Welding flash in public places?

[DaleK]

On the odd occasion when I can't get something in the shop my outdoor welding area is about 40' off a well-travelled road. I generally try to keep my back between the road and the flash, and for the most part I think it's far enough not to be a big risk, but what do you all do about the flash when you have to weld close to or in public areas since it's pretty obvious you can't trust people to use common sense anymore?

 

[green.bubbly]

I do service work in a lot of machine shops and fabrication shops. I see a lot of the welders using a welding screen/curtain. Just a portable shield on a stand that they position around where they are welding.

 

[Stephenw]

It's not common sense. Most don't know about the danger from an arc flash.

It pisses me off when I am stopped at a traffic light and look over into a construction site just as a worker strikes an arc.

Use a screen of some kind.

 

[clcartwr]

Yeah screens are almost a must in my opinion for close quarter instances. Like Stephenw said it's not necessarily common sense but as long as you have some sort of sheild between the arc flash the traffic you should be alright. Also they keep down on breezes and such so welding won't be as frustrating.

 

[Dick in Wisconsin]

If you're working in a shop that regularly has any welding going on, post a sign by the front door(s), entrance(s), service door(s), etc that starts with:

WARNING! in big red letters and goes on to say that ...

Throughout this facility there will be welding taking place at any time without notice or warning. The arc (bright light) from welding has been determined by the Surgeon General of the United States and the State of California to cause blindness under circumstances and that under NO circumstances should anyone look at the welding arc (bright light) without specially designed welding eye protection. Sunglasses provide NO protection to your eyes whatsoever.

Beside being a courtesy to you visitors, it makes good sense to remind people of the problem.

I've found many welders routinely look around before they start welding and tell the bystanders to "look away". Makes common sense.

 

[sublimate]

Flash intensity drops with the cube of the distance. So the intensity 10 feet away is 1,000 times less than it is 1 foot away. 20 feet away is 8,000 times less. 30 feet is 27,000 times less.

Once you're 10-15 feet away there's not much issue from a flash as long as the person doesn't sit there and stare at it. If they're 30 feet away there's pretty much no issues even if they do.

 

[djjsr]

Use a welding curtain. Sooner or later, some jackass is probably going to try to sue you.

 

[Dick in Wisconsin]

Flash intensity drops with the cube of the distance.

"cube" ... wow! that is a dramatic drop off. I didn't realize it was that significant.

 

[sberry]

Thats why its not a big problem.

 

[bad_idea]

I agree with sublimate on the limited hazard of flash burning passer-byers. I also agree with others comments on the lack of public knowledge on the issue. I work in ship repair and have to routinely tell the sailors not to look at the pretty light! If you are concerned, buy a weld curtain w/ a frame like green.bubbly posted. Me personally, I don't worry about curtains at the house.

Working on ships, many times in main passageways, it is hard to shield the welding arc effectively. In a ten hour work day I get flashed more than anyone walking down the side walk in front of my house. Please don't beat me up on PPE or safe guards, my point is I have never had flash burn and anyone walking by the house will have MUCH less exposure than I get in a work day.

 

[brownbagg]

hell with them, they stupid enough to stare at the flash

 

[KinzeMech]

The only difference between the arc flash, and staring at the sun, is that no one's going to sue the sun. I know how ridiculous it can be to say things like "no one's going to sue ______", but this is one in which I'm still pretty confident.

Sublimate hit the nail right on the head. The intensity is a function of the cube of the distance, as the single point source is being radiated uniformly in all three dimensions. The intensity drops off quite rapidly, although I would love to know if there is an tested, established distance beyond which no PPE is required for protection from an arc flash. For example, if my unobstructed arc flash is viewable to traffic 40 feet away and I get sued, it will be most beneficial to my case to be able to obtain expert testimony that arc flash is considered harmless beyond 20 feet from source.

 

[oldmerc]

Sadly djssr is probably correct .

 

[Air_Cooled_Nut]

KM, any high school physics teach will back you up.

 

[alpinewhite]

"Inverse square" is what I remember from my Physics classes.

http://wise.ssl.berkeley.edu/documents/The Inverse Square Law of Light_Final.pdf

 

[Kevin C]

I would love to know if there is an tested, established distance beyond which no PPE is required for protection from an arc flash.

http://lmgtfy.com/?q=welding+flash+distance

http://www.aws.org/technical/facts/FACT-26.pdf

That's what I found..... Good info, I had no idea the problem had been worked out to that level of detail.

The second link has a nice chart of distance VS arc current VS time.


PS ... Hope you dont mind the let me google that link, I think its kind of fun to watch.

 

[KinzeMech]

I like lmgtfy links, I think they're funny.

Google's great when you just want an answer. A discussion forum is great when you want to discuss a question and an answer. A forum thread with a google link is the best of both worlds.

 

[KinzeMech]

It was neat to see that for the types of welding I routinely encounter, the exposure limit at one minute exposure time is about 10 feet, or less. That pretty much (IMO) covers the periodic flashes you get when you're nearby, and didn't realize you coworker was about to strike another arc.

 

[Notch1988]

Is it mostly people in cars on this well travelled road? If so, car windows block UV light so at 40' away, inside a car, no way is someone getting flashed

 

[Kevin C]

Still reading about the dangers of UV and eyes. In Oregon a school gym had a broken lamp....

http://uvlightburns.com/page3.html

Lake Oswego Review

UV rays at Bryant Elementary cause health issues

Alandra Johnson 11/17/04



Ultraviolet rays from a broken light fixture in the gym at Bryant Elementary School caused about 50 teachers attending an in-service Friday to experience headaches, burning eyes and red, irritated skin, similar to that of a sunburn.



The cover on the light was broken during a basketball practice on Oct. 27, but the light bulb itself did not break. Without the protective cover, the metal halide light sent UV light into the gym. The school fielded one complaint about the conditions in the gym on Nov. 4 after a group using the gym reported some individuals experiencing irritated skin and burning eyes. Fearing mold spores, custodians cleaned and disinfected the area. The school didn’t receive any other complaints until the in-service Nov. 12.



Of the 110 third to sixth-grade teachers from across the district attending the in-service about math curriculum, about half experienced some type of symptoms according to Lake Oswego School District spokesperson Nancy Duin. Several teachers sought medical treatment and some wet to the emergency room. Six called in sick Monday; four missed work Tuesday and two were still out as of Wednesday. Duin said that at least one teacher reported that her eyes had swollen shut after the exposure.

Ooops.

 

[tymbo]

"cube" ... wow! that is a dramatic drop off. I didn't realize it was that significant.

I believe it is the square of the distance.

 

[clcartwr]

Yeah I really don't believe the arc flash could be a hazard at that distance but definitely could be a nuisance/distraction to drivers.....

 

[KinzeMech]

If someone takes the time to look up the formula for the surface area of a sphere, using that formula, with the radius being the distance from the point source of UV radiation, it will show whether it is the square or the cube of the distance.

edit:

scratch that...that may not be accurate. I may look into further later on if I get time.

 

[BFBOB]

Light (and sound) intensity drop off with the square of the distance. To use the examples given, the intensity of an arc at 10' is 1/100 of the intensity at 1'. At 40', the distance under consideration by the OP, the intensity is 1/1600 of that at 1'.
In the real world, it can be a little more complex. When the environment is reflective, the intesity will drop off at a slower rate, sometimes significantly so. Welding inside aircraft is the example I've heard cited. Workers at the other end of the fuselage, normally far enough away to be safe, were injured by the reflections of the arc making their way to their unprotected eyes. That's an extreme case, but you get the idea.
What I deal with is placement of fire horn/strobes. Both the sound and light are affected by the room. A room full of upholstry, drapes, rugs, etc. may require a louder horn, or more of them, than a room with hard floor walls, ceiling and furniture. Distance matters, and so does reflectivity, for both sound and light.

 

[KinzeMech]

I believe it is the square of the distance.

Upon further consideration, I believe I was wrong, and you are correct.

See here is a particularly effective illustration:
http://en.wikipedia.org/wiki/Inverse-square_law

 

[BFBOB]

Kinzemech--A plane is usually used for demonstrating geometrically the inverse square law, but for small angles (and I suspect large ones too) a sphere would work the same. There is a very simple diagram that makes the inverse square law instantly obvious, but I can't draw it here! Wikipedia should have it - just search the Web (I refuse to use Google) for "inverse square law".

 

[BFBOB]

KinzeMech--
Perhaps you were thinking of wind resistance? It does increase with the cube of speed- for reasons I don't understand. Fluid dynamics get complex in a real big hurry.

 

[DaleK]

Thanks guys. We do get a lot of walkers along this road, no neighbours within a quarter mile though. Think rather than invest in a curtain I can open up a 1-ton seed bag and hang it horizontally on a pole across the front end loader when I'm going to be doing a lot of welding outside, that'll give me a screen roughly 15' long x 5' high

 

[KinzeMech]

Kinzemech--A plane is usually used for demonstrating geometrically the inverse square law, but for small angles (and I suspect large ones too) a sphere would work the same. There is a very simple diagram that makes the inverse square law instantly obvious, but I can't draw it here! Wikipedia should have it - just search the Web (I refuse to use Google) for "inverse square law".

Do you mean like the wiki page I linked in the post directly preceding yours?

KinzeMech--
Perhaps you were thinking of wind resistance? It does increase with the cube of speed- for reasons I don't understand. Fluid dynamics get complex in a real big hurry.

No, I just had a faulty thought process. I was prepared to argue tymbo's statement it was a function of the square of the distance when I realized my error. I think I went to mistakenly thinking of a formula for 3D volume, when I should have been thinking of surface area of a 3d surface.

 

[uhcrandy]

Inverse Square law is a very common model. Radiation is dermined by the same equation. Dont for get the other variables to dermining exposure, Time/Distance/Shielding... also work for radiation.

 

[WVBrady]

Light (and sound) intensity drop off with the square of the distance...

I agree, but there is another consideration. Because the arc is not a point source, it has a nonzero area, which is mapped to a nonzero area on the retina. Thus, even though the intensity drops off with the square of the distance, the area of the retina that is affected drops off at the same rate. You have less energy, but it is concentrated on a smaller area. This is the reason for the surprising statement that the brightness of a streetlight is independent of distance. This is, of course, neglecting atmospheric attenuation and scattering. I don't know how they came up with the numbers in the chart. Maybe at some distance they consider the arc to be a point source.

 

[KinzeMech]

Nothing is a truly perfect point source. In terms of the scale of the dimensions we are considering (an arc of 1/4"-1/2", viewed anywhere from 12" to 480" away), I believe it can be considered point source.

 

[Skin]

i wouldnt even question whether someone might true to sue. Theres a lot of things that dont make sense but are enforced. Its a federal offense to point a green laser at a plane flying 2 miles over you so yea im sure you'd lose in a court if someone claimed they were blinded by your welding flash from a block away.

 

[pipsters]

i wouldnt even question whether someone might true to sue. Theres a lot of things that dont make sense but are enforced. Its a federal offense to point a green laser at a plane flying 2 miles over you so yea im sure you'd lose in a court if someone claimed they were blinded by your welding flash from a block away.

I was hit at 15,000 feet on arrival at night estimating the laser was 10 miles away, it was distracting but not a huge ordeal. Couldn't imagine two miles at 3-5k, or worse in the flare or right at rotation.

Had 3 sheriff and local helicopters over the area in about 10 mins though .

"Lasering" an air carrier aircraft is a pretty big deal...

 

[LSU]

Thanks to all you "Myth Buster Physics folks" for the replies. Reading the posts made me realize that I'd forgotten much of that stuff and after reading what you wrote, I'm not sure I understood it when I took the classes many years ago.

My quick and dirty answer to the outside flash problem is I salvaged some old wooden fence board and built a stand out of 4x4's and 2x4's that shade the flash from passerbys. I picked the wood up when someone was tearing down a fence. Screwed it together and built a simple, portable wooden fence. I figure it was the polite thing to do. I've got good neigbors and want to treat them right.

I got the idea from Jack Olsen when he was building a metal fence at his house. Search for the thread. I stole his idea.

 

[zuk123]

I'm with clcartwr on this one.

Whether or not they would get retinal burns, the bright light is a serious distraction. Our attention is drawn to movement an bright light.
You don't want someone driving around a corner, having their attention drawn to your arc, and hitting someone or something...

Set up something as a shield.

I'm so conditioned, I can't help but blink or look away when I see an arc on TV. Watching the guys on the shows tacking with just their eyes closed all day just kills me. Your lids aren't enough! Once in a while, from a practical standpoint, ok. But all day long?

zuk

 

[sublimate]

Light intensity drops with the square of the distance in a vacuum (like space). But absorption and scattering in the air will also reduce the intensity with distance in this case. So the drop is faster than the square of the distance.

But as others have said, the point is probably moot. Best to shield as much as reasonable.

 

[Twiggss]

It's not common sense. Most don't know about the danger from an arc flash.

It pisses me off when I am stopped at a traffic light and look over into a construction site just as a worker strikes an arc.

Use a screen of some kind.

really? no.... really??

 

[Sureshot]

You guys are making a mountain of a mole hill. Blinded? Looking at construction sites? Just carry on welding and ignore the rest of the world, they will move on no worse for wear and tear.

 

[Big Bad Dad]

hell with them, they stupid enough to stare at the flash

How about the young children that would have no way of knowing not to look? To hell with them too?
Let OSHA catch you welding in a public place without a shield.