Requirements and Design Criteria for Smoke Control, Smoke

Management, and Smoke Removal Systems: An Analysis

Based on NFPA and ASHRAE Standards
I. Introduction to Smoke Control Systems and Governing
Standards
The devastating impact of smoke in building fires is well-documented; it is often the
smoke, not the flames, that poses the primary threat to life by reducing visibility,
impairing respiration, and causing incapacitation.1 To mitigate these hazards,
engineered smoke control systems are employed to manage the movement of smoke
and maintain tenable conditions for occupants and responding fire service personnel.
The design, installation, and performance of these critical life safety systems are
governed by a suite of interconnected codes and standards.

A. Defining Smoke Control, Smoke Containment, and Smoke Management (per

NFPA 92)
The cornerstone standard addressing these systems is NFPA 92, Standard for Smoke
Control Systems. The 2024 edition of NFPA 92 provides comprehensive requirements
for the design, installation, acceptance testing, operation, and ongoing periodic
testing of all types of smoke control systems.2 This standard employs a specific
hierarchy of terminology:
● Smoke Control Systems: This is the overarching term, defined as an engineered
system that includes all methods, used singly or in combination, to modify smoke
movement within a building during a fire.5
● Smoke Containment Systems: This is a sub-classification of smoke control.
These systems are designed to prevent the migration of smoke from the fire zone
into other designated areas of the building. This is achieved by establishing and
maintaining pressure differences across physical barriers (such as walls, floors,
and doors), utilizing either natural buoyancy or mechanical means (fans) to
ensure airflow from the protected (high-pressure) side to the smoke (low-
pressure) side.1 The primary objective is to confine smoke to its zone of origin.
● Smoke Management Systems: This is another sub-classification of smoke
control, typically applied to large-volume spaces like atriums, malls, or covered
arcades. These systems aim to maintain tenable conditions within such spaces by
actively managing the smoke layer (e.g., maintaining its interface at a specific
height above the highest level of occupant egress) or by exhausting smoke from
 the space at a controlled rate.1

The current terminology in NFPA 92 represents a significant step towards clarity and
consistency in the field. Historically, there was considerable confusion arising from
predecessor documents: NFPA 92A, Standard for Smoke-Control Systems Utilizing
Barriers and Pressure Differences, referred to pressurization systems as "smoke
control systems," while NFPA 92B, Standard for Smoke Management Systems in
Malls, Atria, and Large Spaces, used the term "smoke management systems." Building
codes and other standards, however, generally used "smoke control systems" as an
umbrella term for all such approaches.5 Recognizing this discrepancy, NFPA
consolidated NFPA 92A (withdrawn in 2011 8) and NFPA 92B into the unified NFPA 92
standard. This merger, formalized during the NFPA Annual 2011 code cycle, adopted
"smoke control systems" as the comprehensive designation, with "smoke
containment" and "smoke management" as distinct methods or sub-classifications.5
This unification was a deliberate effort to resolve inconsistencies between NFPA's
own documents and the terminology used in broader building codes, thereby
reducing ambiguity for designers, installers, and enforcing authorities. Adherence to
the current, unified terminology in NFPA 92 is therefore essential for clear
communication and correct application of standards in design and enforcement.

B. Overview of Key Standards and Their Interrelation

Several key documents form the regulatory and guidance framework for smoke
control:
● NFPA 92, Standard for Smoke Control Systems: As mentioned, the 2024 edition
is the current primary standard.2 It encompasses design fundamentals,
calculation procedures for smoke management, building equipment and controls
specifications, documentation requirements, and protocols for acceptance and
periodic testing.2
● NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating
Systems: The 2024 edition of this standard is crucial because HVAC systems can
significantly influence smoke movement.10 NFPA 90A provides requirements for
the construction, installation, operation, and maintenance of air conditioning and
ventilating systems, including filters, ducts, and related equipment, with the
specific aim of protecting life and property from fire, smoke, and gases.10 Its
provisions for ductwork, fire dampers, smoke dampers, and controls are often
integral to, or must be carefully coordinated with, smoke control system
designs.13
● ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning
Engineers) Guidance: ASHRAE plays a vital role by providing extensive technical
resources. The most notable is the Handbook of Smoke Control Engineering, a
collaborative effort with the International Code Council (ICC), NFPA, and the
Society of Fire Protection Engineers (SFPE).17 This handbook, along with the "Fire
and Smoke Control" chapter in the ASHRAE Handbook—HVAC Applications
volume 18, offers in-depth engineering principles, detailed calculation
methodologies (including software tools like AtriumCalc for atrium systems),
analysis of design fires, and guidance on complex factors such as wind and stack
effects, which may be beyond the direct prescriptive scope of NFPA 92.17 ASHRAE
also contributes through ongoing research and specialized guidelines, such as
Guideline 44-2024, Protecting Building Occupants From Smoke During Wildfire
and Prescribed Burn Events.21

The relationship between NFPA standards and ASHRAE guidance is complementary.

NFPA standards, such as NFPA 92 and NFPA 90A, typically establish the minimum
safety requirements, performance objectives, and compliance pathways for smoke
control systems, often driven by the mandates of overarching life safety codes.
ASHRAE, through its comprehensive handbooks, research programs, and technical
committees, provides the detailed engineering principles, sophisticated calculation
methodologies, and critical data necessary to design systems that can effectively
meet these NFPA requirements. This is particularly true for complex scenarios
involving unique building geometries, challenging environmental conditions (like wind
or significant stack effect in tall buildings), or where detailed fire modeling is
necessary to predict smoke behavior accurately. For instance, while NFPA 92
provides the equations for smoke management calculations, the ASHRAE Handbook
of Smoke Control Engineering offers more extensive guidance on selecting the
appropriate design fire (a critical input) and analyzing its characteristics. Thus, a
robust and reliable smoke control system design often necessitates a synergistic
application of NFPA's prescriptive and performance requirements with ASHRAE's in-
depth engineering guidance and analytical tools.

II. Mandatory Installation: When and Where are Smoke Control

Systems Required?
Understanding the triggers for the installation of smoke control systems is paramount
for compliance and safety.
A. The Role of Adopted Codes (IBC, NFPA 101)
It is a common misconception that NFPA 92 itself dictates when and where smoke
control systems must be installed. However, NFPA 92's role is to provide the criteria
for how these systems are to be designed, installed, and tested once their installation
is mandated by other governing codes or chosen as a design solution to meet
specific performance objectives.7

The actual requirement to install a smoke control system typically originates from the
locally adopted building code (such as the International Building Code - IBC) and/or
the fire and life safety codes (such as NFPA 101, Life Safety Code).7 For example,
NFPA 101 outlines general system requirements in its Section 9.3, while the specific
occupancy chapters (Chapters 11 through 43) detail the conditions under which
smoke control is obligatory for different types of buildings.7 Similarly, the IBC,
particularly in its Section 909 ("Smoke Control Systems") and various occupancy-
specific sections, is a primary driver for smoke control system mandates.23

This establishes a clear hierarchy: the process begins with an analysis of the building
against the adopted building and life safety codes. These codes determine if and
where a smoke control system is mandated based on factors such as occupancy
type, building height, the presence of atria, or specific hazards. Once a requirement
for smoke control is established by these governing codes, NFPA 92 then provides
the detailed standards for how that system must be designed, installed, tested, and
maintained. Understanding this hierarchy is critical; designers must first consult the
governing building and fire codes to identify the need for a system before turning to
NFPA 92 for design guidance.

Furthermore, beyond these prescriptive mandates found in code chapters, smoke

control systems are also frequently employed as part of a performance-based design
approach.7 This pathway allows for innovative solutions to meet the underlying safety
intent of the codes, especially in buildings with unique architectural features or
existing structures where strict adherence to prescriptive rules is impractical or overly
restrictive. In such cases, smoke control can be a vital engineered system used to
demonstrate an equivalent (or superior) level of safety, often requiring sophisticated
engineering analysis, modeling, and close collaboration with the Authority Having
Jurisdiction (AHJ).

B. Requirements by Occupancy and Building Type (Examples from IBC and NFPA
101)
The specific occupancies and building features that trigger the need for smoke
control systems are numerous and detailed within the IBC and NFPA 101. Some
common examples include:
● High-Rise Buildings: Generally, buildings exceeding a certain height (e.g., 75
feet above the lowest level of fire department vehicle access) require smoke
control. IBC Sections 403.4.7 (smoke removal/ventilation) and 403.5.4 (stairway
door operation with pressurization) are relevant.23 NFPA 101 often mandates
smokeproof enclosures, typically achieved through stairwell pressurization, in
high-rise buildings to protect means of egress.26
● Atriums: Smoke control is commonly required in buildings with atriums,
particularly those connecting multiple stories (e.g., three or more stories in
covered malls per IBC 402.7.2, or generally per IBC 404.5).23 Exceptions may
apply, for instance, to atriums connecting only two stories in certain occupancies
or meeting other specific criteria.23
● Underground Buildings: Structures with occupied floor levels significantly below
the level of exit discharge 23 typically mandate smoke control systems to restrict
smoke migration and ensure the usability of egress routes.23
● Assembly Occupancies: NFPA 101, for instance, requires smoke control systems
for assembly occupancies that include stages or platforms. The objective is to
maintain the smoke layer at least 6 feet (1.83 meters) above the highest seating
level or floor of the means of egress.7 IBC Section 410.2.7.1 also addresses stage
ventilation requirements.23
● Healthcare Occupancies (Group I-2): These facilities, such as hospitals and
nursing homes, require smoke barriers to subdivide stories used by patients into
at least two smoke compartments, with each compartment generally not
exceeding 22,500 square feet.23 While 27 does not explicitly call for NFPA 92
systems, it mandates emergency power for smoke control if such systems are
present. IBC Section 407.5 provides detailed requirements for these smoke
barriers and compartments.
● Detention and Correctional Occupancies (Group I-3): Smoke barriers are
required to divide stories occupied by residents. IBC Section 408.9 23 mandates
smoke control for these facilities.23
● Covered Mall Buildings: Atriums within covered mall buildings that connect
three or more stories necessitate a smoke control system in accordance with IBC
Section 402.7.2.23
● Windowless Buildings: The IBC requires an engineered smoke control system
designed in accordance with Section 909 for each windowless smoke
 compartment to provide a tenable environment for exiting.23
● Motor Vehicle Related Occupancies (Enclosed Parking Garages): IBC Section
406.6.2 and International Mechanical Code (IMC) Section 404 require mechanical
ventilation systems. These systems often operate based on carbon monoxide
(CO) and nitrogen dioxide (NO2) detection for pollutant control, with specified
airflow rates (e.g., 0.75 cfm per square foot for full operation, 0.05 cfm per
square foot for standby).23 Some jurisdictions may also impose requirements for
post-fire smoke removal, potentially based on achieving 6-10 Air Changes Per
Hour (ACH).23 NFPA 88A, Standard for Parking Structures, also provides relevant
guidelines.
● Group F-1 and S-1 (Moderate and High Hazard Factory and Storage
Occupancies): For buildings or portions thereof with large undivided areas (e.g.,
exceeding 50,000 square feet), the IBC mandates either smoke and heat vents
(per Section 910.3) or a mechanical smoke removal system (per Section 910.4).23
● High-Piled Combustible Storage: Areas with high-piled combustible storage
typically require smoke and heat removal systems in accordance with IBC Section
910 and International Fire Code (IFC) Table 3206.2.23

The following table summarizes some of these common triggers:

Table 1: Summary of IBC/NFPA 101 Triggers for Smoke Control Systems

Building Specific Relevant IBC Relevant NFPA Brief

Type/Occupan Condition Section(s) 101 Section(s) Description of
cy Triggering (Examples) (Examples) Smoke Control
Requirement Objective

High-Rise Exceeding a 403.4.7, Occupancy Stairwell

Buildings defined height 403.5.4, 909, Chapters, 9.3 pressurization
(e.g., >75 ft) 1023.12 (smokeproof
enclosures),
elevator
hoistway
pressurization,
other measures
to maintain
egress integrity.

Atriums Connecting a 404.5, 402.7.2 Occupancy Maintain smoke

 specified (Malls), 909 Chapters, 9.3 layer above
number of occupied levels,
stories (e.g., ≥ 3 prevent smoke
stories) spread to
communicating
spaces.

Underground Occupied floor 405.5, 405.4.1, Occupancy Restrict smoke

Buildings levels 405.4.2, 909, Chapters, 9.3 migration,
significantly 1023.12 maintain usable
below exit egress, often
discharge (e.g., involves
>30 ft or >60 ft) compartmentati
on and
pressurization
of egress
routes.

Assembly Presence of 410.3.4 (as per Occupancy Maintain smoke

Occupancies stages or 909), 410.2.7.1 Chapters (e.g., level ≥ 6 ft
(with stages) platforms (vents) Ch 12, 13), 9.3 above highest
seating/egress
path.

Healthcare Subdivision of 407.5 (smoke Occupancy Primarily smoke

(Group I-2) stories into barriers), 909 (if Chapters (e.g., compartmentati
smoke applied) Ch 18, 19), 9.3 on via barriers;
compartments pressurization
may be used to
enhance barrier
effectiveness or
for specific
areas.

Detention/ Subdivision of 408.6 (formerly Occupancy Smoke

Correctional stories into 408.9), 909 Chapters (e.g., compartmentati
(Group I-3) smoke Ch 22, 23), 9.3 on, often with
compartments pressurization
of non-smoke
zones or egress
 routes.

Windowless Lack of exterior 402.8.1 (as per Occupancy Engineered

Buildings openings for 909) Chapters, 9.3 smoke control
ventilation/acce to provide a
ss tenable
environment for
exiting.

Enclosed Pollutant control 406.6.2 NFPA 88A Ventilation for

Parking Garages (CO, NO2); (references IMC pollutant
some 404) dilution (0.75
jurisdictions for cfm/ft²);
post-fire smoke potentially 6-10
removal ACH for post-
fire smoke
removal.

Large Undivided Undivided area 910.2.1 Not directly Smoke and heat
F-1 & S-1 >50,000 sq ft (references specified as venting or
910.3 or 910.4) smoke control mechanical
smoke removal
to assist
firefighting and
limit fire spread.

High-Piled Presence of 910.2.2 Not directly Smoke and heat

Combustible high-piled (references IFC, specified as removal to
Storage storage 910.3 or 910.4) smoke control assist
firefighting,
control fire
growth, and
protect
structure.

Note: This table provides examples and is not exhaustive. Always consult the specific
locally adopted codes and standards for definitive requirements.

III. Design Criteria for Smoke Containment Systems

(Pressurization Methods)
Smoke containment systems, which rely on pressurization, are a fundamental
approach to smoke control, particularly for protecting means of egress and refuge
areas.

A. Principles and Applications

The core principle of smoke containment is to establish and maintain a positive
pressure differential across the physical barriers (such as walls, floors, and doors)
that separate a protected space from an area where smoke may be present.1 This
positive pressure ensures that any airflow through leakage paths in these barriers
(e.g., cracks around doors, utility penetrations) is directed from the high-pressure
(protected) side towards the low-pressure (smoke-affected) side, thereby preventing
smoke from entering the protected space.

NFPA 92 outlines several common applications or "approaches" for smoke

containment systems 1:
● Stairwell Pressurization: This involves supplying air into exit stairwells, creating
a positive pressure relative to adjacent building spaces. This is critical in high-rise
or underground buildings to keep stairwells free of smoke, ensuring a safe
evacuation route for occupants and providing a clear access path for
firefighters.1
● Elevator Hoistway Pressurization: Similar to stairwell pressurization, this
approach pressurizes elevator shafts to prevent smoke infiltration. This can be
vital for maintaining the usability of elevators for occupant evacuation (especially
for those with mobility impairments) or for fire department access and
operations.1
● Zoned Smoke Control: This method typically involves dividing a building (often
floor by floor) into smoke control zones. During a fire, the zone where the fire is
located (the "smoke zone") may be exhausted, while adjacent non-smoke zones
are positively pressurized relative to the smoke zone. This is often achieved using
the building's HVAC system in a modified operational mode.1
● Vestibule Pressurization: Pressurized vestibules located at the entrances to
stairwells or elevator shafts act as an additional air lock or buffer zone, further
enhancing protection against smoke entry into these critical vertical egress
paths.1
● Smoke Refuge Area Pressurization: In facilities where immediate evacuation of
all occupants may not be feasible (e.g., hospitals, prisons, or certain areas in
 high-rise buildings), designated smoke refuge areas can be pressurized. These
areas provide a temporary safe haven for occupants to await rescue or further
instruction.1

B. Key Design Parameters (NFPA 92, Chapter 4 & ASHRAE Guidance)

Chapter 4 of NFPA 92, "Design Fundamentals," lays out many of the essential criteria
for smoke containment systems. These are often supplemented by detailed
engineering guidance from ASHRAE.
● Minimum Design Pressure Differential: A critical parameter is the minimum
pressure difference to be maintained across smoke barriers.
○ NFPA 92, in its Table 4.4.2.1.1 (as referenced in multiple sources 5), typically
specifies a minimum design pressure differential of 0.05 inches water gage
(in. w.g.) (approximately 12.4 Pascals) across smoke barriers in buildings
equipped with automatic sprinkler systems.
○ For buildings without automatic sprinkler protection, the minimum required
pressure differential is generally higher and depends on the ceiling height of
the fire compartment, as detailed in the same NFPA 92 table.5 This is because,
in unsprinklered fires, smoke temperatures are likely to be higher, resulting in
greater buoyancy forces that the pressurization system must overcome.
○ It is crucial to understand that these are minimum values. Designers are
explicitly required by NFPA 92 to consider other forces that can affect
pressure relationships within a building, such as stack effect (due to
temperature differences between the building interior and exterior), wind
pressures, the buoyancy of hot smoke, and imbalances caused by the normal
operation of the HVAC system. If an engineering analysis indicates that a
higher pressure differential is necessary to counteract these forces and
effectively contain smoke, then that higher, calculated value must be used for
the design, superseding the tabulated minimums.5 This underscores that
simply applying the 0.05 in. w.g. from the table without analyzing these
external forces, especially in tall buildings or those with significant openings
or leakage paths, can lead to an under-designed system that fails under real-
world fire conditions.
● Maximum Design Pressure Differential & Door Opening Forces: While
ensuring sufficient pressure to contain smoke, the system must not create
pressures so high that they impede egress.
○ NFPA 92 does not specify a numerical maximum pressure differential. Instead,
it limits the maximum pressure by referencing the maximum allowable door
 opening force stipulated in NFPA 101, Life Safety Code.5
○ NFPA 101 5 typically limits the force required to open a door against the
pressure differential to 30 pounds-force (lbf) (approximately 133 Newtons)
to set the door in motion, and 15 lbf (67 N) to swing it fully open. The 30 lbf
value for initiating door movement is the critical design constraint.5
○ The design of smoke containment systems therefore involves a critical
balance: the pressure differential must be high enough to effectively prevent
smoke infiltration across barriers, yet low enough to ensure that doors can be
opened by occupants for egress without excessive force. Achieving this
balance often requires detailed calculations of air leakage and careful
selection of door hardware, especially door closers. The ASHRAE Smoke
Control Manual (and the more current Handbook of Smoke Control
Engineering) provides methodologies and tabular data to assist in these
calculations, relating door size, closer force, and allowable pressure
differences.19
● Air Leakage: The quantity of air that must be supplied by the pressurization
system is directly dependent on the cumulative leakage area of the barriers
forming the protected space (e.g., cracks around doors, windows, utility
penetrations, and through porous construction).19 Accurate estimation of these
leakage areas is fundamental for correct fan sizing. NFPA 92 does not provide
detailed calculation procedures for smoke containment systems; engineers
typically rely on resources like the ASHRAE Handbook of Smoke Control
Engineering and the SFPE Handbook of Fire Protection Engineering for these
complex calculations.5
● System Activation: All smoke control systems, including containment systems,
must be designed for automatic activation. This is typically initiated by signals
from approved fire detection devices such as smoke detectors, heat detectors,
or sprinkler water flow switches.5 Manual pull stations are generally not
considered suitable for initiating smoke control systems that rely on pinpointing
the fire's location, due to the uncertainty of activation at the precise origin.7
● Additional Design Considerations from ASHRAE: The ASHRAE Handbook of
Smoke Control Engineering emphasizes several factors crucial for robust design
19
:
○ The analysis methods should directly incorporate the effects of airflow
friction losses in shafts, temperature differences that drive stack effect, and
wind forces.
○ The buoyancy effect of hot smoke is indirectly incorporated into the analysis
 by the careful selection of minimum design pressure differences.
○ While systems are designed for steady-state pressure, short-term deviations
(e.g., up to 50% of the minimum design pressure) may be tolerable in some
cases, but this depends on factors such as barrier tightness, smoke toxicity,
airflow rates, and space volumes.

The following table summarizes the minimum design pressure differentials from NFPA
92:

Table 2: NFPA 92 Minimum Design Pressure Differentials for Smoke Barriers

(Ref: Based on Table 4.4.2.1.1 information)

Building Condition Ceiling Height of Minimum Design Minimum Design

Fire Compartment Pressure Pressure
(for Non- Differential (in. Differential (Pa,
Sprinklered w.g.) approx.)
Buildings)

Building is protected Not Applicable 0.05 12.4

by automatic
sprinklers

Building is NOT ≤ 9 ft (2.7 m) 0.10 24.9

protected by
automatic sprinklers

Building is NOT > 9 ft (2.7 m) and ≤ 21 0.14 34.8

protected by ft (6.4 m)
automatic sprinklers

Building is NOT > 21 ft (6.4 m) 0.18 44.8

protected by
automatic sprinklers

Note: These values are minimums. The design pressure difference must be sufficient
to overcome forces from stack effect, wind, and fire buoyancy. The maximum
pressure difference is limited by door-opening force requirements in NFPA 101.
Consult the current edition of NFPA 92 for the authoritative table and all
accompanying notes and conditions.

IV. Design Criteria for Smoke Management Systems

(Exhaust/Large Volume Spaces)
Smoke management systems are typically employed in buildings with large, open
interconnected spaces, such as atriums, malls, exhibition halls, and sports arenas,
where smoke containment via simple pressurization is impractical.

A. Principles and Applications

The core principle of smoke management in large volume spaces is to control the
behavior of smoke generated by a fire to maintain a tenable environment for
occupants during the time required for egress, and potentially to assist firefighting
operations.1 This is often achieved by allowing smoke to accumulate in an upper
"reservoir" within the large space, while ensuring that the lower portion, including
egress paths, remains relatively free of smoke for a specified duration. Alternatively,
active smoke exhaust can be used to limit the descent or spread of the smoke layer.
These systems are essential in architectural designs that feature expansive vertical
openings which can otherwise allow rapid smoke spread throughout multiple levels.1

B. Methods of Smoke Management

Several methods can be employed for smoke management in large spaces:
● Mechanical Smoke Exhaust: This is an active method that utilizes fans to
extract smoke from the upper portion of the large volume space at a calculated
volumetric flow rate.1 A critical component of mechanical exhaust systems is the
provision of adequate makeup air to replace the exhausted air and smoke,
preventing excessive negative pressurization of the space.
● Natural (Gravity) Smoke Venting: This method relies on the natural buoyancy
of hot smoke. Strategically located vents are installed at or near the top of the
large space. As hot smoke rises, it exits through these vents. The size, number,
and location of these vents are determined by engineering calculations based on
the anticipated fire size and smoke production rate.1
● Smoke Filling (Passive Management): In some scenarios, particularly where the
volume of the upper portion of the space is very large and the fire is expected to
be relatively small or controlled by sprinklers, a passive approach may be used.
This involves allowing the smoke to naturally fill the upper, unoccupied part of the
space, forming a smoke layer. The design must ensure, through calculation, that
 the interface of this smoke layer remains above the highest level of occupant
egress for the time required for all occupants to safely exit the building.1
● Opposed Airflow: This technique is used to prevent smoke from migrating from
a large, smoke-filled space (like an atrium) into an adjacent, smaller,
communicating space (such as a shop opening onto the atrium or an egress
corridor). It involves discharging a curtain of air from the protected space
towards the smoke-affected space. The velocity of this opposing airflow must be
sufficient to counteract the forces driving smoke movement into the protected
area.1

C. Key Design Parameters (NFPA 92, Chapter 4 & 5, ASHRAE Guidance)

The design of smoke management systems is complex and relies on a number of
critical parameters and calculations, primarily found in Chapters 4 and 5 of NFPA 92
(Chapter 5 incorporates much of the technical content formerly in NFPA 92B) and
supplemented by extensive guidance from ASHRAE.
● Design Objectives: As per NFPA 92, Section 4.1.2, the specific design objectives
for the smoke management system must be clearly defined at the outset. These
may include maintaining a tenable environment for occupant egress, providing
conditions that assist fire department operations, limiting smoke damage to
property, or facilitating fire suppression activities.5
● Smoke Layer Interface Height: A primary performance criterion for many
smoke management systems is the maintenance of the smoke layer interface at a
safe height above the highest occupiable level or any means of egress within the
large volume space.5
○ NFPA 92 generally requires that the smoke layer depth (the distance from the
ceiling down to the smoke layer interface) be a minimum of 20% of the overall
floor-to-ceiling height of the space, or be based on a more detailed
engineering analysis.5
○ For specific occupancies, such as assembly spaces with stages or platforms,
NFPA 101 mandates that the smoke control system maintain the smoke level
at least 6 feet (1.83 meters) above the highest seating level or the top of a
proscenium opening.7
● Heat Release Rate (HRR) of the Design Fire (Q): The selection of the Heat
Release Rate (HRR) for the design fire is arguably the most pivotal decision in
designing a smoke management system. This value directly influences the
calculated smoke production rate and, consequently, the required exhaust
capacity.20 NFPA 92 provides equations that use HRR as an input for calculating
 smoke production but does not prescriptively define the HRR value itself.20 This
determination is left to the design engineer and must be based on a careful
analysis of potential fuel loads, the presence and effectiveness of sprinklers, and
other building-specific factors. The ASHRAE Handbook of Smoke Control
Engineering (Chapter 5 specifically addresses fire development and design fires
17
) is an essential resource for this analysis. While ASHRAE guidance may suggest
starting points, such as 2,100 kW for a transient fire in some contexts, it also
cautions against the universal application of such values without thorough
evaluation.20 An example calculation provided in one source uses a steady-state
HRR of 6,500 Btu/s (approximately 6,850 kW).30 An underestimation of HRR can
lead to an ineffective system unable to manage the smoke produced, while a
significant overestimation can result in an unnecessarily costly and oversized
system. This decision point is critical and carries significant responsibility.
● Volumetric Exhaust Rate (V): Once the design fire HRR (specifically, its
convective portion, Qc) and the desired smoke layer interface height (Z) are
established, the required volumetric exhaust rate can be calculated using
equations provided in NFPA 92 (Chapter 5). These equations vary depending on
the type of fire plume (e.g., axisymmetric plume from a fire in the center of a
large space, balcony spill plume, window plume).5
○ For example, for an axisymmetric plume where the smoke layer height Z is
greater than a limiting elevation zl, one such equation for the mass flow rate
of smoke (m) is m=0.022QcZ5/3+0.0042Q (in imperial units, lb/s), and the
volumetric exhaust rate (V) is then V=60ρm (in CFM, where ρ is the density of
smoke).30
○ It is critical to assess if special plume conditions, such as balcony spill plumes
(where smoke spills from under a balcony into the main atrium volume), are
present, as these often require significantly higher exhaust rates than simple
axisymmetric plumes and must be evaluated accordingly.20 Calculated
exhaust rates for large atriums can be substantial, sometimes exceeding
100,000 CFM 20 or even 250,000 CFM.30
● Makeup Air: For mechanical smoke exhaust systems to function effectively, a
properly designed makeup air system is indispensable. It is not merely about
replacing the volume of air exhausted; the velocity, location, and distribution of
makeup air are critical.7
○ The velocity of makeup air entering the space, particularly near the fire plume
or in occupied zones below the smoke layer, is typically limited to a maximum
of 200 feet per minute (1.02 m/s), or must be based on an engineering
 analysis. This limit is to prevent the makeup air from disrupting the natural
rise of the smoke plume (which could entrain more air and increase the
volume of smoke to be exhausted), deflecting smoke into areas intended to
be kept clear, or causing uncomfortable drafts for occupants.5
○ Makeup air inlets must be strategically located: well below the design smoke
layer interface, distributed to avoid creating localized high velocities, and
positioned so they do not draw in smoke from the exhaust outlets or other
contaminated areas.7 The influence of wind on makeup air openings must also
be carefully considered, as wind can significantly alter intake velocities and
distribution patterns.20 The makeup air system must be engineered in concert
with the exhaust system as an integral component of the overall smoke
management strategy.
● Tenability and Egress Analysis: NFPA 92 (e.g., Section 4.5) often requires that a
tenability analysis and an egress analysis be performed if the stated design
objectives for the smoke management system include maintaining a tenable
environment for the time necessary for occupants to exit the building or
preventing occupants from being exposed to untenable smoke conditions.5 These
detailed analyses, which assess factors like smoke temperature, toxicity, and
visibility against human tolerance limits over time, are generally considered
outside the direct scope of NFPA 92 itself. Engineers typically rely on guidance
from the ASHRAE Handbook of Smoke Control Engineering or the SFPE
Handbook of Fire Protection Engineering for methodologies. The smoke
management system must then be designed to remain operational for the full
duration calculated for egress.5
● Activation Time: The overall response time of the smoke management system is
a critical factor. This includes the time required for the fire to be detected, for
control signals to be processed, and for all mechanical equipment (fans,
dampers) to achieve their operational state.5 This activation sequence must be
swift enough to establish smoke control before conditions become untenable.

The following table summarizes some of these key design parameters:

Table 3: Key Design Parameters for Atrium/Large Volume Smoke Management

(NFPA 92 & ASHRAE)

Parameter Guideline/Requirement Typical Value/Range or Key

 Source (NFPA 92 Section / Consideration
ASHRAE)

Design Objectives NFPA 92 (Sec 4.1.2) Must be selected first (e.g.,

maintain tenable egress,
assist FD).

Design Fire Heat Release Rate Engineering analysis; ASHRAE Not prescribed by NFPA 92.
(HRR or Q) Handbook (Ch. 5); SFPE Critical input based on fuel
Handbook load, sprinklers. Example:
2,100 kW (ASHRAE starting
point 20), 6,500 Btu/s
(example 30).

Smoke Layer Interface Height NFPA 92 (Sec 4.3, 4.5); NFPA Min. 20% of ceiling height as
(Z) 101 (Assembly) clear height 5 or ≥ 6 ft above
highest occupied
level/egress.7

Volumetric Exhaust Rate (V) NFPA 92 (Ch. 5); ASHRAE Calculated based on HRR, Z,
Handbook plume type (axisymmetric,
balcony spill, window, etc.).
Can be very large (e.g.,
>100,000 CFM 20).

Plume Type Considerations NFPA 92 (Ch. 5); ASHRAE Must identify correct plume
Handbook type (axisymmetric, balcony
spill, etc.) as equations differ
significantly.20

Makeup Air Quantity NFPA 92; ASHRAE Handbook Must balance exhaust;
prevent excessive negative
pressure.

Maximum Makeup Air Velocity NFPA 92 (Sec 4.4); ASHRAE Typically ≤ 200 ft/min (1.02
Handbook m/s) near plume or in
occupied zones.5
 Makeup Air Inlet Location Engineering judgment; Below smoke layer, avoid
ASHRAE Handbook plume disruption, avoid re-
entrainment of smoke,
consider wind.20

Tenability Analysis NFPA 92 (Sec 4.5); Often required if objective is

ASHRAE/SFPE Handbooks tenable egress; analysis
methods outside NFPA 92
scope.5

System Activation Time NFPA 92 (Sec 4.4.3) Must account for detection,
signal processing, and
mechanical equipment
operation time.5

V. Understanding "Smoke Removal Systems"

The term "smoke removal system" is often used in discussions of fire safety, but its
specific meaning and applicable standards can vary.

A. Clarification of Terminology in Context of NFPA/ASHRAE

Within the primary classification structure of NFPA 92, "smoke removal system" is not
established as a distinct, third category alongside "smoke containment systems" and
"smoke management systems".1 Instead, the function of "smoke removal" is typically
achieved by systems that fall under one of the two main NFPA 92 classifications or by
systems mandated under specific building code provisions for particular hazards:
● Smoke Management Systems: Mechanical exhaust systems designed under
smoke management principles for large volume spaces like atria are
fundamentally performing a smoke removal function. Their purpose is to extract
smoke at a calculated rate to maintain a defined smoke layer height or to clear
smoke from the space.1
● Specific Building Code Mandates: The International Building Code (IBC), for
instance, explicitly requires "mechanical smoke removal" systems under Section
910.4 for certain occupancies, such as large, undivided Group F-1 (factory
industrial) or S-1 (storage) areas, or for buildings with high-piled combustible
storage.23 These systems have design objectives and criteria that are often
detailed directly within IBC Section 910 or standards referenced therein, which
may differ from the calculations used for atrium smoke management under NFPA
 92 (and IBC Section 909).
● HVAC System Functionality: NFPA 90A, which governs HVAC systems,
acknowledges that one of the goals of HVAC system controls during a fire (when
integrated with smoke detection) is to "preferably, to exhaust a significant
quantity of smoke to the outside".14 This describes a smoke removal function that
can be part of the HVAC system's fire response mode.

This indicates that "smoke removal" is more aptly understood as a functional

description of what a system does rather than a formal classification category like
"smoke containment" or "smoke management" within the primary smoke control
standards (NFPA 92). The applicable design criteria depend heavily on the specific
context (e.g., atrium life safety vs. warehouse post-fire ventilation) and the code
section mandating the smoke removal function. Engineers should not look for a
generic "smoke removal system" design chapter in NFPA 92 that covers all such
applications. Instead, they must identify the specific occupancy, hazard, or
performance objective driving the need for smoke removal and then consult the
relevant code section (e.g., IBC Section 909 for atrium smoke control, IBC Section
910 for warehouse smoke and heat venting or mechanical smoke removal) and the
standards referenced therein. The design approach for atrium smoke management
(focused on maintaining a tenable smoke layer for occupant egress) can be very
different from that for warehouse smoke removal (which might focus on heat venting
to aid structural integrity and firefighting, or post-fire smoke clearance).

B. Design Criteria for Specific "Smoke Removal" Applications (e.g., IBC Section
910)
When "smoke removal" refers to systems specifically mandated by code sections like
IBC Section 910 (which covers both "Smoke and Heat Vents" and "Mechanical Smoke
Removal Systems"), the design criteria are found within that code section or in
standards directly referenced by it.

For example, IBC Section 910.3 for smoke and heat vents typically includes
requirements based on the type of occupancy, the area of the space, and sometimes
the height of the smoke accumulation area. It may specify the number and size of
vents, their spacing, and activation methods (often heat-activated).

Mechanical smoke removal systems under IBC Section 910.4 might have airflow rates
specified in terms of air changes per hour (ACH) for the space being served, or a
minimum exhaust rate in CFM per square foot of floor area, or a total CFM based on
the building volume or number of stories. However, 23, while referencing IBC 910.4,
does not provide these specific rates, indicating that the IBC itself or referenced
standards like NFPA 204 (Standard for Smoke and Heat Venting) would need to be
consulted for these quantitative details.

The objectives of these IBC Section 910 systems can also differ from typical NFPA 92
smoke management systems. They are often aimed at:
● Limiting fire spread by venting heat and smoke.
● Maintaining lower smoke temperatures to protect structural elements.
● Improving visibility for firefighting operations.
● Facilitating post-fire smoke clearance.

These objectives may prioritize property protection and firefighting support more
heavily than maintaining a precisely defined smoke layer for occupant egress
throughout an extended period, which is common for atrium systems.

VI. Air Change Requirements in Smoke Control Design

The user query specifically asked about air change requirements. It's important to
contextualize how parameters like Air Changes per Hour (ACH) or CFM per square
foot (CFM/ft²) fit into the design of smoke control systems.

A. Contextualizing Air Changes per Hour (ACH) vs. Performance-Based Design

The design philosophy underpinning life safety smoke control systems as outlined in
NFPA 92 is fundamentally performance-based. This means systems are designed to
achieve specific outcomes related to managing smoke behavior, rather than simply
moving a fixed volume of air based on prescriptive rates like ACH.
● Smoke Containment Systems (Pressurization): These systems are designed to
achieve and maintain specific pressure differentials (e.g., 0.05 in. w.g.) across
smoke barriers.5 The airflow required to achieve this pressure is a result of the
leakage characteristics of the barriers and the desired pressure, not a
predetermined ACH rate.
● Smoke Management Systems (Large Volume Spaces): These systems are
designed to manage a smoke layer interface at a certain height or to exhaust a
calculated volumetric flow rate (CFM or m³/s) of smoke. This exhaust rate is
determined by fire dynamics principles, considering the heat release rate of the
fire, the type of smoke plume, and the geometry of the space.5 Again, this is a
performance-based calculation, not a fixed ACH or CFM/ft² value applied
 universally.

Prescriptive ventilation rates like ACH or CFM/ft² are more commonly associated with:
● General ventilation for maintaining Indoor Air Quality (IAQ) under normal building
operations.
● Dilution ventilation for controlling specific pollutants (e.g., carbon monoxide in
parking garages).
● Certain highly specific, often localized, hazard control applications or prescriptive
code requirements that fall outside the typical scope of dynamic life safety
smoke control systems designed under NFPA 92.

Applying a generic ACH value to a complex smoke control scenario like an atrium or a
stairwell pressurization system would likely be inappropriate and fail to meet the
specific performance objectives of NFPA 92. Designers must use the calculation
methods specified or referenced by NFPA 92 for these critical life safety applications.
Misapplication of ACH could lead to ineffective systems that do not provide the
intended level of protection during a fire.

B. Specific ACH or CFM/ft² Mandates Identified in Research

While not the primary basis for most NFPA 92 systems, some specific applications do
have mandated ACH or CFM/ft² rates:
● Motor Vehicle Related Occupancies (Enclosed Parking Garages - IBC/IMC):
○ For pollutant control (primarily CO and NO2), mechanical ventilation systems
are required to operate based on detector signals.23
■ When operating at full capacity, the system must provide an airflow rate
of not less than 0.75 cfm per square foot of the floor area served.
■ During standby operation (e.g., when pollutant levels are low), a minimum
airflow rate of 0.05 cfm per square foot of the floor area served is
required.
○ For post-fire smoke control or smoke removal in parking garages, some
jurisdictions, particularly those outside the USA or those referencing
standards like BS 7346-7, may require systems capable of achieving 6 to 10
Air Changes Per Hour (ACH).23 NFPA 88A, Standard for Parking Structures,
also provides guidance that may include ventilation rates for smoke
management or clearance.23
● NFPA 99 - Health Care Facilities Code (Specific Storage Rooms):
○ For certain indoor storage rooms or areas designated for the storage of
 flammable or combustible liquids (e.g., in excess of specified quantities),
NFPA 99 may require mechanical exhaust ventilation. One cited requirement
is for an exhaust rate of 1 cfm for each 5 cubic feet of fluid designed to be
stored in the space, with a minimum total exhaust of 50 cfm and a maximum
of 500 cfm.33 The mechanical exhaust inlets for such systems are to be
located within 1 foot (300 mm) of the floor and adjacent to the stored
cylinders or containers.33 This is a highly specialized requirement for local
hazard control, not for general building smoke control for life safety.
● NFPA 90A - Standard for the Installation of Air-Conditioning and Ventilating
Systems:
○ NFPA 90A does not specify ACH rates for overall smoke control design.
However, it does establish capacity thresholds for the installation of duct
smoke detectors. For example, smoke detectors are typically required in air
supply systems having a capacity greater than 2,000 cfm (cubic feet per
minute) and in return air systems under certain conditions.14 The function of
these detectors is to shut down fans or actuate dampers to prevent smoke
circulation, rather than to modulate airflow for a specific ACH-based smoke
control strategy.

The following table summarizes these specific instances where ACH or CFM/ft² rates
are mentioned:

Table 4: Specific Airflow/Air Change Rate Requirements for Specialized

Ventilation/Smoke Systems

System/ Prescriptive Rate Governing Primary Purpose

Occupancy/ (CFM/ft², ACH, or Standard/Code
Application other) Section (Examples)

Enclosed Parking ≥ 0.75 cfm/ft² IBC 406.6.2 (ref. IMC Carbon Monoxide
Garage Ventilation 404) 23 (CO) & Nitrogen
(Pollutant Control - Dioxide (NO2)
Full Operation) dilution.

Enclosed Parking ≥ 0.05 cfm/ft² IBC 406.6.2 (ref. IMC Minimum ventilation
Garage Ventilation 404) 23 for CO/NO2 control.
(Pollutant Control -
 Standby)

Enclosed Parking 6-10 ACH BS 7346-7 (example) Post-fire smoke

Garage (Post-Fire 23
; NFPA 88A clearance, aiding
Smoke Removal - firefighting.
some jurisdictions)

NFPA 99 Healthcare - 1 cfm per 5 ft³ of fluid NFPA 99 33 Localized hazard

Flammable Fluid stored (min 50 cfm, control, preventing
Storage Room max 500 cfm) vapor accumulation.
Exhaust

HVAC Systems (Duct > 2,000 cfm system NFPA 90A (Sec Threshold for
Smoke Detector capacity 6.4.2.1) 14 requiring duct smoke
Trigger) detection to prevent
smoke spread (not a
design ACH for
smoke control).

VII. Integration with HVAC Systems: NFPA 90A Requirements

The building's Heating, Ventilation, and Air-Conditioning (HVAC) system plays a
critical role in fire safety. Its design and operation, governed primarily by NFPA 90A,
must be carefully integrated with any smoke control strategy.

A. Role of HVAC in Smoke Movement and Control

NFPA 90A, Standard for the Installation of Air-Conditioning and Ventilating Systems,
covers the construction, installation, operation, and maintenance of these systems,
including their components like filters, ducts, and related equipment. A key objective
of NFPA 90A is to protect life and property from fire, smoke, and gases resulting from
a fire or similar conditions.10

Untreated, an HVAC system can become a primary pathway for the rapid spread of
smoke, toxic gases, and even flames from the area of fire origin to other parts of the
building through its interconnected ductwork.14 Therefore, NFPA 90A includes
provisions specifically aimed at preventing this distribution of smoke through supply
air ducts and, where feasible, to facilitate the exhaust of a significant quantity of
smoke to the outside. This is typically achieved by automatically shutting down fans
and/or actuating dampers upon the detection of smoke.14 The HVAC system can thus
be an adversary if uncontrolled, or an ally if properly integrated into the fire safety
plan.

B. Critical Components and Requirements (NFPA 90A)

Several components and requirements within NFPA 90A are vital for effective smoke
control:
● Duct Smoke Detectors: These devices are installed within HVAC ductwork to
detect the presence of smoke circulating in the air distribution system. NFPA 90A
specifies their required locations, such as downstream of air filters and ahead of
any branch connections in air supply systems with a capacity greater than 2,000
cfm.14 Upon detection of smoke, these detectors initiate control actions, which
may include shutting down HVAC fans, closing smoke dampers, or signaling the
fire alarm control unit. It is important to note that duct smoke detectors are
intended to prevent the spread of smoke through the HVAC system and are not a
substitute for area smoke detectors required for open area protection.14
● Fire Dampers: Fire dampers are installed in HVAC ducts where they penetrate
fire-rated barriers (such as fire walls, fire partitions, and floor assemblies) to
maintain the integrity of these separations.15 They are designed to close
automatically upon detection of heat, typically via a fusible link that melts at a
predetermined temperature, thereby preventing the passage of flames through
the duct opening.15 Fire dampers are classified as either:
○ Static: For use in HVAC systems that are designed to shut down completely
in the event of a fire.
○ Dynamic: Tested and rated for closure under airflow conditions, for use in
systems that may continue to operate during a fire (e.g., some smoke control
modes).15
● Smoke Dampers: Smoke dampers are installed in ducts that penetrate smoke
barriers or smoke partitions, or at other locations within an engineered smoke
control system, to resist the passage of smoke.15 They are designed to operate
automatically upon a signal from a smoke detection system and can often be
controlled (opened or closed) from a remote fire command station if required as
part of a smoke control strategy.15 Unlike fire dampers (which are primarily heat-
actuated and focused on flame passage), smoke dampers are leakage-rated
(e.g., Class I or II) to minimize the amount of smoke that can pass through them
when closed.15
● Combination Fire/Smoke Dampers: These dampers meet the requirements of
both UL 555 (for fire dampers) and UL 555S (for smoke dampers).15 They are used
 in duct penetrations of barriers that are required to resist the passage of both
flame and smoke. Combination dampers close upon the detection of either heat
(via a fusible link or similar device) or smoke (via a signal from a smoke
detector).15
● Fire-Rated Ductwork and Shaft Integrity: For certain smoke control
applications, particularly stairwell or elevator hoistway pressurization systems,
the ductwork delivering pressurization air may need to be fire-rated.
Pressurization ducts serving these critical shafts are considered extensions of
the shaft's own fire-resistive rating.13 NFPA 90A, in Section 5.3.4, addresses the
fire resistance of shafts. For buildings with four or more stories, stair and elevator
shafts typically require a minimum two-hour fire-resistance rating, which must
address fire exposure from both the inside and the outside of the shaft.13 If a fire-
rated duct is used as both the air conduit and the protective enclosure, it must
fully meet the criteria for a duct under NFPA 90A Section 4.3 while also providing
the required fire-resistance rating of the shaft (e.g., two hours). This often implies
the use of robust duct systems, such as those meeting Duct B (ISO)/Conditions C
& D (ASTM) criteria.13

The following table summarizes these critical NFPA 90A components:

Table 5: NFPA 90A Components Critical for Smoke Control Integration

Component Key NFPA 90A Interaction/Relevance to

Requirement/Function NFPA 92 Smoke Control
Systems

Duct Smoke Detectors Detect smoke in HVAC Prevents HVAC system from
ductwork (>2,000 cfm distributing smoke from fire
systems, etc.); initiate fan area; can initiate non-
shutdown/damper dedicated smoke control
operation.14 mode.

Fire Dampers Close on heat (fusible link) at Maintain fire

fire barrier penetrations to compartmentation. Critical for
stop flame spread.15 passive protection. May
conflict with active smoke
control if closes prematurely
 (see Insight 7.2).

Smoke Dampers Close on smoke detection at Essential for zoned smoke

smoke barrier penetrations; control (containment) and
leakage-rated to resist smoke preventing smoke migration
passage.15 via ducts in other systems.
Can be actively controlled.

Combination Fire/Smoke Close on heat or smoke; meet Used where both flame and
Dampers both fire and smoke damper smoke resistance are required
standards.15 at a duct penetration of a
rated assembly.

Fire-Rated Ducts / Shafts Shafts (e.g., stairs, elevators Essential for maintaining
in buildings $\geq$4 stories) integrity of pressurization
require 2-hr fire rating. pathways (e.g., stairwell,
Pressurization ducts serving elevator hoistway
shafts extend this rating.13 pressurization systems)
ensuring air delivery during
fire.

C. Interaction with NFPA 92 Smoke Control Systems

The interplay between NFPA 90A requirements and NFPA 92 smoke control strategies
is direct and critical:
● Non-Dedicated Systems: HVAC systems are often designed to serve a dual
purpose. Under normal conditions, they provide environmental control. In a fire
event, they can be reconfigured (via automated controls, damper repositioning,
and fan modulation) to function as a "non-dedicated" smoke control system.6
This requires careful design of the HVAC system components and controls to
meet the specific operational demands of the smoke control sequence (e.g.,
exhausting a smoke zone while pressurizing adjacent zones).
● Damper Operation in Pressurization Systems: A nuanced but critical aspect of
integrating HVAC components with smoke control systems arises with fire-rated
pressurization ducts, such as those used for stairwell pressurization. NFPA 90A
generally requires fire dampers where ducts penetrate fire-rated barriers.
However, a standard fire damper with a fusible link (typically rated around 286°F)
may activate and close at a temperature lower than the fire-rated duct itself is
designed to withstand (e.g., internal surface temperatures around 400°F during a
 fire exposure).13 If such a damper closes prematurely, it would obstruct airflow
from the pressurization fan, effectively disabling the smoke control system. In
situations where the pressurization duct itself is appropriately fire-rated (e.g.,
meeting Duct B (ISO)/Conditions C & D (ASTM) criteria) and maintains the
integrity of the fire separation, the omission of a standard fire damper that would
otherwise compromise the smoke control system's operation may be a necessary
and justifiable engineering decision.13 This ensures the life safety function of the
pressurization system is preserved. This is a sophisticated design consideration
that requires a deep understanding of both fire resistance and smoke control
principles, and it is not a blanket permission to omit dampers but rather a specific
engineering judgment for particular systems where the fire-rated duct provides
the necessary separation and the damper would be detrimental to the smoke
control system's life safety function.

VIII. ASHRAE Guidance and Key Design Considerations

While NFPA standards provide the foundational requirements for smoke control
systems, ASHRAE offers invaluable in-depth engineering guidance, particularly
through its Handbook of Smoke Control Engineering.

A. The ASHRAE Handbook of Smoke Control Engineering: A Cornerstone

Resource
The ASHRAE Handbook of Smoke Control Engineering is widely regarded as the "most
exhaustive and complete treatment of smoke control and related topics" in the United
States.17 Its development as a cooperative effort involving the ICC, NFPA, and SFPE
underscores its broad acceptance and authority within the fire protection and
building engineering communities.

The Handbook's scope is extensive, covering:

● Fundamental concepts of smoke movement and control.
● Detailed design guidance for various smoke control system types, including
stairwell pressurization, elevator pressurization, zoned smoke control, and atrium
smoke control systems.17
● Methods of analysis, ranging from algebraic equations to recommendations for
computational fluid dynamics (CFD) modeling.
● Crucial aspects of design fire analysis, including considerations for different fuel
types, heat release rates, and the influence of automatic sprinkler systems and
shielded fires.17
● System controls, fire and smoke control in specialized environments like transport
tunnels, and protocols for full-scale fire testing.17

To aid practicing engineers, for whom the Handbook is an essential resource 17, it
includes numerous example calculations, simplified instructions for using analysis
software (such as CONTAM and CFAST 17), and downloadable tools like AtriumCalc
(an Excel-based application for analyzing atrium smoke control systems) and climatic
design data for assessing wind effects at various global locations.17

B. Key Engineering Principles Emphasized by ASHRAE

ASHRAE's guidance brings a layer of engineering depth crucial for the successful
design and implementation of smoke control systems:
● Design Fire Analysis: A cornerstone of designing effective smoke management
systems, particularly for large-volume spaces like atria, is the characterization of
the design fire, primarily its Heat Release Rate (HRR). The ASHRAE Handbook
(specifically Chapter 5 in the Second Edition) provides critical information for
analyzing potential fire scenarios, considering fuel loads, the impact of sprinklers,
shielded fires, and transient fuels.17 Both NFPA 92 and ASHRAE underscore the
importance of this parameter. However, neither provides simple, universally
applicable prescriptive HRR values. NFPA 92 includes HRR in its calculation
procedures but expects the designer to determine its value. The ASHRAE
Handbook of Smoke Control Engineering offers guidance on analyzing potential
fire scenarios, considering fuel loads, the impact of sprinklers, and other
variables. This means the selection of an appropriate HRR is a significant
engineering judgment, requiring a thorough understanding of fire science
principles and careful consideration of the specific building and its use. This
decision, which profoundly impacts system sizing and cost, must be well-
documented and defensible.
● Environmental Factors:
○ Wind Effects: Wind can have a profound impact on the performance of
smoke control systems, affecting pressure differentials across building
envelopes, the behavior of smoke plumes, the effectiveness of natural vents,
and the performance of makeup air inlets and exhaust outlets. ASHRAE
dedicates specific guidance (e.g., Chapter 25 of the Handbook) to
understanding and mitigating these adverse wind impacts.17
○ Stack Effect: In taller buildings, temperature differences between the interior
and exterior create vertical pressure gradients known as the stack effect. This
 can significantly influence smoke movement and the performance of
pressurization systems. ASHRAE provides methods to analyze and account
for stack effect in smoke control design.19
● Pressure Differentials: For smoke containment systems, ASHRAE offers detailed
analytical methods for calculating required pressure differentials. These methods
consider not only the buoyancy forces of hot smoke but also the influences of
stack effect and wind, as well as the practical constraint of allowable door
opening forces.19 The Handbook often suggests minimum design pressure
differences based on calculated fire gas temperatures and incorporates safety
factors.19
● Airflow Design:
○ Makeup Air Velocity: ASHRAE's guidance generally aligns with NFPA 92 in
recommending limits on makeup air velocity (e.g., typically not exceeding 200
fpm or 1.02 m/s) in critical areas to prevent adverse disruption of smoke
plumes or occupant discomfort.5
○ Opposed Airflow: The Handbook provides methodologies for designing
opposed airflow systems used to prevent smoke migration through fixed
openings between smoke control zones, including considerations for airflow
velocity limits (e.g., not exceeding 200 fpm directed towards the fire).31
○ Parking Garage Ventilation: The ASHRAE Handbook—HVAC Applications 34
presents a calculation-based approach for designing parking garage
ventilation systems, which can differ from the more prescriptive, fixed-
multiplier methods found in some codes like the IMC. For smoke control in
parking garages, a critical airflow velocity of 10 fps (3 m/s) is often cited as a
design target to move smoke away from means of egress.34
○ Stack Exhaust Velocity (Specialized Applications): For applications like
laboratory exhaust systems where contaminant dilution and plume rise are
primary concerns (distinct from life safety smoke exhaust), ASHRAE
recommends significantly higher stack exhaust velocities (e.g., 2000-4000
fpm, with NFPA 45 suggesting a minimum of 3000 fpm for some lab stacks)
to ensure effective dispersion.35
● Tenability Analysis: A common requirement for smoke management systems,
particularly those designed to protect occupants during egress from large
spaces, is to ensure that tenable conditions (regarding temperature, toxicity, and
visibility) are maintained. The ASHRAE Handbook provides methodologies and
data to support these tenability analyses, which are often beyond the direct
prescriptive scope of NFPA 92.5
 ● System Reliability and Balanced Approach: ASHRAE promotes a "balanced
approach" to fire protection, where smoke control is one component of an
integrated strategy that also includes detection, suppression, and
compartmentation. The concept is that if one fire safety feature is compromised,
other features will continue to provide a level of protection. The Handbook also
addresses considerations for smoke control system reliability.17
● Calculation Methodologies: ASHRAE provides a wealth of detailed calculational
procedures for various smoke control systems, often offering more in-depth
treatment and considering more variables than might be found directly in NFPA
standards.5 This includes algebraic methods for hand calculations as well as
guidance on the application of more sophisticated computer modeling tools like
CONTAM (for multizone airflow and contaminant transport) and CFAST (a zone
fire model).17

While NFPA standards like NFPA 92 define what performance objectives a smoke
control system must achieve (e.g., maintain a certain pressure, keep a smoke layer
above a certain height), ASHRAE's Handbook of Smoke Control Engineering and
related resources provide the detailed engineering "how-to." This includes the
analytical methods, complex calculations, and consideration of nuanced variables
(like wind behavior, specific fire characteristics, and detailed leakage path analysis)
needed to actually design a system to meet those objectives reliably. This makes
ASHRAE's guidance indispensable for engineers tackling complex smoke control
designs, ensuring that systems are not only compliant with the letter of NFPA
standards but are also robust and effective under real-world conditions.

The following table highlights key areas where ASHRAE provides critical design
considerations:

Table 6: Key ASHRAE Design Considerations & Guidance for Smoke Control

Design Summary of ASHRAE Typical ASHRAE Handbook

Aspect/Consideration Guidance/Methodology Reference (Example)

Design Fire Selection & Analysis of fuel loads, fire Handbook of Smoke Control
Characterization (HRR) growth, sprinkler effects; Engineering, Ch. 5 ("Fire
methods to estimate HRR. Development and Design
Guidance on transient vs. Fires")
 steady-state fires.17

Wind Effect Analysis Methods to assess wind Handbook of Smoke Control

pressure coefficients, impact Engineering, Ch. 25 ("Wind
on openings, makeup air, and Effects")
exhaust. Use of climatic data
and wind roses.17

Stack Effect in Tall Buildings Calculation of pressure Handbook of Smoke Control

differentials due to Engineering, Ch. 8 ("Stack and
temperature differences; Wind Effects") (Typical
impact on stairwell/elevator content area)
pressurization and zoned
systems.19

Tenability Criteria & Analysis Data on human tolerance to Handbook of Smoke Control
heat, smoke, and irritant Engineering, Ch. 6
gases; methods for predicting ("Tenability") (Typical content
conditions within spaces and area)
comparing to tenability limits.5

Air Leakage Path Estimation Guidance on identifying and Handbook of Smoke Control
quantifying leakage areas Engineering, Ch. 11 ("Flow
through building construction, Areas") (Typical content area)
doors, windows for
pressurization calculations.5

Makeup Air Design for Sizing, location, and velocity Handbook of Smoke Control
Exhaust Systems limits for makeup air to Engineering, Ch. 15 ("Atrium
support exhaust systems Smoke Control") (Typical
without disrupting plumes or content area for atria)
causing adverse conditions.5

Pressure Differential Detailed methods for Handbook of Smoke Control

Calculations calculating pressure Engineering, Ch. 9 ("Basics of
differences required for Passive and Pressurization
smoke containment, Systems")
considering fire buoyancy,
 wind, stack effect, and door
forces.19

Software Application Examples and simplified Handbook of Smoke Control

Guidance instructions for using tools Engineering, Appendices or
like AtriumCalc, CONTAM, relevant chapters.
CFAST for analysis.17

IX. Conclusion and Recommendations

The design and implementation of effective smoke control, smoke containment, and
smoke management systems are critical for life safety and property protection in
modern buildings. This analysis, based on key NFPA and ASHRAE standards, reveals a
complex but structured framework guiding these efforts.

A. Summary of Key Principles and Standard Interdependencies

Smoke control strategies are broadly categorized by NFPA 92 into smoke
containment systems, which use pressurization to prevent smoke spread (e.g., in
stairwells, elevator shafts, or between zones), and smoke management systems,
which aim to control smoke movement and maintain tenable conditions in large
volume spaces (e.g., atriums, malls) typically through smoke exhaust or by managing
smoke layer height. The term "smoke removal" is generally a functional descriptor for
actions achieved by these systems or by specific code-mandated ventilation for
particular hazards, rather than a distinct third classification under NFPA 92.

Crucially, the mandate for when and where these systems are required does not stem
from NFPA 92 itself. Instead, these requirements are established by the locally
adopted building codes (e.g., International Building Code) and life safety codes (e.g.,
NFPA 101, Life Safety Code), based on occupancy type, building geometry, height,
and specific hazards. Once mandated, NFPA 92 provides the comprehensive
standard for the design, installation, testing, and maintenance of the smoke control
system.

Effective smoke control is not achieved by applying a single standard in isolation. It

demands a holistic, integrated design process that synthesizes requirements from
multiple codes and standards. This involves:
1. Governing Building/Life Safety Codes (e.g., IBC, NFPA 101): Determine if and
where a system is needed.
 2. NFPA 92 (Standard for Smoke Control Systems): Dictates how the smoke control
system itself should be designed, including performance objectives, calculation
methodologies for smoke management, and pressure differential requirements
for containment.
3. NFPA 90A (Standard for the Installation of Air-Conditioning and Ventilating
Systems): Governs the critical integration with HVAC systems, including
requirements for ductwork, fire dampers, smoke dampers, and controls that are
essential for preventing smoke spread via air distribution systems or for utilizing
HVAC components in non-dedicated smoke control strategies.
4. ASHRAE Guidance (primarily the Handbook of Smoke Control Engineering):
Provides the in-depth engineering principles, detailed calculation methodologies,
data on fire dynamics, and analysis techniques for complex variables (such as
design fire characterization, wind effects, stack effect, and tenability
assessments) that are essential for robustly designing systems to meet NFPA
requirements.

A failure to consider any of these interconnected elements can lead to system

incompatibilities, non-compliance, or, most critically, a system that fails to perform its
intended life safety function during a fire.

B. Emphasis on Qualified Engineering and AHJ Consultation

The design of smoke control systems, particularly for complex buildings or
challenging scenarios, is a sophisticated engineering endeavor. It requires competent
and qualified professionals, typically fire protection engineers and mechanical
engineers, who possess a thorough understanding of fire dynamics, fluid mechanics,
heat transfer, building construction, and the specific requirements of all relevant
codes and standards.6

While codes and standards provide prescriptive rules and calculation methods, the
design of smoke control systems inherently involves significant engineering judgment.
This is particularly true in areas such as selecting an appropriate design fire (Heat
Release Rate), accurately estimating air leakage paths in complex building envelopes,
accounting for unique architectural geometries, assessing the impact of variable
environmental conditions like wind and stack effect, and interpreting performance-
based objectives. This judgment must be exercised by qualified professionals, be
thoroughly informed by fire science principles and best practices, and be
meticulously documented to support the design rationale.
Given the complexity and critical life safety implications, early and ongoing
consultation with the Authority Having Jurisdiction (AHJ) is highly recommended. This
collaborative approach helps to establish clear agreement on design objectives, the
selection of design fire scenarios, proposed calculation methodologies, assumptions
made in the design, and the criteria for acceptance testing, ultimately facilitating a
smoother approval process and a more effective system.

C. The Evolving Landscape of Smoke Control

The field of smoke control is not static. Standards are periodically updated to reflect
new research, technological advancements, and lessons learned from fire incidents.
For example, NFPA 92 has seen recent updates in its 2024 edition, including revised
definitions and testing requirements.2 Similarly, ASHRAE continues to conduct
research (e.g., on pressurized stairwells, atrium smoke control 18) and develop new
guidance, such as the recent Guideline 44-2024 addressing protection from wildfire
smoke.21 This underscores the importance for professionals involved in the design,
installation, and maintenance of smoke control systems to engage in continuous
professional development and stay abreast of the latest revisions to codes,
standards, and engineering best practices.

In conclusion, ensuring the safety of building occupants through effective smoke

control requires a diligent application of established standards, a deep understanding
of engineering principles, and a commitment to integrated design. By carefully
navigating the requirements of NFPA 92, NFPA 90A, and leveraging the
comprehensive guidance provided by ASHRAE, designers can create systems that
significantly reduce the risks associated with smoke in building fires.

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