No filling of any kind which may be injured by frost shall be placed between said floor-beams during freezing weather, and if the same is so placed during any winter month, it shall be temporarily covered with suitable material for protection from hieing frozen. On top of any arch, lintel, or other device which does not ex tend to and from a horizontal line with the top of the floor-beams, cinder concrete or other suit able fireproof material shall be placed to fill up solidly the space to a level with the top of the floor-beams, and shall he carried to the under side of the wood floor-boards in case such be used. All fireproof floor systems shall be of sufficient strength safely to carry the load to be imposed thereon without straining the material in any case beyond its safe working load. The bottom flanges of all wrought-iron or rolled-steel floo•-beams and fiat roof-beams, and all exposed portions of such beams below the abutments of the floor arches, shall be entirely incased with hard-burnt clay. porous terra-cotta, or other fireproof ma teria.l allowed to be used for the filling between
the beams, to which such incasing material shall be properly secured. The exposed sides and bottom plates or flanges of wrought-iron or rolled-steel girders supporting iron or steel floor beams, or supporting floor-arches or floors, shall be entirely incased in the same manner. After the floors are constructed no opening greater than eight inches squate shall be cut through said floors unless properly boxed or framed around with iron. And such openings shall be filled in with fireproof material after the pipes or con duits are in place. All columns, including the lugs and brackets on same, used in the interior of any fireproof building, or used to support any fireproof floor, shall be protected with not less than two inches of fireproof material. securely applied. The extreme outer edge of lugs, brack ets, and similar supporting metal may project tc within seven-eighths of an inch of the surface of the fireproofing.