CHAPTER VIII.

FIREPROOF BUILDINGS.

II. _Patent Systems of Construction, and their Application._

Many of the suggestions in the preceding chapter have been embodied in the numerous patents brought out by engineers and others for what are termed ‘Fireproofing Systems.’ Among these inventions may be named Messrs. Moreland and Son’s, Messrs. Fox and Barrett’s, Mr. Nasmyth’s, Messrs. Dennett and Co.’s, &c.

Messrs. Fox and Barrett’s patent is one of the oldest, and is still largely used, having been, among other instances, recently applied to portions of the Criterion, in Piccadilly Circus. It consists mainly in substituting iron for wooden joists; and upon the lower flanges of these iron joists are placed pieces of wood, which bear the concrete filling up the space to the floor-boards or tiles above.

The other systems have all, more or less, ordinary concrete as a constituent part, depending largely for its support upon iron or wood beams, and thus probably being, after all, only fireproof to a certain point. One exception must be made in favour of the Dennett system, as in this is introduced a new concrete, treated in a novel and somewhat bold though successful fashion.

This system, known as the ‘Dennett Fireproof Construction,’ is one of great advantage, inasmuch as iron is dispensed with as far as possible, while the space occupied by arched floors is reduced to a minimum. In some cases, indeed, no iron at all is wanted, and yet no room is wasted by heavy piers or supports of brick.

A very superior description of concrete is the body which forms the fireproof medium in this construction. This concrete, unlike that used for foundation and other purposes, is not mixed with any of the ordinary limestone cements, the action of which under fire is well known. A piece of the hardest limestone, when deprived by calcination of its carbonic acid, becomes a body which may be crushed by the least pressure, or if treated with water assumes double its original bulk and falls to powder. Concrete composed of the ordinary lime, inasmuch as it approximates, when set, to the original carbonate, would of course manifest the same characteristics under similar treatment. The concrete which forms the chief element of the Dennett construction has, however, for its cementitious component the _sulphate_ of lime, a body which loses little of its cohesion by calcination. Experiments as to the character of this concrete prove that it remains intact though reduced to a white heat, and that the application of water while in that state does not materially impair its strength or cohesion.

The arch form is that which is usually adopted for the construction of floors (diagram A), the spandrels of the same being, however, in some cases filled in with the material, so as to form a horizontal floor (diagram B). These arches, when thoroughly set, exert no thrust upon the outer walls, and, in fact, from their slight rise and thoroughly homogeneous character, they possess as much the nature of a beam or landing as that of an arch. For this reason their use is, in many cases, advantageous, where that of brick arches would be altogether inadmissible. The arches are supported at the points where they abut upon the walls by projecting courses of brickwork, and at intermediate points by rolled iron joists or rivetted girders. They have a minimum rise in the soffit of one inch to every foot of width, and they are turned in this proportion up to spans of 10 or 12 feet. Corridors and cottage floors are formed in this manner without the introduction of any joist or beam whatever (diagram C); the soffits of the arches, after the removal of the centres, simply require to be finished with the last or setting coat of plastering. In cellars or other basement offices no extra coat whatever is necessary.

The floor or upper surface can be finished in the material itself, at a small cost, equal to stone in durability and appearance. When covered with kamptulicon or other similar material a floor at once noiseless to the tread and free from vibration is obtained. These qualities are, for banks and other public offices, very important _desiderata_. The arch may, of course, if preferred, be paved with any other material, such as stone, tiles, asphalte, or cement.

Floors formed in the simple manner described are excellent in a sanitary point of view. They are clean, non-absorbent, and are non-conductors of sound and heat. These qualities particularly recommend them for adoption in hospitals, unions, barracks, and other large buildings; while for houses of the artisan class, especially in crowded districts, no other method of construction presents so many advantages.

If a flat ceiling is required, ceiling-joists are fixed to the lower flanges of the iron girders, and lathed and plastered in the ordinary manner (diagram D). It is generally preferred, however, in buildings of a public character, such as banks, offices, &c., to leave exposed the lower flanges of the iron girders. This is the most constructional mode of treatment, and by the judicious application of coloured decoration a very effective ceiling is obtained. The ceilings of the bedrooms at Kelham Hall, Notts, a building designed by Sir Gilbert Scott, are finished in this manner. This mansion was made thoroughly fireproof on its re-erection nine years ago, after the destruction of the former building by fire. The ceilings of the reception-rooms are formed by groined vaults of considerable rise springing from carved stone corbels. The roof is protected from fire by light segmental vaults springing from wall to wall.

When used for flat roofing--for which purpose the strength and freedom from vibration of the construction renders it particularly adapted--a layer of asphalte or other impervious coating is required to protect the arches from the weather.

The description of asphalte most approved for this purpose, and used by the patentees with the greatest success, is that known as the ‘Pyrimont,’ and supplied by the Seyssel Asphalte Company.

The formation of vaults or domes, particularly those of an ornamental character, is one of the most advantageous applications of the concrete. As no expense is involved in the cutting of groins, coffers, ribs, &c., it is in itself less costly than brick or stone, besides saving considerable expense in the strength of the outer walls, which would be required to withstand the lateral thrust of ordinary vaulting. It is moreover better adapted for decorative treatment in colour or relief.

Large vaults have recently been formed over the principal apartments of the Foreign Office. The ceiling of the principal staircase-hall, 70 feet long by 26 feet wide, is divided into three compartments, two of which are semi-cylindrical coffered vaults, and the centre one is formed as a dome, with solid pendentives. The ceiling over the Cabinet-room has a span of 36 feet; it is semi-circular in form, with groined openings to the side-windows, and is divided into compartments by plain arched rims formed in the concrete. The vault itself is only 9 inches in thickness. A section of this ceiling is shown (diagram E).

The largest work upon which the Dennett system of fireproof flooring has yet been adopted is the new St. Thomas’s Hospital. It is here applied in the ordinary flat-arched form to the corridors, wards, and other rooms as the foundation for the asphalte covering of the flat roofs, and as coffered vaulting in large spans to the chapel, Governor’s hall, &c. Some idea of the extent of this building may be formed when it is stated that the fireproof arching covers an area of more than eight acres.

The strength of the arches has been frequently tested by actual experiments, both as to their capacity for bearing dead pressure and with regard to their resistance to impact from falling weights, moving loads, &c. These experiments have been generally instituted by the architects upon whose works the construction has been adopted, and they have invariably produced the most satisfactory results.

The cost of the construction varies somewhat, according to the distance from the gypsum quarries, which are almost entirely confined to the counties of Derby and Nottingham. The cost of the arching in London, in ordinary spans, as shown by diagram A, including centreing, is about 75_s._ per square of 100 superficial feet. A finished upper surface, where such is required, involves an additional expense of from 15_s._ to 25_s._ per square. These prices do not, of course, include iron girders; but as so few of these are required, as compared with other methods of fireproof construction in which concrete is used, this system will be found to possess, besides the acknowledged merits of strength, rigidity, and highly fireproof character, the advantage of economy, being from 25 to 50 per cent. cheaper than other methods.

But whatever the cost of these highly advantageous systems of construction, there are certain buildings which demand the application of the very best methods of erection in order to secure their safety from the devouring flames. In public museums and art galleries we have buildings which cannot have too much attention and money paid to make them safe; and their safety from or liability to fire is a topic of much interest. It is but seldom that one hears of a serious fire in any of these places; the truth is, though many of them would, if once a-light, make a wonderful blaze, they are generally so well watched that fire can obtain no hold without being discovered. The real danger is more from surrounding buildings being on fire than from within.

The Bodleian Library, at Oxford, about which there has been some stir lately, is a noticeable example. The building is itself highly combustible; it is filled with combustible though invaluable contents, for which there is no fireproof receptacle; and around it are other structures at least as likely to burn, and if burnt to cause the destruction of the library. Captain Galton has reported on this state of affairs, and it is now probable that one of the remedies suggested may be adopted.

A return has been made to Parliament of the state of some of the public buildings, and from the digest which has appeared in the ‘Architect’ I take the following:--

‘The return from the British Museum acknowledges that generally, except in the basement, the materials of the building are only partially incombustible. The basement is constructed chiefly of brick, with piers and groined arches, except in a few cases, where cast-iron columns are used, the floors being either stone, slate, or cement. The principal staircases are of stone, and the smaller ones of iron. The ceilings throughout are lath-and-plaster, with fir ceiling-joists. The roofs are of wood and iron, covered with copper, the principals being in most cases cast-iron.

‘The reading-room has a cement floor, with brick arches beneath. The main ribs of the dome are iron, with brickwork between them, this being covered externally with copper, and internally with papier mâché fastened to wood ribs. The lantern is of wood and iron. The new libraries on basement and ground floors are built externally of brick, internally chiefly of iron.

‘Some of the floors of the National Gallery are arched with brick, on iron girders; the floors of a portion of the rooms of the ground storey in each wing, the rooms under the dome, and others adjoining them, are of ordinary timber construction, with iron girders. The floors of the picture galleries and of most of the rooms are boarded; those of the other rooms, the entrance-halls, lobbies, staircases, and principal parts of the passages, are of stone. All portions of the floors on each storey traversed by hot-water pipes are of stone, on brick chambers, with metal gratings. The ceilings of the rooms generally are of lath-and-plaster, with fir ceiling-joists; internally the rooms are plastered or cemented, except those of the picture galleries, which are lined with wood, for dryness and facility of hanging. The roofs and lantern-lights are constructed of iron and wood, covered with lead. The lanterns of the westernmost galleries have iron shutters. Those on the top and the sides opposed to adjacent buildings are closed every night.

‘At South Kensington the floors, except the official residences, are fireproof, on Fox and Barrett’s principle. In the Museum they are covered with tiles or marble mosaic, and in the schools, offices, &c. in some places with wood, and others with asphalte. The floors of Bethnal Green Museum are of wood, and not fireproof, and the same may be said of the Kew Museum. The whole of the ground floors, and in some cases the one-pair floors, of the Royal Hospital, Greenwich, are constructed on brick groined arches, and with the exception of the wood floor covering are fireproof. The remainder of the floors are of framed timbers and joists, with boarded floors, which would readily ignite. In the Edinburgh Museum of Science and Art, the whole of which is not yet completed, the greater portion of the main floor is formed of stone arches, with encaustic tiles, but the two galleries surrounding the principal halls are of wood, supported by iron columns or girders. In the east wing there is a lecture-room, with rooms, one for the exhibition of specimens, of which the floors are entirely of wood. This building would appear to be in danger if a fire occurred in any of the neighbouring premises. The National Gallery of Scotland is constructed of stonework of the best kind, and is therefore little liable to conflagration. Of museums in Dublin, the College of Science alone appears to have floors which may be considered to be incombustible. The wood in the Dublin Society’s house is returned as being “very old and dry.” In the Royal Irish Academy, which contains a collection of antiquities, there is but one room which is fireproof. The Hibernian Academy has also wooden floors.

‘The means for prevention of fires differ much in the different buildings. The British Museum has connection with the mains, with sufficient hydrants and hose-pipes and buckets, and the tanks contain 26,000 gallons of water. There are sixteen fire-engines, six of them being kept on the roof, and two firemen are constantly on duty; besides, the police employed are drilled in the use of the engines and appliances. The National Gallery has also hydrants and hose; the tanks contain 3,900 gallons. There is only one hand-pump. There are no watchmen, and no resident officer is charged with the duty of supervision. The care of the building is entrusted to the police. In South Kensington the arrangements to secure safety are very complete, and far superior to those in any other public building. Four-inch mains are used throughout the building and grounds, but the supply is constant only as long as the company’s mains are in action. A tank in the grounds, which holds 25,000 gallons, is, however, always available, should the supply from the mains be deficient. The return says that a tower is to form part of the South Kensington building when the design is complete, and in it there are to be tanks at sufficient elevation to command the buildings by means of hydrants. Pending the erection of the tower, it is recommended that tanks to contain 50,000 gallons should be placed in the highest possible positions. There is always a fire-brigade of Royal Engineers resident on the premises, who daily examine all the appliances; and one of the assistant-directors, who is also an officer of Engineers, has the superintendence. A story is told in the Parliamentary paper which is worth giving, not only as showing that there are two ways of extinguishing a fire, but as proving the superiority of a special to a general system:--‘In March 1857, at about 4.30 A.M., a fire broke out in one of the temporary wooden buildings, at that time used as art schools. The alarm was given by the police, and a man was despatched in a cab to the nearest Fire Brigade station. But before the arrival of the Metropolitan Fire Brigade engine the detachment of Royal Engineers had completely got the fire under, and had saved the contents, principally pictures, of the building. Mr. Braidwood, then Chief of the Metropolitan Brigade, on his inspection complimented the Royal Engineers on the way in which the fire had been put out. He said it was the “prettiest stop” he had ever seen, but unscientific, and that with his men he would not have attempted to extinguish the fire, but would have directed their efforts to pulling down adjoining buildings, in order to prevent the fire spreading. The fire originated from some woodwork touching a stone, in the immediate neighbourhood of a hot air heating apparatus which had been put in by the Office of Works before the buildings were handed over to the charge of the department. Since this time the use of hot air apparatus has been discontinued, and the permanent buildings are all heated by hot water. The Geological Museum has a tank and other appliances, and the watching is wholly in the charge of the police.

‘The Edinburgh Museum has an insufficient provision in water supply. In the forenoon there is no water available from the hydrants on the upper floor of the building, which is forty feet below the ridge of the roof, and there are no fire-engines. The Scottish National Gallery has six cisterns, each containing 100 gallons, but in the opinion of a superintendent of the Fire Brigade the building is adequately protected against fire. The Dublin buildings, owing to the high pressure of water supply, are supposed to be sufficiently secure without tanks.

‘In nearly all of the buildings there has been hitherto no fire, and in those where there was the damage was not very great. A fire in one of the out-buildings of the British Museum, in 1865, caused a loss of a little beyond 500_l._ The fire at South Kensington has been already described. In all the buildings there is more or less constant supervision, and with this, risk is reduced to a minimum. Still the reports show how much need there is of the constant service being generally extended over the metropolis. At South Kensington, in the daytime, the pressure is usually not sufficient to command the lower roofs of the Museum buildings, and sometimes is as low as 20 feet, although at night (when there is often most danger) it rises to 160 feet.’

Respecting St. Paul’s Cathedral I believe the arrangements for extinguishing fire are fairly good, but the building itself is far more combustible than most persons imagine; and though the risk of fire commencing from the interior is very slight (except when the enormous quantity of timber is introduced for seats at special festivals), there is always a certain amount of danger from the tall warehouses so closely hemming it in on all sides. The chief director of the Salvage Corps thinks it very possible that the conflagration of one of these buildings would set on fire the dome of St. Paul’s, provided the building burnt freely and the wind was strong in the direction of the Cathedral. The inevitable plumber is doubtless often at work on some portion of the roof with his open fire and the mode of handling it that almost burnt Canterbury Cathedral, and thoroughly succeeded at the Alexandra Palace.

The following is from the ‘Bulletin de la Société Centrale des Architectes,’ 1871, communicated by the Secretary of that society to the Royal Institute of British Architects, and is most valuable, as the practical experience of the results of fires at Paris during the Commune:--

‘1. Walls of freestone.--The walls constructed of freestone are seriously deteriorated, the stone being destroyed by disintegration and the calcination of the limestone. 2. Walls of rough stone.--Rubble walls, covered with a thick layer of plaster, have, owing to this preservative coating, remained unchanged, and generally they will be retained in the process of reconstruction. 3. Brick and (calcareous Sicilian) millstone walls.--Walling of these kinds has generally resisted better in cellars and underground construction; and as to the brick in partition-walls, the brick flues of chimneys remained almost intact. 4. Floors, roofs, and timber partitions.--Wood in floors and roofs has been completely consumed, but in wooden partitions, where a coat of plaster sufficiently thick was exposed to the action of the fire, the wood has been completely preserved. Some curious facts have been the result. An angle-post having been attacked in an upper storey, the fire afterwards extended itself in the interior of the post without gaining the external surface, so that the post assumed the appearance of a pipe, the interior of which had been hollowed out by the fire.

‘Oak lintels covered with plaster have resisted without injury the flames which traversed the bays of which the lintels formed the upper part. 5. Floors and roofs of iron.--Iron has not resisted the action of fire. If it has not been consumed like wood, it has undergone twisting and contortion, which render it unfit to be used again. Numerous fantastic examples have been observed, especially at the Palais de Justice, the Hôtel de Ville, and the Théâtre Lyrique. The character of iron is not to propagate combustion, but, under the influence of a very high temperature, to undergo such extension that it allows the escape of the masonry it was intended to retain.’