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Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Well... if I don't want to risk damaging my eyes by the UV emitted from a Jacobs ladder arc, what can be considered "safe" value of its current? For example, is a MOT arc (~1A) safe to look at?
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
There is something like a safe dose of UV light which is measured in joules/m2 exposing each cell surface. I can tell you from my experience that energies above 10J can damage the cell which is not protected very seriously (I would compare it to 3-4 Gy of gamma irradiation). I have no idea how to recalculate these values to the light produced by an arc. The damaging wavelength producing so called photoproducts (thymidine dimmers - cross-links in your DNA) is below 300nm and the most damaging is around 250nm. In case you can measure the spectrum of the arc and the amount of energy falling onto the surface of your retina you can get an idea. But remember, there is a quite a good protection provided by your vitreous body so your eyes are quite UV resistant. Generally the exposure to UV light produced by sun in the summer (and/or in the mountains) is far stronger. Anyway, remember the retina cells can not reproduce – so once you loose it is forever. (BTW the snow blindness is not caused by retina damage but by the outer surface of cells of vitreous body - that’s why it is reversible). Moreover the cross-links are mutagenic and theoretically can lead to a tumor (but as far as I know retinoblastoma is extremely rare unless you have strong genetic predispositions). Just to make this story short – do not expose your self (any part of your body) to any mutagenic (DNA damaging) agent, because there is nothing like a training of your body to that. You are only increasing the problem of accumulation of mutation leading to cell senescence, loss of function, cell death or worse to tumor transformation. In the case of UV light produced by an arc - any sunglasses do the necessary protection - so use them! Additionally you can wear long sleeves to protect your skin to be double safe (but here we are talking about really big arc energies to induce skin cancer. But it can be your case in the future ).
Registered Member #690
Joined: Tue May 08 2007, 03:47AM
Location: New Jersey, USA
Posts: 616
If I were doing extended tests and not just brief runs, I would probably wear sunglasses. I would think the real danger comes when you have capacitive discharges creating a white-hot arc that is obviously emitting all kinds of UV.
My first TC had a static gap in a PVC endcap. If you've ever worked with PVC before, you'd probably know that PVC will turn yellow and brittle slowly (~a few weeks to a month) when left in sunlight. The intense UV from the sparkgap turned the PVC dark yellow in less than 15min of runtime.
With 1A, you'll be fine for short runs. Just don't stare too long...
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"safe" arc current?
:D
). 