[MEDIK418]

Ii have no idea what the difference is in medical grade nitrous or industrial grade. I suspect there is none. However, i do know that yes, sulfur dioxide is added to the stuff we get for automotive use but it isn't designed to make you sick or prevent lung freeze.
SO2 as we call it (we manufacture the stuff) is a by-product of oil refining and there's tons of the stuff here. If you burn hydrogen sulfide gas, SO2 is what you wind up with. If introduced to water of any concentrate it turns to sulfuric acid (hydrogen sulfide and water make sulfurous acid) THe strength depends on the amount of SO2 and the amount of water present. What this does to you if you inhale it is BURN. It will instantly make your nose feel like someone lit a match in it. The further into your lungs it goes the more area it starts to burn. Will it kill you? Yes, if you are mean enough to stand the burning nose, throat and everything else in between your face and your lungs, and still continue to huff the stuff, it can lead to pulmonary edema (among other things) and then you may die. Most ordinary humans can't stand it long enough to do this. There is a small chance that people with COPD (asthma, emphysema, chronic bronchitis) might react to the stuff in a bad way and thier lungs will shut down but for most of the world, it will just be a painful reminder you ain't supposed to inhale this stuff and to please stop it.
If you do happen to get a whiff of the stuff wnhen changing bottles, don't worry, most likely you'll get a snotty nose and you'll look funny for a little while but, it won't poison you.