If you intend the glasses in question to protect you, then test them out in advance by mounting them against something solid and letting a full auto burst into them from close range. If you're afraid they'll break, you really ought not use them to protect your eye sight.

I power the fan with a 4 AAA switched battery box that I attached to the goggle strap with a clip, but a velcro band would be better. You just have to solder two wires and seal them with shink tube.

I also have a set ov Uvex XC safety glasses with Rx inserts I use for actual shooting or when I admin a game. I've fired my 450fps G36 at them repeatedly and it only leaves a tiny mark on the lens, which wipes off. Never had a crack or breakage. BUT they do have openings around the sides, which is an entry point, so most fields won't allow them for play.