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Chapter 1: Fire geometry and smoke movement in buildings
Figure 6: Simplified fire protection decision tree
Fire protection
Prevent fire
initiation
OR
Eliminate
Isolate fuel
ignition
and ignition
sources
sources
Includes:
Includes:
Electrical Power
Storage
Flames
Flammables
Arson
Trash/Litter
Smoking Material
Combustibles
Smoke management mechanisms
Mechanisms for managing smoke impact include:
•
Compartmentation in the form or walls, floors, doors
and other barriers
•
Dilution (also known as smoke purging, smoke
removal, smoke exhaust, or smoke extraction)
•
Airflow in the form of large flow rates and used
primarily in subway, railroad, and highway tunnels
•
Pressurization using mechanical fans under
NFPA 92A
•
Buoyancy effects that employ mechanical systems
when ceiling heights exceed 33 ft.(10 m)
Design factors
Many factors affect the design of a smoke control
system. Before the actual mechanical design of the
system can proceed, the potential constraints on the
system must be determined and the design criteria
established.
Unique factors in the design of a smoke control system
include:
•
Occupancy type and characteristics
•
Evacuation plans
•
Areas of refuge
8
OR
Manage fire
impact
OR
Manage
Manage
threat
exposure
Includes:
Includes:
Sprinklers
Smoke
Fire Walls
Management:
Fire Doors
Smoke Control
Fire Dampers
Smoke Venting
Smoke Barriers
•
Occupant density and distribution
•
Human life support requirements (medical facilities)
•
Detection and alarm systems (exclusive of smoke
control)
•
Fire department response to fire emergencies in the
building
•
Fixed fire suppression systems
•
Type of HVAC systems (in place or proposed)
•
Energy management systems and controls
•
Building security provisions
•
Status of doors in a fire emergency
•
Potential fire sources
•
Internal compartmentation and architectural
characteristics
•
Building leakage paths
•
Exterior building temperatures
•
Wind velocity and effects
All of these factors funnel into a consideration of how
much smoke will be present in an expected fire. The
amount of smoke, expressed as smoke density, can
reduce visibility, trap occupants in the building, prevent
escape, and expose occupants over an extended period
of time to toxic and irritant gases which could become
lethal.
The ASHRAE manual Design of Smoke Management
Systems contains guidelines for designers who wish to
provide active smoke control systems for buildings.
Smoke control systems are intended to provide systems
that exhaust smoke from the immediate fire area, and
provide pressurized outside air to adjacent areas,
access corridors, and stairwells. It is fully recognized that
this approach would apply more to large HVAC units
servicing individual floors or large systems with volume
control dampers at each floor. The integrity of the
HVAC/smoke control system must be at a level that will
maintain safe exit routes with sufficient exiting time for
building occupants to either leave or move to designated
safe refuge areas.
Smoke zones
A building or area is typically divided into several zones.
Zones are delineated by fire or smoke barrier walls or
VM-1 Smoke Management Application Guide
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