It should also be noted that the public is altogether too apt to minimize the importance of exposures to fireproof buildings. The danger of fire to contents within a fireproof building is much greater because of the presence of a poor risk in the immediate neighborhood. On the other hand, a fireproof building radiates very little of its exposure to surrounding risks. "Probably no class of risks," writes Mr. F. C. Moore, is more inadequately treated in the matter of computing danger from exposures than fireproof buildings, because rating bureaus so frequently overlook the obvious fact that plate glass and wooden window frames and sashes are not fireproof, and that a so-called fireproof building offering nothing more substantial to an outside fire than plate glass has no greater fire-resisting properties than an ordinary show case would present. More than 75 per cent of the fireproof structures of the country have window openings to the extent of from 40 to 75 per cent of the superficial area of each enclosing wall, which are not protected by fireproof shutters. Heat from a burning building across a wide street finds ready entrance through such openings, and the various fireproof floors serve only to hold, like a great gridiron, ignitable merchandise in the most favorable form of distribution for ignition and combustion, to the full force of an outside fire. If fire once secures entrance to a fireproof building through the windows of any story, the contents of such a story, especially if at great height from the floor, are almost certain to be destroyed, and the danger of ignition is greater where the fireproof structure is higher than the one which is burning.” 1

Fireproof Buildings in Recent Conflagrations.-In the recent Baltimore and San Francisco conflagrations the fact was brought out very strikingly that many so-called "fireproof" buildings were not after all fireproof, as generally

1 Francis C. Moore, "Fire Insurance and How to Build,” p. 73.

supposed, and that there were present many deficiencies in the construction of such buildings which might easily have been averted. The statistics for the Baltimore conflagration, as far as fireproof structures are concerned, have been carefully compiled, and show that the insurance loss on such buildings was in almost the same ratio as on the ordinary buildings and combustible stock. This striking fact is to be attributed mainly to the large damage done to such buildings, and the comparatively small amount of insurance held as compared with the value of the structures. Of the seven so-called fireproof "skyscrapers" of steel-cage construction, it appears that 64 per cent, or nearly two thirds of the value of these buildings, was destroyed. This large proportion becomes still more striking when it is remembered that these seven buildings were all used exclusively for offices, and contained but small amounts of combustibles which could have caused a serious and prolonged fire. The opinion prevails among experts that, had these buildings been filled with large quantities of combustible materials, the loss would certainly have been much greater and in all probability might have been a total one. These skyscrapers were practically without any form of fire protection, partly because there was no apparent need for the same, and partly because of the impossibility of the fire department being able to approach them during the conflagration.

1

In San Francisco, likewise, the conflagration tested thoroughly the various types of fireproof steel structures, and gave to the world a most valuable lesson as to the future construction of such buildings. Terra cotta, so generally used in San Francisco, was shown to be wholly inadequate. Wherever steel work was protected by terra cotta, the cover

1 See the Special Report to the National Board of Fire Underwriters, Committee of Twenty, on the San Francisco Conflagration, by S. Albert Reed, Consulting Engineer to the Committee.

ing was in nearly every case torn off and destroyed. As stated in one of the reports on the durability of different fireproofings in the San Francisco fire: "When terra cotta was used the partitions fell down, the fireproofing around the columns came off, and a very large proportion of the floor arches either fell out or the bottom plates of the arches broke off and left the arches in a very bad shape." In most cases the fireproofing of columns was of terra cotta. With the destruction of the column covering by the excessive heat, little protection was left, and the result was that very few buildings in San Francisco did not present the sight of badly bent or buckled columns.

As contrasted with terra cotta, concrete stood the test of the conflagration well in nearly every instance, little or no damage resulting to steel work which was fireproofed with this substance. Another form of column covering, which withstood the fire well, consisted of two thicknesses of wire lath and plaster, with an air space between them. While in many cases the outside covering was torn off, it seems to have resisted the fire during the most intense stage, thus enabling the inner covering to protect the column.

The best material for the construction of walls is hard burned brick. Stone, contrary to common opinion, is a very undesirable building material, and if used extensively, especially for supporting heavy weights, may serve as a means of wrecking the entire building. One of the most prominent fire underwriters in the country, in speaking of this, declares that: "The best fire-resisting materials for walls, it may safely be asserted, is hard burned brick. It is also the best material for the floor arches between the iron beams of fireproof buildings. It is incomparably better than stone, because stone is utterly unreliable for resisting fire, especially the limestones, granites, marbles, etc. In fact, stone is a dangerous material wherever it is subjected to fire and water, and carries a heavy superimposed weight."

Of all the materials used in the fronts of the buildings in San Francisco, stone showed by far the worst effects of the recent conflagration. In the Postal Telegraph Building the granite columns in the first story almost entirely disappeared through the splitting and crumbling of the stone. Accord

ing to one official report: "This is true of every place where the flames or heat touched the stone; it spalled off and left the fronts in such a bad condition that they will probably have to be taken down." Terra cotta did not resist the effects of heat and fire much better than stone.

Semi-fireproof Buildings and Slow Burning Buildings. -Semi-fireproof buildings differ from fireproof buildings in so far that, while constructed of non-inflammable material, they are equipped with structural or tension metal members, which are not properly insulated against heat. These buildings are constructed because of their greater cheapness as compared with fireproof buildings, and because the prevailing building code in many cities does not prevent their erection. They are constructed very often to serve for office purposes or as dwelling apartments, or for other uses of a similar character, in which it is presumed that the limited amount of combustible stock which they contain will make it extremely unlikely that sufficient heat will be generated to seriously injure the ironwork in the building.

Slow-burning or "mill construction" buildings are to be distinguished from semi-fireproof buildings. The floors in slow-burning buildings are without openings, and consist of heavy plank laid on heavy timbers, spaced from 5 to 12 feet apart, such timbers resting on stout wooden posts. It is also prescribed that there must be a tight top flooring, with waterproof paper between it and the plank flooring below, which must never be less than 3 inches in thickness. The aim of such requirements is to separate the different stories by a floor of considerable thickness so that, though large stocks of combustible material may be contained in the

building, it will require several hours under normal conditions for a fire to burn through the flooring. Before this is accomplished it is presumed that the fire department will be able to get the fire under control and prevent its spread.

Fire Doors and Shutters and Wire Glass.-A number of special features must be noted in the construction of buildings designed to retard the rapid spread of fire. The first of these is fire doors and shutters. The door now commonly used is made of wood covered with metal and provided with special lock-jointed tin plates. The idea is to allow the wood to carbonize in case of great heat, and to permit the gas resulting from the carbonizing of the wood to escape through the lock joints instead of permitting it to accumulate and throw off the metal sheets. As the wood carbonizes the charcoal will drop to the bottom of the metal covering, but the metal will hold together, thus preventing the passage of the fire.

Wire glass is also of considerable importance. It gives splendid protection when the sash is fireproof and when the glass is double with an air space between. Wire glass in most cases serves a better purpose than shutters, because the latter must not only be closed to become effective, but will deteriorate if not properly cared for. Moreover, where there is not an exposing risk to be guarded against, shutters are regarded by many underwriters as a nuisance. It should be remembered, however, that wire glass radiates heat, so that in case of a severe exposing fire it may happen that combustibles within the building and near the glass may ignite. In this respect wire glass is inferior to well-designed shutters.