As plasma cutting is an electric arc I would always recommend eye protection which will provide protection against ultra violet light. Gas welding goggles do not provide this protection. http://en.wikipedia.org/wiki/Welding_goggles. The correct eye protection is available in either helmet or spectacle format and so it is not worth risking your eyes!
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You can take a horse to water but you can't make it drink
I used to use sunglasses with 100% UV protection but I got 'panda face' (skiers will know what I mean)
These days I go for the light reactive helmet set to Grind function.
Funny how good sense creeps up on you...
Everyone can of course wear what they wish but I wouldn't take a chance with my eyesight. The product data sheet for Esab Pro glasses specifies they are for "gas welding/cutting"
EN 175 is simply a standard for personal protection by which all equipment for eye and face protection during welding and allied processes must meet rather than a confirmation of individual processes. A shade 5 is intended for gas welding/cutting only and thus often will include the reference GWF (gas welding filter) rather than EWF (electric welding filter). The minimum shade for plasma cutting up to 300amps, being an electric arc, is a shade 8 as recommended all major plasma system manufacturers.
At risk of a good verbal shoeing, I find that when cutting sheet horizontally with the torch tip in contact, there's next to no arc visible, just a shower of sparks under the plate, so I don't bother...
I just cannot believe some people think that because an electric arc plasma system cuts like a gas torch they are all right to use a gas welding filter lenses goggle to protect their eyes when all the major suppliers, including the market leader Hypertherm, advise that a shade 8 electric welding filter lense is the minimum. They do cost a little more but, as mfletch says, it's better safe than sorry, especially when plasma cutting glasses can easily be 'googled'
I don't really care what major suppliers recommend shade 8 is too dark for me (and I think you'll find they only recommend shade 8 to completely cover they're arses from litigation, rather than because its required) I use my optrel on shade 5.
I have to say I agree. Shade 5 works perfectly for me and the Bolle has the required UV protection. I certainly don't have any ill effects from using them.