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Anvils in America, THE book about anvils

Blacksmithing and metalworking questions answered.

Blacksmithing and Metalworking Tools Historical Preservation.

International Ceramics Products

Vision Safety :

Filter Lenses:

IR and UV protection in the blacksmith shop

Hazards in the shop come in many forms. The need to protect our eyes from flying objects and sparks is obvious, other hazards are not so obvious. Infrared and ultraviolet light are generaly invisible but can do great damage to our eyes. It is agreed among those in the medical community that both damage the eyes and the damage from both is cumulative. Beyond that there is little or no concensus and the no specific recommendations for many kinds of ocupational exposure.

The Official Literature (US):

You will find many articles on this subject in print and on the Internet, many in highly respected publications, that appear to have specific answers but they DO NOT. All the articles you will find refer to OSHA CFR 29.1910.133 and ANSI Z87.1-1989

OSHA requires every employer to provide adequate eye protection to prevent damage to employees eyes BUT does not give specific recommendations leaving the employer on their own to determine the correct level of protection.

OSHA documents are U.S. government documents and considered part of Federal law. As such they are freely available and on-line. However OSHA's CFR 29.1910.133 refers heavily to ANSI Z87.1-1989 for all technical content. The problem here is that ANSI (American National Standards Institute) is not a government entity and you must BUY their documents if you need to refer to them. So, most authors blithly refer to the "details" as being in the ANSI spec without knowing the content.

It would SEEM that the ASTM spec referred to by OSHA and many others would be the last word on the subject. So I purchased the spec on eye protection (yeah, OSHA a US government agency refers to it in their standard but you must BUY it).

What ANSI Z87.1 says is that "the responsible person must make the decision as to the correct eye protection", including the filter shade (how dark, type of filter). They do not say how. They do not say what is too much or how bright is too bright. But you MUST make the correct decision. This is the infamous "Catch 24" AKA as a SNAFU. The standard is VERY specific about how to test and measure degrees of shade and impact testing and so on. But no help in application other than common welding applications.

Under welding ANSI Z87.1 repeats the same welding shade recomendations that are given in the OSHA document and were taken by both from some un-named welding reference that predates both organizations.

Under "HEAT, furnace operations, pouring, casting, hot dipping, gas cutting and welding" they only refer to a note that says "may also involve optical radiation". There are no specific recomendations.

There is only one reference to didymium glasses in the standard and that is as an aside relative to special purpose applications stating that didymium "may not" provide the necessary filtering of IR and UV.

OSHA refers to the ASTM spec and the ASTM spec back to OSHA. OSHA's web site refers to a medical site where the only content on the subject is a reference back to OSHA. (Circular references). This is a common problem in modern documents and a very easy way for authors and the government to appear credible when in fact they know nothing.

The Facts

The medical information I've read indicated that there was very little good research on this subject and the only conclusions were that it IS cumulative and bad for your eyes. The type of damage that occurs can result in all types of things eventualy related to blindness, glocoma, cataracts. . . Apparently there is lots of data on UV since everyone is worried about exposure to the sun. With IR most of the research and data is related to the use of lasers.

Glasses: MvRC, Its a complicated question and I have spent some money recently trying to get answers.

Contrary to Thomas's post about sources of information (OSHA ect). I went to ALL those places and more. I carefully read all the literature and followed all the links. There are NO specifics. They all refered me to the ANSI Z87.1 standard with the exception of a few specific instances in welding applications.

So, I broke down and bought a copy of ANSI Z87.1. This, after having eroneously purchased an electronic version of the Swedish standard. It was in English but gave no useful info. NO, even though hundreds of public documents refer to the ANSI document you can't get the information from a public source, you have to PAY for it. This is our US government at work. . .

The literature on didymium is conflicted. However, it all agrees that didymium is designed specificaly for filtering the sodium flare of a glass furnace. This is so that the worker can SEE through the flare. New didymium glasses with a gold coating are supposed to be very good at filtering the flare as well as IR. There is a report on that but I have yet to obtain a copy.

Didymium WILL help you see better in a borax flux filled forge environment because the sodium in the borax does cause some sodium flare. However, one second hand source says that one manufacturer of didymium glasses insisted they were NOT suitable for metal working applications. But many blacksmiths have recommended them over the years.

What I do know it that #3 shades are used for brazing and light welding and cutting. #1.5 to #3 shades are used for torch soldering (with an oxy-acetylene flame). #2 shades have been recommended as "flash glasses" to be worn by people working near welding and by welders under their welding hoods. #2 shades are also used in many foundry environments and the glasses below are the type that were used in our local foundry.

Distance and intensity is an important factor in the necessary shade. The further away from the source the less intense it is and the lower the shade. In typical welding applications you have your face very close to the work. This is not so in working with a forge. However, the intensity factor is not just brightness but the area of the source to a lesser degree.

Another safety consideration addressed by ANSI is that no matter what shade is best it must not be so dark as to cause lack of visibility hazzard in use.
IR Damage: Consider this, heat cooks protein (meat, egg whites), IR is pure thermal radiation, your eyes are mostly protein, the lens of your eye absorbs that radiation as heat . . . I knew a guy in school that thought he could arc weld by squinting. . . His eyes swelled up to where they stuck out beyond any other part of his face. . . It would be interesting to know how his eyes are holding up 40 years later. . .

The medical information I've read indicated that there was very little good research on this subject and the only conclusions were that it IS cumulative and bad for your eyes. The type of damage that occurs can result in all types of things eventualy related to blindness. Apparently there is lots of data on UV since everyone is worried about exposure to the sun. With IR most of the research and data is related to the use of lasers.

From Canada's CCOSH
A serious concern is the "blue light hazard" which is the temporary or permanent scarring of the retina due to its sensitivity to blue light, around 440 nm wavelength. Blindness may result.

Exposure to infrared light can heat the lens of the eye and produce cataracts over the long term.
I just did another review of the data on the web and there are MANY articles on this subject and they all refer the reader to the "specifics" in OSHA CFR 29.1910.133 which refers to ANSI Z87.1-1989 "Practice for Occupational and educational eye and face protection".

The only specific recomendations ANSI Z87.1-1989 has for filter lenses is under welding. Under HEAT, furnace operations, pouring, casting, hot dipping, gas cutting and welding they give no specifics and refer to a note that says "may also involveoptical radiation".

Glass blowing is not mentioned. In blowing there are two situations. Those that work with furnace melted molten glass and those that work with an oxy-fuel torch. The oxy-fuel torch is a UV and blue light source as well as IR. In the furnace operation IR is the only concern.

One study of glass blowers showed that they had more trouble with the furnace side eye from the constant periferal glare than with their other eye. Most of what I have found on the glass blowing issue was ancedotal eveidence. Articles claiming factual data fell short.

In the case of foundry and forge workers it seems that there are no specific recomendations from the government and that there is no current research on the subject. I found ONE Spanish company that had recomendations for foundry workers. Seybol listed:
Glass shade 5 for medium source temperature 1,390°C. (2435°F)
Glass shade 6 for medium source temperature 1,500°C. (2732°F)

Infrared filters must protect the user against IR radiation, allowing proper vision, of the task being done, and safety signal recognition. The filter must allow colour identification, specially allowing a correct evaluation of Fusion baths temperature.
This is one question that there are no really definitive answers for. However, the best information is that you should wear IR protection when you work with any hot material and combined protection when dealing with welding arcs OR oxy-fuel flames. We offer the #2 shade glasses as an economical replacement for expensive Didymium glasses when used by metal workers. However, if you can stand a #3 shade then you can wear welding goggles. However, I have trouble with the reduced periferial vision of welding goggles and find myself tripping over things if I try to wear them as general shop protection. They also do not provide the same impact protection as the safety glasses.
   - guru - Thursday, 10/23/03 18:08:10 EDT

Didymium Lens Please note that these are designed to filter the light created by the sodium flare in a glass blowers melting furnace. They are not the correct filter for metal working using a torch or forge. Standard filter welding lenses are available for this.

Sunglasses NO MATTER HOW DARK are not filter lenses. They may let you see through the bright light but they WILL NOT protect your eyes from the harmful rays in the wavelengths that do damage. Filter lenses have specific chemical dyes that absorb the harmful wavelengths.

Do you recomend filterd lenses for work in a coal forge? How about a gas forge?

Lastly, as everything I've read, and seen at demo's and so on, most of a working smith's temperature control comes from the color of the steel or iron he's working on, how do the lenses affect that?

Mattmaus - Wednesday, 06/12/02 15:05:00 GMT
Some smiths use filtered lenses and others do not. If you do a lot of forge welding you should, particularly if done in a gas forge.

The level of filter lens varies with the distance from the work as well as intensity of the source. Filters in the 2-3 range are used for flash glasses and in foundries and are suitable for forge work. When gas welding or cutting your face is generaly close to the work so that you can see the puddle or into the kerf. So you need a darker shade for welding than when at a distance.

Judging color temperature has more to do with ambient lighting than anything else. An orange heat in low light will just barely appear hot in direct sunlight and will appear to be a yellow heat in the dark. So, it is what you are used to seeing. Judging heat wearing filter lenses is the same. With practice you will know just as well as someone without filter lenses.

It would SEEM that the ASTM spec referred to by OSHA and many others would be the last word on the subject. So I purchased the spec on eye protection (yeah, OSHA a US government agency refers to it in their standard but you must BUY it).

Forging and casting operations are NOT given any specific consideration. The only recommended shades are those for specific gas and arc welding operations and THIS was taken from an old AWS recommendation that is the same as is quoted in every welding book. Otherwise most of the spec is standards and testing methods for manufacturing of the filter and safety lenses.

OSHA requires every employer to provide adequate eye protection to prevent damage to employees eyes BUT does not give specific recommendations leaving the employer on their own to determine the correct protection. OSHA refers to the ASTM spec AND to medical sources which in turn refer back to the same ASTM spec AND OSHA (Circular references).

Dididyium lens are mentioned for glass blowers but not as a specific recomendation. Dididyium lens ARE referred to as not being suitable for metal working. So we offer the much cheaper #2 shades as an alternative for working at the forge.

Since all IR exposure is cummulative any amount of protection helps. How much protection is enough is not defined except for welding operations.

As far as judging color is concerned, ambient light has a GREAT deal to do with it and is different in every shop. For judging welding heat you can go more you the surface texture (especially using shaded lenses) than actual color. Many folks also use a test bar to touch the weld area and see if it is sticky (see our iForge demo on forge welding).

- guru - Tuesday, 03/04/03 17:38:56 GMT

I was reading in the new Edge of The Anvil that when forge welding a great deal of ultra-violet light is produce. So you probably should use goggles, but then wouldn't it be difficult to judge the color. Does anyone wear goggles or even worry about this?

Thanks. Hayes - Tuesday, 03/04/03 06:26:02 GMT
Forge welding and IR: Hayes, There is no UV in the forge fire but the infrared IS intense and CAN damage the eyes. All infrared exposure is bad for the eyes and the damage is cummulative throughout your life. Staring into the fire for long periods is not wise and should only be done as needed. As with many things different people have different sensitivities to IR and what is damaging to one person may not be to another.

The problem is worse with gas and oil forges than with solid fuel due to the large luminesent area of the forge interior.

For those that worry about such things we sell #2 shade safety glasses. These are made using the same filtering material as welding glasses except they are not as dark. Standard gas welding shades are a #3 for small work and #4 or #5 for heavy work or cutting. Distance is also a factor. The farther away from the work the lighter the shade can be. In most torch welding your face is much closer to the work than when forge welding.

The rule on welding shades is to use as dark as is safe to see and work with. If you cannot see the work well enough then you are supposed to go to the next lightest shade. The #2 shades are fairly selective in what they filter and you can actually see the hot metal better WITH them than without. I've used them while working in the dark and they kill the glare of the fire while still letting you see well enough to work. . . strange but true.
An elemental salt, isolated and first described in 1842. It is a form of the rare earth lanthanide metal Praseodymium situated between cerium and niobium on the periodic table. All the various salts and oxides of this element, when mixed with glass, filter out specific wavelengths of the electromagnetic spectrum. This info is from the Los Alamos Natl. Labs periodic table web page.
Alan L - Tuesday, 07/04/00 19:51:28 GMT

Rose Didymium Filter Glass
Developed for high temperature glass work, this glass offers protection at the sodium line (589nm) and UV spectral wavelengths. The visible light transmittance of this glass at 3.2mm thickness is 50%, allowing good visibility indoors. This glass is dichroic, meaning it's color will look aqua green under fluorescent lighting but under natural and incandescent lights it will have a light rose color.
Van Nostrand's Scientific Encyclopedia", Fifth Edition. (co Frank Turley)
DIDYMIUM GLASS. Didymium glass is a special optical glass which is tinted with mixed oxides of neodymium and praseodymium to give very narrow and sharp absorption bands. One in particular falls at the wavelength of yellow sodium light, so that the glass, which is only faintly tinted to white light, is almost opaque to the yellow sodium light.

Welding videos dangerous?
Is there any danger to the eyes when watching videos of various types of welding?
- nrobertb - Tuesday, 11/19/19 04:19:59 UTC

The brightest that a video monitor OR film projector screen can get is a normal bright white. Like looking at white backgrounds on your monitor. While it looks intense that is a result of contrast (dark against light) and the rapidly changing exposure levels in the camera.

-guru - Tuesday, 11/19/19

References and Links

  • Alphabet Soup What's that acronym?
  • OSHA

  • ASM Metals Reference Book, American Society for Metals International
  • ASM Heat Treater's Guide to Ferrous Metals, American Society for Metals International
  • Tempil - Basic Guide to Ferrous Metallurgy Chart, Tempil Division, Big Three Industries, Inc.
  • MACHINERY'S HANDBOOK, Industrial Press

2002 Jock Dempsey,

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