You don't have to change the absolute filter in a
dust free environment
but I wouldn't do it out in the garage or a dusty workshop or during a
sand storm :-)
When you change the filter, there is nothhing critical that's exposd to
'normal' air that is not also epxosed ewhen you change the disk pack. So
if you are happy changing disk packs in your machine room, then it shoud
lebn OK to change the filter there too.
-tony