COl^STRUCTIOlsr AND FIRE PROTECTION OF COTTON WAREHOUSES. 19 



later. With this as a minimum, walls oi 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 re<}uired 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 

 criunbling.- 



The proper increase in thiclmess for a, division fire wall beyond 

 that set as a minimum depends largely on the height and numl)er 

 of stories and the length (unbraced) of the wall. Discussion of the 

 thickness has reference to brick bearing walls, while the pro\asions 

 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 

 diA'ision wall, such wall shoidd be 16 inches thick, while for every 

 additional 12 feet or fraction thereof in height this thickness should 

 be increased 4 inches. If the wall is several stories in height, the 

 miniinimi wail thickness for the two top stories should be 16 inches, 

 while for each two successive stories belaw (each not over 15 feet 



"V\Tiere tile- is usee! as panel walls in a frame of reinforced concrete or be- 

 tween piers of concrete or lieavy masonry, tbis clanger is intensified because the 

 tile is securely i-estrained 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 tiestroyed 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 xise 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 shoMm that even here 

 clay tile affords mnich less protection than brick or concrete, which now is being 

 used for protecting important columns. 



■ 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. 



