I had to reinforce the lenses to make it safe to use. It came with a small fan in the filter, I ripped it out and put in a 12V CPU cooling fan which I connected to a length of wires and a small tamiya connector. Battery pack in my shirt pocket powers it.
yes its the same. The lenses will become detached from the mask if it's shot in the right place so to use one you need to epoxy around the inside edge of the lenses to be safe. I found the fan unreliable so I cut the whole internal structure out of the filter and cut the corners off a CPU fan to cram it in. The wires then go inside the mask and out the bottom. The design of these masks is that the fan blows the air into a channel taking it to the top part of the mask and blowing air over the lenses. The bottom of the mask is basically sealed off so that the condensation from you breath doesn't go up to where the lenses are. With a real gas mask you may need some serious alteration to achieve the same effect but a fan increasing airflow should be beneficial. Some sort of antifog coating for the lenses should also help.
It depends what type of gas mask you mean. If you are thinking of getting a British Army S10 Respirator...
...you don't need to worry much about it because its internal design
makes the air circulate around the inside every time you inhale, carrying any moisture build up away from the lenses. You need to get some replacement lenses for these however, because they are not ballistic protection rated and do crack under BB fire. There's a bloke on here who makes the ballistic replacement lenses: Blueangelical
Of course the usual anti-fog gunks will help for those days when you're sweating like a blind lesbian in a fish shop. Fog[Tech] seems to be the best reviewed. I've recently given it a go on some goggles (and I sweat like a Nazi paedophile wearing a pope dress at a French Catholic Mothers' Union meeting) and it did work for about 2.5-3 hours, then carried on working after a wipe and a reapplication. I did also use the standard anti-fog wipe cloth which comes with ESS goggles/glasses as well, as I was told it works really well in combination - it does. Another option is some Russian surplus stuff which looks like a miniature lip stick and works like a wax crayon - you scribble on the lens and then polish it smear free - it's pretty good, but not as good as Fog[Tech] + ESS cloth.