54 THE SAN FRANCISCO EARTHQUAKE AND FIRE. 
terra-cotta tile is largely, if not entirely, devoid of merit for fire- 
proofing purposes. Even when it is of the best grade and workman- 
ship it can hardly be considered a first-class building material. At 
a comparatively low temperature the tiles fail, the thin webs spalling 
from unequal expansion. A more porous tile, with thicker webs 
keyed together and laid in Portland-cement mortar with tight joints, 
would unquestionably be more suitable for the purpose. It may be 
true that in case of repairs after a fire damaged tile of the usual 
commercial type can readily be detected and renewed. Terra-cotta 
tiling may, however, allow sufficient heat to pass through it to soften 
slightly the steel member which it encases and still remain in posi- 
tion, thus hiding the defect. Several examples of this condition were 
found. 
The advocates of terra-cotta tile contend that concrete may be 
seriously damaged by dehydration without noticeable change in its 
appearance. While this contention may be justified, it should be 
noted that any weakness or softness may be as readily detected and 
repaired in concrete as in terra cotta. Concrete, moreover, has the 
great advantage of being a nonconductor of heat, and so will with- 
stand a prolonged heat before the damage extends to any great depth ; 
and it usually remains in place, maintaining its protective qualities. 
The value of a structure or of a method of fireproofing is determined 
largely by ascertaining what portion of the structure is left avail- 
able for use after the fire. The word " fireproof " is of course a 
misnomer, for no building is absolutely fireproof; and the resist- 
ance offered to fire is one of degree only, for if the heat be sufficiently 
high and prolonged, nothing can withstand it. The best materials 
are nonconductors of heat, having high fusing points. At high 
temperature concrete loses its water of crystallization, but the depth to 
which this dehydration goes and the rate at which it takes place are 
the factors that determine the effectiveness of the material. The 
heat insulation afforded by concrete is of a high order, and to obtain 
the best results a sufficient thickness must be applied. This required 
thickness is naturally a variable quantity; 2 inches, or even 1 inch, 
may be sufficient for an office building, but would be inadequate for 
a warehouse. These remarks concerning concrete also apply to all 
other forms of fireproofing. The prime point on which information 
should be procured is the thickness of the insulation for proper pro- 
tection against fire. 
Perhaps the most important problem is that of protecting a build- 
ing from fire from without. To do so means the protecting of all 
openings and the making of the roof equally as resistant as the other 
parts of the structure. Buildings should be self-contained — that is, 
protected against exterior fires and capable of fighting fire from the 
inside; and in earthquake countries, where the outside water service 
