Neb. Rev. Stat. §§ 48-430
All contractors and owners, when constructing buildings where the plans and specifications require the floors to be arched between the beams thereof, or where the floors or filling in between the floors are fireproof material or brick work, shall complete the flooring or filling in as the building progresses, to within at least two tiers or beams below that on which the iron work is being erected. If the plans and specifications of such building do not require filling in between the beams of floors with brick or fireproof material, all contractors for carpenter work in the course of construction shall lay the underflooring thereof, or a safe temporary floor on each story as the building progresses to within at least two stories or floors below the story where the work is being performed. If the floor beams are of iron or steel, the contractors for the iron or steel work of buildings in the course of construction, or the owners of such buildings shall thoroughly plank over the entire tier or iron or steel beams on which the structural iron or steel work is being erected, except such spaces as may be reasonably required for the proper construction of such iron or steel work and for the raising and lowering of materials to be used in the construction of buildings, or such spaces as may be designated by the plans and specifications for stairways and elevator shafts.
Neb. Rev. Stat. §§ 48-430