The importance of the factor of area is recognized in all the widely-used fire insurance rating schedules by charging an extra premium for areas exceeding the °standard?) In the Universal Mercantile Schedule, widely used in modified form in the East, 2,500 square feet is figured as a basis. In the Analytic Schedule also provision is made for this feature and recent schedules have shown no tendency to minimize its importance. It is nevertheless true that practical considerations often restrict its application. In office buildings, hotels and apartment houses comparatively little difficulty is presented, but in factories, warehouses, man ufacturing plants and even wholesale, retail and department stores, large areas are often deemed indispensable. The same is true of transporta tion terminals, armories and theatres. Often, however, ingenuity will suggest at least partial measures of protection if the necessity is recognized.
6. Non-communicating Floors and Vertical Openings.— If the above facts demonstrate the necessity for the subdivision of horizontal areas, the surpassing need for the subdivision of vertical areas is a corollary. It is this neces sity which has given the principle of the fire resisting floor its importance, an importance so great that the name °fireproof° is now sel dom applied to a building with non-isolated floors. But the effectiveness of floor protection and fire-resisting design may be largely nulli fied by a building feature in common use be cause of its pretentiousness and the difficulty of otherwise obtaining adequate illumination. This is the interior court or open light-well, prominent in many hotels and office buildings. In some cases it emanates from practical diffi culties of otherwise obtaining light and. in others from the desire to give the impression of extensive interior area. But past experience shows that this feature has resulted in rapid spread of fire, impossibility of extinction and threatened suffocation by smoke. A classic illustration of the results are found in the Horne Building fire, where a fire in an ex tremely hazardous adjoining risk was communi cated to the Horne store and office buildings. Pittsburgh. The store building was pierced vertically by a 20 x 50 light-well, extending from the first floor to the roof. The intense heat and tremendous uprush of flame thus in duced and promoted was the immediate cause of a $2,500,000 loss. The building was recon structed, with the retention of several of the vital defects, and in 1900 was again seriously damaged by fire. Again the open light-well
made a generous contribution to the damage.
All vertical openings, including elevator shafts, stairways and small light and ventila tion shafts are open to the same defects. Where vertical openings must exist their haz ard should be ameliorated by protective de vices, preventing them from functioning as fire passageways. This necessity has given rise to numerous mechanical devices and protective construction, which are described later.
7. Isolation of Special Hazards.— Wherever a known hazard exists, of course, special meas ures of protection should be taken. The most common illustration of the application of this idea is the isolation of boiler and engine rooms. a requirement enforced by all good municipal building codes. In connection with many manu facturing enterprises there are numerous spe cial hazards incidental to the processes and ma terial used which should be isolated and since conditions vary greatly a general discussion is without value.
8. Reduction of Combustible Material.— The extent of the fire loss would be considerably reduced by the elimination of combustible mate rials in trim and finish. A study of 23 so-called *fireproof') buildings in the Baltimore conflagra tion showed, even in these better types of con struction, a ratio of insurance losses to total insurance on this item of about 90 per cent. A study of eight of the larger buildings showed the proportion of fire damage to value on the various construction items to be: Foundations 4 Per cent Steel Frame 13 Mason Work 40 " Equipment 63 • Trim and finish 84 • General Expenses 62 The San Francisco fire also exhibited large losses sustained on ornamental fronts, com bustible finish anti trim, ornamental columns, etc.
Protective Devices.— In addition to design and material human ingenuity has been exer cised in another and supplementary field of pro tection, devising more or less mechanical inven tions for extinguishing, preventing the spread and giving warning of fire. They form an im portant adjunct to the other factors in fire prevention and protection and are described elsewhere under the designation FIRE PROTEC TION.
Special Features of Construction.— It is desirable to consider at greater length a few of the more important individual features of fire proof buildings, including some which are usually fundamental to the support of the building, such as walls, girders, columns, arches and others which contribute to the safety or peril of these fundamental features such as vertical and horizontal openings.