Building Design and Construction Handbook - Merritt - Ventech!

PROTECTION AGAINST HAZARDS 3.33
with the fire-resistance rating and structural stability under fire conditions required
for the type of occupancy and construction of the building to bar the spread of fire
between adjoining buildings or between parts of the same building on opposite
sides of the division. A fire division may be an exterior wall, fire window, fire door,
fire wall, ceiling, or firestop.
A fire wall should be built of incombustible material, have a fire rating of at
least 4 hr, and extend continuously from foundations to roof. Also, the wall should
have sufficient structural stability in a fire to allow collapse of construction on either
side without the wall collapsing. Building codes restrict the size of openings that
may be provided in a fire wall and require the openings to be fire-protected (Art.
11.55).
To prevent spread of fire through hollow spaces, such spaces should be firestopped.
A firestop is a solid or compact, tight closure set in a hollow, concealed
space in a building to retard spread of flames, smoke, or hot gases. All partitions
and walls should be firestopped at every floor level, at the top-story ceiling level,
and at the level of support for roofs. Also, very large unoccupied attics should be
subdivided by firestops into areas of 3000 ft 2 or less. Similarly, any large concealed
space between a ceiling and floor or roof should be subdivided. For the purpose,
firestops extending the full depth of the space should be placed along the line of
supports of structural members and elsewhere, if necessary, to enclose areas not
exceeding 1000 ft 2 when situated between a floor and ceiling or 3000 ft 2 when
located between a ceiling and roof.
Openings between floors for pipes, ducts, wiring, and other services should be
sealed with the equal of positive firestops. Partitions between each floor and a
suspended ceiling above are not generally required to be extended to the slab above
unless this is necessary for required compartmentation. But smoke stops should be
provided at reasonable intervals to prevent passage of smoke to noninvolved areas.
3.5.5 Height and Area Restrictions
Limitations on heights and floor areas included between fire walls in any story of
a building are given in every building code and are directly related to occupancy
and construction. From the standpoint of fire protection, these provisions are chiefly
concerned with safety to life. They endeavor to ensure this through requirements
determining minimum number of exits, proper location of exits, and maximum
travel distance (hence escape time) necessary to reach a place of refuge. The limitations
are also aimed at limiting the size of fires.
Unlimited height and area are permitted for the most highly fire-resistant type
of construction. Permissible heights and areas are decreased with decrease in fire
resistance of construction. Area permitted between fire walls in any story reduces
to 6000 ft 2 for a one-story, wood-frame building.
Installation of automatic sprinklers increases permissible heights and areas in all
classes, except those allowed unlimited heights and areas.
Permissible unlimited heights and areas in fire-resistive buildings considered
generally satisfactory in the past may actually not be safe. A series of fires involving
loss of life and considerable property damage opened the fire safety of such
construction to question. As a result, some cities have made more stringent the
building-code regulations applicable to high-rise buildings.
Many building codes prohibit floor areas of unlimited size unless the building
is sprinklered. Without automatic sprinklers, floor areas must be subdivided into
fire-wall-protected areas of from 7500 to 15,000 ft 2 and the enclosing fire walls
must have 1- or 2-hr fire ratings, depending on occupancy and construction.