If you are going to run a plasma cutter then you need extraction and filtration.
Fumes from cutting mild steel are bad enough and will kill and if you decide to cut stainless steel then they will kill you quicker.
You can always have a read of this http://www.hse.gov.uk/foi/internalop...9/oc668_22.htm and then decide for yourself if you want to take the risk.
There are also quite a few documents available from searching google for more information.