It is not good to be breathing any fumes, but the ones eminating from stainless steel are the worst since they contain vaporized cadimum, nickel, and other toxic heavy metals. Galvinized metal is also very hazardous for the same reasons.
Many of the substances in normal welding smoke, such as chromium, nickel, arsenic, asbestos, manganese, silica, beryllium, cadmium, nitrogen oxides, phosgene, acrolein, fluorine compounds, carbon monoxide, cobalt, copper, lead, ozone, selenium, and zinc can be extremely toxic.
In addition, it is imperative NOT to use any degreasing chemicals as they will release deadly chlorine gas when exposed to welding or plasma arc temperatures.
Of course, even vaporized iron will deposit in your aveoli and diminish the vital capacity of your lungs, creating fibrotic scar tissue that will never heal and permanently reduce your air intake and respiration.