as the structure of a modern steel-frame fireproof building is concerned, it may be desirable to consider it apart from the present article and under the head of STEEL SKELETON CONSTRUCTION (q.v.), in which the engineering and other structural problems involved in the design of a modern skyscraper or other city building are discussed, leaving for the present article the form and the method of the protection which

FIG. 6. ROOF CONSTRUCTION.

must be applied to the main structure. Of all fire-resisting materials probably burnt clay has the widest application in fireproof building, for it is an excellent nonconductor, and having once passed through the ordeal of fire it is practically indestructible. For the construction of floors and partitions and for the protection of columns and girders, the clay is molded into hollow blocks or tiles of suitable shapes.

Three kinds of terra cotta are used for making blocks-porous, semiporous or semiglazed, and dense or glazed. Each has its own particular field of usefulness.

Porous terra cotta is made by mixing about one-third, in bulk, of finely cut straw or sawdust with fine clay, which, after being tempered and molded, is burnt under a high heat, causing

the combustion of the straw or sawdust and leaving the material in a porous state like pumice stone. It will not crack or break from unequal heating or sudden cooling, it can be cut easily and is soft enough to allow the driving in of nails or screws for securing the interior trim, and it is elastic, tough, and light and nonheat-conducting in itself, so that it can be made in solid as well as in hollow blocks. Because of these properties it is generally used for interior partitions, for column and girder protection, and for furrings generally; but it is not used in the construction of outside walls or where excessive dampness occurs because it is absorbent, nor is it suitable for floor construction on account of its lack of strength.

In the manufacture of semiporous or semiglazed terra cotta, a smaller percentage of sawdust is used, or finely screened boiler cinders are substituted instead. The result is a material slightly more porous than the best grade of brick, but still not so soft as the ordinary porous terra cotta. Semiporous terra cotta is used largely for floor construction, for column and girder protection, and for the building of outside walls.

Dense or glazed terra cotta is made generally of some natural fire clay without the addition of any combustible material. The only ingredients added are low grades of clay, crushed bricks, or terra cotta, or sand, to prevent excessive shrinkage. Dense terra cotta cannot be cut without breaking; it is brittle and liable to failure under sudden shocks. In places where suddenly applied loads are expected, porous material should be used, but under static loads dense terra cotta is better than porous, being stronger; and because it is also cheaper it is very generally used for floor construction. On account of its nonabsorbent qualities it is largely employed for building exterior walls, the blocks being grooved or scored to provide a key for the stucco, as there is not sufficient suction to hold the stucco on the smooth glazed surface. Dense tiles, because of their brittle nature, require wooden grounds and nailing strips, which detract from their fireproof qualities, so they are not used for interior partitions, furrings, or column protections.

Floor Arches. Hollow tile floors may be built of flat arches (Fig. 1) or of segmental arches (Fig. 4). Flat hollow tile arches are made of two "skews," or "skewbacks," resting against the web of the beams and fitting around the lower flanges, one "key," or "centre block," and "fillers," "part fillers," or "intermediates," as they are variously designated, sufficient in number to fill the spaces between the skewbacks and the key. A safe rule for finding the proper depth of the arch in inches is to multiply the span in feet by 14 inches and add the thickness of the protection below the beams. The blocks are divided into hollow spaces by interior webs or partitions from 3 to 4 inches apart, the number depending upon the size of the block. The lower flanges of the beams carrying the floors should be covered with at least 11 inches of fireproofing. To accomplish this, the skews are made either with a bevel on the bottom to receive a protection tile for the beam (as shown at X, Fig. 3), or with the protection burnt upon the skew itself (as shown at Y). The former is more generally used because it is easier to make. In manufacturing the skew with the beam protection burnt on the block, it is difficult

to keep the flanges straight; during drying and burning they frequently become so warped as to break off when placed on the beam, and in addition the projection is liable to be broken off in careless handling.

There are three general types of flat arched floors used in modern fireproof buildings. The first and oldest is known as the "side-method construction," in which the tiles are set side by side between the beams (as shown in Fig. 1). In the second type, known as the "end-method construction," the blocks run at right angles to the beams abutting end to end (as shown in Fig. 2). The third type is a combination of the first and second, the skewback and the key being made as in the side method, and the fillers abutting end to end between them, as in the end

limited to the buildings above mentioned. Segmental arches are always made after the sidemethod construction.

Girder Protection. Girders projecting below the ceiling line are especially exposed to the effects of fire and water as intense heat is brought to bear on the corners of the protection and the streams from the fire hose tend to tear it off, so that they should be provided with not less than 2 inches of terra cotta. In general it may be said that the protection in which stability depends upon the use of metal clamps or anchors (as shown in X, Fig. 5) is not so efficient as that in which the soffit protection holds its position independently of them (as in Y).

Roof Arches. Nearly all fireproof buildings have flat roofs, pitched just enough to cause

Hollow Tile Wallthe projecting dovetails are scored for

stucco and

plaster

3" Facing Tile "Tile Slab

Reinforced Hollow Tile Floor

"Cement Reinforced with Rods and Metal Fabric

method (as shown in Fig. 3). So far as absolute strength is concerned, the end method is about 50 per cent stronger than the side method. The objections to the end-method arch are, it is wasteful of mortar and it is difficult to bed properly the edges of the blocks. Also, as there is no bond between the rows of blocks, if a single block in a row becomes broken or is knocked out of place, the entire row may fall, and for the same reason a single block cannot be omitted for making a temporary hole as may be done in the side-method arch. Notwithstanding these objections the end-method arch, being just as cheap and much stronger for the same weight, has largely superseded the side-method arch.

Where a flat ceiling is not essential, and for warehouses, factories, and buildings of a similar character, the segmental arch (shown in Fig. 4) makes the strongest, cheapest, and best fireproof floor that can be built of hollow terra cotta; but on account of the arched ceiling resulting from its employment, its use has generally been

water to run to the lowest point, as it is easier to make a flat roof thoroughly fireproof than a pitched roof. The usual and also the best method of constructing flat roofs is to lay the beams with the required pitch and then build the roof in the same way as the floor. Where the ceiling is suspended (as shown in Fig. 6), segmental arches may be used. Pitched roofs are generally covered with 2 or 3 inch porous terracotta tiles (shown at X in Fig. 6), called book tiles, because the joints resemble the backs and edges of a book. They are set on the flanges of light T-irons spaced the proper distance on

centres.

Walls and Partitions. Since about 1908 hollow tile blocks have been largely used for building the outside walls of dwellings and of other buildings of moderate height. The wall blocks are made of semiporous or dense material, 8, 10, and 12 inches thick and 12 inches high, and are scored on all sides to provide a key for the plaster (as shown in Fig. 7). They are always

set with the voids or cells running vertically and with the joints broken in each course. Special blocks are made for corners and also for sills, joints, and lintels. A special form of floor construction used in connection with these walls is also shown in Fig. 7. Interior partitions are built of brick-shaped hollow blocks (as shown in Y, Fig. 6), a 4-inch thick block being used in most cases.

Column Covering. The most common form of column protection consists of a layer of 2 or

No.16 Sheet Iron I'Mortar Plaster

X

rous terra cotta is used, the two consecutive layers shall be so applied that neither the ver tical nor the horizontal joints in the same shall be opposite each other, and each course shall be so bonded and anchored within itself as to form an independent and stable structure. In places where there is trucking, or wheeling, or other handling of packages, the lower 5 feet of the fireproofing shall be incased in a protective covering of sheet iron 1 inch away from it, with the space filled in with mortar [X, Fig. 8], or of oak slats [Y], or of angle irons set at the corners and tied together with iron bands."

Other Fireproof Materials. Next to terra cotta, concrete and plaster are the most commonly used materials for fireproofing. Concrete floor arches are shown in Figs. 10 and 11. For

FIG. 10. REENFORCED CONCRETE ARCH.

further description of these systems, see section on Reënforced Concrete in article CONCRETE. Partitions are frequently built of reënforced concrete, and so are column coverings. Reënforced concrete is naturally a fire-resisting material, and reënforced-concrete structures are essen

FIG. 8. COLUMN PROTECTION.

3 inch hollow partition blocks (shown in Fig. 8), laid against a solid backing of concrete or tiles, where the blocks do not bear against the column. Consideration of appearance, or the amount of floor space to be occupied, is frequently allowed to influence unduly the shape or size of the fireproofing material for columns to the detriment of the protection and often leads to the use of very thin solid slabs, which should not be permitted. The Chicago Building Ordinance is very explicit in its requirements for the protection of columns and is a good guide to follow in all

FIG. 9. COLUMN PROTECTION.

cases. It is: "The covering of columns shall be of brick not less than 8 inches thick, or of two consecutive layers of hollow tiles [Fig. 9], not less than 21⁄2 inches thick, or of two layers of porous terra cotta not less than 2 inches thick each. Whether hollow tile or po

FIG. 11. EXPANDED METAL CONCRETE ARCH.

tially fireproof and safe if their construction is attended with proper precautions, and especially itself, so that it can resist the high temperatures if proper materials are selected for the concrete results with reënforced concrete from the standwhich may be experienced. To secure the best point of fire protection, it is, of course, necessary

to make sure that the areas of the concrete floor arches are restricted, the bearing columns and reënforcement are adequate, and the design is such as to provide against failure in case any individual portion of the structure becomes unduly heated. Plaster, in the form of blocks, is also used for building interior partitions. For further description, see article on PLASTER; also that on FIRE PROTECTION, MUNICIPAL.

Bibliography. Consult volumes of the various engineering papers for the last 10 years. Among the books which may be consulted are: Freitag. Fire Prevention and Protection (New York, 1912); Birkmire, The Planning and Construction of High Office Buildings (ib., 1898); Kidder, Building Construction, part i, "Masons' Work" (ib., 1896); Fuller, Fireproof Building Construc tion (ib., 1904): Moore, Fire Insurance and How to Build (ib., 1903); Kidder, Building Construc tion and Superintendence (9th ed., ib., 1913); id., Architects' and Builders' Pocket Book (ib., 1914). See ARCHITECTURE; CONCRETE; FOUNDA TION; FIRE PROTECTION, MUNICIPAL; STEEL SKELETON CONSTRUCTION.

FIREPROOFING. The coating or impregnation of combustible materials, such as textile fabrics and wood, with chemical preparations so as to prevent their burning either partially or entirely. Such substances for the most part act

by coating the material with a crust of mineral matter on the surface of the fibres that serves to prevent the combustion, but does not interfere with decomposition. Cotton and linen may be steeped in certain saline solutions such as alum, ammonium chloride, ammonium phosphate, borax, zinc sulphate, and sodium tungstate, in order to render them uninflammable. Preparations of these salts in various combinations and proportions find extensive use in the treatment of canvas used for scenery in theatres, and in many places it is required by law that the drop curtain at least shall be fireproof. Papers that are both fireproof and waterproof may be made from a pulp consisting of vegetable fibre to which asbestos and salts, such as alum and borax, in suitable proportions, have been added. The Perkin Non-Flam Process, an English process of fireproofing cotton fabrics, consists in impregnating the material with a solution of sodium stannate of 1.22 sp. gr., drying thoroughly, and further treating with an ammonium sulphate solution of about 1.75 sp. gr. Stannic oxide is precipitated in the fabric. sulphate is also formed, and is removed by washing. The material is then ready for drying and finishing. It is claimed that the fireproofing is so permanent that the fabric can be washed repeatedly.

Sodium

For the impregnating of timber to make it fireresistant and uninflammable, numerous processes have been proposed. As deliquescent salts cannot be used, and certain compounds like sodium silicate cannot be made to penetrate the wood satisfactorily, treatment of the timber in practice has been limited to ammonium salts such as sulphate and phosphate, and aluminium and ferric sulphates.

Fairly good fire-resistant results are at times obtained by means of so-called fireproof paints. These include paints in which sodium silicate and zinc chloride have been incorporated. Dense coatings of whitewash have considerable fireresistant value and with the addition of silicate of soda are often used. See FIREPROOF CON

STRUCTION.

FIREPROOF SAFES. See SAFES AND SAFE DEPOSIT VAULTS.

FIRE PROTECTION, MUNICIPAL. The protection of a community against sudden outbreaks of fire and the restriction of such fires to the narrowest possible limits is a function that usually by common consent is assumed by the local government, though it may be supplanted by private organizations where such are especially required. To deal with the emergencies involved in an outbreak of fire sudden and rapid efforts are required, and there is involved a certain amount of organization and equipment, as well as disciplined men. Such discipline must be practically military, since where a fire department is called to act there must be no confusion or hesitation, as no other work requires greater promptness, both in reaching the scene of action and in taking the necessary measures to check the outbreak.

In most municipalities the fire-protection service or fire department, as it is usually termed -includes the fire alarm and telegraph, the fire engines and other apparatus, and men organized and trained to a degree rarely, if ever, found in other departments of municipal service. The water works, which naturally are an integral feature of any scheme of fire protection, more usually are under separate organization.

(See

WATER WORKS.) In European cities the fire department may be directly under military organization, or it may be composed of soldiers and sailors who have seen military service and are under the control of retired officers, thus maintaining all the characteristics of an active military organization.

In the United States the fire departments are exclusively civil and local and are marked by varying degrees of efficiency and discipline, but in practically all there are traditions of loyalty and personal heroism which not only act for the good of the department and general effectiveness, but render it the pride of the citizens of the municipality. In fact such service is considered highly honorable and carries with it the same immunities as militia duty.

The problem in an American or Canadian city is quite different from that in Europe, where the buildings are usually of stone and where building regulation, both for sound construction and maintenance, has been in force for many years. In the United States and Canada, where the growth of cities has been rapid and wood has been the usual material on account of its cheapness and availability, large cities of inflammable character have grown up, and various practices, due to carelessness and lack of foresight, have prevailed which entail an enormous annual fire loss.

While the true function of a fire department is to prevent fires and confine them to as narrow an area as possible, in America the fire department has been called upon to deal not only with occasional and sporadic outbreaks, but with large conflagrations, and the public at large has been apt to consider a fire department's efficiency as consisting in its ability to handle a large conflagration rather than its ability to restrict a fire to its point of origin and prevent fires by adequate inspection and suitable rules and regulations in coöperation with building and other departments. Vast sums annually are appropriated for fire protection, and in many cases they are not even commensurate with the hazards which exist in the various cities. Of recent years the problem of fire prevention has been brought before the general public by insurance authorities and municipal officials, so that its importance is realized as never previously, and efficient inspection and suitable regulations are no longer considered infringements of individual rights, but as necessary to the safety and welfare of the community. Accordingly the safety requirements of building departments are being increased, and often the intervals between fires are being utilized by having uniformed members of the fire department inspect various buildings with an idea to detecting violations of rules and regulations and improper conditions, as well as becoming acquainted with the character of the buildings in the districts where they serve.

While it cannot be said that satisfactory methods and organization for fire prevention universally have been adopted in the United States and Canada, yet there has been great improvement, and various laws and regulations in addition to the requirements of insurance companies are bringing about better conditions. In many States, as a result of recent legislation, there are State fire marshals, who supplement efforts of local officials when they are lax or when such supervision is absent altogether, and their powers vary in kind and degree. Methods of fire