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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.

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 brickarching 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 millowners 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 fireproof buildings, they are of all others the most dangerous.[D] The following are the principles on which Mr. Fairbairn proposes to build fireproof warehouses:— The whole of the building to be composed of non-combustible materials, such as iron, stone, or bricks.

In order to prevent fire, whether arising from accident or spontaneous combustion, every opening, or crevice, communicating with the external atmosphere to be closed.

An isolated staircase, of stone, or iron, well protected on every side by brick, or stone walls, to be attached to every story, and be furnished with a line of water-pipes, communicating with the mains in the street, and ascending to the top of the building.

In a range of stores, the different warehouses to be divided by strong partition-walls, in no case less than eighteen inches thick, and no more openings to be made than are absolutely necessary for the admission of goods and light.

That the iron columns, beams, and brick arches be of strength sufficient, not only to support a continuous dead pressure, but to resist the force of impact to which they are subject by the falling of heavy goods upon the floors.

That in order to prevent accident from the columns being melted by intense heat in the event of fire in any of the rooms, a current of cold air should be introduced into the hollow of the columns, from an arched tunnel under the floors.

There is no doubt that if the second principle could be carried out, namely, the total exclusion of air, the fire would go out of itself; but it seems, to say the least of it, very doubtful indeed if this can be accomplished, and if it could, the carelessness of a porter leaving open one of the doors or windows, would make the whole useless. The fifth principle shows that Mr. Fairbairn has omitted to allow for the loss of strength the iron may sustain from the increase of temperature. The last principle would not be likely to answer its purpose, even if it was possible to keep these tunnels and hollow columns clear for a number of years, which is scarcely to be expected. A piece of cast-iron pipe, one-and-a-half inch in diameter, was heated for four minutes in a common forge, both ends being carefully kept open to the atmosphere, when, on one end being fixed in a vice, and the other pulled aside by the hand, it gave way.

One of the principal objections to the kind of fire-proof buildings above described, is, that absolute perfection in their construction is indispensable to their safety; whereas buildings of a more common description are comparatively safe, although there may be some errors or omissions in their construction.

Indeed, Mr. Fairbairn states in the same Report, that "it is true that negligence of construction on the one hand, and want of care in management on the other, might entail risk and loss to an enormous extent." The following is a very clear proof of the inability of cast iron to resist the effects of fire:— "A chapel in Liverpool-road, Islington, seventy feet in length and fifty-two feet in breadth, took fire in the cellar, on the 2nd October, 1848, and was completely burned down. After the fire, it was ascertained that of thirteen cast-iron pillars used to support the galleries, only two remained perfect; the greater part of the others were broken into small pieces, the metal appearing to have lost all power of cohesion, and some parts were melted. It should be observed, that these pillars were of ample strength to support the galleries when filled by the congregation, but when the fire reached them, they crumbled under the weight of the timber only, lightened as it must have been by the progress of the fire." In this case it mattered little whether the pillars stood or fell, but it would be very different with some of the large wholesale warehouses in the City, where numbers of young men sleep in the upper floors; in several of those warehouses the cast-iron pillars are much less in proportion to the weight to be carried than those referred to, and would be completely in the draught of a fire. If a fire should unfortunately take place under such circumstances, the loss of human life might be very great, as the chance of fifty, eighty, or one hundred people escaping in the confusion of a sudden night alarm, by one or two ladders, to the roof, could scarcely be calculated on, and the time such escape must necessarily occupy, independent of all chance of accidents, would be considerable.

For the reasons here stated, I submit that large buildings, containing considerable quantities of combustible goods, with floors of brick-arches, supported by castiron beams and columns, are not, practically speaking, fire-proof; and that the only construction which would render large buildings fire-proof; where considerable quantities of combustible goods are deposited, would be groined brick-arches, supported by pillars of the same material, laid in proper cement. I am fully convinced, from a lengthened experience, that the intensity of a fire,— the risk of its ravages extending to adjoining premises, and also the difficulty of extinguishing it, depend, cæteris paribus, on the cubic contents of the building which takes fire, and it appears to me that the amount of loss would be very much reduced, if, instead of building immense warehouses, which give the fire a fortified position, warehouses were made of a moderate size, with access on two sides at least, completely separated from each other by party-walls, and protected by iron-doors and window-shutters. In the latter case, the probability is, that not more than one warehouse would be lost at a time, and perhaps that one would be only partially injured.

It is sincerely to be hoped that the clause in the last Metropolitan Building Act, restricting the size of warehouses, may be more successful than its predecessor, for it is not only property that is at stake, but human life. In many of these "Manchester warehouses," there are fifty or one hundred and upwards of warehousemen and servants sleeping in the upper floors, whose escape, in case of fire, would be very doubtful, to say the least of it.[E] Covering timber with sheet-iron is very often resorted to as a protection against fire. I have never found it succeed; but Dr. Faraday, Professor Brande, Dr. D. B.

Reid, and Mr. W. Tite, M.P., are of opinion that it may be useful against a sudden burst of flame, but that it is worse than useless against a continued heat.

In wadding manufactories the drying-rooms were frequently lined with ironplates, and when a fire arose there, the part covered with iron was generally found more damaged than the rest; the heat got through the sheet-iron, and burnt the materials behind it, and there was no means of touching them with water until the iron was torn down; sheet iron should not, therefore, be used for protecting wood.

Even cast iron, one inch thick, laid on tiles and cement three inches thick, has allowed fire to pass through both, to the boarding and joisting below, merely from the fire in an open fire-place being taken off and laid on the hearth. This arises from iron being so good a conductor that, when heat is applied to it, it becomes in a very short time nearly as hot on the one side as the other. If the smoke escapes up a chimney, or in any other way, there may be a serious amount of fire before it is noticed.

In a fire at the Bank of England, the hearth on which the stove was placed was cast iron an inch thick, with two-and-a-half inches of concrete underneath it; but the timber below that was fired.

With regard to the subject of fire-proof dwelling-houses of average size, I consider that such houses when built of brick or stone, with party-walls carried through the roof; the partitions of brick, the stairs of slate or stone, the joists of wrought iron filled in with concrete, and the whole well plastered, are practically fire-proof because, as stated at the opening of this chapter, there is no probability that the furniture and flooring in any one room would make fire enough to communicate to another. The safest manner of heating such houses is with open fire-places, the hearths not being laid upon timber. Stone staircases, when much heated, will fracture from cold water coming suddenly in contact with them; but in a dwelling-house built as described above, there is very little chance of such a circumstance endangering human life, even with wooden steps carried upon brick walls, and rendered incombustible by a ceiling of an inch and a quarter of good hair mortar and well pugged, all the purposes of safety to human life would be attained.

There is a particular description of floor, which, although not altogether fireproof, is certainly (at least so far as I can judge), almost practically so for dwelling-houses. It is composed simply of plank two and a-half or three inches thick, so closely joined, and so nicely fitted to the walls, as to be completely airtight.

Its thickness and its property of being air-tight, will be easily observed to be its only causes of safety. Although the apartment be on fire, yet the time required to burn through the floor above or below, will be so great, that the property may be removed from the other floors, or, more probably, if the means of extinguishing fire be at hand, it may be subdued before it can spread to any other apartment. The doors must of course be made in proportion, and the partitions of brick or stone.

Before closing the subject of fire-proof structures, I will add a few words upon fire-proof safes. These are all constructed with double casings of wrought iron, the interstices being in some filled with non-combustible substances, such as pumice stone and Stourbridge clay, and in others with metal tubes, that melt at a low temperature, and allow a liquid contained in them to escape, and form steam round the box, with the intention of preventing the heat from injuring the contents. Such safes I have never found destroyed; and in some cases, after large fires, the whole of the contents have been found uninjured, while the papers in common safes, merely made strong enough to prevent their being broken into, were generally found consumed.

FOOTNOTES: [A] Vide Seventh Report of the British Association, 1837, vol. vi. page 409.

[B] Vide Report on the Fall of the Cotton Mill, at Oldham, and part of the Prison at Northleach, page 4.

Folio. London: Clowes and Sons, 1845.

[C] Vide Report of W. Fairbairn, Esq., on the Construction of Fire-proof Buildings. With introductory Remarks by Samuel Holme, page 11, et seq. Tract, 8vo. Liverpool: T. Baines, 1844.

[D] The Author has been informed by Mr. Farey, M. Inst. C.E., that a fire took place, in 1827, in a mill belonging to Mr. Marshall, of Leeds, the whole of which, with the exception of the roof, was fire-proof.

The upper floor was filled with flax, which took fire; the roof fell in, and the heat so affected the iron beams of the floor, as to cause them to give way.

[E] In the year 1858, when reporting to the Insurance Offices upon the Warehouses in the Metropolitan Docks, Mr. Braidwood made the following suggestions which are applicable to all large buildings. That all the party-walls where the roofs do not rise above the wall, should be 3 feet 6 inches above such roof. That all the party-walls in the valleys of the roofs should be raised to the level of the highest ridge on either side, all openings in such walls being closed by wrought-iron doors on each side of the walls, at least a quarter of an inch thick in the panels, and such openings not to exceed 42 superficial feet in the clear. That all windows which look upon other windows, or loop-hole doors in other warehouses or compartments, within 100 feet, should be bricked up, or have wrought-iron shutters at least 3/16th of an inch thick in the panels.

That all loop-hole doors similarly situated should be made entirely of wrought iron, frames included, or bricked up. That all shafts for lifts or other purposes, should be of brick, with wrought-iron doors where necessary to receive or deliver goods, and that all openings whatever for machinery should be included in such shaft. That every hatchway or opening in the floors for "shooting" goods from floor to floor should have a strong flap hinged on to the floor, to be closed when not in use, especially at night.

That there should be direct access to every room, of every compartment, of every warehouse, from a fireproof staircase, by iron doors, and that all such staircases should enter from the open air, as well as from under any warehouse on the quay; in the latter case the doors must be of iron only.

All the windows in the entresol and ground floors to be bricked up, or have iron shutters, and the doors and frames to be of iron.

Wherever the warehouses face each other within 100 feet, the front parapet walls to be carried up to the level of the ridge of the roof.

When it is stated in this report that the windows or loop-hole doors should be bricked up, it is not meant to exclude the use of thick glass, three or four pieces being built into each door or window space, not exceeding 6 inches in diameter or square, in the clear, and set in the mortar or cement at least 3/4 of an inch all round, the glass to be not less than 1-1/2 inches thick, flat on both sides, and so placed that no goods can be stored within 18 inches of the inner surface.

There should be a tank on the top of each staircase, with a tap from it on each landing, with six fire buckets hung near it, and three small hand pumps in every staircase; the officers and workpeople seeing these every day would be certain to run to them in case of fire, and by having a constant supply of water on every floor small accidents might be extinguished at once, and the iron doors and roofs kept cool in case of one room taking fire.

Reference book: Fire prevention

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