ISO 24678-5:2023
(Main)Fire safety engineering — Requirements governing algebraic formulae — Part 5: Vent flows
Fire safety engineering — Requirements governing algebraic formulae — Part 5: Vent flows
This document specifies the requirements governing the application of a set of explicit algebraic formulae for the calculation of specific characteristics of vent flows.
Ingénierie de la sécurité incendie — Exigences régissant les formules algébriques — Partie 5: Ecoulements au travers d'une ouverture
Le présent document spécifie les exigences régissant l’application d’un ensemble de formules algébriques explicites pour le calcul de caractéristiques spécifiques des écoulements au travers d’une ouverture.
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INTERNATIONAL ISO
STANDARD 24678-5
First edition
2023-06
Fire safety engineering —
Requirements governing algebraic
formulae —
Part 5:
Vent flows
Ingénierie de la sécurité incendie — Exigences régissant les formules
algébriques —
Partie 5: Ecoulements au travers d'une ouverture
Reference number
ISO 24678-5:2023(E)
© ISO 2023
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ISO 24678-5:2023(E)
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© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
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Published in Switzerland
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ISO 24678-5:2023(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. 2
6 Requirements governing limitations . 2
7 Requirements governing input parameters . 2
8 Requirements governing the domain of applicability . 3
9 Example of documentation . 3
Annex A (informative) Formulae for vent flows . 4
Annex B (informative) Examples of flow coefficient values .39
Bibliography .42
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ISO 24678-5:2023(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 16737:2012, 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 former Annexes A and B have been merged into a new Annex A;
— comparisons with experimental data have been added in Annex A;
— a new Annex B has been added to describe the examples of flow coefficient values.
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 24678-5:2023(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 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-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 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 information 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 24678-5:2023(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, ISO 24678-5 (this document), 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 24678-5:2023(E)
Fire safety engineering — Requirements governing
algebraic formulae —
Part 5:
Vent flows
1 Scope
This document specifies the requirements governing the application of a set of explicit algebraic
formulae for the calculation of specific characteristics of vent flows.
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
datum
elevation used as the reference elevation for evaluation of hydrostatic pressure profiles
Note 1 to entry: This is typically the lowest boundary of the enclosure.
3.3
effective flow area
flow area effective to air and smoke movement
3.4
flow coefficient
fraction of effective flow area over total area of a vent
3.5
hydrostatic pressure
atmospheric pressure profile associated with height
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ISO 24678-5:2023(E)
3.6
neutral plane height
elevation at which the pressure inside an enclosure is the same as the pressure outside the enclosure
3.7
pressure difference
difference between the pressure inside an enclosure and outside the enclosure at a specified elevation
3.8
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
3.9
smoke layer height
interface position
interface height
elevation of the smoke layer interface relative to a reference elevation
3.10
vent
opening in an enclosure boundary through which air and smoke can flow as a result of naturally- or
mechanically-induced forces
3.11
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 flow through a vent is a complex thermo-physical phenomenon that can be highly
transient or nearly steady-state. Vent flows may contain regions involved in flaming combustion and
regions where there is no combustion taking place. In addition to buoyancy, vent flows can be influenced
by dynamic forces due to external wind or mechanical fans.
4.3 Physical phenomena (e.g. natural vent flow, mechanical smoke exhaust, pressurization smoke
control) to which specific formulae apply shall be clearly identified.
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.
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ISO 24678-5:2023(E)
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 provided in Annex A.
Annex B contains examples of flow coefficient values to be used as input to calculations of vent flow.
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ISO 24678-5:2023(E)
Annex A
(informative)
Formulae for vent flows
A.1 Scope
This annex is intended to document the methods to calculate mass flow rate through vents. The formula
set covers the flow through vents connecting two enclosures with the same temperature, with uniform
but different temperatures, or with two-layered temperature profiles.
A.2 Symbols and abbreviated terms used in this annex
2
A equivalent area of multiple seral vents (m )
eq
2
A area of vent connecting enclosures i and j (m )
ij
B width of a vent (m)
B equivalent width of multiple seral vents (m)
eq
B width of vent connecting enclosures i and j (m)
ij
c specific heat of air and smoke (kJ/kg·K)
p
C flow coefficient (-)
D
2
g gravity acceleration (m/s )
h height above the datum (m)
h height of vent connecting enclosures i and j (m)
ij
h height of lower edge of vent above the datum (m)
l
h height of the bottom of middle segment above the datum (m)
m
h neutral plane height above the datum (m)
n
h height of the bottom of top segment above the datum (m)
t
h height of upper edge of vent above the datum (m)
u
H enthalpy flux from enclosure i to enclosure j (kW)
ij
max(x ,x ) maximum of x and x
1 2 1 2
min(x , x ) minimum of x and x
1 2 1 2
p (h) pressure in enclosure i at height h above the datum (Pa)
i
p (h) pressure in enclosure j at height h above the datum (Pa)
j
q mass flow rate of smoke or air from enclosure i to j (kg/s)
m,ij
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ISO 24678-5:2023(E)
q mass flow rate of smoke or air from enclosure i to j through bottom segment (kg/s)
m,ij,b
q mass flow rate of smoke or air from enclosure i to j through middle segment (kg/s)
m,ij,m
q mass flow rate of smoke or air from enclosure i to j through top segment (kg/s)
m,ij,t
q mass flux of chemical species from enclosure i to enclosure j (kg/s)
w,ij
T air layer temperature in enclosure i (K)
a,i
T temperature of enclosure i (K)
i
T temperature of enclosure j or outside (K)
j
T smoke layer temperature in enclosure i (K)
s,i
T reference temperature, typically the outside temperature (K)
0
u flow velocity from enclosure i to enclosure j (m/s)
ij
Y mass fraction of chemical species in enclosure i (kg/kg)
i
z smoke layer height in enclosure i (m)
i
ρ gas density of air layer in enclosure i (kg/m)
a,i
3
ρ gas density of smoke (or air) in enclosure i (kg/m )
i
3
ρ gas density of smoke (or air) in enclosure j (kg/m )
j
3
ρ gas density of smoke layer in enclosure i (kg/m )
s,i
3
ρ gas density of smoke (or air) at reference temperature (kg/m )
0
Δp (h) pressure difference between enclosure i and j at height h; that is, p (h)-p (h) (Pa)
ij i j
Δp minimum pressure difference to cause uni-directional flow (Pa)
flood
ζ height used as an integration variable (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
The methods permit calculation of flows through vents in enclosure boundaries arising from pressure
differences that develop between an enclosure and adjacent spaces as a result of temperature
differences. Pressure differences may also result from fire gas expansion, mechanical ventilation, wind
or other forces acting on the enclosure boundaries and vents, but these forces are not addressed in this
document. Given a pressure difference across a vent and the temperatures of the enclosures that the
vent connects, mass flow rate is calculated by using orifice flow theory.
The properties of an enclosure, such as smoke layer height, temperature, and other properties
are calculated by the principle of heat and mass conservation for the smoke layer as described in
ISO 24678-4.
A.3.1.2 Vent flow properties to be calculated
The formula set provides the mass, enthalpy and chemical species flow rates.
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ISO 24678-5:2023(E)
A.3.2 Scenario elements to which the formula set is applicable
The set of formulae is applicable to quasi-steady state vent flows driven by buoyancy caused by fire.
Dynamic pressure effects, such as wind, are not considered. Methods to calculate vent flow conditions
are developed for two types of temperature profiles: one is a uniform temperature profile while the
other is a two-layered profile as calculated by ISO 24678-4. The calculation conditions are summarized
in Table A.1.
Table A.1 — Summary of calculation conditions of vent flows
Temperature Arrangement of vent(s) flow patterns
profile
Uniform a) Single vent
Single layer b) Single vertical vent (general case, flow may be either
uni-directional or bi-directional)
c) Single vertical vent (special case, flow is bi-direction-
al)
d) Multiple vertical vents (general case, flow may be
either uni-directional or bi-directional)
e) Multiple vertical vents (special case of two small
vents in one enclosure, flow is bi-directional)
f) Multiple serial vertical vents (combination of multiple
serial vents into equivalent single vent)
g) Single horizontal vent (stable uni-directional flow
only)
Two layers h) Single vertical vent (general case, flow may be either
uni-directional or bi-directional)
i) Multiple vertical vents (general case, flow may be
either uni-directional or bi-directional)
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).
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ISO 24678-5:2023(E)
A.3.4 Standards and other documents where the formula set is used
ISO 24678-4 uses vent flow formulae to calculate smoke layer properties.
A.4 Formula-set documentation of calculation procedure
A.4.1 General aspects of vent flow
A.4.1.1 Classifications of vent flows
The velocity of flow through a vent is calculated according to the orifice flow theory based on application
of Bernoulli's theory. Methods to calculate vent flows are developed for the conditions shown in
Table A.2. For the case of vertical and horizontal vents, flow may be uni-directional or bi-directional.
Explicit formulae presented in this annex are applicable to bi-directional and uni-directional flows
through vertical vents and uni-directional flow through horizontal vents. For horizontal vents, bi-
directional flow takes place when the pressure difference is small. No general formula is available in
this annex because the flow is unstable.
Table A.2 — Classifications of vent flows
Uni-directional flows Bi-directional flows
Vertical
vent
Horizontal
vent
A.4.1.2 Orifice flow formula — uniform pressure difference over vent area
When uniform pressure difference is created by actions such as mechanical fans, the mass flow rate
through the vent is given by Formula (A.1):
qC==Au CA 2ρ Δp (A.1)
m,ij DDij ij ij iij
where Δp is calculated using Formula (A.2):
ij
Δp = p - p (A.2)
ij i j
It is assumed that the pressure difference across the vent is uniform over the entire vent area as shown
in Figure A.1.
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ISO 24678-5:2023(E)
Key
1 enclosure i
2 enclosure j
3 vent
4 stream lines
Figure A.1 — Streamlines and flow coefficient for isothermal orifice flow
A.4.1.3 General flow formula – non-uniform pressure difference over vent area
When a vertical temperature profile T (h) exists in enclosure i as shown in Figure A.2, the gas density,
i
ρ , at height h above the datum is calculated by Formula (A.3):
i
ρ T
353
00
ρ ()h =≈ (A.3)
i
Th() Th()
ii
NOTE Smoke is approximated by an ideal gas whose property is identical to air at normal atmospheric
pressure.
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ISO 24678-5:2023(E)
The hydrostatic pressure in enclosure i is calculated by integrating gas density over height, using
Formula (A.4):
h
ph()=−pg()0 ρζ() dζ (A.4)
ii i
∫
0
Hydrostatic pressure difference between enclosures i and j at height h is calculated using Formula (A.5):
Δph()=−ph() ph()
ij ij
h
=−{(pp00)( )}−−ρζ() ρζ() gdζ (A.5)
{}
ij ij
∫
0
h
=Δp (()0 −−ρζ() ρζ() gdζ
{}
ij ij
∫
0
where the pressure difference at the datum is determined by Formula (A.6):
Δpp()00=−() p ()0 (A.6)
ij ij
Flow through a vertical vent is calculated by applying the orifice flow theory to each vertical segment
of the vent. Given the hydrostatic pressure difference calculated using Formula (A.5), mass flow rates
between enclosures are calculated using Formulae (A.7) and (A.8):
h
u
qC= Bp20ρς()max(Δ ()ςς,)d (A.7)
m,ij D iij
∫
h
l
h
u
qC=−Bp20ρζ()max( Δ ()ζζ,)d (A.8)
m,ji Dj ij
∫
h
l
Key
1 enclosure i
2 enclosure j
Figure A.2 — Hydrostatic pressure difference between two adjacent enclosures
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ISO 24678-5:2023(E)
A.4.2 Flow through a vent connecting two enclosures of uniform, identical temperature
A.4.2.1 Scenario element
A vent is connecting two enclosures i and j. The temperatures of both enclosures are uniform and
identical. Pressure difference, Δp , is created across the vent as shown in Figure A.3.
ij
Key
1 enclosure i
2 enclosure j
Figure A.3 — Pressure difference across vertical vent and corresponding flow in case of
uniform, identical temperature
A.4.2.2 Mass flow rate through a vent
When a pressure difference is imposed across a vent with a uniform temperature profile, the mass flow
rate is calculated using Formula (A.9):
qC= Ap2ρ Δ (A.9)
m,ij D ij iij
where Formulae (A.10) and (A.11) apply:
Δpp=−p (A.10)
ij ij
353
ρ = (A.11)
i
T
i
A.4.2.3 Enthalpy flow rate through a vent
Enthalpy flow rate is calculated using the mass flow rate as shown in Formula (A.12):
Hc=−()TT q (A.12)
ij pmii0, j
NOTE Formula (A.12) is not repeated in the following subclauses but it is applicable to all cases in this annex.
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ISO 24678-5:2023(E)
A.4.2.4 Flow of chemical species through a vent
The flow rate of chemical species through a vent is calculated using the mass flow rate as shown in
Formula (A.13):
q = Y q
w,ij i m,ij
(A.13)
NOTE Formula (A.13) is not repeated in the following subclauses but it is applicable to all cases in this annex.
A.4.3 Flow through single vertical vent connecting two enclosures of uniform but
different temperatures — General case
A.4.3.1 Scenario element
As shown in Figure A.4, flow patterns are classified in accordance with the neutral plane height.
When the neutral plane locates below the lower edge of the vent (h < h ), flow is unidirectional from
n l
enclosure i to enclosure j. When the neutral plane locates within the range of vent (h
l n u
bi-directional. When the neutral plane locates above the upper edge of the vent (h < h ), flow is uni-
u n
[28],[29]
directional from enclosure j to enclosure i.
Key
1 enclosure i
2 enclosure j
3 neutral plane
Figure A.4 — Pressure difference across a vertical vent and corresponding flow directions in
case of T >T , (ρ < ρ )
i j i j
A.4.3.2 Gas densities of enclosures
The gas densities of enclosures are calculated using Formulae (A.14) and (A.15):
353
ρ = (A.14)
i
T
i
353
ρ = (A.15)
j
T
j
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ISO 24678-5:2023(E)
A.4.3.3 Neutral plane height above the datum
The neutral plane height above the datum is calculated using Formula (A.16):
Δp (0)
ij
h = (A.16)
n
()ρρ− g
i j
A.4.3.4 Mass flow rates
The mass flow rates are calculated by the following formulae according to temperature difference. In
case of T > T , (ρ < ρ ), see Formulae (A.17) and (A.18):
i j i j
2
32//32
CB 2ρρ()−−ρ gh{( hh)(−−hh)} ()
Duij ij i nl nn l
3
2
32/
q = C BBg2ρρ()−−ρ ()hh ()hh≤
m,ij D ij ij i un ln u
3
0 ()hh≤
un
0 ()hh<
nl
2
32/
q = CB 2ρρ()−−ρ gh()hh()≤
m,ji Dnij jj i ll nu
3
2
32//32
CB 2ρρ()−−ρ gh{( hh)(−−hh)} ()≤h
D ijjj ji nl nu un
3
and in case of T < T (ρ > ρ ), see Formulae (A.19) and (A.20):
i j i j
0 ()hh<
nl
2
32/
q = CB 2ρρ()−−ρ gh()hh()≤
m,ij Dnij ii j ll nu
3
2
32//32
CB 2ρρ()−−ρ gh{( hh)(−−hh)} ()≤h
D ijji ij nl nu un
3
2
32//32
CB 2ρρ()−−ρ gh{( hh)(−−hh)} ()
Duij ji j nl nn l
3
2
32/
q = C BBg2ρρ()−−ρ ()hh ()hh≤
m,ji D ij ji j un ln u
3
0 ()hh≤
un
In non-dimensional form, the mass flow rates can be expressed using Formulae (A.21) and (A.22):
q
m,ij
*
q = (A.21)
m,ij
32/
2ρρ()−−ρ Bh()h
ij iij ul
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ISO 24678-5:2023(E)
q
m,ji
*
q = (A.22)
m,ji
32/
2ρρ()−−ρ Bh()h
jj iij ul
Formulae (A.21) and (A.22) are plotted in Figure A.5 against non-dimensional neutral plane height; see
Formula (A.23):
hh−
* nl
h = (A.23)
n
hh−
ul
Key
*
X
non-dimensional neutral plane height, h
n
*
Y
non-dimensional mass flow rates, q
m
1 uni-directional flow
2 bi-directional flow
*
non-dimensional mass flow rate from enclosure i to enclosure j, q
m,ij
*
non-dimensional mass flow rate from enclosure j to enclosure i, q
m,ji
Figure A.5 — Non-dimensional mass flow rates through a vertical vent in case of T > T (ρ < ρ )
i j i j
A.4.4 Flow through single vertical vent connecting t
...
DRAFT INTERNATIONAL STANDARD
ISO/DIS 24678-5
ISO/TC 92/SC 4 Secretariat: AFNOR
Voting begins on: Voting terminates on:
2022-07-08 2022-09-30
Fire safety engineering — Requirements governing
algebraic formulae —
Part 5:
Vent flows
Ingénierie de la sécurité incendie — Exigences régissant les formules algébriques —
Partie 5: Ecoulements au travers d'une ouverture
ICS: 13.220.01
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ISO/DIS 24678-5:2022(E)
DRAFT INTERNATIONAL STANDARD
ISO/DIS 24678-5
ISO/TC 92/SC 4 Secretariat: AFNOR
Voting begins on: Voting terminates on:
Fire safety engineering — Requirements governing
algebraic formulae —
Part 5:
Vent flows
Ingénierie de la sécurité incendie — Exigences régissant les formules algébriques —
Partie 5: Ecoulements au travers d'une ouverture
ICS: 13.220.01
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PROVIDE SUPPORTING DOCUMENTATION. © ISO 2022
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ISO/DIS 24678-5:2022(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 vent flows . 3
Annex B (informative) Examples of flow coefficient values .38
Bibliography .41
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ISO/DIS 24678-5:2022(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 16737:2006), which has been technically
revised.
The main changes compared to the previous edition are as follows:
— the main body was simplified by referring to Part 1 of this standard;
— the former Annexes A and B were merged into new Annex A;
— comaprisons with experimental data were added in Annex A;
— new Annex B was added to describe the examples of flow coefficient values;
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 24678-5:2022(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 24678-5:2022(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 16735, ISO 16736, ISO 16737,
ISO/TR 16738, ISO 24678.
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ISO/DIS 24678-5:2022(E)
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 24678-5:2022(E)
Fire safety engineering — Requirements governing
algebraic formulae —
Part 5:
Vent flows
1 Scope
This document specifies the requirements governing the application of explicit algebraic formula sets
to the calculation of specific characteristics of vent flows.
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 13943:2017, Fire safety — Vocabulary
ISO 24678-1:2019, 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
vent
an opening in an enclosure boundary through which air and smoke can flow as a result of naturally- or
mechanically-induced forces
3.2
vent flows
the flows of smoke or air through a vent in an enclosure boundary
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 flow through a vent is a complex thermo-physical phenomenon that can be highly
transient or nearly steady-state. Vent flows may contain regions involved in flaming combustion and
regions where there is no combustion taking place. In addition to buoyancy, vent flows can be influenced
by dynamic forces due to external wind or mechanical fans.
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ISO/DIS 24678-5:2022(E)
4.3 Physical phenomena, e.g., natural vent flow, mechanical smoke exhaust, pressurization smoke
control, to which specific formulae apply shall be clearly identified.
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 provided in Annex A.
Annex B contains examples of flow coefficient values to be used as input to calculations of vent flow.
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ISO/DIS 24678-5:2022(E)
Annex A
(informative)
Formulae for vent flows
A.1 Scope
This Annex is intended to document the methods to calculate mass flow rate through vents. The formula
set covers the flow through vents connecting two enclosures with the same temperature, with uniform
but different temperatures, with two-layered temperature profiles.
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
datum
the elevation used as the reference elevation for evaluation of hydrostatic pressure profiles
A.2.3
enclosure
a room, space or volume that is bounded by surfaces
A.2.4
flow coefficient
an empirical efficiency factor that accounts for the difference between the actual and the theoretical
flow rate through a vent
A.2.5
hydrostatic pressure
the atmospheric pressure profile associated with height
A.2.6
neutral plane height
the elevation at which the pressure inside an enclosure is the same as the pressure outside the enclosure
A.2.7
pressure difference
the difference between the pressure inside an enclosure and outside the enclosure at a specified
elevation
A.2.8
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.2.9
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
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ISO/DIS 24678-5:2022(E)
A.2.10
smoke layer
the 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
A.2.11
Smoke layer height
the elevation of the smoke layer interface relative to a reference elevation, typically the lowest boundary
of the enclosure. Also referred to as the interface position
A.3 Symbols and abbreviated terms used in this Annex
A equivalent area of muitiple seral vents (m)
eq
2
A area of vent connecting enclosures i and j (m )
ij
B equivalent width of muitiple seral vents (m)
eq
B width of vent connecting enclosures i and j (m)
ij
c specific heat of air and smoke (kJ/kg·K)
p
C flow coefficient (-)
D
2
g gravity acceleration (m/s )
h height above the datum (m)
h height of vent connecting enclosures i and j
ij
h height of lower edge of vent above the datum (m)
l
h height of the bottom of middle segment above the datum (m)
m
h neutral plane height above the datum (m)
n
h height of the bottom of top segment above the datum (m)
t
h height of upper edge of vent above the datum (m)
u
H enthalpy flux from enclosure i to enclosure j (kW)
ij
max(x ,x ) maximum of x and x
1 2 1 2
min(x , x ) minimum of x and x
1 2 1 2
p (h) pressure in enclosure i at height h above the datum (Pa)
i
q mass flow rate of smoke or air from enclosure i to j (kg/s)
m,ij
q mass flow rate of smoke or air from enclosure i to j through bot-
m,ij,b
tom segment (kg/s)
q mass flow rate of smoke or air from enclosure i to j through mid-
m,ij,m
dle segment (kg/s)
q mass flow rate of smoke or air from enclosure i to j through top
m,ij,t
segment (kg/s)
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ISO/DIS 24678-5:2022(E)
q mass flux of chemical species from enclosure i to enclosure j
w,ij
(kg/s)
T reference temperature, typicall the outside temperature (K)
0
T temperature of enclosure i (K)
i
T air layer temperature in enclosure i (K)
a,i
T smoke layer temperature in enclosure i (K)
s,i
u flow velocity from enclosure i to enclosure j (m/s)
ij
w mass fraction of chemical species in enclosure i (kg/kg)
i
ρ gas density of air layer in enclosure i (kg/m)
a,i
3
ρ gas density of smoke (or air) in enclosure i (kg/m )
i
3
ρ gas density of smoke (or air) in enclosure j (kg/m )
j
3
ρ gas density of smoke layer in enclosure i (kg/m )
s,i
3
ρ gas density of smoke (or air) at reference temperature (kg/m )
0
Δp (h) pressure difference between enclosure i and j at height h; that is,
ij
p (h)-p (h), (Pa)
i j
Δp minimum pressure difference to cause uni-directional flow (Pa)
flood
ζ height used as an integration variable (m)
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
The methods permit calculation of flows through vents in enclosure boundaries arising from pressure
differences that develop between an enclosure and adjacent spaces as a result of temperature
differences. Pressure differences may also result from fire gas expansion, mechanical ventilation, wind,
or other forces acting on the enclosure boundaries and vents, but these forces are not addressed in this
document. Given a pressure difference across a vent and the temperatures of the enclosures that the
vent connects, mass flow rate is calculated by using orifice flow theory.
The properties of an enclosure, such as smoke layer height, temperature, and other properties
are calculated by the principle of heat and mass conservation for the smoke layer as described in
[1]
ISO 24678-4 .
A.4.1.2 Vent flow properties to be calculated
Formulae provide the mass, enthalpy and chemical species flow rates.
A.4.2 Scenario elements to which the formula set is applicable
The set of formulae is applicable to quasi-steady state vent flows driven by buoyancy caused by fire.
Dynamic pressure effects, such as wind, are not considered. Methods to calculate vent flow conditions
are developed for two types of temperature profiles: One is a uniform temperature profile while
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ISO/DIS 24678-5:2022(E)
[1]
the other is a two-layered profile as calculated by ISO 24687-4. The calculation conditions are
summarized in Figure A.1.
Temperature Arrangement of vent(s) flow patterns
profile
Uniform (a) Single vent
Single layer (b) Single vertical vent
(general case, flow may be either uni-directional or
bi-directional)
(c) Single vertical vent
(special case, flow is bi-directional)
(d) Multiple vertical vents
(general case, flow may be either uni-directional or
bi-directional)
(e) Multiple vertical vents
(special case of two small vertical vents in one enclo-
sure, flow is bi-directional)
(f) Multiple serial vertical vents
(Combination of multiple serial vents into equivalent
single vent)
(g) Single horizontal vent
(stable uni-directional flow only)
Two layered (h) Single vertical vent
(general case, flow may be either uni-directional or
bi-directional)
(i) Multiple vertical vents
(general case, flow may be either uni-directional or
bi-directional)
Figure A.1 — Summary of calculation conditions of vent flows
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).
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ISO/DIS 24678-5:2022(E)
A.4.4 Standards and other documents where the formula set is used
[1]
ISO 24678-4 uses vent flow formulae to calculate smoke layer properties.
A.5 Formula-set documentation of calculation process
A.5.1 General aspects of vent flow
A.5.1.1 Classifications of vent flows
The velocity of flow through a vent is calculated according to the orifice flow theory based on application
of the Bernoulli's theory. Methods to calculate vent flows are developed for the conditions shown in
Figure A.2. For the case of vertical and horizontal vents, flow may be uni-directional or bi-directional.
Explicit formulae presented in this Annex are applicable to bi-directional and uni-directional flows
through vertical vents and uni-directional flow through horizontal vents. For horizontal vents, bi-
directional flow takes place when the pressure difference is small. No general formula is available in
this Annex because the flow is unstable.
uni-directional flows bi-directional flows
vertical vent
horizontal
vent
Figure A.2 — Classifications of vent flows
A.5.1.2 Orifice flow formula – uniform pressure difference over vent area
When uniform pressure difference is created by some actions such as mechanical fans, the mass flow
rate through the vent is given by:
qC==Au CA 2ρ Δp (A.1)
m,ij DijijD ij iij
where
Δp = p - p (A.2)
ij i j
It is assumed that the pressure difference across the vent is uniform over the entire vent area as shown
in Figure A.3.
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ISO/DIS 24678-5:2022(E)
Key
1 enclosure i
2 enclosure j
3 vent
4 stream lines
Figure A.3 — Streamlines and flow coefficient for isothermal orifice flow
A.5.1.3 General flow formula – non-uniform pressure difference over vent area
When a vertical temperature profile T (h) exists in enclosure i as shown in Figure A.4, the gas density ρ
i i
at height h above the datum is calculated by:
ρ T
353
00
ρ ()h =≈ (A.3)
i
Th() Th()
ii
NOTE Smoke is approximated by an ideal gas whose property is identical to air at normal atmospheric
pressure.
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ISO/DIS 24678-5:2022(E)
The hydrostatic pressure in enclosure i is calculated by integrating gas density over height:
h
ph()=−pg()0 ρζ() dζ (A.4)
ii i
∫
0
Hydrostatic pressure difference between enclosures i and j at height h is:
Δph()=−ph() ph()
ij ij
h
=−{(pp00)( )}−−ρζ() ρζ() gdζ (A.5)
{}
ij ij
∫
0
h
=Δp (()0 −−ρζ() ρζ() gdζ
{}
ij ij
∫
0
where the pressure difference at the datum is determined by:
Δpp()00=−() p ()0 (A.6)
ij ij
Flow through a vertical vent is calculated by applying the orifice flow theory to each vertical segment
of the vent. Given the hydrostatic pressure difference by (Formula A.5), mass flow rates between
enclosures are calculated by:
h
u
qC= Bp20ρς()max(Δ ()ςς,)d (A.7)
m,ij Di ij
∫
h
l
h
u
qC=−Bp20ρζ()max( Δ ()ζζ,)d (A.8)
m,ji Dj ij
∫
h
l
Key
1 enclosure i
2 enclosure j
Figure A.4 — Hydrostatic pressure difference between two adjacent enclosures
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ISO/DIS 24678-5:2022(E)
A.5.2 Flow through vent connecting two enclosures of uniform, identical temperature
A.5.2.1 Scenario element
A vent is connecting two enclosures i and j. The temperatures of both enclosures are unform and
identical. Pressure difference, Δp , is created across the vent as shown in Figure A.5.
ij
Key
1 enclosure i
2 enclosure j
Figure A.5 — Pressure difference across vertical vent and corresponding flow in case of
uniform, identical temperature
A.5.2.2 Mass flow rate through a vent
When a pressure difference is imposed across a vent with a uniform temperature profile, the mass flow
rate is calculated by:
qC= Ap2ρ Δ (A.9)
m,ij Diji ij
Δpp=− p (A.10)
ij ij
353
ρ = (A.11)
i
T
i
A.5.2.3 Enthalpy flow rate through a vent
Enthalpy flow rate is calculated using the mass flow rate:
Hc=−()TT q (A.12)
ij pi 0 m,ij
NOTE Formula for enthalpy flow rate is not repeated in the following clauses but (Formula A.12) is applicable
to all the cases in this Annex.
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ISO/DIS 24678-5:2022(E)
A.5.2.4 Flow of chemical species through a vent
Flow rate of chemical species through vent is calculated using the mass flow rate:
q = w q (A.13)
w,ij i m,ij
NOTE Formula for flow rate of chemical species is not repeated in the following clauses but (Formula A.13)
is applicable to all the cases in this Annex.
A.5.3 Flow through single vertical vent connecting two enclosures of uniform but
different temperatures - general case
A.5.3.1 Scenario element
As shown in Figure A.6, flow patterns are classified in accordance with the neutral plane height. When
the neutral plane locates below the lower edge of the vent (h < h ), flow is unidirectional from enclosure
n l
i to j. When the neutral plane locates within the range of vent (h
l n u
When the neutral plane locates above the upper edge of the vent (h < h ), flow is uni-directional from
u n
[2][3]
enclosure j to i .
Key
1 enclosure i
2 enclosure j
3 neutral plane
Figure A.6 — Pressure difference across a vertical vent and corresponding flow directions in
case of T >T , (ρ < ρ )
i j i j
A.5.3.2 Gas densities of enclosures
The gas densities of enclosures are calculated by:
353
ρ = (A.14)
i
T
i
353
ρ = (A.15)
j
...
PROJET DE NORME INTERNATIONALE
ISO/DIS 24678-5
ISO/TC 92/SC 4 Secrétariat: AFNOR
Début de vote: Vote clos le:
2022-07-08 2022-09-30
Ingénierie de la sécurité incendie — Exigences régissant
les formules algébriques —
Partie 5:
Ecoulements au travers d'une ouverture
Fire safety engineering — Requirements governing algebraic formulae —
Part 5: Vent flows
ICS: 13.220.01
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OBSERVATIONS, NOTIFICATION DES DROITS
DE PROPRIÉTÉ DONT ILS AURAIENT
ÉVENTUELLEMENT CONNAISSANCE ET À
© ISO 2022
FOURNIR UNE DOCUMENTATION EXPLICATIVE.
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ISO/DIS 24678-5:2022(F)
ISO/TC 92/SC 4
Date : 2022-09-30
ISO/DIS 24678-5:2022
ISO/TC 92/SC 4/GT 9
Secrétariat : AFNOR
Ingénierie de la sécurité incendie — Exigences régissant les formules
algébriques — Partie 5 : Écoulements au travers d’une ouverture
Fire Safety Engineering — Requirements governing algebraic formulae — Part 5: Vent Flows
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.
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droits de propriété dont ils auraient éventuellement connaissance et à fournir une documentation
explicative.
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ISO/DIS 24678-5:2022(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 écoulements au travers d’une ouverture .3
Annexe B (informative) Exemples de valeurs de coefficient de débit . 44
Bibliographie . 48
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ISO/DIS 24678-5:2022(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 16737:2006), 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 ;
— les anciennes Annexes A et B ont été fusionnées en une nouvelle Annexe A ;
— des comparaisons avec des données expérimentales ont été ajoutées à l’Annexe A ;
— une nouvelle Annexe B a été ajoutée pour décrire les exemples des valeurs de coefficient de débit.
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 24678-5:2022(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.
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.
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ISO/DIS 24678-5:2022(F)
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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ISO/DIS 24678-5:2022(F)
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 16735, l’ISO 16736,
l’ISO 16737, 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 24678-5:2022(F)
Ingénierie de la sécurité incendie — Exigences régissant les
formules algébriques — Partie 5 : Écoulements au travers
d’une ouverture
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 écoulements au travers d’une ouverture.
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 datées, seule l’édition citée s’applique.
Pour les références non datées, la dernière édition du document de référence s’applique (y compris les
éventuels amendements).
ISO 13943:2017, Sécurité au feu — Vocabulaire.
ISO 24678-1:2019, 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 donnés dans 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
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
3.2
écoulements au travers d’une ouverture
écoulements de fumée ou d’air au travers d’une ouverture dans la limite physique d’une enceinte
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.
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4.2 L’écoulement flottant de fumée au travers d’une ouverture est un phénomène thermophysique
complexe qui peut être extrêmement transitoire ou quasi stationnaire. Les écoulements au travers
d’une ouverture peuvent comprendre des zones impliquées dans la combustion avec flamme et des
zones où il ne se produit pas de combustion. Outre la flottabilité, les écoulements au travers d’une
ouverture peuvent être influencés par des forces dynamiques dues au vent ou à des ventilateurs
mécaniques.
4.3 Les phénomènes physiques, tels qu’un écoulement naturel au travers d’une ouverture, un système
d’extraction mécanique de la fumée, un système de désenfumage par pressurisation, auxquels
s’appliquent des formules spécifiques doivent être clairement identifiés.
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.
L’Annexe B contient des exemples de valeurs de coefficient de débit à utiliser dans les calculs
d’écoulement au travers d’une ouverture.
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ISO/DIS 24678-5:2022(F)
Annexe A
(informative)
Formules pour les écoulements au travers d’une ouverture
A.1 Domaine d’application
La présente annexe est destinée à documenter les méthodes permettant de calculer le débit massique
au travers d’ouvertures. L’ensemble de formules couvre l’écoulement au travers d’ouvertures reliant
deux enceintes présentant la même température, des températures uniformes mais différentes, et des
profils de température à deux couches.
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
plan de référence
élévation utilisée comme élévation de référence pour l’évaluation des profils de pression hydrostatique
A.2.3
enceinte
pièce, espace ou volume limité par des surfaces
A.2.4
coefficient de débit
facteur d’efficacité empirique qui tient compte de la différence entre le débit réel et le débit théorique
par une ouverture
A.2.5
pression hydrostatique
profil de pression atmosphérique associé à la hauteur
A.2.6
hauteur du plan neutre
élévation à laquelle la pression à l’intérieur d’une enceinte est la même que la pression à l’extérieur de
l’enceinte
A.2.7
différence de pression
différence entre la pression à l’intérieur d’une enceinte et à l’extérieur de cette enceinte à une élévation
spécifiée
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A.2.8
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.2.9
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.2.10
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 »
A.2.11
hauteur de la couche de fumée
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 « position de l’interface »
A.3 Symboles et abréviations utilisés dans la présente annexe
A surface équivalente de plusieurs ouvertures en série (m)
eq
2
Aij surface de l’ouverture qui relie les enceintes i et j (m )
B largeur équivalente de plusieurs ouvertures en série (m)
eq
B largeur de l’ouverture qui relie les enceintes i et j (m)
ij
c chaleur spécifique de l’air et de la fumée (kJ/kg·K)
p
C coefficient de débit (-)
D
2
g accélération due à la pesanteur (m/s )
h hauteur au-dessus du plan de référence (m)
h hauteur de l’ouverture qui relie les enceintes i et j
ij
h hauteur du bord inférieur de l’ouverture au-dessus du plan de référence (m)
l
h hauteur de la partie basse du segment du milieu au-dessus du plan de référence (m)
m
h hauteur du plan neutre au-dessus du plan de référence (m)
n
h hauteur de la partie basse du segment supérieur au-dessus du plan de référence (m)
t
h hauteur du bord supérieur de l’ouverture au-dessus du plan de référence (m)
u
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H flux d’enthalpie de l’enceinte i vers l’enceinte j (kW)
ij
max(x ,x ) maximum de x et x
1 2 1 2
min(x , x ) minimum de x et x
1 2 1 2
p (h) pression dans l’enceinte i à la hauteur h au-dessus du plan de référence (Pa)
i
q débit massique de fumée ou d’air de l’enceinte i vers l’enceinte j (kg/s)
m,ij
q débit massique de fumée ou d’air de l’enceinte i vers l’enceinte j dans le segment
m,ij,b
inférieur (kg/s)
q débit massique de fumée ou d’air de l’enceinte i vers l’enceinte j dans le segment du
m,ij,m
milieu (kg/s)
q débit massique de fumée ou d’air de l’enceinte i vers l’enceinte j dans le segment
m,ij,t
supérieur (kg/s)
q flux de masse d’espèces chimiques de l’enceinte i vers l’enceinte j (kg/s)
w,ij
T température de référence, généralement la température extérieure (K)
0
T température de l’enceinte i (K)
i
T température de la couche d’air dans l’enceinte i (K)
a,i
T température de la couche de fumée dans l’enceinte i (K)
s,i
u vitesse d’écoulement de l’enceinte i vers l’enceinte j (m/s)
ij
w fraction massique d’espèces chimiques dans l’enceinte i (kg/kg)
i
ρa,i masse volumique de la couche d’air dans l’enceinte i (kg/m)
3
ρ masse volumique de la fumée (ou de l’air) dans l’enceinte i (kg/m )
i
3
ρ masse volumique de la fumée (ou de l’air) dans l’enceinte j (kg/m )
j
3
ρ masse volumique de la couche de fumée dans l’enceinte i (kg/m )
s,i
3
ρ masse volumique de la fumée (ou de l’air) à la température de référence (kg/m )
0
Δp (h) différence de pression entre l’enceinte i et l’enceinte j à la hauteur h ; c’est-à-dire
ij
p (h)-p (h), (Pa)
i j
Δp différence de pression minimale pour déclencher un écoulement unidirectionnel (Pa)
flot
ζ hauteur utilisée comme variable d’intégration (m)
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ISO/DIS 24678-5:2022(F)
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
Les méthodes permettent le calcul des écoulements au travers d’ouvertures situées sur les limites
physiques d’une enceinte résultant de différences de pression qui se produisent entre une enceinte et
les espaces adjacents, à cause de leur différence de température. Les différences de pression peuvent
également résulter de la dilatation des gaz brûlés, de la ventilation mécanique, du vent ou d’autres
forces agissant sur les limites des enceintes et les ouvertures, mais ces forces ne sont pas abordées dans
le présent document. À partir de la différence de pression au travers d’une ouverture et des
températures des enceintes reliées par l’ouverture, le débit massique est calculé selon de la théorie de
l’écoulement à travers un orifice.
Les propriétés d’une enceinte, telles que la hauteur de la couche de fumée, la température et d’autres
propriétés, sont calculées selon le principe de conservation de la chaleur et de la masse pour la couche
[1]
de fumée comme décrit dans l’ISO 24678-4 .
A.4.1.2 Propriétés d’un écoulement au travers d’une ouverture à calculer
Les formules donnent le débit massique, le débit d’enthalpie et le débit des espèces chimiques.
A.4.2 Éléments de scénario auxquels est applicable l’ensemble de formules
L’ensemble de formules s’applique aux écoulements quasi stationnaires au travers d’une ouverture
gouvernés par les forces de flottabilité sous l’effet du feu. Les effets de pression dynamique, comme le
vent, ne sont pas pris en compte. Des méthodes permettant de calculer les conditions d’écoulement au
travers d’une ouverture sont développées pour deux types de profils de température : l’un est un profil
de température uniforme alors que l’autre est un profil à deux couches, tel que calculé par
[1]
l’ISO 24687-4. Les conditions de calcul sont résumées à la Figure A.1.
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ISO/DIS 24678-5:2022(F)
Profil de Disposition de l’ouverture ou des ouvertures Configurations de l’écoulement
température
Uniforme (a) Une seule ouverture
Une seule (b) Une seule ouverture verticale
couche (cas général, l’écoulement peut être unidirectionnel ou
bidirectionnel)
(c) Une seule ouverture verticale
(cas particulier, l’écoulement est bidirectionnel)
(d) Ouvertures verticales multiples
(cas général, l’écoulement peut être unidirectionnel ou
bidirectionnel)
(e) Ouvertures verticales multiples
(cas particulier de deux petites ouvertures verticales
dans une enceinte, l’écoulement est bidirectionnel)
(f) Ouvertures verticales multiples en série
(combinaison de plusieurs ouvertures verticales en une
seule ouverture équivalente)
(g) Une seule ouverture horizontale
(écoulement unidirectionnel stable uniquement)
Deux couches (h) Une seule ouverture verticale
(cas général, l’écoulement peut être unidirectionnel ou
bidirectionnel)
(i) Ouvertures verticales multiples
(cas général, l’écoulement peut être unidirectionnel ou
bidirectionnel)
Figure A.1 — Synthèse des conditions de calcul des écoulements au travers d’une ouverture
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).
© ISO 2022 – Tous droits réservés
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ISO/DIS 24678-5:2022(F)
A.4.4 Normes et autres documents dans lesquels est utilisé l’ensemble de formules
[1]
L’ISO 24678-4 utilise des formules liées à l’écoulement au travers d’une ouverture pour calculer les
propriétés de la couche de fumée.
A.5 Documentation de l’ensemble de formules du processus de calcul
A.5.1 Aspects généraux d’un écoulement au travers d’une ouverture
A.5.1.1 Classification des écoulements au travers d’une ouverture
La vitesse de l’écoulement au travers d’une ouverture est calculée conformément à la théorie
d’écoulement par un orifice, d’après l’application de la théorie de Bernoulli. Des méthodes pour calculer
les écoulements au travers d’une ouverture sont développées pour les conditions représentées à la
Figure A.2. Dans le cas d’ouvertures verticales et horizontales, l’écoulement peut être unidirectionnel ou
bidirectionnel. Les formules explicites de la présente annexe s’appliquent aux écoulements
bidirectionnel et unidirectionnel au travers d’ouvertures verticales et à un écoulement unidirectionnel
au travers d’ouvertures horizontales. Pour les ouvertures horizontales, un écoulement bidirectionnel se
produit lorsque la différence de pression est faible. Aucune formule générale n’est proposée dans la
présente annexe, car l’écoulement est instable.
écoulements unidirectionnels écoulements bidirectionnels
ouverture verticale
ouverture horizontale
Figure A.2 — Classification des écoulements au travers d’une ouverture
A.5.1.2 Formule pour l’écoulement au travers d’un orifice – différence de pression uniforme
sur la surface de l’ouverture
Lorsqu’une différence de pres
...
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