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Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work. |
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Safe distance to watch arc welding
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 |
#2
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
"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 |
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Safe distance to watch arc welding
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. |
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Safe distance to watch arc welding
"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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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
"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? |
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Safe distance to watch arc welding
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. |
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
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. |
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Safe distance to watch arc welding
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. |
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
"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. |
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
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? ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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Safe distance to watch arc welding
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. ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- |
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Safe distance to watch arc welding and further.
"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 |
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Safe distance to watch arc welding
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#22
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
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 |
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Safe distance to watch arc welding
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 -- |
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Safe distance to watch arc welding
"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 |
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Safe distance to watch arc welding
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 |
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