as far as i know that would be ok, seeing as air is 70% n2 anyway
so this impure n2 may just be air anyway,
02 is just a bad idea because if it breaks and sparks, its highly oxidising (duh) so itll blow up nicely
i would of though that air would be cheapest by far because all you need to do it pump it in from the air, no nitrogen etc producing kit needed. ?
beedle