12 Jul 01 and 22 Oct 01 have threads on this subject.

The intensity of any illumination declines as the inverse of the square of the distance. Twice as far 1/4 as strong three times as far 1/9 etc. If there is smoke or dust suspended in the air it would be even faster but these are things you would not want to count on.

I don't believe oxy fuel produces significant UV.

Bill

The flame and pool of molten metal, either welding or cutting, emit both ultraviolet and infrared rays. Both types of rays may cause eye injury if welding is viewed at a close distance. Gas welding on medium material (1/8 to 1/2 inch requires a shade 5 or 6 lens for protection. Oxyfuel cutting on medium material (1 to 6 inch requires a shade 4 or 5 lens). These numbers can vary depending on the sensitivity of the welders eyes. If you doubt this just gas weld for a couple of hours without protection and prepare for a " sun burn". Hope this helps protect someone from eye damage.

Paul Gilley
Welding Instructor
Mountain Empire Community College
pgilley@me.vccs.edu

To answer you question about does uv diminish with distance Yes it does. How much i don't really know. Think about it like looking at a star. U can because it is so far away. The wave lengths get less concentrated the futher you get away from there source. Don't know the exact distance you can be away from an acr and not be affected by it, but like you said it veryies from person to person. Oxyfuel welding will damage your eyes without a filter or shaded lens. R.C I'd say your safe catching a flash from an arc about 50 feet or so,but you still can't sit there and look at it.LOL I'm just guessing on the distance,but going on experience. R.C

All forms of light are part of the electromagnetic spectrum as are the gamma and x-rays used in industrial radiography. Visible light is on the low end of the spectrum ultraviolet is farther up the spectrum and still farther up are the gamma and x-rays. The Farther up the spectrum the shorter the wavelength which is part of the reason why x-rays will penetrate or pas thru steel and other materials that will not allow the passage of light. With that in mind it holds that the intensity of the "ray" in question is subject the same laws of physics as all others in the spectrum. The same principle used in determining the safe working distance from an x-ray souurce would be the same as that for determinig the safe working distance from an ultraviolet source and is known commonly as "The inverse Square law". Bear in mind though that diiferent forms of radiation have differing effects on the various parts of the human body and as such , while the formula would be the same, the units of measure would not nor would the safe working distance from a welders arc necessarily be the same as the safe working distance fromm an x-ray or gamma ray source.

Chris,
Yardville, huh?
I doubt if the rest of us in NJ would want our rehabilitated convicts suffering retina damage. There have been a few posts recent months in the education forum I think about UV, but I am not sure if you really want your question to be so narrowly phrased.

If you are considering general safety, not research specific to UV, you will also need to consider IR as well as the long term effects of intense "safe" light.
They all cause eye injury of various descriptions. OSHA is as good a guideline as any I guess.

There is an element of radiation hazard even at the beach, or I guess anywhere in full summer sun, so what "safe" actually is may be open to an individual's interpretation. I wonder even if halogen lamps create enough IR to cause injury; they fade many dies.

Perhaps the most dangerous effects of the UV come from the particle, or quantum, characteristic of light energy. It falls just to the visible side of the Xray spectrum and can cause mollecular changes when this radiation collides with various atoms such as those bonded in DNA molecules. As they strike various atoms these particles tend to impart their energy to them and in so doing their "life"... this delineates the practical limit to my mastery of the subject...

...relying on logic from this point, it seems reasonable to expect not merely distance but the density of the atmosphere through which the UV travels to determine the rate of "decay" (if I could only think of the word I want when I want it) You will find it easy to obtain aquarium filtration design texts (AQUARIUM HANDBOOK by Martin Moe is one)which will tell you how much more rapidly water filters this UV than air (as used in UV filtration for advanced aquarists and fishkeepers) but here and now the exact numbers escape me; indeed even the envelope and tubes through which the UV is intended to pass must be made of quartz glass as plastic and [silicon] window glass tends to filter the intense radiation at the source so seriously as to rendeer the filter useless... this tends to support the fact that distance does indeed diminish over distance, as well as, in addition to the effect of diffusion, tend to explain why.

A little deeper, in the field of photography, UV/HAZE filters are in common use to solve a problem typical to landscape photography. Certain parts of the UV spectrum (to which the [silver chemistry] film is more sensitive than the human eye) will unfortunately tend to cause a hazy fog to photograph on an apparently clear landscape. The physics beyond this phenomenon also relate to the question as well as the science behind the answer. It might suggest that UV intensity does not deteriorate as rapidly as visible light... but you can be certain it does indeed deteriorate.

(to digress, the IR film focus curve (a red curved line on some lenses' body with distance delineated along it) demonstrates another interesting characteristic about the nature of light)

I forgot the "safe" distance I learned; of course it depends to an extent on the initial intensity (translate to weld parameters)

Check out this month's Welding Journal on this web page. Info several people was trying to help you with, including myself, that did not completely answer your question, is in an article by Terry L. Lyon.
http://www.aws.org/wj/dec02/feature.html
Hope this helps,
John Wright