ISO 24678-4:2023
(Main)Fire safety engineering — Requirements governing algebraic formulae — Part 4: Smoke layers
Fire safety engineering — Requirements governing algebraic formulae — Part 4: Smoke layers
This document specifies the requirements governing the application of a set of explicit algebraic formulae for the calculation of specific characteristics of smoke layers.
Ingénierie de la sécurité incendie — Exigences régissant les formules algébriques — Partie 4: Couches de fumée
Le présent document spécifie les exigences qui régissent l’application d’un ensemble de formules algébriques explicites pour le calcul de caractéristiques spécifiques des couches de fumée.
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INTERNATIONAL ISO
STANDARD 24678-4
First edition
2023-06
Fire safety engineering —
Requirements governing algebraic
formulae —
Part 4:
Smoke layers
Ingénierie de la sécurité incendie — Exigences régissant les formules
algébriques —
Partie 4: Couches de fumée
Reference number
ISO 24678-4:2023(E)
© ISO 2023
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ISO 24678-4:2023(E)
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ISO 24678-4:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Requirements governing the description of physical phenomena.2
5 Requirements governing the calculation process. 3
6 Requirements governing limitations . 3
7 Requirements governing input parameters . 3
8 Requirements governing the domain of applicability . 3
9 Example of documentation . 3
Annex A (informative) Formulae for smoke layers in an enclosure . 4
Bibliography .33
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ISO 24678-4:2023(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO document should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use
of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed
patent rights in respect thereof. As of the date of publication of this document, ISO had not received
notice of (a) patent(s) which may be required to implement this document. However, implementers are
cautioned that this may not represent the latest information, which may be obtained from the patent
database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all
such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 4, Fire
safety engineering.
This first edition cancels and replaces ISO 16735:2006, which has been technically revised.
The main changes are as follows:
— the main body has been simplified by making reference to ISO 24678-1;
— the arrival time of smoke front has been introduced in the calculations of smoke filling time in
Annex A;
— comparisons with experimental data have been added in Annex A.
A list of all parts in the ISO 24678 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO 24678-4:2023(E)
Introduction
The ISO 24678 series is intended to be used by fire safety practitioners involved with fire safety
engineering calculation methods. It is expected that the users of this document are appropriately
qualified and competent in the field of fire safety engineering. It is particularly important that users
understand the parameters within which particular methodologies may be used.
Algebraic formulae conforming to the requirements of this document are used with other engineering
calculation methods during a fire safety design. Such a design is preceded by the establishment of a
context, including the fire safety goals and objectives to be met, as well as performance criteria when a
trial fire safety design is subjected to specified design fire scenarios. Engineering calculation methods
are used to determine if these performance criteria are met by a particular design and if not, how the
design needs to be modified.
The subjects of engineering calculations include the fire-safe design of entirely new built environments,
such as buildings, ships or vehicles, as well as the assessment of the fire safety of existing built
environments.
The algebraic formulae discussed in this document can be useful for estimating the consequences of
design fire scenarios. Such formulae are valuable for allowing the practitioner to quickly determine
how a proposed fire safety design needs to be modified to meet performance criteria and to compare
among multiple trial designs. Detailed numerical calculations can be carried out up until the final
design documentation. Examples of areas where algebraic formulae have been applicable include
determination of convective and radiative heat transfer from fire plumes, prediction of ceiling jet flow
properties governing detector response times, calculation of smoke transport through vent openings,
and analysis of compartment fire hazards such as smoke filling and flashover. However, the simple
models often have stringent limitations and are less likely to include the effects of multiple phenomena
occurring simultaneously in the design scenarios.
The general principles of fire safety engineering are described in ISO 23932-1, which provides a
performance-based methodology for engineers to assess the level of fire safety for new or existing built
environments. Fire safety is evaluated through an engineered approach based on the quantification
of the behaviour of fire and based on knowledge of the consequences of such behaviour on life safety,
property and the environment. ISO 23932-1 provides the process (i.e. necessary steps) and essential
elements for conducting a robust performance-based fire safety design.
ISO 23932-1 is supported by a set of fire safety engineering documents on the methods and data
needed for all the steps in a fire safety engineering design as summarized in Figure 1 (taken from
ISO 23932-1:2018, Clause 4). This set of documents is referred to as the Global fire safety engineering
analysis and information system. This global approach and system of standards provides an awareness
of the interrelationships between fire evaluations when using the set of fire safety engineering
documents. The set of documents includes ISO/TS 13447, ISO 16730-1, ISO 16732-1, ISO 16733-1,
ISO/TS 16733-2, ISO/TR 16738, ISO 24678-1, ISO 24679-1, ISO/TS 29761 and other supporting Technical
Reports that provide examples of and guidance on the application of these documents.
Each document supporting the global fire safety engineering analysis and information system includes
language in the introduction to tie that document to the steps in the fire safety engineering design
process outlined in ISO 23932-1. ISO 23932-1 requires that engineering methods be selected properly to
predict the fire consequences of specific scenarios and scenario elements (ISO 23932-1:2018, Clause 12).
Pursuant to the requirements of ISO 23932-1, this document provides the requirements governing
algebraic formulae for fire safety engineering. This step in the fire safety engineering process is shown
as a highlighted box in Figure 1 and described in ISO 23932-1.
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ISO 24678-4:2023(E)
a
See also ISO/TR 16576 (Examples).
b
See also ISO 16732-1, ISO 16733-1, ISO/TS 16733-2, ISO/TS 29761.
c
See also ISO 16732-1, ISO 16733-1, ISO/TS 16733-2, ISO/TS 29761.
d
See also ISO/TS 13447, ISO 16730-1, ISO/TR 16730-2 to ISO/TR 16730-5 (Examples), ISO/TR 16738, ISO
24678-1, ISO 24678-2, ISO 24678-3, ISO 24678-4 (this document), ISO 24678-5, ISO 24678-6, ISO 24678-7
and ISO 24678-9.
e
See also ISO/TR 16738, ISO 16733-1, ISO/TS 16733-2.
NOTE Documents linked to large parts of the fire safety engineering design process: ISO 16732-1,
ISO 16733-1, ISO 24678-1, ISO 24679-1, ISO/TS 29761, ISO/TR 16732-2 and ISO/TR 16732-3 (Examples),
ISO/TR 24679-2 to ISO/TR 24679-4, ISO/TR 24679-6, ISO/TR 24679-8 (Examples).
Figure 1 — Flow chart illustrating the fire safety engineering (FSE) design process (adapted
from ISO 23932-1:2018)
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INTERNATIONAL STANDARD ISO 24678-4:2023(E)
Fire safety engineering — Requirements governing
algebraic formulae —
Part 4:
Smoke layers
1 Scope
This document specifies the requirements governing the application of a set of explicit algebraic
formulae for the calculation of specific characteristics of smoke layers.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 13943, Fire safety — Vocabulary
ISO 24678-1, Fire safety engineering — Requirements governing algebraic formulae — Part 1: General
requirements
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
boundary
surface that defines the extent of an enclosure
3.2
enclosure
room, space or volume that is bounded by surfaces
3.3
fire plume
upward turbulent fluid motion generated by a source of buoyancy that exists by virtue of combustion
and often includes an initial flaming region
3.4
fire source diameter
effective diameter of the fire source, equal to the actual diameter for a circular source or the diameter
of a circle having an area equal to the plan area of a non-circular source
3.5
flow coefficient
fraction of effective flow area over total area of a vent
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ISO 24678-4:2023(E)
3.6
fuel mass burning rate
mass generation rate of fuel vapours
3.7
heat release rate
rate at which heat is actually being released by a source of combustion (such as the fire source)
3.8
interface position
elevation of the smoke layer interface relative to a reference elevation
Note 1 to entry: It is also referred to as the smoke layer height.
3.9
quasi-steady state
state in which it is assumed that the full effects of heat release rate changes at the fire source are felt
everywhere in the flow field immediately
3.10
smoke layer
relatively homogeneous volume of smoke that forms and accumulates beneath the boundary having the
highest elevation in an enclosure as a result of a fire
Note 1 to entry: This is also referred to as the hot upper layer and the hot gas layer.
3.11
smoke layer interface
horizontal plane separating the smoke layer from the lower, smoke-free layer
3.12
species yield
mass of a combustion product species generated by the combustion of unit mass of combustibles
3.13
thermal inertia
parameter representing the ability of enclosure materials to absorb heat, calculated by the square root
of the product of thermal conductivity, density and specific heat of the material
3.14
vent
opening in an enclosure boundary through which air and smoke can flow as a result of naturally- or
mechanically-induced forces
3.15
vent flow
flow of smoke or air through a vent in an enclosure boundary
4 Requirements governing the description of physical phenomena
4.1 The requirements governing the description of physical phenomena as specified in ISO 24678-1
apply, in addition to the requirements specified in the following subclauses.
4.2 The buoyant smoke layer resulting from a fire source in an enclosure is a complex thermo-physical
phenomenon that can be highly transient or nearly steady state. In addition to buoyancy, smoke layers
can be influenced by dynamic forces due to wind and mechanical fans.
4.3 Smoke layer characteristics to be calculated and their useful ranges shall be clearly identified,
including those characteristics inferred by association with calculated quantities (e.g. the association
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ISO 24678-4:2023(E)
of smoke mass fraction with excess gas temperature based on the analogy between energy and mass
conservation) and those associated with heat exposure to objects and occupants by the smoke layer, if
applicable.
5 Requirements governing the calculation process
The requirements specified in ISO 24678-1 governing the calculation process apply.
6 Requirements governing limitations
The requirements specified in ISO 24678-1 governing limitations apply.
7 Requirements governing input parameters
The requirements specified in ISO 24678-1 governing input parameters apply.
8 Requirements governing the domain of applicability
The requirements specified in ISO 24678-1 governing the domain of applicability apply.
9 Example of documentation
An example of documentation meeting the requirements in Clauses 4 to 8 is given in Annex A.
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ISO 24678-4:2023(E)
Annex A
(informative)
Formulae for smoke layers in an enclosure
A.1 Scope
This annex is intended to describe the methods that can be used to calculate interface position, average
temperatures and average mass fractions of specific chemical species of smoke layers that form beneath
boundaries during a fire in an enclosure. These calculation methods are based on the principles of mass,
species and energy conservations as applied to the smoke layer as a thermodynamic control volume. In
this annex, four different sets of formulae are provided. One is for the smoke filling process in a single
enclosure during the initial stage of fire. The other three sets are for steady state smoke control by
mechanical exhaust or by natural vents.
A.2 Symbols and abbreviated terms used in this annex
2
A floor area of enclosure (m )
2
A area of a side vent (m )
side
2
A area of a ceiling vent (m )
top
2
A surface area of enclosure boundary in contact with smoke layer (m )
wall
B width of a side vent (m)
c specific heat of enclosure boundary material (kJ/kg·K)
c specific heat of air at constant pressure (=1,0) (kJ/kg·K)
p
C flow coefficient
D
D thickness of enclosure boundary material (m)
wall
D fire source diameter (m)
2
g acceleration due to gravity (m/s )
2
h effective heat transfer coefficient of enclosure boundary (kW/m ·K)
wall
H height of enclosure (m)
H height of lower bound of a side vent (m)
l
H height of upper bound of a side vent (m)
U
k thermal conductivity of enclosure boundary material (kW/m·K)
1/2 2
thermal inertia of enclosure boundary material (kW·s /m ·K)
kcρ
L mean flame height (m)
m
mass flow rate of air coming into an enclosure (kg/s)
a
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ISO 24678-4:2023(E)
m
mass flow rate of smoke exhaust (kg/s)
e
m
error in mass flow rate (kg/s)
error
m
mass flow rate of gases in fire plume (kg/s)
p
heat release rate of a fire source (kW)
Q
heat release rate of a steady fire source (kW)
Q
0
t time (s)
t arrival time of plume front at ceiling (s)
ar
t characteristic time for heat absorption by enclosure boundary (s)
c
T reference temperature, often taken by outside temperature (K)
0
T smoke layer temperature (K)
s
3
V volumetric flow rate of mechanical exhaust system (m /s)
e
Y mass fraction of specific chemical species (kg/kg)
Y mass fraction of specific chemical species at reference state (kg/kg)
0
z interface position above base of fire source (m)
2
α fire growth rate of time-squared growing fires (kW/s )
β fire growth rate of linearly growing fires (kW/s)
ΔH heat of combustion (kJ/kg)
c
Δp pressure difference (Pa)
η species yield (kg/kg)
λ fraction of heat absorbed by enclosure boundary during smoke filling period
3
ρ gas density of air at reference temperature (kg/m )
0
3
ρ gas density of smoke (kg/m )
s
3
ρ density of enclosure boundary material (kg/m )
A.3 Description of physical phenomena addressed by the formula set
A.3.1 General descriptions of calculation method
A.3.1.1 Calculation procedure
Estimating the smoke layer properties involves the following steps:
— determination of characteristics of the fire source (burning area, fuel mass burning rate, etc.);
— calculation of the height of the smoke layer interface;
— calculation of the temperature and mass fraction of chemical species in the smoke layer.
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ISO 24678-4:2023(E)
A.3.1.2 Smoke layer properties to be calculated
The formula set provides interface position, average gas temperature and mass fractions of chemical
species. Uniform temperature and mass fractions are assumed over the entire smoke layer volume.
A.3.2 Scenario elements to which the formula set is applicable
The formula set is applicable to smoke layers above a fire source in a quiescent environment. If flow-
disturbance by non-fire related phenomena is significant, the formula set is not applicable. For example,
the effect of airflow caused by heating, ventilation and air conditioning (HVAC) systems or by external
wind should be considered if they have a significant effect. If active fire suppression systems, such as
sprinklers, interact significantly with the smoke layer, the formula set is not applicable.
The fire source needs to be small enough so that the mean flame height is lower than the interface
position and the characteristic plume width is less than the width of the enclosure (subject to additional
restrictions imposed by the formulae used to obtain plume characteristics).
Methods to calculate smoke layer properties are developed for two limit stages. One limit stage is
a simple enclosure smoke filling process during the initial stage of the fire when the smoke control
system is not yet in operation. The other limit stage is a quasi-steady vented condition when the smoke
production rate equals the rate of outflow from the smoke layer. An intermediate stage (i.e. smoke
filling is still occurring even though a smoke venting system is in operation) is not treated in this Annex.
A.3.3 Self-consistency of the formula set
The formula set provided in this annex has been derived and reviewed by many researchers (see
Clause A.5) to ensure that calculation results from different formulae in the set are consistent (i.e. do
not produce conflicts).
A.3.4 International Standards and other documents where the formula set is used
None specified.
A.4 Formula-set documentation of calculation procedure
A.4.1 General description of calculation methods
A.4.1.1 Basic assumptions
As shown in Figure A.1, a smoke layer is generated over a fire source in an enclosure. Smoke is
accumulated in the upper part of an enclosure as a result of burning. It is assumed that smoke forms a
layer of fairly uniform temperature and species mass fraction. Based on the principles of mass, species
and energy conservations applied to the smoke layer, average values of temperature, species mass
[27],[28],[29]
fraction and interface position are calculated. Descriptions of fire plumes and vent flows are
given in ISO 24678-2 and ISO 24678-5, respectively.
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ISO 24678-4:2023(E)
Key
1 fire source
2 plume flow
3 vent flow
4 smoke layer (control volume)
5 heat absorption by enclosure boundary
6 heat flow
7 mass flow
Figure A.1 — General heat and mass conservation of smoke layer in an enclosure with a fire
source
A.4.1.2 Mass conservation
Conservation of mass in the smoke layer is considered over an appropriately chosen control volume as
shown in Figure A.1 by broken lines. The mass flow rate incoming across each interface (negative for
outgoing flow) of the control volume is equal to the rate of mass accumulation in the smoke layer. Plume
flow, vent flows and other flows are considered where necessary.
A.4.1.3 Energy conservation
Conservation of energy in the smoke layer is considered in a similar way to mass conservation. The
energy flow rate incoming across each interface (negative for outgoing flow) of the control volume
is equal to the rate of energy accumulation in the smoke layer. In addition to plume and vent flows,
radiation losses and heat absorption by the enclosure boundary are considered appropriately.
NOTE When it is difficult to determine the radiation heat loss from the flame, the energy flow rate from the
fire plume can be approximated by the total heat release rate.
A.4.1.4 Conservation of specific chemical species
Mass conservation of specific chemical species is considered in a similar way to total mass conservation.
In addition, if the gas phase chemical reaction can take place in the smoke layer, the reaction rate can be
considered appropriately.
A.4.1.5 Mass flow rate of fire plume through interface position
The mass flow rate of the fire plume at the interface position (bottom surface of smoke layer) is given
as a function of the heat release rate of the fire and the vertical distance between the base of the fire
source and the interface position. An example of a set of explicit formulae for mass flow rate is given in
ISO 24678-2.
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ISO 24678-4:2023(E)
A.4.1.6 Mass flow rate of smoke through vent
The mass flow rate through a vent is given as a function of the temperatures of the smoke layer and
those of the adjacent enclosures, the pressure differences between the smoke layer and the adjacent
enclosures, the vent width, and the vent height. Examples of explicit formulae for vent flows are given
in ISO 24678-5.
A.4.1.7 Equation of state
Smoke temperature and density are correlated by the equation of state. Typically, smoke is approximated
by an ideal gas whose properties are identical with air.
A.4.2 Enclosure smoke filling
A.4.2.1 Scenario element
Until the interface descends to the upper edge of a vent, smoke is accumulated in the upper part of an
enclosure as shown in Figure A.2. Due to thermal expansion, excess air is pushed out of the enclosure.
NOTE This assumption is valid as long as the smoke layer interface is above the upper boundary of the side
vent. After the smoke layer interface descends below the upper boundary of the side vent, smoke flows out of
enclosure while fresh air flows into the enclosure.
Key
1 fire source
2 plume flow
3 smoke layer
4 excess air pushed out due to thermal expansion
Figure A.2 — Mass conservation during enclosure smoke filling process
The interface position is given by Formula (A.1):
∂z
−ρ A =m (A.1)
sp
∂t
The mass flow rate of plume at the interface position, z (m), above the fire source, is given by
[30]
Formulae (A.2):
13//53
mQ=0,076 z (A.2)
p
NOTE Formula (A.2) is an approximation of the plume formula described in ISO 24678-2:2022, Annex A. This
formula is valid only above the mean flame height. If the interface position is lower than the mean flame height,
calculation results can be inaccurate.
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ISO 24678-4:2023(E)
The formula set is constructed for steady state fires, linearly growing fires and time-squared growing
fires, as expressed in Formula (A.3):
Q (steadystate fires)
0
Qt()= βt (linearly growingfires) (A.3)
2
αt (time--squared growingfires)
A.4.2.2 Interface position
Interface position is calculated so that plume mass flow accumulates in the upper layer of uniform
[31]
density. By inserting Formulae (A.2) and (A.3) into Formula (A.1) and integrating with respect to
time, Formula (A.4) is derived:
−32/
0,076 2 1
13/
Qt()−+t (steadystatefirres)
ar
0
23/
ρ A 3
H
s
−32/
0,076 1 1
13//43
zt()= β ()tt−+ (linearly growiingfires) (A.4)
ar
23/
ρ A 2
H
s
−32/
0,076 2 1
13//53
α ()tt−+ (time-squuared fires)
ar
23/
ρ A 5
s H
where the arrival time of plume front to ceiling is given for a steady state fire as shown in
[32][33]
Formula (A.5):
−13/ 43/
tQ=17, H (A.5)
ar
0
In case of linearly growing and time-squared fires, the explicit form for the arrival time is not known,
but Formula (A.5) can be applied by using a conservative estimate of the heat release rate. For linearly
growing fires, approximating that heat release rate is constant and equal to βt during 0 to t
ar ar,
Formula (A.6) applies:
−13//43
tt=17,(β ) H (A.6)
ar ar
This results in Formula (A.7):
−14/
tH=14, 9β (A.7)
ar
Similarly, in case of time-squared fires, Formula (A.8) is applicable:
−15//45
tH=13, 7α (A.8)
ar
To calculate interface position, it is necessary to assume the gas density of smoke. For practical
applications, ρ =1,0 gives conservative results for the initial smoke filling process in large enclosures.
s
During the latter stage of smoke filling, thermal expansion is significant. In such cases, Formula (A.9) is
2
[34],[35]
applicable for time-squared-fires (i.e. Qt=α ):
95/
ΛX
zX()=−H(1 ) (A.9)
1−TT/
s 0
where Formulae (A.10) and (A.11) provide the values for X and Λ:
23/
H
13//53
Xt=−0,(026 8α t ) (A.10)
ar
A
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ISO 24678-4:2023(E)
45/
A
25/
Λ=−0,(754 1 λα) (A.11)
11/5
H
A.4.2.3 Smoke layer temperature
Heat released by a fire is accumulated in a smoke layer of volume A(H-z). The smoke layer temperature
is calculated using Formula (A.12). A fraction of λ of released heat is assumed to be absorbed by the
enclosure boundary.
Qt()−t (steadystatefires)
0 ar
()1−λ β
2
Tt()=+T (tt− ) (linearly growingfires) (A.12)
s 0 aar
cAρ ()Hz− 2
ps
α
3
()tt− (time-squaredfires)
ar
3
NOTE 1 The value of λ = 0,3 is conventionally used during the initial smoke filling. For precise calculations,
coupling convective and radiative heat transfer between plume, smoke layer and enclos
...
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Smoke layers
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ii
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
---------------------- Page: 2 ----------------------
ISO/DIS 24678-4:2022(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and Definitions .1
4 Requirements governing description of physical phenomena . 1
5 Requirements governing calculation process . 2
6 Requirements governing limitations . 2
7 Requirements governing input parameters . 2
8 Requirements governing domain of applicability . 2
9 Example of documentation . 2
Annex A (informative) Formulae for smoke layers in an enclosure . 3
Bibliography for Annex A .31
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ISO/DIS 24678-4:2022(E)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 92, Fire safety, Subcommittee SC 4, Fire
safety engineering.
This second edition cancels and replaces the first edition (ISO 16735:2006), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the main body was simplified by making reference to Part 1 of this standard;
— arrival time of smoke front was introduced in the calculations of smoke filling time in Annex A;
— comparisons with experimental data were added in Annex A;
A list of all parts in the ISO 24678 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
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ISO/DIS 24678-4:2022(E)
Introduction
This document is intended to be used by fire safety practitioners involved with fire safety engineering
calculation methods. It is expected that the users of this document are appropriately qualified and
competent in the field of fire safety engineering. It is particularly important that the users understand
the parameters within which particular methodologies can be used.
Algebraic formulae conforming to the requirements of this standard are used with other engineering
calculation methods during a fire safety design. Such a design is preceded by the establishment of a
context, including the fire safety goals and objectives to be met, as well as performance criteria when
a trial fire safety design is subject to specified design fire scenarios. Engineering calculation methods
are used to determine if these performance criteria are met by a particular design and if not, how the
design needs to be modified.
The subjects of engineering calculations include the fire safety design of entirely new built
environments, such as buildings, ships or vehicles as well as the assessment of the fire safety of existing
built environments.
The algebraic formulae discussed in this standard can be useful for estimating the consequences of
design fire scenarios. Such formulae are valuable for allowing the practitioner to quickly determine
how a proposed fire safety design needs to be modified to meet performance criteria and to compare
among multiple trial designs. Detailed numerical calculations can be carried out until the final
design documentation. Examples of areas where algebraic formulae have been applicable include
determination of convective and radiative heat transfer from fire plumes, prediction of ceiling jet flow
properties governing detector response times, calculation of smoke transport through vent openings,
and analysis of compartment fire hazards such as smoke filling and flashover. However, the simple
models often have stringent limitations and are less likely to include the effects of multiple phenomena
occurring in the design fire scenarios.
The general principles are described in ISO 23932-1, which provides a performance-based methodology
for engineers to assess the level of fire safety for new or existing built environments. Fire safety is
evaluated through an engineered approach based on the quantification of the behaviour of fire and
based on knowledge of the consequences of such behaviour on life safety, property and the environment.
ISO 23932-1 provides the process (i.e., necessary steps) and essential elements to conduct a robust
performance-based fire safety design.
ISO 23932-1 is supported by a set of fire safety engineering International Standards and Technical
Specifications available on the methods and data needed for the steps in a fire safety engineering design
summarized in Figure 1 (taken from ISO 23932-1:2018, Clause 4). This set of documents is referred to
as the Global fire safety engineering analysis and information system. This global approach and system
of standards provides an awareness of the interrelationships between fire evaluations when using
the set of fire safety engineering documents. The set includes ISO 16732-1, ISO 16733-1, ISO 16734,
ISO 16735, ISO 16736, ISO 16737, ISO 24678, ISO/TS 24679, ISO 16730-1, ISO/TS 29761, ISO/TS 13447,
and other supporting Technical Reports that provide examples of and guidance on the application of
these documents.
Each document supporting the global fire safety engineering analysis and information system includes
language in the introduction to tie that document to the steps in the fire safety engineering design
process outlined in ISO 23932-1. ISO 23932-1 requires that engineering methods be selected properly to
predict the fire consequences of specific scenarios and scenario elements. (ISO 23932:2018, Clause 12)
Pursuant to the requirements of ISO 23932-1, this document provides the requirements governing
algebraic formulae for fire safety engineering. This step in the fire safety engineering process is shown
as a highlighted box in Figure 1 and described in ISO 23932-1.
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ISO/DIS 24678-4:2022(E)
a
See also ISO/TR 16576 (Examples).
b
See also ISO 16732-1, ISO 16733-1, ISO/TS 29761.
c
See also ISO 16732-1, ISO 16733-1, ISO/TS 29761.
d
See also ISO/TS 13447, ISO 16730-1, ISO/TR 16730-2 to 5 (Examples), ISO/TR 16738, ISO 24678.
e
See also ISO/TR 16738, ISO 16733-1.
NOTE Documents linked to large parts of the fire safety engineering design process: ISO 16732-1,
ISO 16733-1, ISO 24678, ISO/TS 24679-1, ISO/TS 29761, ISO/TR 16732-2 and ISO/TR 16732-3 (Examples),
ISO/TR 24679-2, ISO/TR 24679- 4, ISO/TR 24679-5 and ISO/TR 24679-6 (Examples).
Figure 1 — Flow chart illustrating the fire safety engineering design process
(from ISO 23932-1:2018)
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DRAFT INTERNATIONAL STANDARD ISO/DIS 24678-4:2022(E)
Fire Safety Engineering - Requirements governing
algebraic formulae —
Part 4:
Smoke layers
1 Scope
This document specifies the requirements governing the application of explicit algebraic formula sets
to the calculation of specific characteristics of smoke layers.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For undated references, the latest edition of the referenced
document (including any amendments) applies.
ISO 13943, Fire safety — Vocabulary
ISO 24678-1, Fire safety engineering — Requirements governing algebraic formulae — Part 1: General
requirements
3 Terms and Definitions
For the purpose of this document, the terms and definitions given in ISO 13943 and the following
applies.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3.1
smoke layer
relatively homogeneous volume of smoke that forms and accumulates beneath the boundary having the
highest elevation in an enclosure as a result of a fire. Also referred to as the hot upper layer and the hot
gas layer
4 Requirements governing description of physical phenomena
4.1 The requirements governing the description of physical phenomena as specified in ISO 24678-1
apply, in addition to the requirements specified in the following subclauses.
4.2 The buoyant smoke layer resulting from a fire source in an enclosure is a complex thermo-physical
phenomenon that can be highly transient or nearly steady state. In addition to buoyancy, smoke layers
can be influenced by dynamic forces due to wind and mechanical fans.
4.3 Smoke layer characteristics to be calculated and their useful ranges shall be clearly identified,
including those characteristics inferred by association with calculated quantities (e.g., the association
of smoke mass fraction with excess gas temperature based on the analogy between energy and mass
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ISO/DIS 24678-4:2022(E)
conservation) and those associated with heat exposure to objects and occupants by the smoke layer, if
applicable.
5 Requirements governing calculation process
The requirements specified in ISO 24678-1 governing the calculation process apply.
6 Requirements governing limitations
The requirements specified in ISO 24678-1 governing limitations apply.
7 Requirements governing input parameters
The requirements specified in ISO 24678-1 governing input parameters apply.
8 Requirements governing domain of applicability
The requirements specified in ISO 24678-1 governing domain of applicability apply.
9 Example of documentation
An example of documentation meeting the requirements in clauses 4 to 8 is given in Annex A.
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ISO/DIS 24678-4:2022(E)
Annex A
(informative)
Formulae for smoke layers in an enclosure
A.1 Scope
This Annex is intended to describe the methods that can be used to calculate interface positions,
average temperatures and average mass fractions of specific chemical species of smoke layers that form
beneath boundaries during fires in an enclosure. These calculation methods are based on the principles
of mass, species and energy conservation as applied to the smoke layer as a thermodynamic control
volume. In this annex, four different sets of formulae are provided. One is for the smoke filling process
in a single enclosure during the early stage of fire. The other three sets are for steady state smoke
control by mechanical exhaust or by natural vents.
A.2 Terms and definitions used in this Annex
The terms and definitions defined in the main body apply in addition to the followings:
A.2.1
boundary
a surface that defines the extent of an enclosure
A.2.2
enclosure
a room, space or volume that is bounded by surfaces
A.2.3
fire plume
upward turbulent fluid motion generated by a source of buoyancy that exists by virtue of combustion
and often includes an initial flaming region
A.2.4
fire source diameter
effective diameter of the fire source, equal to the actual diameter for a circular source or the diameter
of a circle having an area equal to the plan area of a non-circular source
A.2.5
flame
luminous region of fire plume associated with combustion
A.2.6
flow coefficient
fraction of effective flow area over total area of a vent
A.2.7
fuel mass burning rate
mass generation rate of fuel vapours
A.2.8
heat release rate
rate at which heat is actually being released by a source of combustion (such as the fire source)
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ISO/DIS 24678-4:2022(E)
A.2.9
interface position
the elevation of the smoke layer interface relative to a reference elevation, typically the lowest bounda-
ry of the enclosure. Also referred to as the smoke layer height
A.2.10
quasi-steady state
the assumption that the full effects of heat release rate changes at the fire source are felt everywhere
in the flow field immediately
A.2.11
smoke
the airborne solid and liquid particulates and gases evolved when a material undergoes pyrolysis or
combustion, together with the quantity of air that is entrained or otherwise mixed into the mass
A.2.12
smoke layer Interface
the horizontal plane separating the smoke layer from the lower, smoke-free layer.
A.2.13
species yield
mass of a combustion product species generated by the combustion of unit mass of combustibles
A.2.14
thermal inertia
a parameter representing the ability of enclosure materials to absorb heat, calculated by the square
root of the product of thermal conductivity, density and specific heat of the material.
A.2.15
vent
an opening in an enclosure boundary through which air and smoke can flow as a result of naturally- or
mechanically-induced forces
A.2.16
vent flow
the flow of smoke or air through a vent in an enclosure boundary.
A.3 Symbols and abbreviated terms used in this Annex
2
A floor area of enclosure (m )
2
A area of a side vent (m )
side
2
A area of a ceiling vent (m )
top
2
A surface area of enclosure boundary in contact with smoke layer (m )
wall
B width of a side vent (m)
c specific heat of enclosure boundary material (kJ/kg·K)
C flow coefficient
D
c specific heat of air at constant pressure (=1,0) (kJ/kg·K)
p
D thickness of enclosure boundary material (m)
wall
D fire source diameter (m)
2
g acceleration due to gravity (m/s )
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ISO/DIS 24678-4:2022(E)
2 1
h effective heat transfer coefficient of enclosure boundary (kW/m ·K )
wall
H height of enclosure (m)
H height of lower bound of side vent (m)
l
H height of upper bound of side vent (m)
u
k thermal conductivity of enclosure boundary material (kW/m·K)
1/2 2 1
thermal inertia of enclosure boundary material (kW·s /m ·K )
kcρ
L mean flame height (m)
m mass flow rate of air coming into enclosure (kg/s)
a
m mass flow rate of smoke exhaust (kg/s)
e
m mass flow rate of gases in fire plume (kg/s)
p
Δp pressure difference (Pa)
Q heat release rate of fire source (kW)
heat release rate of steady fire source (kW)
Q
0
t time (s)
t arrival time of plume front to ceiling (s)
ar
t characteristic time for heat absorption by enclosure boundary (s)
c
T reference temperature, often taken by outside temperature (K)
0
T smoke layer temperature (K)
s
3
volumetric flow rate of mechanical exhaust system (m /s)
V
e
Y mass fraction of specific chemical species (kg/kg)
Y mass fraction of specific chemical species at reference state (kg/kg)
0
z interface height above base of fire source (m)
2
α fire growth rate of time-squared fires (kW/s )
β fire growth rate of linearly growling fires (kW/s)
ΔH heat of combustion (kJ/kg)
c
η species yield (kg/kg)
λ fraction of heat absorbed by enclosure boundary during smoke filling period
3
ρ air density at reference temperature (kg/m )
0
3
ρ gas density of smoke (kg/m )
s
3
ρ density of enclosure boundary material (kg/m )
5
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ISO/DIS 24678-4:2022(E)
A.4 Description of physical phenomena addressed by the formula set
A.4.1 General descriptions of calculation method
A.4.1.1 Calculation procedure
Estimating the smoke layer properties involves the following steps:
— determination of characteristics of the fire source (burning area, fuel mass burning rate, etc.);
— calculation of height of smoke layer interface;
— calculation of temperature and mass fraction of chemical species in the smoke layer.
A.4.1.2 Smoke layer properties to be calculated
Formulae provide interface position, average gas temperature and mass fractions of chemical species.
Uniform temperature and mass fractions are assumed over entire smoke layer volume.
A.4.2 Scenario elements to which the formula set is applicable
The formula set is applicable to smoke layers above a fire source in a quiescent environment. If flow-
disturbance by non-fire related phenomena is significant, the formula set is not applicable. For example,
the effect of airflow caused by HVAC systems or by external wind should be considered if they have a
significant effect. If active fire suppression systems, such as sprinklers, interact significantly with the
smoke layer, the formula set is not applicable.
The fire source must be small enough so that the mean flame height is lower than the interface position
and the characteristic plume width is less than the width of the enclosure (subject to additional
restrictions imposed by the formulae used to obtain plume characteristics).
Methods to calculate smoke layer conditions are developed for two limit stages. One limit stage is
a simple enclosure smoke filling process during the initial stage of the fire when the smoke control
system is not yet in operation. The other limit stage is a quasi-steady vented condition when the smoke
production rate equals the rate of outflow from the smoke layer. An intermediate stage (i.e., smoke
filling is still occurring even though a smoke venting system is in operation) is not treated in this Annex.
A.4.3 Self-consistency of the formula set
The set of formulae provided in this annex have been derived and reviewed by many researhers (see
clause A.6) to ensure that calculation results from different formulae in the set are consistent (i.e., do
not produce conflicts).
A.4.4 International standards and other documents where the formula set is used
None specified.
A.5 Documentation of the set of formulae
A.5.1 General description of calculation methods
A.5.1.1 basic assumptions
As shown in Figure A.1, a smoke layer is generated over a fire source in an enclosure. Smoke is
accumulated in the upper part of an enclosure as a result of burning. It is assumed that smoke forms a
layer of fairly uniform temperature and species mass fraction. Based on the principles of mass, species
and energy conservation applied to the smoke layer, average values of temperature, smoke mass
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ISO/DIS 24678-4:2022(E)
[1],[2],[3]
fraction and interface positions are calculated . Descriptions of fire plumes and vent flows are
[4] [5]
given in ISO 24678-2 and ISO 24678-5 , respectively.
Key
1 fire source
2 plume flow
3 vent flow
4 smoke layer (control volume)
5 heat absorption by enclosure boundary
6 heat flow
7 mass flow
Figure A.1 — General heat and mass conservation of smoke layer in an enclosure with a fire
source
A.5.1.2 Mass conservation
Conservation of mass in the smoke layer is considered over an appropriately chosen control volume as
shown in Figure A.1 by broken lines. The mass flow rate incoming across each interface (negative for
outgoing flow) of the control volume is equal to the rate of mass accumulation in the smoke layer. Plume
flow, vent flows and other flows are considered where necessary.
A.5.1.3 Energy conservation
Conservation of energy in the smoke layer is considered in a similar way to mass conservation. The
energy flow rate incoming across each interface (negative for outgoing flow) of the control volume
is equal to the rate of energy accumulation in the smoke layer. In addition to plume and vent flows,
radiation losses and heat absorption by the enclosure boundary are considered appropriately.
Note When it is difficult to determine the radiation heat loss from the flame, the energy flow rate by fire
plume may be approximated by the total heat release rate.
A.5.1.4 Conservation of specific chemical species
Mass conservation of specific chemical species is considered in a similar way to total mass conservation.
In addition, if the gas phase chemical reaction may take place in the smoke layer, the reaction rate is
considered appropriately.
A.5.1.5 Mass flow rate of fire plume through smoke layer interface
The mass flow rate of the fire plume at the smoke layer interface (bottom surface of smoke layer) is
given as a function of the heat release rate of the fire and the vertical distance between the base of the
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ISO/DIS 24678-4:2022(E)
fire source and the smoke layer interface. An example of a set of explicit formulae for mass flow rate is
[4]
given in ISO 24678-2 .
A.5.1.6 Mass flow rate of smoke through vent
The mass flow rate through a vent is given as a function of the temperature of the smoke layer and that of
the adjacent enclosures, pressure differences between the smoke layer and the adjacent enclosure, vent
[5]
width, and vent height. Examples of a set of explicit formulae for vent flows are given in ISO 24678-5 .
A.5.1.7 Equation of state
Smoke temperature and density are correlated by the equation of state. Typically, smoke is approximated
by an ideal gas whose properties are identical with air.
A.5.2 Enclosure smoke filling
A.5.2.1 Scenario element
Until the smoke layer interface decends to the upper edge of a vertical vent, smoke is accumulated in
the upper part of an enclosure as shown in Figure A.2. Due to thermal expansion, excess air is pushed
out of the enclosure.
Note This assumption is valid as long as the smoke layer height is above the upper boundary of the side
vent. After the smoke layer descends below the upper boundary of the side vent, smoke flows out of enclosure
while fresh air flows into the enclosure.
Key
1 fire source
2 plume flow
3 smoke layer
4 excess air pushed out due to thermal expansion
Figure A.2 — Mass conservation during enclosure smoke filling process
The heigt of smoke layer interface is given by:
∂z
−ρ A =m (A.1)
sp
∂t
[6]
Mass flow rate of plume at the smoke layer interface, z (m) above the fire source, is given by :
13//53
mQ=0,076 z (A.2)
p
[4]
Note (Formula A.2) is an approximation of the plume formula in Annex A to ISO 24678-2 . This formula is
valid only above the mean flame height. If the interface position is lower than the mean flame height, calculation
results may be inaccurate.
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ISO/DIS 24678-4:2022(E)
The formula set is constructed for steady state fires, linearly growling fires and time-squared growing
fires:
Q (steadystatefires)
0
Qt()= βt (linearlygrowingfires) (A.3)
2
αt (time--squaredgrowingfires)
A.5.2.2 Interface position
Interface position is calculated so that plume mass flow accumulates in upper layer of uniform
[7]
density . By putting (Formulae A.2 and A.3) into (Formula A.1) and integrate with respect to time:
−32/
0,076 2 1
13/
Qt()−+t (steadystatefirres)
ar
0
23/
ρ A 3
H
s
−32/
0,0761 1
13//43
zt()= β ()tt−+ (linearly growlling fiires) (A.4)
ar
23/
ρ A 2
H
s
−32/
0,076 2 1
13//53
α ()tt−+ (time-ssquaredfires)
ar
23/
ρ A 5
H
s
[8][9]
where the arrival time of plume front to ceiling is given for a steady state fire as :
−13/
43/
tQ=17, H (A.5)
ar
0
In case of linearly growing and time-squared fires, explicit form for the arrival time is not known but the
(Formula A.5) may be applied by using conservative estmate of heat release rate. For lin
...
PROJET DE NORME INTERNATIONALE
ISO/DIS 24678-4
ISO/TC 92/SC 4 Secrétariat: AFNOR
Début de vote: Vote clos le:
2022-06-28 2022-09-20
Ingénierie de la sécurité incendie — Exigences régissant
les formules algébriques —
Partie 4:
Couches de fumée
Fire Safety Engineering - Requirements governing algebraic formulae —
Part 4: Smoke layers
ICS: 13.220.01
CE DOCUMENT EST UN PROJET DIFFUSÉ POUR
OBSERVATIONS ET APPROBATION. IL EST DONC
SUSCEPTIBLE DE MODIFICATION ET NE PEUT
ÊTRE CITÉ COMME NORME INTERNATIONALE
AVANT SA PUBLICATION EN TANT QUE TELLE.
Le présent document est distribué tel qu’il est parvenu du secrétariat du comité.
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RÉGLEMENTATION NATIONALE.
Numéro de référence
LES DESTINATAIRES DU PRÉSENT PROJET ISO/DIS 24678-4:2022(F)
SONT INVITÉS À PRÉSENTER, AVEC LEURS
OBSERVATIONS, NOTIFICATION DES DROITS
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ÉVENTUELLEMENT CONNAISSANCE ET À
© ISO 2022
FOURNIR UNE DOCUMENTATION EXPLICATIVE.
---------------------- Page: 1 ----------------------
© ISO 2022 – Tous droits réservés
ISO/DIS 24678-4:2022(F)
ISO/TC 92/SC 4
Date : 2022-09-20
ISO/DIS 24678-4:2022(F)
ISO/TC 92/SC 4
Secrétariat : AFNOR
Ingénierie de la sécurité incendie — Exigences régissant les formules
algébriques — Partie 4 : Couches de fumée
Fire Safety Engineering — Requirements governing algebraic formulae — Part 4: Smoke Layers
ICS : 13.220.01
Avertissement
Ce document n'est pas une Norme internationale de l'ISO. Il est distribué pour examen et observations.
Il est susceptible de modification sans préavis et ne peut être cité comme Norme internationale.
Les destinataires du présent projet sont invités à présenter, avec leurs observations, notification des
droits de propriété dont ils auraient éventuellement connaissance et à fournir une documentation
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ii
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ISO/DIS 24678-4:2022(F)
Sommaire Page
Avant-propos . iv
Introduction . v
1 Domaine d’application .1
2 Références normatives .1
3 Termes et définitions .1
4 Exigences régissant la description des phénomènes physiques .1
5 Exigences régissant le processus de calcul .2
6 Exigences régissant les limites .2
7 Exigences régissant les paramètres d’entrée .2
8 Exigences régissant le domaine d’application .2
9 Exemple de documentation .2
Annexe A (informative) Formules pour les couches de fumée dans une enceinte .3
Bibliographie pour l’Annexe A . 37
© ISO 2022 – Tous droits réservés
iii
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ISO/DIS 24678-4:2022(F)
Avant-propos
L’ISO (Organisation internationale de normalisation) est une fédération mondiale d’organismes
nationaux de normalisation (comités membres de l’ISO). L’élaboration des Normes internationales est
en général confiée aux comités techniques de l’ISO. Chaque comité membre intéressé par une étude a le
droit de faire partie du comité technique créé à cet effet. Les organisations internationales,
gouvernementales et non gouvernementales, en liaison avec l’ISO participent également aux travaux.
L’ISO collabore étroitement avec la Commission électrotechnique internationale (IEC) en ce qui
concerne la normalisation électrotechnique.
Les procédures utilisées pour élaborer le présent document et celles destinées à sa mise à jour sont
décrites dans les Directives ISO/IEC, Partie 1. Il convient, en particulier, de prendre note des différents
critères d’approbation requis pour les différents types de documents ISO. Le présent document a été
rédigé conformément aux règles de rédaction données dans les Directives ISO/IEC, Partie 2
(voir www.iso.org/directives).
L’attention est attirée sur le fait que certains des éléments du présent document peuvent faire l’objet de
droits de propriété intellectuelle ou de droits analogues. L’ISO ne saurait être tenue pour responsable
de ne pas avoir identifié de tels droits de brevets. Les détails concernant les références aux droits de
propriété intellectuelle ou autres droits analogues identifiés lors de l’élaboration du document sont
indiqués dans l’Introduction et/ou dans la liste des déclarations de brevets reçues par l’ISO
(voir www.iso.org/brevets).
Les appellations commerciales éventuellement mentionnées dans le présent document sont données
pour information, par souci de commodité, à l’intention des utilisateurs et ne sauraient constituer un
engagement.
Pour une explication de la nature volontaire des normes, la signification des termes et expressions
spécifiques de l’ISO liés à l’évaluation de la conformité, ou pour toute information au sujet de l’adhésion
de l’ISO aux principes de l’Organisation mondiale du commerce (OMC) concernant les obstacles
techniques au commerce (OTC), voir le lien suivant : www.iso.org/iso/fr/avant-propos.
Le présent document a été élaboré par le comité technique ISO/TC 92, Sécurité au feu, sous-comité SC 4,
Ingénierie de la sécurité incendie.
Cette deuxième édition annule et remplace la première édition (ISO 16735:2006), qui a fait l’objet d’une
révision technique.
Les principales modifications par rapport à l’édition précédente sont les suivantes :
— le corps principal du texte a été simplifié par l’introduction d’une référence à la Partie 1 de la
présente norme ;
— le temps d’arrivée du front de fumée a été inclus dans les calculs du temps de remplissage par la
fumée dans l’Annexe A ;
— des comparaisons avec des données expérimentales ont été ajoutées à l’Annexe A.
Une liste de toutes les parties de la série ISO 24678 se trouve sur le site web de l’ISO.
Il convient que l’utilisateur adresse tout retour d’information ou toute question concernant le présent
document à l’organisme national de normalisation de son pays. Une liste exhaustive desdits organismes
se trouve à l’adresse www.iso.org/fr/members.html.
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ISO/DIS 24678-4:2022(F)
Introduction
Le présent document est destiné à être utilisé par les praticiens de la sécurité incendie impliqués dans
les méthodes de calcul utilisées dans l’ingénierie de la sécurité incendie. Il est attendu que les
utilisateurs du présent document possèdent une qualification et une compétence appropriées dans le
domaine de l’ingénierie de la sécurité incendie. Il est particulièrement important que les utilisateurs
comprennent les paramètres pour lesquels des méthodologies particulières peuvent être employées.
Les formules algébriques conformes aux exigences de la présente norme sont utilisées conjointement
avec d’autres méthodes de calcul d’ingénierie lors de la conception de la sécurité contre l’incendie.
Cette conception est précédée de la détermination d’un contexte, y compris les buts et objectifs de
sécurité contre l’incendie à atteindre, ainsi que de critères de performance lorsqu’un plan expérimental
de sécurité incendie est confronté à des scénarios d’incendie de dimensionnement spécifiés. Les
méthodes de calcul d’ingénierie sont utilisées pour déterminer si ces critères de performance seront
satisfaits par une conception donnée et, dans la négative, la manière dont la conception nécessite d’être
modifiée.
Les aspects couverts par les calculs d’ingénierie incluent la conception de la sécurité incendie des
environnements bâtis entièrement neufs, par exemple les bâtiments, les navires ou les véhicules,
ainsi que l’évaluation de la sécurité incendie des environnements bâtis existants.
Les formules algébriques mentionnées dans la présente norme peuvent être utiles pour estimer les
conséquences des scénarios d’incendie de dimensionnement. Ces formules sont utiles dans la mesure
où elles permettent au praticien de déterminer rapidement la manière dont il est nécessaire de modifier
un plan de sécurité incendie proposé pour répondre aux critères de performance, et de le comparer
avec de multiples plans expérimentaux. Des calculs numériques détaillés peuvent être réalisés jusqu’à
l’étape de documentation de la conception finale. Les domaines dans lesquels des formules algébriques
se sont révélées applicables comprennent, par exemple, la détermination du transfert thermique
convectif et radiatif des panaches de feu, la prédiction des propriétés des écoulements en jet sous
plafond régissant les temps de réponse des détecteurs, le calcul du transport de la fumée dans les
ouvertures de ventilation et l’analyse des dangers d’un feu en compartiment tels que le remplissage par
la fumée et l’embrasement généralisé. Cependant, les modèles simples ont souvent des limites
contraignantes et sont moins susceptibles d’inclure les effets des multiples phénomènes qui se
produisent dans les scénarios d’incendie de dimensionnement.
Les principes généraux sont décrits dans l’ISO 23932-1, qui fournit une méthodologie axée sur les
performances permettant aux ingénieurs d’évaluer le niveau de sécurité incendie des environnements
bâtis neufs ou existants. La sécurité incendie est évaluée selon une approche d’ingénierie reposant sur
la quantification du comportement au feu et sur la connaissance des conséquences d’un tel
comportement sur les personnes, les biens et l’environnement. L’ISO 23932-1 décrit le processus
(à savoir, les étapes nécessaires) et les éléments essentiels pour mener à bien une conception de la
sécurité incendie robuste et axée sur les performances.
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L’ISO 23932-1 s’appuie sur un ensemble de Normes internationales et de Spécifications techniques
relatives à l’ingénierie de la sécurité incendie, qui contiennent les méthodes et les données nécessaires
aux étapes de la conception d’un processus d’ingénierie de la sécurité incendie résumées à la Figure 1
(issue de l’ISO 23932-1:2018, Article 4). Cet ensemble de documents est appelé Système global
d’information et d’analyse de l’ingénierie de la sécurité incendie. Cette approche globale ainsi que le
système de normes permettent de mieux comprendre les interactions qui existent entre les évaluations
des incendies lorsque l’ensemble de documents relatif à l’ingénierie de la sécurité incendie est utilisé.
Cet ensemble comprend l’ISO 16732-1, l’ISO 16733-1, l’ISO 16734, l’ISO 16735, l’ISO 16736, l’ISO 16737,
l’ISO 24678, l’ISO/TS 24679, l’ISO 16730-1, l’ISO/TS 29761, l’ISO/TS 13447 ainsi que d’autres Rapports
techniques d’accompagnement qui fournissent des exemples et des recommandations relatives à
l’application de ces documents.
Chaque document se rapportant au système global d’information et d’analyse de l’ingénierie de la
sécurité incendie comprend, dans son introduction, du vocabulaire permettant de relier ledit document
aux étapes correspondantes du processus de conception en ingénierie de la sécurité incendie présenté
dans l’ISO 23932-1. L’ISO 23932-1 exige que les méthodes d’ingénierie soient sélectionnées de manière
appropriée afin de prédire les conséquences d’un incendie dans le cadre de scénarios et d’éléments de
scénario spécifiques (ISO 23932:2018, Article 12). Conformément aux exigences de l’ISO 23932-1,
le présent document spécifie les exigences régissant les formules algébriques liées à l’ingénierie de la
sécurité incendie. Cette étape du processus de l’ingénierie de la sécurité incendie est présentée dans
l’encadré grisé de la Figure 1 et décrite dans l’ISO 23932-1.
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a
Voir également l’ISO/TR 16576 (exemples).
b
Voir également l’ISO 16732-1, l’ISO 16733-1, l’ISO/TS 29761.
c
Voir également l’ISO 16732-1, l’ISO 16733-1, l’ISO/TS 29761.
d
Voir également l’ISO/TS 13447, l’ISO 16730-1, l’ISO/TR 16730-2 à 5 (exemples), l’ISO/TR 16738, l’ISO 24678.
e
Voir également l’ISO/TR 16738, l’ISO 16733-1.
NOTE Documents liés à des parties importantes du processus de conception en ingénierie de la sécurité
incendie : ISO 16732-1, ISO 16733-1, ISO 24678, ISO/TS 24679-1, ISO/TS 29761, ISO/TR 16732-2 et
ISO/TR 16732-3 (exemples), ISO/TR 24679-2, ISO/TR 24679- 4, ISO/TR 24679-5 et ISO/TR 24679-6 (exemples).
Figure 1 — Diagramme illustrant le processus de conception en ingénierie de la sécurité
incendie (ISI) (issu de l’ISO 23932-1:2018)
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PROJET DE NORME INTERNATIONALE ISO/DIS 24678-4:2022(F)
Ingénierie de la sécurité incendie — Exigences régissant les
formules algébriques — Partie 4 : Couches de fumée
1 Domaine d’application
Le présent document spécifie les exigences régissant l’application d’ensembles de formules algébriques
explicites pour le calcul de caractéristiques spécifiques des couches de fumée.
2 Références normatives
Les documents suivants sont cités dans le texte de sorte qu’ils constituent, pour tout ou partie de leur
contenu, des exigences du présent document. Pour les références non datées, la dernière édition du
document de référence s’applique (y compris les éventuels amendements).
ISO 13943, Sécurité au feu — Vocabulaire.
ISO 24678-1, Ingénierie de la sécurité incendie — Exigences régissant les formules algébriques —
Partie 1 : Exigences générales.
3 Termes et définitions
Pour les besoins du présent document, les termes et définitions de l’ISO 13943 ainsi que les suivants
s’appliquent.
L’ISO et l’IEC tiennent à jour des bases de données terminologiques destinées à être utilisées en
normalisation, consultables aux adresses suivantes :
— ISO Online browsing platform : disponible à l’adresse https://www.iso.org/obp ;
— IEC Electropedia : disponible à l’adresse https://www.electropedia.org/.
3.1
couche de fumée
volume de fumée relativement homogène qui se forme et qui s’accumule au-dessous de la limite
physique la plus haute dans une enceinte à la suite d’un incendie Également désignée « couche chaude
de fumée » ou « couche de gaz chaud »
4 Exigences régissant la description des phénomènes physiques
4.1 Les exigences régissant la description des phénomènes physiques spécifiées dans l’ISO 24678-1
s’appliquent, en complément des exigences spécifiées dans les paragraphes suivants.
4.2 La couche flottante de fumée générée par une source d’incendie dans une enceinte est un
phénomène thermophysique complexe qui peut être extrêmement transitoire ou quasi stationnaire.
Outre la flottabilité, les couches de fumée peuvent être influencées par des forces dynamiques dues au
vent et à la ventilation mécanique.
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ISO/DIS 24678-4:2022(F)
4.3 Les caractéristiques des couches de fumée à calculer et leurs domaines d’utilité doivent être
clairement identifiés, y compris les caractéristiques déduites par association aux grandeurs calculées
(par exemple association d’une fraction massique de fumée et d’une température excessive des gaz
fondée sur l’analogie entre énergie et conservation de la masse) et celles associées à l’exposition à la
chaleur d’objets et d’occupants par la couche de fumée, le cas échéant.
5 Exigences régissant le processus de calcul
Les exigences spécifiées dans l’ISO 24678-1 régissant le processus de calcul s’appliquent.
6 Exigences régissant les limites
Les exigences spécifiées dans l’ISO 24678-1 régissant les limites s’appliquent.
7 Exigences régissant les paramètres d’entrée
Les exigences spécifiées dans l’ISO 24678-1 régissant les paramètres d’entrée s’appliquent.
8 Exigences régissant le domaine d’application
Les exigences spécifiées dans l’ISO 24678-1 régissant le domaine d’application s’appliquent.
9 Exemple de documentation
Un exemple de documentation répondant aux exigences des Articles 4 à 8 est donné dans l’Annexe A.
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ISO/DIS 24678-4:2022(F)
Annexe A
(informative)
Formules pour les couches de fumée dans une enceinte
A.1 Domaine d’application
La présente annexe est destinée à décrire les méthodes qui peuvent être utilisées pour calculer les
positions d’interface, les températures moyennes et les fractions massiques moyennes d’espèces
chimiques spécifiques dans les couches de fumée qui se forment au-dessous des limites physiques lors
d’incendies dans une enceinte. Ces méthodes de calcul sont fondées sur les principes de conservation de
la masse, des espèces et de l’énergie, tels qu’ils sont appliqués à la couche de fumée considérée comme
un volume de contrôle thermodynamique. Quatre ensembles de formules différents sont fournis dans la
présente annexe. L’un concerne le processus de remplissage d’une enceinte simple par la fumée
pendant la phase initiale d’un incendie. Les trois autres ensembles se rapportent au désenfumage
continu par un système d’extraction mécanique ou par des ouvertures naturelles.
A.2 Termes et définitions utilisés dans la présente annexe
Les termes et définitions donnés dans le corps principal du présent document ainsi que les suivants
s’appliquent :
A.2.1
limite physique
surface qui définit l’étendue d’une enceinte
A.2.2
enceinte
pièce, espace ou volume limité par des surfaces
A.2.3
panache de feu
mouvement turbulent ascendant d’un fluide généré par une source de flottabilité qui est liée à une
combustion et qui comprend souvent une zone d’inflammation initiale
A.2.4
diamètre de la source d’incendie
diamètre utile de la source d’incendie, égal au diamètre réel pour une source circulaire ou au diamètre
d’un cercle ayant une surface égale à la surface plane d’une source non circulaire
A.2.5
flamme
partie lumineuse d’un panache de feu associée à la combustion
A.2.6
coefficient de débit
fraction de la section d’écoulement effective sur la surface totale d’une ouverture
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A.2.7
débit massique de combustion du combustible
vitesse de production massique des vapeurs de combustible
A.2.8
débit calorifique
débit de chaleur dégagée par une source de combustion (telle qu’une source d’incendie)
A.2.9
position de l’interface
altitude de l’interface d’une couche de fumée par rapport à une altitude de référence, habituellement la
limite inférieure de l’enceinte. Également désignée « hauteur de la couche de fumée »
A.2.10
état quasi stationnaire
hypothèse selon laquelle la totalité des effets liés à des variations du débit calorifique au niveau de la
source d’incendie sont ressentis immédiatement partout dans le champ d’écoulement
A.2.11
fumée
particules solides et liquides et gaz émis dans l’atmosphère lorsqu’un matériau subit une pyrolyse ou
une combustion, associés à la quantité d’air qui est entraînée ou mélangée d’une autre manière dans la
masse
A.2.12
interface de la couche de fumée
plan horizontal séparant la couche de fumée de la couche inférieure exempte de fumée
A.2.13
taux de production d’espèces
masse des espèces d’un produit de combustion générées par la combustion d’une unité de masse de
combustibles
A.2.14
inertie thermique
paramètre représentant la capacité des matériaux d’une enceinte à absorber la chaleur, calculé comme
étant la racine carrée du produit de la conductivité thermique, de la masse volumique et de la chaleur
spécifique du matériau
A.2.15
ouverture (évent)
ouverture dans la limite physique d’une enceinte par laquelle l’air et la fumée peuvent s’écouler sous
l’action de forces induites naturellement ou mécaniquement
A.2.16
écoulement au travers d’une ouverture
écoulement de fumée ou d’air par une ouverture dans la limite physique d’une enceinte
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A.3 Symboles et abréviations utilisés dans la présente annexe
2
A surface de plancher de l’enceinte (m )
2
A surface d’une ouverture latérale (m )
latéral
2
A surface d’une ouverture en plafond (m )
plafond
2
A aire de la limite physique de l’enceinte en contact avec la couche de fumée (m )
paroi
B largeur d’une ouverture latérale (m)
c chaleur spécifique du matériau de la limite physique de l’enceinte (kJ/kg·K)
C coefficient de débit
D
c chaleur spécifique de l’air à pression constante (= 1,0) (kJ/kg·K)
p
D épaisseur du matériau de la limite physique de l’enceinte (m)
paroi
D diamètre de la source d’incendie (m)
2
g accélération due à la pesanteur (m/s )
2 1
h coefficient effectif de transfert de chaleur de la limite physique de l’enceinte (kW/m ·K )
paroi
H hauteur de l’enceinte (m)
H hauteur de la limite inférieure d’une ouverture latérale (m)
l
H hauteur de la limite supérieure d’une ouverture latérale (m)
u
k conductivité thermique du matériau de la limite physique de l’enceinte (kW/m·K)
1/2 2 1
inertie thermique du matériau de la limite physique de l’enceinte (kW·s /m ·K )
krc
L hauteur moyenne des flammes (m)
& débit massique d’air entrant dans l’enceinte (kg/s)
m
a
& débit massique du système d’extraction de fumée (kg/s)
m
e
& débit massique de gaz dans le panache de feu (kg/s)
m
p
Δp différence de pression (Pa)
&
débit calorifique de la source d’incendie (kW)
Q
&
débit calorifique de la source d’incendie stable (kW)
Q
0
t temps (s)
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t temps nécessaire au front du panache pour arriver au plafond (s)
ar
t temps caractéristique pour l’absorption de chaleur par la limite physique de l’enceinte (s)
c
T température de référence, souvent prise comme la température extérieure (K)
0
T température de la couche de fumée (K)
f
3
&
débit volumique du système d’extraction mécanique (m /s)
V
e
Y fraction massique d’espèces chimiques spécifiques (kg/kg)
Y fraction massique d’espèces chimiques spécifiques à l’état de référence (kg/kg)
0
z hauteur de l’interface par rapport à la base de la source d’incendie (m)
α taux d’augmentation du débit calorifique d’un incendie à croissance proportionnelle au carré
2
du temps (kW/s )
β taux d’augmentation du débit calorifique d’un incendie à croissance linéaire (kW/s)
ΔH chaleur de combustion (kJ/kg)
c
η taux de production d’espèces (kg/kg)
λ fraction de chaleur absorbée par la limite physique de l’enceinte pendant la période de
remplissage par la fumée
3
ρ masse volumique de l’air à la température de référence (kg/m )
0
3
ρ masse volumique de la fumée (kg/m )
s
3
ρ masse volumique du matériau de la limite physique de l’enceinte (kg/m )
A.4 Description des phénomènes physiques traités par l’ensemble de
formules
A.4.1 Description générale de la méthode de calcul
A.4.1.1 Mode opératoire de calcul
L’estimation des propriétés de la couche de fumée implique les étapes suivantes :
— détermination des caractéristiques de la source d’incendie (surface en combustion, débit massique
de combustion du combustible, etc.) ;
— calcul de la hauteur de l’interface de la couche de fumée ;
— calcul de la température et de la fraction massique des espèces chimiques dans la couche de fumée.
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A.4.1.2 Propriétés de la couche de fumée à calculer
Les formules permettent de calculer la position de l’interface, la température moyenne des gaz et les
fractions massiques des espèces chimiques. Il est présumé que la température et les fractions
massiques sont uniformes dans tout le volume de la couche de fumée.
A.4.2 Éléments de scénario auxquels est applicable l’ensemble de formules
L’ensemble de formules est applicable aux couches de fumée surmontant une source d’incendie dans un
environnement calme. Si la perturbation de l’écoulement due à des phénomènes non liés à l’incendie est
importante, l’ensemble de formules n’est pas applicable. Par exemple, il convient de tenir compte de
l’effet du flux d’air engendré par les systèmes CVCA ou par le vent extérieur si cet effet est significatif.
Lorsque des systèmes d’extinction d’incendie actifs, tels que des extincteurs automatiques (sprinklers),
interagissent de manière significative avec la couche de fumée, l’ensemble de formules n’est pas
applicable.
La source d’incendie doit être suffisamment petite pour que la hauteur moyenne des flammes soit
inférieure à la position de l’interface et que la largeur caractéristique du panache soit inférieure à la
largeur de l’enceinte (en fonction de restrictions supplémentaires imposées par les formules utilisées
pour obtenir les caractéristiques du panache).
Des méthodes de calcul des conditions de la couche de fumée sont développées pour deux phases
limites. Une phase limite est un processus simple de remplissage d’une enceinte par la fumée au cours
de la phase initiale d’un incendie, alors que le système de désenfumage n’est pas encore en service.
L’autre phase limite est une condition de ventilation quasi continue, lorsque le débit de fumée produite
est égal au débit de sortie de la couche de fumée. Une phase intermédiaire (à savoir, poursuite du
remplissage par la fumée alors même qu’un système d’extraction des fumées est en service) n’est pas
traitée dans la présente annexe.
A.4.3 Cohérence interne de l’ensemble de formules
L’ensemble de formules de la présente annexe a été élaboré et vérifié par de nombreux chercheurs
(voir l’Article A.6) en vue de garantir la cohérence des résultats de calcul issus des différentes formules
de cet ensemble (en d’autres termes, garantir l’absence de conflit entre les résultats).
A.4.4 Normes internationales et autres documents dans lesquels est utilisé l’ensemble de
formules
Aucun n’est spécifié.
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A.5 Documentation relative à l’ensemble de formules
A.5.1 Description générale des méthodes de calcul
A.5.1.1 Hypothèses de base
Comme représenté à la Figure A.1, une couche de fumée est générée au-dessus d’une source d’incendie
dans une enceinte. La fumée s’accumule dans la partie supérieure d’une enceinte à la suite d’une
combustion. Il est présumé que la fumée forme une couche dont la température et la fraction massique
d’espèces sont relativement uniformes. Les valeurs moyennes de température, de fraction massique de
[1],[2],[3]
la fumée et de positions de l’interface sont calculées à partir des principes de conservation de la
masse, des espèces et de l’énergie appliqués à la couche de fumée. Des descriptions des panaches de feu
[4]
et des écoulements au travers d’une ouverture sont respectivement données dans l’ISO 24678-2 et
[5]
l’ISO 24678-5 .
Légende
1 source d’incendie
2 écoulement du panache
3 écoulement au travers d’une ouverture
4 couche de fumée (volume de contrôle)
5 absorption de chaleur par la limite physique de l’enceinte
6 flux de chaleur
7 débit massique
Figure A.1 — Conservation générale de la chaleur et de la masse d’une couche de fumée dans
une enceinte contenant une source d’incendie
A.5.1.2 Conservation de la masse
La conservation de la masse dans la couche de fumée est prise en compte dans un volume de contrôle
approprié choisi, comme représenté à la Figure A.1 par des lignes discontinues. Le débit massique
entrant par chaque interface (négatif pour un écoulement sortant) du volume de contrôle est égal au
débit d’accumulation de masse de la couche de fumée. L’écoulement du panache, les écoulements au
travers d’une ouverture et autres écoulements sont, si nécessaire, pris en compte.
© ISO 2022 – Tous droits réserv
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