All the cats I've owned have had a common desire in life - to be allowed in the darkroom and they never have been! While you can do a pretty good job of dust proofing a room that is a dedicated darkroom it is much harder in a room that has to do service as something else, even it's just storage of surplus household goods. A double door light trap, if you have the room, also keeps out a lot of dust as does air conditioning of the type that introduces fresh air (most split systems only recirculate) using the same air pressure effect mentioned by another poster. In the end, unless you build a clean room and suit-up appropriately to work in there, there will always be times when dust will spoil a print or two. Good reason to learn spotting. OzJohn