FIRE PROTECTION AND RESISTANCE

FIRE PROTECTION AND RESISTANCE

How Far Existing Methods are Available for Practical Use,

In a paper recently read by Horace Porter, M. A., before the Institute of British Architects, the author adverted to the number and value of the existing methods of fire prevention and fire resistance, and also showed how far they are available for practical use. He came to the conclusion that the only fires that could definitely be prevented were those due to mechanical or constructional causes. These were of importance, and should be carefully considered because of their being to a large extent preventable by the exercise of proper care and watchfulness. He instanced Glasgow as making for his side of the question. Before the introduction of the Buildings Regulation act in 1885 the returns Of that city showed that 27.8 per cent, of the fires there were due to defective hearths and flues, as against 9.65. per cent, in London during the same period. It is the same all over the British Islands; defective hearths and flues account for the great majority of fires, especially in old houses—and in country houses particularly, in which all possible means of safety in the construction, repair, or alteration of chimneys and flues should be insisted upon. Today, in old London houses, flues which were sound enough for the oldfashioned open kitchen range are found detective, in respect of chimney-backs, for the modern close kitchener, which creates great and concentrated heat. Timber mantelpieces constitute another source of risk,, from the way in which they are frequently fitted, with the metal of the grate touching the wood. In fixing the mantelpiece there is often left a small pocket, in which soot accumulates, and may become ignited. Wallplugs for joinery must also be regarded as sources of danger when near flues, especially in old houses, where the pargeting of the flues has worn away, and the joints of the brickwork have become open. Another risk is due to the practice of boarding-up unused fireplaces, or making them the receptacles of scraps of paper and other inflammable materials, which may easily be set on fire by a spark falling down the chimney from some other flue. The Glasgow Building act compels all such fireplaces to be stopped up with incombustible material, and the chimney-top as well. Fire prevention is practicable only in about twenty-five per cent, of all the present outbreaks. Fire-resistance, therefore, claims our most immediate attention. The degree of perfection to which this can be carried depends not only on the building itself, but also on its contents and immediate surroundings. This has to be kept in mind, as it is useless to expect owners to spend large sums on “fireproof construction.” which they are perfectly aware will benefit their neighbors rather than themselves. The two chief elements in fire-resisting construction are: (1) The materials used; (2) the general design of the building and details of construction. As regards building materials, good brickwork is no doubt best for fire-resistance. The chemical composition of the clay is the great element in determining both the fireresisting and weight-carrying properties of a brick, which depend chiefly on the proportions of silica and alumina in the clay, and, secondly, on the oxide of iron, lime, magnesia, potash, etc. Terra cotta used for structural purposes may be porous or hard-burned. The porous is made by the addition of some combustible material, such as sawdust or finely-chopped straw, to the pure clay, which is then burned under great heat. By this means the straw or sawdust is consumed, leaving the clay in a porous state. Hard-burned terra cotta is made from pure clay without the addition of any combustible substance. The porous form is non-conductive of heat, but does not carry weight so well as the solid; and, if the straw or sawdust has not been thoroughly burned out of it, there is danger of disintegration under the combined effects of fire and water. The hard-burned terra-cotta has to depend greatly on the hollow spaces with which the blocks are moulded, and is liable to crack on being suddenly cooled. For the protection of girders or columns, where it has little or no weight to carry, the porous form seems the best. Mr. Porter next discussed the fire-resisting qualities of mortar plaster, and cement. In so doing he referred to a series of tests with cement mortars carried out in Chicago in 1896. From these it was discovered that concrete floors after a fire test might hang together under heavy loads; but they are, nevertheless, weakened—to what extent depends upon the duration of the heat. Cement mortar can hardly be relied upon to resist high temperatures satisfactorily. Common lime and sand mortar in small quantities have probably greater fire-resisting properties than any other plastic material, and would be a better protection than cement mortar, if it were strong enough to be used to a thickness of—say, four inches or more. As regards concrete, tests have been made by which the material has been subjected to as much as 1.976 degrees Fahr. for several hours, and allowed to cool slowly, and also suddenly by application of water. The concrete composed of sand, gravel, or stone mixture crumbled or gave signs of great weakness, while that composed of cinders showed good coherence, and did not suffer by wetting while hot. The highest degree of coherence was found in a mixture of one part cement to seven of coarse cinders. The conclusion, therefore, is, that, where concrete has been made with care and knowledge, it will bear ery high temperature for a long time, even with the application of cold water. Wrought iron, cast iron, and steel, although non-inflammable, are not good fire-resisting materials, and must be cased in some fireproof covering. Unprotected iron may not itself suffer by fire; but its expansion under great heat may cause serious damage to the building. Steel will expand one inch in 125 feet for every too degrees Fahr. Combustible materials for the fitting-up of buildings should be used as sparingly as possible. Shelves might in many cases be made of wire netting supported on metal uprights; counters might be constructed on the principle of fireproof doors and shutters. The use of wood, however, cannot be eliminated altogether. Careful tests seem to prove that wood can be so treated as to be made efficiently fire-resisting; that the treatment does not injure it for structural purposes; and that its effect is permanent. But the process adds about thirty per cent, to the cost of joinery in soft woods, and is looked upon as too expensive for general use. Design, construction, and fittings are the most important questions in the problem of fire-resistance. Errors in design and construction will cause what might have been a small fire to spread over a large area, and work practically unlimited destruction. The Horne building fire in Pittsburg, Pa., and, though less destructive, a recent fire at the Haymarket Stores, in London, are cases in point. In both buildings the fire spread through an elevator shaft, which served as a flue on a large scale. The problem immediately before the notice of architects is the treatment of all such vertical shafts or openings in the interior of buildings. The author went on to consider the treatment necessary for the different purposes for which well-holes arc required—-dealing first with well-holes and light shafts; secondly, with well-holes for stairs and elevator inclosures. The use of wire-glass in iron frames for skylights in well-holes he thought desirable, as it helps to prevent the fire from bursting through from below, or burning embers falling in from above. Wireglass withstands not only great heat, but also the sudden cooling when water is poured upon it. Tt is, therefore, admirably suited not only for skylights, but also for warehouse windows overlooking narrow well-holes or streets. Judged from the standpoint of fire-resisting design, the usual position of staircases and elevator shafts in mercantile offices and hotels is totally wrong. Such well-holes should be inclosed by fire-resisting walls, with access to large floors or corridors by doorways only, which could be fitted with fire-resisting doors. The walls inclosing well-holes should be carried through, and above the roof in the same manner as party walls, and the skylights over should be of thick plate glass, or preferably wire-glass. Extra fireproof doors for stairs and elevator openings are recommended. To check the rush of flame up a shaft, a system of automatic sprinklers might be fitted round the sides of the opening near the roof, or perforated pipes in connection with an outside standpipe would serve the purpose. A staircase made of oak or teak, with two-inch threads and risers and soffits, and the spandrels filled in solid with some hard wood, the author thought, would be found the most reliable. Sub-division of large areas, where possible, is an important consideration. A fire in a large undivided area increases both in intensity and volume with much more rapidity than in a smaller one. Where areas are divided into rooms or offices, the partitions should be fireproof. Fire-resisting floors the author classed as ft) concrete. (2) terra-cotta, or brick. Some half-dozen exceedingly severe tests have been made of concrete floors, and not one of the floors failed. Experimental tests show that hollow tile arches, of good design and not too long span, have a strength sufficient to be safe under any load likely to be brought upon them in any ordinary building; also, that their resistance to fire is entirely satisfactory. except that the dense tile is likely to go to pieces, if struck by a stream of water when heated. A satisfactory fire-resisting covering for columns and girders should be a non-conductor of heat; should be able to withstand the action of fire and water; should not break away from the column under the action of fire and water; and should contain no joints through which fire could find its way. The covering may be of plaster, concrete, brick, or terracotta. Metal lathing should only be used where plaster is adopted for the covering material, and the column should first be wrapped with asbestos lining bound with wire. Mr. Porter next described the best forms of fire-resisting partitions, dealing with (1) solid plaster partition; (2) hollow plaster partition; (3) terra-cotta, or porous brick partition., lie thought it most important that terra-cotta partitions should start directly upon the masonry of the floor, and the terra-cotta blocks should be of sufficient width to secure stability. Special attention was called to the importance of protecting all openings made through floors for the passage of pipes for steam, gas, or any heating apparatus; and private apparatus, as aids for fire resistance—such, for instance, as automatic alarms, automatic sprinklers, standpipe and hose—were briefly referred to. In conclusion, Mr. Porter said he had tried to bring forward one by one the main features in the problem under discussion. “The more carefully we go into it (he said) the more apparent it becomes that the real problem is not to be solved merely by devising further improvements in details of materials, construction. or design. We are already admirably equipped in these respects, and modern inventions are continually adding to our resources. Fire-resisting construction involves a considerable increase of expenditure. coupled often with a sacrifice of space and artistic effect. The practical problem for architects is, how best to minimise these drawbacks. A useful basis for a discussion might be afforded by giving as a subject for a student’s competition the designing of an hotel, retail store, or mercantile house, on fire resisting principles, having special regard to internal effect in the first two cases, and in the third to economy of space.”

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