Testing an Auto-Dark Welding helm's IR protection

[Sigurthr]

So, I needed to open up my 25mW 473nm DPSS lab laser head, and didn't want to go blind in the process. The aformentioned scenario requires IR protection in order for the desired result to be achieved!

I do not have IR laser goggles. I DO have welding equipment, however.

http://www.youtube.com/watch?v=wvFDLitZALg

You can see the DPSS head with the non-linear crystal out of alignment (no visible lasing) through the helm, but when the camera is moved outside, it sure is lit up. No worries, I disaligned the laser head with the power off. With the helm on, I was able to realign the unit safely.

Edit: fixed the video

 

[Cyparagon]

That's one of the B&W tech units, yes? They have IR filters. You'll only need protection while the head is open.

"superb IR laser goggles" - I wouldn't trust those without measurements. The video seems to show it passes less, but I certainly wouldn't call them superb just yet.

 

[Sigurthr]

Ah, thanks! Yes it is a B&W Tech unit. I feel much better about it now; since it is a lab unit with unlimited duty cycle, I have the beam difusing against my matte ceiling.

Very true, but without a spectrometer, it's the best I can do to use my camera as a gauge for IR. I didn't see any IR via the cam through the helm though, so I called it "superb", if I had seen some, I probably would have called it mediocre/poor.

 

[gbravetti]

what about the ir pass filter you can found on IR receivers, for example the ir pass filter used on the camera of a wiimote from nintendo wii?

 

[Fiddy]

Welding helmet....poor mans unproven IR glasses..

Seriously, if you value your eye sight and want to play with the alignment of the B&W 473

Either:

Do your alignments then put the black cover back on top before powering it back up.

OR

Buy some OEM Lasers IR Glasses.

They use a 2W pump AFAIK which is uber strong, wouldnt be taking chances with a welding helmet.

 

[Sigurthr]

Yeah, I know.. not the wisest haha. It was a test of the viability initially.

I know the light from welding isn't coherent, but if you've ever seen the w/cm2 coming off of a tig arc at a distance of 5 inches while running at 500amps, well it makes the threat from carefully aligning the 473nm labby pale in comparisson. You will burn out your entire retinas from a split second exposure from the above welding scenario. I've trusted my eyes to that helm for years and after my phone's camera did not show any transmittance of IR, I felt it safe enough. I took the risk knowingly. I have a black shirt I wore while welding that has been bleached to an almost purple/gray color with the outline of my helm unbleached. IIRC I was working with 1/2" T6 6061 aluminum plates in a cabinet function; the polished aluminum reflected and focused all the light in my direction. One day's work bleached that shirt.

So, I agree, and you ARE right. Proper certified goggles are the way to go, but if you're aware of the risks and have nothing better, at least this is a viable bare minimum substitute.

 

[Benm]

One issue with these auto-darkening devices is their response time. Perhaps its fast enough, but is it specified how fast it is for a give wavelength?

The latter part could be extremely important: if the darkening effect is only triggered by short wavelenghts emitted by a welding arc, it's conceivable they would not respond at all to a near IR or visible laser regardless of its power output.

Self-darkening sunglasses, for example, are sensitive only to shorter wavelengths, and will probably not darken at all if you shot yourself in the face with a 200 mw/660 nm laser for a minute.

 

[Sigurthr]

I forget the exact responce time of my helm, but it is around 1/100 of a second. Note though, I did not use the autodark feature. I simply set it to a low shadw (about 3 to 3.5) and left it "darkened" (on).

Autodark helms use sensors placed strategically around the lens, so unless a laser beam was very diverged it would have to specifically hit a sensor (which is NOT in the center of your vision) to trigger the auto darkening. So you couldn't use the auto feature for laser safety, but if a helm has manual modes like mine, you can use it.

 

[Things]

I really wouldn't recommend this. The light from an arc is MUCH more dominant in UV wavelengths, not IR!

It may work for blocking slight reflections, but it's not going to do much for you if you accidentally catch a direct hit.

 

[Sigurthr]

The IR content from welding is actually from the radiance of the weld pool, and not from the arc. The arc as you said is primarily UV and white light with very little IR content. The weldpool acts like a full spectrum black body radiator though.

I would not have trusted the helm on faith without a test, nor would I trust the auto sensing, but after checking with the camera I was satisfied enough to procede. Direct hit protection? Untested, and I do not want to test it.

However, the Eagle Pair goggles are the first laser goggles I've ever owned to completely stop a beam, even a low power one of <50mW. I DO think that is a standard others should be held to, and I don't think many goggles on the market today will measure up to it. So, you're absolutely right about direct hits.

Still, indirect protection is better than no protection. All things considered, I think what I did was safer than trying to align it while off and turning it back on again to see if it worked. Who knows how much IR could have leaked out of the aperture and possibly reflected back at me.

 

[Cyparagon]

Perhaps the helmet blocks IR regardless of the darkening condition it is in?

 

[Sigurthr]

That was one of my initial conjectures, as I know it blocks UV regardless of the darkening state. I don't really have the equipment to test it for sure though as I would need to be able to measure small changes in IR transmission, if any. That of course would require that I have truly adequate eye protection and a stable IR source as well, haha.

 

[Bluefan]

UV is easily blocked by most plastics, NIR however not, so I'd assume it won't be blocked. If the arc gives visible and UV light and the heat generated only far IR than near IR may not be attenuated that much at all, you'd have to measure to know.

 

[Benm]

Considering the temperature of welding pools i'm sure it will block near IR as a safety feature, but the question remains to what extent it reliably does so.

Especially with pump diodes you could need OD4 blocking, while i don't think that would be required to look straight into molten metal for eye safety. If you stand the chance of getting hit with 1000nm-ish light in the face i would recommend using only goggles certified for using lasers at that wavelength.

Using anything else is like wearing a seatbelt made of out duct tape - sure it helps, but to what degree is anyones guess.

 

[Sigurthr]

I like that analogy!

What I'm wondering now is if the lens shade number corresponds to OD number. Also, there isn't any spectral response graphs for my helm, haha.

What I did just find was a formula for welding lens shade numbers;

Some filters, notably welding glass, are rated by shade number, which is 7/3 times the absorbance plus one:
shade number = ((7 - Log10 x T) / 3 ) + 1

If my math is right then a #10 lens would be OD3.85 and a #11 would be OD4.3 . Now if only we could get a spectral graph to tell -where- these OD ratings are at. I do know that these lenses transmit green and greenish-yellow better than anything else.

After digging a bit deeper I also found:

In the United States, the industry standard for welding helmets is ANSI Z87.1 which specifies performance of a wide variety of eye protection devices. The standard requires that auto-darkening helmets provide full protection against both UV and IR even when they are not in the darkened state.

My helm is indeed certified to that standard.


Now then, all we need is someone with a very sensitive LPM and a wide array of wavelengths to test out some various welding lenses and report the findings. Perhaps a shade can be found which is a strong enough attenuator across the visible spectrum which also blocks NIR/IR. Would not be good for all the time use as welding lenses are hard to see though, but perhaps would be ideal for aligning/testing a RGB system.