There has been no case, as far as I am aware, of a large concrete building being subjected to a severe test; therefore, unless other objects were aimed at, I should prefer a brick building. But some warehouses and mills are so large that brick cannot be used internally in arches; and a subdivision by party walls would destroy the business purpose of the building, and allow of only small compartments in it. Cannot iron girders be used in _any_ way to make them safe? To a certain extent they can, if protected over the entire surface by cement or lumps of fire-clay. There should be but few employed, and allowance must be made for the girders, in case they get heated, to expand without thrusting out the walls. They should be supported on corbels of brick, and be as light as possible consistently with the strength required. If used as means to carry a wall they must be covered as suggested, and with the utmost care, for in this case any twisting or bulging sideways will endanger the wall above.
Whatever system of construction is adopted, there are three things not yet mentioned of high importance to the fireproof quality of the building; namely, the communication between the various floors, the style of window, and the construction of the roof. With regard to the first of these, there is little doubt that the ordinary staircase and the open lift are important aids to the spread of fire; by them the various floors of a warehouse are, when combustion begins, converted into so many furnaces with a connecting flue, and the extension of fire is accelerated by the draught rushing upwards. Though the stairs may be uninflammable and even indestructible, they will be in some measure a source of weakness, unless completely separated from the open rooms, as shown in the designs engraved in the Appendix. For these designs of a thoroughly fire-proof warehouse, I am indebted to Mr. E. Hoole, of Russell Square, London; who has succeeded in planning a building adapted to commercial requirements, and yet possessing the necessary elements of a fireproof structure.
All openings must be fitted with _double_ iron doors if perfect security is required, but with a single door if only ordinary risk is to be guarded against. The construction and fixing of these doors are a most important matter, and should be quite as carefully attended to as if the doorway were to a strong-room. Details of fixing them will be found in the chapter on strong-rooms, and the strength of doors should be the same as there shown. The outer plate of door being a half-inch solid boiler-plate, there must be an air-space behind it, partly occupied by the working parts of the lock, and inside that a casing of non-conducting material. The bolts should be six in number, three in front and three at the back, secured by a lock; and the frame into which they fasten must be solid iron, well built into the wall. The price of such a door, 6 feet high by 2 feet 4 inches wide, is 22_l._ 10_s._, and money thus spent would many a time have saved thousands in property.