If you live in a city, the air outside is way more toxic than any mining rigs. All your rigs are doing is circulating and heating up the air already in your rooms, dust may heat up too but you breathe that in every time so.
Don't worry about it! As long you're not got a breathing aide connected to the rigs I think you'll be fine. Just remember to open the windows and let some fresh air in from time to time.