Iron columns filled with concrete support the vaulting of the various floors, and are protected by a casing of fire-brick, between which and the column an air space is left. In warehouses in which the brick casing of the columns is likely to be damaged by the shifting of the goods it can itself be protected by a covering of sheet-iron. But this, of course, is no additional safeguard against the action of fire.
The thrust of the vaulting is counteracted by iron tie-bars embedded in the brickwork below the flooring of each compartment; the ends of the bars are well turned up and down in the external walls, besides being connected to the brickwork near the base of each column. It will be seen that all parts of the building which have to sustain any weight are protected from any great change of temperature, and that all iron-work is especially screened from it.
In constructing the staircase the same precautions are adopted. A wall carried up the centre affords a springing for the arches carrying the steps and landings, which are constructed entirely of brick, and may be covered either with tiles, stone, or even wooden treads, if desired. The thrust of the arches carrying the steps is overcome by building in a tie-bar above each arch, which thus protects it from any contact with fire.
In order to prevent the staircase from acting as a flue in case of fire, and causing a draught of air to rush through the parts of the building opening into it, one side of it is left open to the external air, being only enclosed by a light arcade of open arches on each floor. Thus it gains the advantage of
