(d) Concrete.— This method is simply the application of solid concrete to the exterior of the column and received its first practical test in the San Francisco fire. The showing made was exceptionally good, being only equaled by brick protection and the use of concrete for the purpose has subsequently considerably increased as a consequence.
(e) Brick.— Brick column protection must be conceded to be the most efficient general form. This was demonstrated in the Baltimore fire, where brick was practically the only satis factory protection found and in the San Fran cisco fire, where both brick and concrete pro tection could be observed, with the consensus of opinion in favor of the brick It is, however, undesirable from the standpoint of weight and expense.
(I) Reinforced Concrete Columns.—In spite of their constituent material these columns re quire protection. Tests show a loss of 70 per cent load-carrying capacity under extreme heat but no such loss when protected.
3..Floors, Beams and Girders.— Floors may be constructed of terra-cotta, concrete and com binations of these. Brick must be practically eliminated because of its weight and expensive ness. There is great variation in the evidence afforded by actual tests of arches. In individual building fires the damage has sometimes been small and. sometimes great, while in the San Francisco conflagration the use of hard-burned tile exclusively and poor workmanship make a judgment difficult. The conclusion seems to be that in the main hollow tile arches will carry the necessary loads and are usually damaged little by fire. Concrete floors, as shown by tests, may be so constructed as to sustain heavy loads and a very high de gree of heat. Stone concrete and gravel con iron, rolling steel, kalamine and hollow-metal lic. Tin-clad doors are the best cheap protection available, although they are subject to deteriora tion and damage by rust, bending and breaking. Plate-iron doors are superior to tin-clad except that they radiate twice as much heat. Corru gated-iron doors are accepted by underwriters as the equivalent of the standard door. Steel rolling doors are excellent, though expensive, and are generally automatic in action, a feature discussed later. Kalamine doors are wood-con structed, covered with asbestos paper and en closed with sheet metal, being extensively used in office buildings, but are not approved by the underwriters for fire walls. One of the most
important features of the fire door is an ar rangement which will close the door auto matically at a high temperature, usually con sisting of a fusible link, pulley and weight. This insures that at the important moment the door will not be left open through carelessness or inability to reach it. The importance of the fire door as a means of protection is illustrated in the San Francisco disaster by the experience of the Pacific States Telephone and Telegraph Company building, which would probably have suffered little damage except for an open rear door, the effect of which was disastrous.
crete, however, lose some strength under tem peratures unusual in ordinary building fires, On the other hand if damage to the floor en sues complete replacement is generally neces sary.
The protection of beams and girders is of the highest importance, judging by the failures which have taken place in many instances, and terra-cotta and concrete are chiefly used for the purpose. Both are satisfactory if the work manship is good.
4. Fire Doors, Windows and Shutters.— On the general principle that openings should not be materially weaker from the standpoint of fire protection than the wall, partition or floor in which they are placed, fire-resisting doors are an important part of the construction. These are fin-clad, plate-iron, composite, corrugated Fire shutters and fire-resisting windows are particularly important by reason of the enor mous number of losses caused by exposure. Conditions within the owner's own building can be controlled, but this does not eliminate the danger from neighboring buildings. It will be remembered that a fire-resisting building was defined as one which would protect itself and the contents against contiguous and adjacent fire. In addition there is the danger of fire spreading from floor to floor by means of the windows. For the purpose of protecting win dows open sprinklers, shutters and metal frames in combination with special glass are used. Open sprinklers are intended to throw a cur tain of water over the windows to prevent fire from entering and to extinguish any ignition.