I am a huge fan of world war 2 gas masks myself, but since they are damn expensive these days i suggest the Israeli civilian gas mask, looks pretty awesome and not that expensive, if you're really that broke get Respirator half masks.
And it does cause oxygen deprivation if you wear it for too many hours, but that would mean wearing it all day long, which is rather stupid.
Also note, that wearing world war 2 used gas masks is rather dangerous, they have concentrated a lot of chemicals in the filters that by their age transform into a substance i forgot its name, which causes cancer.
so stick with new masks kids
