Gaseous Nitrogen will displace air and asphyxiate, as will a bunch of other gases, but it is not a toxin. It does not have enough thermal mass to cause freeze burns either. Air in the -60F degree range can be safely breathed for a short duration with no freezing. There are several cases of people breathing pure Nitrogen boiling off the liquid with no burns...mostly idiot kids thinking it would be like Nitrous.

http://terpconnect.umd.edu/~choi/MSD...s/NITROGEN.pdf