There is a secret level in the Hotel level it gives u a gasmask that you can give to ashe and I assume save him in the end of the game.
Location lvl 3 top right room where there is a floor panel path that leads to a generator (small) destroy that then head back down the left side of the generator there will be sneakily hidden stairs downward. be warned enemies in the area are tougher so expect 1-2 hit KO's