CONSTRUCTION AND FIRE PROTECTION OF COTTON WAREHOUSES. 19 
later. With this as a minimum, walls of concrete properly rein- 
forced with steel may be 4 inches less in thickness than is required 
for brick, while walls of plain concrete should be 4 inches thicker 
than the nominal thickness required for brick because of the fact 
that severe or concentrated heat will produce such unequal expan- 
sion in a thin wall as would be likely to cause dangerous cracks or 
crumbling. 2 
The proper increase in thickness for a, division fire wall beyond 
that set as a minimum depends largely on the height and number 
of stories and the length (unbraced) of the wall. Discussion of the 
thickness has reference to brick bearing walls, while the provisions 
for other material and designs explain the modification such change 
would involve. The number of stories and their height should be 
the first consideration in determining the thickness, and should be 
based on a wall not exceeding 100 feet in length. For a single 
story building having a story height not exceeding 18 feet at the 
lowest or 20 feet at the highest part of the roof adjacent to the 
division wall, such wail should be 16 inches thick, while for every 
additional 12 feet or fraction thereof in height this thickness should 
be increased 1 inches. If the wall is several stories in height, the 
minimum wall thickness for the two top stories should be 16 inches, 
while for each two successive stories below (each not over 15 feet 
Where tile is used as panel walls in a frame of reinforced concrete or be- 
tween piers of concrete or heavy masonry, this danger is intensified because the 
tile is securely restrained by the piers or concrete frame which expands much 
more slowly with the result that the tile is subjected to an expansive stress 
which is likely to destroy it. The idea that the tile is destroyed by the forma- 
tion of steam at such pressure as to cause an explosion is not tenable for the 
reason that sufficient moisture is not always present and, where it is, the mortar 
joints are rarely sufficiently tight to prevent the escape of steam as it forms. 
The cracking of tile when water is applied is due to uneven contraction from 
sudden cooling. These statements appear in conflict to the use of tile for 
insulation of steel frame buildings. This, however, is a use where the ar- 
rangement of the tile permits ' more expansion as it is less restrained, and 
usually the fire is less severe. However, experience has shown that even here 
clay tile affords mmch less protection than brick or concrete, which now is being 
used for protecting important columns. 
2 This action in a concrete wall adequately reinforced with steel would not 
occur to a serious extent, while in a brick wall the bonding or tying together 
of the face or outside brick would result in a decided tendency to limit the 
penetration of the damage to the outer 4 inches of the thickness of the wall. 
Furthermore, the wall of unreinforced concrete affords a chance for conceal- 
ment of dangerously poor workmanship which the introduction of steel re- 
inforcement would tend to overcome. The thickness of 12 inches, or even 10 
inches for reinforced concrete panels, is entirely satisfactory in retarding the 
passage of heat, though it must be increased when required by certain 
conditions. 
