button shirt, but
thought, what the heck, it's only a few inches. I did wear helmet and
gloves.

I burned each arm with a hot dingleberry. I got lots of little white dots
from dingleberries over the years.

Nothing like doing it safely, even if it is a short amount of welding. And
nothing like being safe when it comes to your eyes, too.

Steve

Do you wear glasses? Glass will filter out the UV.

The distance does vary with the type of welding and the power. Tig
seems to bleach my shirts much more than stick.

Dan

On Sun, 30 Oct 2005 17:45:22 GMT, Ignoramus26744
wrote:

On 30 Oct 2005 09:41:10 -0800, wrote:
Do you wear glasses? Glass will filter out the UV.

I guess that that's why I did not get hurt when I flashed myself with
a tig arc recently.

It takes a minimum amount of UV to cause enough damage for you to feel
it. Like a sunburn. Obviously, the UV is going to start damaging
tissue right away but if only a tiny amount is damaged you will not be
aware of it. I have been flashed, by myself accidently stepping on the
pedal, from tig welding many times. They have all been brief enough
not to cause pain. So that may also be why you weren't burned.
ERS

The distance does vary with the type of welding and the power. Tig
seems to bleach my shirts much more than stick.

Dan



--

"Ignoramus26744" wrote in message
...
On 30 Oct 2005 09:41:10 -0800, wrote:
Do you wear glasses? Glass will filter out the UV.

I guess that that's why I did not get hurt when I flashed myself with
a tig arc recently.


Iggy, I have flashed myself many times over the years without any noticable
problems, no burn. Some people seem more sensitive to flash than others.
Greg

wrote in message
ups.com...
Do you wear glasses? Glass will filter out the UV.

The distance does vary with the type of welding and the power. Tig
seems to bleach my shirts much more than stick.

Dan


When I was doing a lot of TIG on stainless kitchen equipment, I had to add a
snood to my hood to keep from getting my throat and top of my chest burned.
I used a piece of suede leather, and stitched it to holes drilled in the
bottom lip of the hood. It looked cool, and I got lots of compliments, and
even a few guys copied the idea. Man, I got burned before the snood.

BTW, snood is actually a word used in OSHA CFRs for such a device.
Actually, I believe it is a word meaning a turkey's beard, or the fleshy
thing that is on their neck.

Steve