It is needless to point out the danger to which an ordinary town house is liable from the ignition of its external woodwork. Safety from external fire may be secured by the application of the same construction of fire-clay doors and shutters already described to the external doors and windows. These fire-clay shutters have been made to slide over the wall-faces both internally and externally, and, better still, into recesses in the wall itself; so that on the first alarm of fire the premises may be rendered impervious to the enemy in a very short space of time. One further source of external danger lies in the ordinary construction of roofs with wooden framings, generally as dry as tinder, and readily inflammable, even through their slated coverings in most cases. These should be universally superseded by the cheaper, more durable, and fire-resisting flat roof, now proved, by several examples, to be quite practicable when constructed of concrete, or concrete faced with tiles.
Whilst advocating the provision of all available appliances for " knocking out" incipient fire, such as hydrants, hose, etc, the necessity should, above all, be recognised for such construction as would facilitate the safe and rapid combustion - if burn they must - of the contents of any one compartment, rather than risk the contents of other compartments, through accumulated heat, by denying to the flames from a portion ignited a safe and free exit by a recognised channel. To this end a sufficient shaft should be constructed from the ceiling level of each compartment (which ordinarily would prove an excellent means of ventilation) for the purpose of discharging the fire, so to speak, harmlessly up the chimney. The condition of each compartment would be the reverse of an ordinary brick oven, which is constructed to accumulate intense heat without the slightest risk to its surroundings), whereas the arrangement under consideration would provide compartments structionally as non-inflammable as ovens, with the ever-present means of discharging instantaneously accidental fire, whereby accumulated heat would be rendered impossible.
A porous tile for fireproofing has been introduced by S. E. Loring. It consists of granular organic matter mixed with clay, the former burning out in the oven and leaving a porous tile that will bear nails being driven into it. It forms an excellent base for plaster in place of laths, and thus greatly increases the fireproof character of walls where it is applied, and may be used to surround iron columns, girders, etc.
A compound termed magneso-calcite has been successfully tried in America as a lining for safes, bank-vaults, shutters, express chests, jewellery cases, etc. It is applied to sheets of asbestos paper and paper board, and forms a tough and elastic material.
Wrought iron, as commonly employed to resist the action of fire, and 'even when protected by concrete, has shown itself to be entirely unreliable in fireproof structures. It is, however, well known that fireclay forms a much more efficient material for protecting wrought iron from the destructive action of intense heat, and it is with the application of this material by J. Whichcord, the engineer to the National Safe Deposit Company, that good results are obtained. The arrangement consists merely in employing a number of fireclay blocks, about 9 in. long and 1 1/2 in. to 2 in. thick, formed on one side with recesses of an form, so as to fit closely to the web and bottom flange of the wrought-iron girder. The outer sides of the blocks can be made of any desired form to receive ceiling arches or joists. The blocks being placed upon the girders, meet underneath the bottom flange, and the longitudinal as well as the transverse joints are made good with fireclay. In some experiments at Erith, a furnace, 15 ft. long and 4 ft. wide in the clear, was constructed, and across the top a rolled-iron joist of I section, 17 ft. long, 10 in. deep, and with 5 in. flanges, was laid, spanning the length of the furnace.
This girder was protected with blocks in the manner above described, and on each side of the girder brick arches were built abutting against the side-walls of the furnace. Over the top of the arches and girders a thickness of concrete was laid, and the floor thus formed was loaded with pig-iron to one-fourth of its breaking-weight. After the structure was thoroughly dried, a fierce wood fire was made up in the furnace, and was maintained for 2 1/2 hours, when large quantities of water were thrown on the heated mass. The deflection of the loaded girder had when heated amounted to 1 1/2 in., but when the weights were removed and the beam had cooled, the deflection disappeared, and it remained apparently uninjured, although the fireclay sheathing was vitrified on the surface. A second experiment was made, when a fierce fire was kept up for 1 1/2 hour, and then maintained moderately for 28 hours more, after which it was suddenly extinguished with cold water. The deflection of the loaded girder had been 3/32in. at the commencement of the trial, and reached a maximum during the fire of 1 3/16 in., reduced to 3/8 in. when the load was removed, but before the beam was cool. Ultimately, however, it returned to the original amount of 3/32 in.
Altogether this experiment, which was carefully carried out, shows the enormous resisting power of the fireclay blocks, and it may be mentioned that one end of the girder which projected through the brickwork of the furnace was quite cool when the fire was at its hottest, and no appreciable expansion was observed. The beam will be employed in the building for which it was originally intended.