FIREPROOFING IN CONGESTED DISTRICTS. 121 
was before; whereas concrete of any kind which has come through a 
fire in which the temperature has exceeded 700° or 800° F. is inevi- 
tably damaged in all cases, owing to the dehydration of the cement, 
although it may ajDpear uninjured to the casual observer. This prop- 
erty of concrete, of maintaining a good face in spite of real and seri- 
ous damage, is likely to lead the layman into dangerous conclusions, 
and consequently into equally dangerous practice. It would seem 
that wherever reenforced-concrete floor construction is used a furred 
ceiling below it should be absolutely required. 
The furred ceilings ordinarily used are too light ; the furring rods 
are not quite heavy enough and they are not adequately secured 
to the floor construction above. If they were made a little heavier, 
and were more firmly secured, it is probable that, as a rule, no loss 
would occur except that of the plaster. Even if the furred ceiling 
comes down bodily, this failure is not apt to occur until so late a 
stage in the fire that the floor construction above will be practically 
undamaged, because there will not be enough left of the fire to raise 
the temperature of the concrete to the point where dehydration of 
the cement will begin. The presence of a furred ceiling, however, no 
matter how good, should never be accepted as an excuse for omitting 
the protection of the lower flanges of the floor beams and girders. A 
hollow-tile floor that would be fully equivalent to a reenforced-con- 
crete floor, with a furred ceiling, could be made by using tiles in 
which the minimum thickness of the webs is 1 inch, and of which the 
material itself is tough, refractory clay, made porous by the addi- 
tion of sawdust; such tiles should, however, be burned to a point 
where the clay itself is just short of vitrification. All the interior 
angles, where the webs of the tiles join each other, should be rounded 
to a radius of at least 1 inch or 1^ inches. If necessary to secure 
proper burning, a small hole three-eighths to five-eighths of an inch 
in diameter might be allowed through the mass of clay at the inter- 
section of the webs. 
Tests recently made of a pattern of tile used at the AVar College 
indicate that floor tiles subjected to a fire test will stand better if 
there is but one interior hole through the tiles, all the material which 
would otherwise be used in the interior webs being concentrated in 
the outer webs, and the opening in the tile being of circular or ellip- 
tical shape, depending on the height and width of the tile. For 
floor arches between steel beams such a tile as this one would have 
to be used on the end-construction plan. A specially heavy skew 
back should be designed to go with it, or else the end tiles should be 
cut to fit the profiles of the beam. The tiles themselves being so 
heavy, the latter method of obtaining a skew back would probably 
make the arch more than strong enough to carry its load, and where 
carefully done might aiford adequate fire protection to the beams, 
