Mr. Wyatt Papworth, architect, has published some very interesting notes on spontaneous ignition, giving several well-authenticated instances.
Incendiarism may be divided into three sorts—malicious, fraudulent, and monomaniac. Of the former there has been very little in London for many years. The second, however, is rather prevalent. The insurance offices, which are the victims, protect themselves as well as they can, but an inquest on each fire is the true mode of lessening the evil. This is much more the interest of the public than at first seems to be the case. In several instances where the criminals were brought to punishment by Mr. Payne's inquests, people were asleep in the upper parts of the houses set fire to, and in one case there were as many as twelve or fifteen persons. This, however, is seldom stated in the indictment, as, if it is, the punishment is still death by the law, and it is supposed that a conviction is more easily obtained, by the capital charge being waived. Monomania is a rare cause of incendiarism, but still several well-certified cases have occurred in which no possible motive could be given. In one instance a youth of fifteen set fire to his father's premises seven times within a few hours. In another, a young female on a visit set fire to her friend's furniture, &c., ten or eleven times in the course of one or two days. In neither case could anything like disagreement or harshness be elicited, but the reverse. In other instances, it has been strongly suspected that this disease was the cause of repeated fires, but there was no positive proof. In all these cases, known or suspected, the parties were generally from fourteen to twenty years of age.
FIRE-PROOF STRUCTURES.
What is "Fire-proof Construction?" is a question which has given rise to a great deal of discussion, simply, as it appears to me, because the size of the buildings, and the quantity and description of the contents, have not always been taken into account. That which may be perfectly fireproof in a dwelling house, may be the weakest in a large warehouse. Suppose an average-sized dwelling-house 20 × 40 × 50 = 40,000 cubic feet, built with brick partitions, stone or slate stairs, wrought-iron joists filled in with concrete, and the whole well plastered. Such a house will be practically fire-proof, because there is no probability that the furniture and flooring in any one room, would make fire enough to communicate to another. But suppose a warehouse equal to twenty such houses, with floors completely open, supported by cast-iron pillars, and each floor communicating with the others by open staircases and wells; suppose, further, that it is half filled with combustible goods, and perhaps the walls and ceilings lined with timber. Now, if a fire takes place below, the moment it bursts through the upper windows or skylights, the whole place becomes an immense blast furnace; the iron is melted, and in a comparatively short time the building is in ruins, and, it may be, the half of the neighbourhood destroyed. The real fire-proof construction for such buildings is groined brick arches, supported on brick pillars only. This mode of building, however, involves so much expense, and occupies so much space, that it cannot be used with advantage. The next best plan is to build the warehouses in compartments of moderate size, divided by party-walls and double wrought-iron doors, so that if one of these compartments takes fire, there may be a reasonable prospect of confining the fire to that compartment only. Again, cast iron gives way from so many different causes, that it is impossible to calculate when it will give way. The castings may have flaws in them; or they may be too weak for the weight they have to support, being sometimes within 10 per cent., or less, of the breaking weight. The expansion of the girders may thrust out the side walls. For instance, in a warehouse 120 feet × 75 feet × 80 feet, there are three continuous rows of girders on each floor, with butt joints; the expansion in this case may be twelve inches. The tie rods to take the strain of the flat arches must expand and become useless, and the whole of the lateral strain be thrown on the girders and side walls, perhaps weak enough already. Again, throwing cold water on the heated iron may cause an immediate fracture. For these and similar reasons, the firemen are not permitted to go into warehouses supported by iron, when once fairly on fire.
Cast and wrought-iron have been frequently fused at fires in large buildings such as warehouses, sugar houses, &c., but according to Mr. Fairbairn's experiments on cast iron in a heated state, it is not necessary that the fusing point should be attained to cause it to give way.[A] He also states, that the loss of strength in cold-blast cast iron, in a variation of temperature from 26° to 190° = 164° Fahr., is 10 per cent., and in hot-blast at a variation of from 21° to 190° = 169° Fahr., is 15 per cent.; now if the loss of strength advances in anything like this ratio, the iron will be totally useless as a support, long before the fusing point is attained.
Much confidence has been placed in wrought-iron tie or tension rods, to take the lateral strain of the arches, and also in trusses to support the beams; but it must be evident that the expansion of the iron from the heat, would render them useless, and under a high temperature, it would be so great as to unsettle the brickwork, and accelerate its fall, on any part of the iron-work giving way: again, the application of cold water to the heated iron, in an endeavour to extinguish the fire, is almost certain to cause one or more fractures. The brick-arching is also very liable to fall, especially if only four and a half inches thick, independently of the weight which may be placed upon it, for it is not uncommon after a fire in a large building, to find the mortar almost completely pulverized to the depth of three inches, or four inches, from the face of the wall. When a fire occurred under one of the arches of the Blackwall Railway, on the 15th July, 1843, a portion of the lower ring fell down, and also a few bricks from the next ring.
Another very serious objection to buildings of this description, is that, unless scientifically constructed, they are very unlikely to be safe, even for the common purposes intended, independent of the risk of fire. In the Report of Sir Henry De la Bêche and Mr. Thomas Cubitt on the fall of the mill at Oldham, in October, 1844,[B] it is stated that the strength of the iron-beams was within ten per cent. of the breaking weight. Now according to Mr. Fairbairn's experiments on heated iron, already referred to, an increase of temperature of only 170° would have destroyed the whole building. It is quite clear, therefore, that so long as mill-owners and others continue to construct such buildings without proper advice, they must be liable to these accidents. In timber-floors there can be no such risk, as the strains are all direct, and any journeyman carpenter, by following good examples, can ascertain the size required; and even if he makes a mistake, the evil is comparatively trivial, as the timber will give notice before yielding, and may be propped up for the time, until it can be properly secured. In the case of fire-proof buildings, an ignorant person may make many mistakes without being aware that he has done so, and the slightest failure is probably fatal to every one within the walls. This also increases the difficulty and danger of extinguishing fires in a large building, as the only method of doing so is for the firemen to enter it with their branches, and in case of the floors falling, there is no chance of escape. On the other hand, timber-floors have repeatedly fallen while the firemen were inside the building, and they have made their escape uninjured.
In a pamphlet published by Mr. S. Holme, of Liverpool, in 1844,[C] and which contains a report from Mr. Fairbairn on fire-proof buildings, it is stated, that many people, especially in the manufacturing districts, are their own architects; that the warehouses in Liverpool may be loaded to one ton per yard of flooring; and that unless great care and knowledge are used in the construction of fire-proof buildings, they are of all others the most dangerous.[D]
The following are the principles on which Mr. Fairbairn proposes to build fire-proof warehouses:—