Introduction To The Fire Problem - Kidde VM-1 Manual

Chapter 1: Fire geometry and smoke movement in buildings
Introduction to the fire
problem
Architectural factors in the spread of
smoke
Smoke is considered the primary hazard that puts
occupants of buildings at risk during a fire. Heat from
fire, while an important threat, is usually confined to the
area of fire origin. In contrast, smoke readily spreads
from the area of fire origin to adjacent rooms or spaces
and to parts of a building remote from the origin of the
fire. Smoke can contaminate escape routes including
stairs and elevators, rendering them unusable and
resulting in occupants who are trapped in or near the fire
due to their inability to escape.
More people in building fires are exposed to the hazards
of smoke than to heat. Smoke is a particularly serious
hazard in buildings requiring long egress times for
complete evacuation. As buildings increase in height the
hazard to occupants increases also, with the time for a
high building to maintain tenability being less than the
building's actual evacuation time.
From a smoke management standpoint, a high-rise
building is one in which evacuation time of able-bodied
and mobility-impaired occupants is considered
excessive. Model building and fire codes typically
classify high-rise buildings as those with the highest floor
75 feet or more above grade. Local modifications to the
nationally recognized codes in some areas classify high-
rise buildings as being six or more floors or as little as
50 feet above grade. The lower height classifications for
high-rise buildings are often based upon the height
which fire department aerial ladders can reach. Buildings
classified as high-rise buildings typically require the
installation of automatic sprinklers.
Early high-rise buildings did not impose major smoke
hazard problems in fires due to noncombustible or
limited combustible construction materials and extensive
compartmentation. Since the 1950s, changes in
construction materials, building designs, and occupancy
practices have resulted in increased fire loads.
Fire compartment size has increased with central core
service areas and open floor plans. Combustible
furnishings, interior linings, ceiling tiles, partitions, and
thermal and electrical insulation in modern buildings
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have increased the fire load compared to earlier
buildings. Modern materials, such as plastics, generate
dense toxic smoke, which increases the threat to
occupants in a fire.
In 1963, John Portman, an architect and developer,
introduced modern large building atriums as a building
element in the 23-story Hyatt Regency hotel in Atlanta,
Georgia. Atrium buildings, which provide large interior
spaces, have gained in popularity to the point of being
used in nearly all types of occupancies.
Atriums in hotels, malls, hospitals and office buildings
interconnect floor spaces and create new problems in
confining fire and smoke movement. In the late 1960s,
building and fire code officials in North America
recognized the increased fire hazards created by atriums
and universally required the installation of automatic
sprinkler systems in larger atriums and adjacent spaces.
Fire and smoke in an atrium initially moves and performs
similar to a fire in an open outdoor area with heat and
smoke rising and spreading towards the ceiling.
However, with the interaction of automatic sprinklers,
mechanical air movement, and the atrium ceiling, the
atrium and adjacent floor spaces can quickly become
contaminated with smoke. Occupants relying upon
egress paths using exits or enclosed stairs through
atriums are dependent upon the ability to use these
spaces in the early stages of a fire event. Smoke control
systems are a critical element in the common space
evacuation scenario.
Smoke management
Smoke management is one of the primary tools used in
the built environments for containing the effects of fire.
Smoke management includes all methods that can be
used alone or in combination to modify smoke
movement for the benefit of occupants or firefighters, or
to reduce property damage. The mechanisms of
compartmentation, dilution, airflow, pressurization, and
buoyancy are used alone or in combination to manage
smoke conditions in fires.
Smoke control is a subset of the smoke management
discipline. Smoke control systems are commonly defined
as engineered systems that use mechanical fans to
produce airflow and pressure differences across smoke
barriers to limit and direct smoke movement.
VM-1 Smoke Management Application Guide