i'm happy as a ___________

i've always wondered way you couldn't use straight nitrogen. the atmosphere is composed of almost 80% of it and it is what keeps the atmosphere stable, keeps fires from burming the world up. so if it's in the atmosphere for that reason why couldn't it be used to extinguish a fire like the chemicals do. after all it doesn't burn and should displace the oxygen and put out the fire and won't deplete the oszone.
oh my heads hurts from thinking.