SIST EN ISO 21805:2023
(Main)Guidance and recommendations on design, selection and installation of vents to safeguard the structural integrity of enclosures protected by gaseous fire-extinguishing systems (ISO 21805:2023)
Guidance and recommendations on design, selection and installation of vents to safeguard the structural integrity of enclosures protected by gaseous fire-extinguishing systems (ISO 21805:2023)
This document gives guidelines for fulfilling the requirements contained in ISO 6183:2022, 6.4.1 and 7.4.1 and ISO 14520‑1:2023, 5.2.1 h) and 5.3 h), in respect to over- and under-pressurization venting and post-discharge extract.
It considers the design, selection and installation of vents to safeguard the structural integrity of enclosures protected by fixed gaseous extinguishing systems and the post-discharge venting provisions where used.
Anleitung für die Konstruktion, Auswahl und Installation von Entlüftungen zur Gewährleistung der strukturellen Integrität von Gehäusen, die durch ortsfeste Gaslöschanlagen geschützt sind (ISO 21805:2023)
Dieses Dokument enthält Anleitungen für die Erfüllung der Anforderungen von ISO 6183:2009, 6.4.1 und 7.4.1, sowie von ISO 14520-1:2015, 5.2.1 h) und 5.3 h), in Bezug auf Über- und Unterdruckentlastungsvorrichtung und die Nachentlüftung.
Es behandelt die Auslegung, Auswahl und Installation von Entlüftungsvorrichtungen, mit dem Ziel, die strukturelle Integrität von Räumen sicherzustellen, die durch ortsfeste Gaslöschanlagen geschützt sind, und betrachtet die Anforderungen an die Nachentlüftung, sofern verwendet.
Lignes directrices et recommandations relatives à la conception, à la sélection et à l'installation d'évents pour préserver l'intégrité structurelle des enceintes protégées par des systèmes d'extinction d'incendie à gaz (ISO 21805:2023)
Le présent document donne des lignes directrices relatives à la manière de satisfaire aux exigences contenues dans l’ISO 6183:2022, 6.4.1 et 7.4.1 et dans l’ISO 14520‑1:2023, 5.2.1 h) et 5.3 h), en ce qui concerne les évents en cas de surpression et de dépression et l’extraction post-émission.
Il couvre la conception, la sélection et l’installation d’évents permettant de préserver l’intégrité structurelle des enceintes protégées par des systèmes fixes d’extinction d’incendie à gaz et les dispositions de ventilation post-émission lorsqu’ils sont utilisés.
Navodilo in priporočila za projektiranje, izbiro in vgradnjo prezračevalnih naprav za zagotavljanje strukturne integritete namestitvenih prostorov, zaščitenih s sistemi za gašenje s plinom (ISO 21805:2023)
Ta dokument vsebuje smernice za izpolnjevanje zahtev iz standarda ISO 6183:2022, točki 6.4.1 in 7.4.1, in standarda ISO 14520‑1:2023, točki 5.2.1 h) in 5.3 h), glede prezračevanja s podtlakom in nadtlakom ter odzračevanja.
Upošteva projektiranje, izbiro in vgradnjo prezračevalnih naprav za zagotavljanje strukturne integritete namestitvenih prostorov, zaščitenih s fiksnimi sistemi za gašenje s plinom, in določbe za naknadno odzračevanje.
General Information
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Standards Content (Sample)
SLOVENSKI STANDARD
SIST EN ISO 21805:2023
01-junij-2023
Nadomešča:
SIST-TS CEN ISO/TS 21805:2019
Navodilo in priporočila za projektiranje, izbiro in vgradnjo prezračevalnih naprav
za zagotavljanje strukturne integritete namestitvenih prostorov, zaščitenih s
sistemi za gašenje s plinom (ISO 21805:2023)
Guidance and recommendations on design, selection and installation of vents to
safeguard the structural integrity of enclosures protected by gaseous fire-extinguishing
systems (ISO 21805:2023)
Anleitung für die Konstruktion, Auswahl und Installation von Entlüftungen zur
Gewährleistung der strukturellen Integrität von Gehäusen, die durch ortsfeste
Gaslöschanlagen geschützt sind (ISO 21805:2023)
Lignes directrices et recommandations relatives à la conception, à la sélection et à
l'installation d'évents pour préserver l'intégrité structurelle des enceintes protégées par
des systèmes d'extinction d'incendie à gaz (ISO 21805:2023)
Ta slovenski standard je istoveten z: EN ISO 21805:2023
ICS:
13.220.10 Gašenje požara Fire-fighting
91.140.30 Prezračevalni in klimatski Ventilation and air-
sistemi conditioning systems
SIST EN ISO 21805:2023 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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SIST EN ISO 21805:2023
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SIST EN ISO 21805:2023
EN ISO 21805
EUROPEAN STANDARD
NORME EUROPÉENNE
March 2023
EUROPÄISCHE NORM
ICS 13.220.10; 91.140.30 Supersedes CEN ISO/TS 21805:2019
English Version
Guidance and recommendations on design, selection and
installation of vents to safeguard the structural integrity of
enclosures protected by gaseous fire-extinguishing
systems (ISO 21805:2023)
Lignes directrices et recommandations relatives à la Anleitung für die Konstruktion, Auswahl und
conception, à la sélection et à l'installation d'évents Installation von Entlüftungen zur Gewährleistung der
pour préserver l'intégrité structurelle des enceintes strukturellen Integrität von Gehäusen, die durch
protégées par des systèmes d'extinction d'incendie à ortsfeste Gaslöschanlagen geschützt sind (ISO
gaz (ISO 21805:2023) 21805:2023)
This European Standard was approved by CEN on 7 August 2022.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this
European Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references
concerning such national standards may be obtained on application to the CEN-CENELEC Management Centre or to any CEN
member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by
translation under the responsibility of a CEN member into its own language and notified to the CEN-CENELEC Management
Centre has the same status as the official versions.
CEN members are the national standards bodies of Austria, Belgium, Bulgaria, Croatia, Cyprus, Czech Republic, Denmark, Estonia,
Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway,
Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and
United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2023 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 21805:2023 E
worldwide for CEN national Members.
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SIST EN ISO 21805:2023
EN ISO 21805:2023 (E)
Contents Page
European foreword . 3
2
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SIST EN ISO 21805:2023
EN ISO 21805:2023 (E)
European foreword
This document (EN ISO 21805:2023) has been prepared by Technical Committee ISO/TC 21
"Equipment for fire protection and fire fighting" in collaboration with Technical Committee CEN/TC
191 “Fixed firefighting systems” the secretariat of which is held by BSI.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by September 2023, and conflicting national standards
shall be withdrawn at the latest by September 2023.
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CEN shall not be held responsible for identifying any or all such patent rights.
This document supersedes CEN ISO/TS 21805:2019.
Any feedback and questions on this document should be directed to the users’ national standards
body/national committee. A complete listing of these bodies can be found on the CEN website.
According to the CEN-CENELEC Internal Regulations, the national standards organizations of the
following countries are bound to implement this European Standard: Austria, Belgium, Bulgaria,
Croatia, Cyprus, Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland,
Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Republic of
North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Türkiye and the
United Kingdom.
Endorsement notice
The text of ISO 21805:2023 has been approved by CEN as EN ISO 21805:2023 without any modification.
3
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SIST EN ISO 21805:2023
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SIST EN ISO 21805:2023
INTERNATIONAL ISO
STANDARD 21805
First edition
2023-02
Guidance and recommendations on
design, selection and installation
of vents to safeguard the structural
integrity of enclosures protected by
gaseous fire-extinguishing systems
Lignes directrices et recommandations relatives à la conception,
à la sélection et à l'installation d'évents pour préserver l'intégrité
structurelle des enceintes protégées par des systèmes d'extinction
d'incendie à gaz
Reference number
ISO 21805:2023(E)
© ISO 2023
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SIST EN ISO 21805:2023
ISO 21805:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
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SIST EN ISO 21805:2023
ISO 21805:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms.2
5 Use and limitations . 3
6 Safety . 4
6.1 Structural safety . 4
6.2 Personnel safety . 4
7 System design — Pressure-relief venting . 4
7.1 General . 4
7.2 Extinguishant characteristics . . 5
7.2.1 Positive and negative pressurization . 5
7.2.2 Pressure graphs . 5
7.3 Enclosure characteristics . 6
7.4 Pressure-relief vent paths . 6
7.5 Types of pressure-relief vents . 7
7.5.1 General . 7
7.5.2 Gravity vents . 7
7.5.3 Counterweighted flap vent . 7
7.5.4 Electrically-operated vents . 8
7.5.5 Pneumatically-operated vent . 8
7.5.6 Vent accessories . 8
7.6 Pressure-relief vent characteristics . 9
7.6.1 Vent efficiency. 9
7.6.2 Minimum opening pressure . 10
7.6.3 Minimum closing pressure . 10
7.6.4 Fire rating . 10
7.7 Vent location and mounting . 10
7.7.1 Vent location . 10
7.7.2 Vent mounting. 11
7.8 Pressure-relief vent area calculations .12
7.8.1 Use of agent-specific formulae .12
7.8.2 Vent area requirement (non-liquefiable gases) .13
7.8.3 Vent area requirement carbon dioxide . 16
7.8.4 Vent area requirements (liquefiable gases) . 16
7.8.5 Leakage . 22
7.9 Cascade venting calculations . 22
7.9.1 Example calculation 3: Cascade venting calculations for IG-541 (peak
discharge) . 23
7.9.2 Cascade vent arrangements . 24
7.9.3 Venting into adjacent enclosures . 25
8 System design — Post-discharge venting .27
9 Acceptance .27
10 Service and maintenance . .27
Annex A (informative) Development of agent-specific formulae for liquefiable gases.29
Annex B (informative) Method for development of agent-specific formulae for liquefiable
gases .34
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SIST EN ISO 21805:2023
ISO 21805:2023(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 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 21, Equipment for fire protection and
firefighting, Subcommittee SC 8, Gaseous media and firefighting systems using gas. in collaboration with
the European Committee for Standardization (CEN) Technical Committee CEN/TC 191, Fixed firefighting
systems, in accordance with the Agreement on technical cooperation between ISO and CEN (Vienna
Agreement).
This first edition cancels and replaces the first edition (ISO/TS 21805:2018), which has been technically
revised.
The main changes are as follows:
— subclause 7.8.3 has been amended to cross-reference ISO 6183 for vent area calculations for CO ;
2
— Annex A has been added, providing guidance on how testing in order to derive the agent-specific
formulae;
— Annex B has been added, providing guidance on the procedure for developing coefficients for any
new agents in the ISO 14520 series.
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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SIST EN ISO 21805:2023
ISO 21805:2023(E)
Introduction
The guidance presented in this document is based on the results of a joint research programme
conducted in 2006 and 2007 by several fire protection system manufacturers and interested parties.
The programme of work consisted of several series of tests to evaluate the peak pressure response and
pressure-relief vent area effects for each agent addressed in this document. The key data used in the
development of this document were the values of peak enclosure pressure response (PMAX) at each
value of the volume-normalized pressure-relief vent area of the test enclosure, hereinafter referred to
as the “leakage-to-volume ratio” or LVR. Other test parameters (enclosure temperature, agent quantity,
discharge time and humidity) were held constant or varied in a specified manner. For each test series
employing a single agent, the several pairs of LVR and resultant PMAX values were graphically analysed,
and a best-fit correlation curve was determined.
The LVR vs. PMAX correlation curve for each agent or system forms the basis of the associated formulae
in cases where the discharge of the agent results in cooling the air temperature below its dew point.
Only halocarbon agents cause sufficient cooling to cause humidity-related effects on the peak enclosure
pressure. Thus, a correction for humidity effects is included in the formulae for estimating vent area
and maximum pressure on the discharge of the following agents:
— FK-5-1-12
— HFC-23
— HFC-125
— HFC-227ea
The humidity corrections used in this document are based on the results of tests conducted with HFC-
227ea at different conditions of humidity.
The resulting values for humidity correction will be assumed to be equally applicable to the agents FK-
5-1-12, HFC-125 and HFC-23 until further data or analyses indicate otherwise.
The correlations of LVR to maximum negative pressure and maximum positive pressure were based
on test work performed in a test chamber at a relative humidity (RH) of approximately 38 %. If the RH
in a protected enclosure differs from 38 % then a correction to the estimated maximum negative and
positive pressures can be required. See 7.8 and 7.9 for further information on the effect of humidity. The
temperature of the test enclosure was 21°C (nominal) for all tests that form the basis of the estimating
methods given in this document.
In conducting the research programme described above, a large number of different venting
arrangements were created in the test enclosure. The equivalent leakage area (ELA) for each test was
determined by a “door fan test” and data analysis. The average enclosure pressure in effect during
the many door fan tests varied from test to test. All values of ELA were normalized to an equivalent
enclosure differential pressure of 125 Pa. The resulting enclosure correlations of peak pressure vs. LVR,
and any resulting estimate of enclosure pressure-relief vent area, reflect a pressure-relief vent area
calculated at an effective enclosure pressure of 125 Pa for a vent with a discharge coefficient of 0,61.
The effectiveness of a gaseous total flooding firefighting system depends, in part, on retention of
the air-extinguishant mixture within the protected volume for a period of time. Retention of the
extinguishant-air mixture requires that gas exchange (“leakage”) between the enclosure and the
ambient environment be restricted. To limit the rate of gas exchange, the enclosure boundary should
have a high degree of integrity. To put it another way, the total of the areas of the various penetrations
in an enclosure’s bounding surfaces should be low, at least during the gas-retention period (hold time)
after the end of the extinguishant discharge.
The addition of a gaseous firefighting extinguishant to an enclosure having a limited pressure-relief
vent area will naturally result in a change of pressure therein. If the enclosure is sealed too tightly
during the extinguishant discharge, i.e. too little pressure-relief vent area, the pressure change could
exceed the structural strength of one or more of its bounding surfaces — windows, doors, walls,
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SIST EN ISO 21805:2023
ISO 21805:2023(E)
ceiling. Conversely, if the enclosure has too much pressure-relief vent area then gas exchange with the
ambient atmosphere will occur rapidly, leading to a short retention time of the extinguishant within the
protected volume.
Thus, the use of gaseous firefighting systems should address two performance considerations:
a) pressure management within the protected volume during the period of extinguishant discharge,
and;
b) retention of the extinguishant-air mixture within the enclosure for a specified period of time after
the completion of the discharge.
This document provides guidance for limiting pressure extremes in an enclosure during the discharge
of a clean agent fire extinguishing system. This document does not provide the information necessary to
determine all of the requirements related to the design, installation, service, maintenance, inspection,
test and/or requalification of fire suppression systems.
Some limitations and restrictions apply to the use of the formulae contained in this document. Please
refer to the text and notes that follow them.
The information in this document does not supersede the manufacturer’s guidance. The information
contained in this document is presented as being supplementary to the guidance provided by the
respective system manufacturers. Guidance from the system manufacturer should always be followed
and used for purposes of system design, installation, operation and maintenance.
It has been assumed in the preparation of this document that the execution of its provisions is entrusted
to people appropriately qualified and experienced in the specification, design, installation, testing,
approval, inspection, operation and maintenance of systems and equipment, for whose guidance it has
been prepared, and who can be expected to exercise a duty of care to avoid unnecessary release of
extinguishant.
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SIST EN ISO 21805:2023
INTERNATIONAL STANDARD ISO 21805:2023(E)
Guidance and recommendations on design, selection and
installation of vents to safeguard the structural integrity
of enclosures protected by gaseous fire-extinguishing
systems
1 Scope
This document gives guidelines for fulfilling the requirements contained in ISO 6183:2022, 6.4.1 and
7.4.1 and ISO 14520-1:2023, 5.2.1 h) and 5.3 h), in respect to over- and under-pressurization venting and
post-discharge extract.
It considers the design, selection and installation of vents to safeguard the structural integrity of
enclosures protected by fixed gaseous extinguishing systems and the post-discharge venting provisions
where used.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
NOTE For the purposes of this document, the term “bar” signifies “gauge”, unless otherwise indicated.
Concentrations or quantities expressed in percentages (%) signify by volume unless otherwise indicated.
3.1
free pressure-relief vent area
sum of all free vent areas of the pressure-relief vents provided
Note 1 to entry: This is determined by the gross pressure-relief vent area multiplied by the vent efficiency.
3.2
gross pressure-relief vent area
total area of the pressure-relief vent
3.3
negative pressure
pressure in the protected room which is lower than the pressure immediately outside the enclosure
boundary
3.4
peak pressure
maximum pressure (positive and negative) generated within an enclosure caused by the discharge of
the gaseous agent
1
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SIST EN ISO 21805:2023
ISO 21805:2023(E)
3.5
positive pressure
pressure in the protected room which is higher than the pressure immediately outside the enclosure
boundary
3.6
enclosure strength
specified differential pressure limit for the protected enclosure
3.7
pressure-relief area
sum of the free pressure-relief vent area and the enclosure leakage area
3.8
pressure-relief vent
device that provides a flow path through an enclosure boundary to limit the pressure therein
3.9
authority
organization, office or individual responsible for approving equipment, installations or procedure
4 Symbols and abbreviated terms
2
A pressure-relief vent area (m )
2 2
A pressure-relief vent area to limit negative pressure to a specified P (cm or in )
N N
2 2
A pressure-relief vent area to limit positive pressure to a specified P (cm or in )
P P
2
A total pressure-relief vent area (m )
T
C agent design concentration (vol. %)
E positive pressure excursion
p,P
E negative pressure excursion
p,N
3 3
f flooding factor (m /m )
F
H relative humidity within the enclosure (%)
L enclosure positive pressure limit
e,p,P
L enclosure negative pressure limit
e,p,N
m minimum design quantity of agent (kg)
M molecular weight of the agent (kg/mol)
AGT
M molecular weight of air (0,029; kg/mol)
AIR
M is the mixture molecular weight of the agent (kg/mol)
H
P pressure (Pa or psf)
P maximum room strength (Pa)
max
P negative pressure (Pa or psf)
N
P positive pressure (Pa or psf)
P
2
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SIST EN ISO 21805:2023
ISO 21805:2023(E)
P and P represent either
N P
— design pressure limits for estimating A or A , or
N P
— estimates of maximum values of P or P for given values of A or A
N P N P
3
Q quantity of agent required at reference temperature of 20 °C (m )
R
R gas law constant, 8,314 (J/mol-K)
3
S specific volume of the agent at the design temperature (m /kg)
3
S specific volume of air (m /kg)
AIR
3
S specific volume of the agent at the reference temperature (m /kg)
R
t discharge time (s)
t gaseous firefighting system discharge time (s)
d
T temperature (K)
3
V volume of the protected space (m )
3
V specific volume of the agent at the design temperature
...
SLOVENSKI STANDARD
oSIST prEN ISO 21805:2021
01-julij-2021
Navodilo za projektiranje, izbiro in vgradnjo prezračevalnih naprav za
zagotavljanje strukturne integritete namestitvenih prostorov, zaščitenih s sistemi
za gašenje s plinom (ISO/DIS 21805:2021)
Guidance on design, selection and installation of vents to safeguard the structural
integrity of enclosures protected by gaseous fire-extinguishing systems (ISO/DIS
21805:2021)
Anleitung für die Konstruktion, Auswahl und Installation von Entlüftungen zur
Gewährleistung der strukturellen Integrität von Gehäusen, die durch ortsfeste
Gaslöschanlagen geschützt sind (ISO/DIS 21805:2021)
Lignes directrices pour la conception, la sélection et l'installation d'évents pour préserver
l'intégrité structurelle des enceintes protégées par des systèmes fixes de lutte contre
l'incendie à gaz (ISO/DIS 21805:2021)
Ta slovenski standard je istoveten z: prEN ISO 21805
ICS:
13.220.10 Gašenje požara Fire-fighting
91.140.30 Prezračevalni in klimatski Ventilation and air-
sistemi conditioning systems
oSIST prEN ISO 21805:2021 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.
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oSIST prEN ISO 21805:2021
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oSIST prEN ISO 21805:2021
DRAFT INTERNATIONAL STANDARD
ISO/DIS 21805
ISO/TC 21/SC 8 Secretariat: SA
Voting begins on: Voting terminates on:
2021-05-20 2021-08-12
Guidance on design, selection and installation of vents to
safeguard the structural integrity of enclosures protected
by gaseous fire-extinguishing systems
Lignes directrices pour la conception, la sélection et l'installation d'évents pour préserver l'intégrité
structurelle des enceintes protégées par des systèmes fixes de lutte contre l'incendie à gaz
ICS: 91.140.30; 13.220.10
THIS DOCUMENT IS A DRAFT CIRCULATED
This document is circulated as received from the committee secretariat.
FOR COMMENT AND APPROVAL. IT IS
THEREFORE SUBJECT TO CHANGE AND MAY
NOT BE REFERRED TO AS AN INTERNATIONAL
STANDARD UNTIL PUBLISHED AS SUCH.
IN ADDITION TO THEIR EVALUATION AS
ISO/CEN PARALLEL PROCESSING
BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
Reference number
NATIONAL REGULATIONS.
ISO/DIS 21805:2021(E)
RECIPIENTS OF THIS DRAFT ARE INVITED
TO SUBMIT, WITH THEIR COMMENTS,
NOTIFICATION OF ANY RELEVANT PATENT
RIGHTS OF WHICH THEY ARE AWARE AND TO
©
PROVIDE SUPPORTING DOCUMENTATION. ISO 2021
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oSIST prEN ISO 21805:2021
ISO/DIS 21805:2021(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2021
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting
on the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address
below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii © ISO 2021 – All rights reserved
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oSIST prEN ISO 21805:2021
ISO/DIS 21805:2021(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Symbols and abbreviated terms . 2
5 Use and limitations . 3
6 Safety . 4
6.1 Structural safety . 4
6.2 Personnel safety . 4
7 System design — Pressure-relief venting . 4
7.1 General . 4
7.2 Extinguishant characteristics . 4
7.2.1 Pressure graphs . 5
7.3 Enclosure characteristics . 5
7.4 Pressure-relief vent paths . 6
7.5 Types of pressure-relief vents . 6
7.5.1 General. 6
7.5.2 Gravity vents . 6
7.5.3 Counterweighted flap vent . 7
7.5.4 Electrically operated vents . 7
7.5.5 Pneumatically operated vent . 8
7.5.6 Vent accessories . 8
7.6 Pressure-relief vent characteristics . 9
7.6.1 Vent efficiency . 9
7.6.2 Minimum opening pressure .10
7.6.3 Minimum closing pressure .10
7.6.4 Fire rating.10
7.7 Vent location and mounting .11
7.7.1 Vent location .11
7.7.2 Vent mounting .11
7.8 Pressure-relief vent area calculations .12
7.8.1 Use of agent-specific equations .12
7.8.2 Vent area requirement (non-liquefiable gases and CO ) .13
2
7.8.3 Vent area requirements (liquefiable gases) .16
7.8.4 Leakage .21
7.9 Cascade venting calculations .21
7.9.1 Example calculation 3 . .23
7.9.2 Cascade vent arrangements .24
7.9.3 Venting into adjacent enclosures .24
8 System design — Post-discharge venting .26
9 Acceptance .27
10 Service and maintenance .27
Annex A (informative) Development of Agent Specific Equations for Liquefiable Gases .28
Annex B (normative) Method for Development of Agent Specific Equations for Liquefiable
Gases .32
Bibliography .34
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oSIST prEN ISO 21805:2021
ISO/DIS 21805:2021(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 21, Equipment for fire protection and
firefighting, Subcommittee SC 8, Gaseous media and firefighting systems using gas.
This edition cancels and replaces ISO/TS 21805: 2018, which has been technically revised.
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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oSIST prEN ISO 21805:2021
ISO/DIS 21805:2021(E)
Introduction
The guidance presented here is based on the results of a joint research program conducted in 2006 and
2007 by several fire protection system manufacturers and interested parties. The program of work
consisted of several series of tests to evaluate the peak pressure response and pressure-relief vent
area effects for each agent addressed in this document. The key data used in the development of this
document were the values of peak enclosure pressure response (PMAX) at each value of the volume-
normalized pressure-relief vent area of the test enclosure, hereinafter referred to as the “leakage-to-
volume ratio” or LVR. Other test parameters (enclosure temperature, agent quantity, discharge time,
and humidity) were held constant or varied in a specified manner. For each test series employing a
single agent, the several pairs of LVR and resultant PMAX values were graphically analysed, and a best-
fit correlation curve was determined.
The LVR vs. PMAX correlation curve for each agent or system forms the basis of the associated
equations in cases where the discharge of the agent results in cooling the air temperature below its
dew point. (See Humidity effects and humidity correction factor below.) In most cases, only halocarbon
agents cause sufficient cooling to cause humidity related effects on the peak enclosure pressure. Thus,
a correction for humidity effects is included in the equations for estimating vent area and maximum
pressure on the discharge of the following agents:
— FK-5-1-12
— HFC-23
— HFC-125
— HFC-227ea
The humidity corrections used in this document are based on the results of tests conducted with HFC-
227ea at different conditions of humidity.
The resulting values for humidity correction will be assumed to be equally applicable to the agents FK-
5-1-12, HFC-125 and HFC-23 until further data or analysis indicate otherwise.
The correlations of LVR to maximum negative pressure and maximum positive pressure were based
on test work performed in a test chamber at a relative humidity (RH) of approximately 38 %. If the RH
in a protected enclosure differs from 38 % then a correction to the estimated maximum negative and
positive pressures may be required. See 7.8 and 7.9 for further information on the effect of humidity.
The temperature of the test enclosure was 21°CF (nominal) for all tests that form the basis of the
estimating methods given in this document.
In conducting the research program, described above, a large number of different venting arrangements
were created in the test enclosure. The equivalent leakage area (ELA) for each test was determined by
a “door fan test” and data analysis. The average enclosure pressure in effect during the many door fan
tests varied from test to test. All values of ELA were normalized to an equivalent enclosure differential
pressure of 125 Pa. The resulting enclosure correlations of peak pressure vs. LVR, and any resulting
estimate of enclosure pressure-relief vent area, reflect a pressure-relief vent area calculated at an
effective enclosure pressure of 125 Pa for a vent with a discharge coefficient of 0,61.
The effectiveness of a gaseous total flooding firefighting system depends, in part, on retention of
the air-extinguishant mixture within the protected volume for a period of time. Retention of the
extinguishant-air mixture requires that gas exchange (“leakage”) between the enclosure and the
ambient environment be restricted. To limit the rate of gas exchange the enclosure boundary should
have a high degree of integrity. To put it another way, the total of the areas of the various penetrations
in an enclosure’s bounding surfaces should be low, at least during the gas-retention period (hold time)
after the end of the extinguishant discharge.
The addition of a gaseous firefighting extinguishant to an enclosure having limited pressure-relief vent
area will naturally result in a change of pressure therein. If the enclosure is sealed too tightly during the
extinguishant discharge, i.e. too little pressure-relief vent area, the pressure change could exceed the
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oSIST prEN ISO 21805:2021
ISO/DIS 21805:2021(E)
structural strength of one or more of its bounding surfaces — windows, doors, walls, ceiling. Conversely,
if the enclosure has too much pressure-relief vent area then gas exchange with the ambient atmosphere
will occur rapidly, leading to a short retention time of the extinguishant within the protected volume.
Thus, the use of gaseous firefighting systems should address two performance considerations:
a) Pressure management within the protected volume during the period of extinguishant
discharge, and;
b) Retention of the extinguishant-air mixture within the enclosure for a specified period of time after
the completion of the discharge.
This document provides guidance for limiting pressure extremes in an enclosure during the discharge
of a clean agent fire extinguishing system. This document does not provide the information necessary to
determine all of the requirements related to the design, installation, service, maintenance, inspection,
test, and/or requalification of fire suppression systems.
Some limitations and restrictions apply to the use of the equations contained in this document. Please
refer to the text and notes that follow.
The information in this document does not supersede the manufacturer’s guidance. The information
contained in this document is presented as supplementary to the guidance provided by the respective
system manufacturers. Guidance from the system manufacturer should always be followed and used
for purposes of system design, installation, operation, and maintenance.
It has been assumed in the preparation of this document that the execution of its provisions is entrusted
to people appropriately qualified and experienced in the specification, design, installation, testing,
approval, inspection, operation and maintenance of systems and equipment, for whose guidance it has
been prepared, and who can be expected to exercise a duty of care to avoid unnecessary release of
extinguishant.
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oSIST prEN ISO 21805:2021
DRAFT INTERNATIONAL STANDARD ISO/DIS 21805:2021(E)
Guidance on design, selection and installation of vents to
safeguard the structural integrity of enclosures protected
by gaseous fire-extinguishing systems
1 Scope
This document provides guidance on fulfilling the requirements contained in ISO 6183:2009, 6.4.1 and
7.4.1 and ISO 14520-1:2015, 5.2.1 (h) and 5.3 (h), in respect to over and under pressurization venting
and post-discharge extract.
It considers the design, selection and installation of vents to safeguard the structural integrity of
enclosures protected by fixed gaseous extinguishing systems and the post-discharge venting provisions
where used.
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 14520-1, Gaseous fire-extinguishing systems — Physical properties and system design — Part 1:
General requirements
EN 15004-1, Fixed firefighting systems — Gas extinguishing systems — Part 1: Design, installation, and
maintenance
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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/
Note 1 to entry For the purposes of this document, the term “bar” signifies “gauge”, unless otherwise indicated.
Concentrations or quantities expressed in percentages (%) signify by volume unless otherwise indicated.
3.1
back pressure
pressure downstream of a vent
3.2
fire damper
device designed to prevent the spread of fire
3.3
free pressure-relief vent area
sum of the free pressure-relief vent areas of the pressure-relief vents provided
Note 1 to entry: Note to entry: This is determined by the gross pressure-relief vent area x the vent efficiency.
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oSIST prEN ISO 21805:2021
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3.4
gross pressure-relief vent area
total area of the pressure-relief vent
3.5
negative pressure
pressure in the protected room which is lower than the pressure immediately outside the enclosure
boundary
3.6
peak pressure
maximum pressure (positive and negative) generated within an enclosure caused by the discharge of
the gaseous agent
3.7
positive pressure
pressure immediately outside the enclosure boundary
3.8
enclosure strength
specified differential pressure limit for the protected enclosure
3.9
pressure-relief area
sum of the free pressure-relief vent area and the enclosure leakage area
3.10
pressure-relief vent
device that provides a flow path through an enclosure boundary to limit the pressure therein
4 Symbols and abbreviated terms
2 2
A pressure-relief vent area to limit negative pressure to a specified P , cm (in )
N N
2 2
A pressure-relief vent area to limit positive pressure to a specified P , cm (in )
P P
C agent design concentration, in percent by volume
M is the molecular weight of air = 0,029 (kg/mol)
AIR
M the molecular weight of the agent, (kg/mol)
AGT
Q minimum design quantity of agent (kg)
P pressure (Pa)
P negative pressure, psf (Pa)
N
P positive pressure, psf (Pa)
P
P and P represent either
N P
— Design pressure limits for estimating A or A , or
N P
— Estimates of maximum values of P or P for given values of A or A
N P N P
R gas law constant, 8,314 (J/mol-K)
% RH relative humidity in hazard space at 21 °C (70 °F), %
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oSIST prEN ISO 21805:2021
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3
s the specific volume of the agent at the design temperature (m /kg)
3
s the specific volume of the homogenous agent-air mixture (m /kg), which is the inverse of the density
H
t agent discharge time, s
3
V the volume of the protected space (m )
3
ρ agent-air mixture density (kg/m )
H
5 Use and limitations
This document is for the use by those competent in the design, installation, servicing, and maintenance
of fixed gaseous firefighting systems. It also serves as guidance for those involved in the design,
construction, and operation of buildings in which such systems are installed.
It does not replace the need for the person responsible for the design, construction, and operation of the
building to fulfil their obligations in respect to providing adequate structural provisions.
There may be other trades and services involved in the complete system and the document is limited to
providing the guidance outlined in the document and does not purport to be an expert in all areas.
After applying the enclosure peak pressure and pressure-relief vent area analysis of this document,
the user may conclude that an enclosure may require additional pressure-relief vent area to avoid
exceeding specified maximum pressure values upon discharge of a gaseous agent system. If that is the
case, it is recommended that the user advise the supplier of a supplemental venting device that such
device be specified and selected by use of this document.
The maximum pressure developed in an enclosure on the discharge of a clean agent fire extinguishing
system is affected by several characteristics of the system itself and the enclosure being protected. Of
particular importance are the thermodynamic properties of the agent and the discharge characteristics
of the hardware. Each of the following sections contains correlation equations that are specific to the
agent type and manufacturer’s hardware. The equations can be used to make estimates of the following:
a) enclosure pressure-relief vent area given a specified enclosure pressure limit;
b) maximum positive or negative pressure developed in an enclosure given a stated or calculated
pressure-relief vent area.
NOTE The formulae in this document for halocarbon agents have a limited range of applicability based on the
parametric limitations of the data from which they were derived. Table 1 indicates the applicable limits of design
concentration, discharge time, and enclosure pressure response for the use of this document. The maximum
peak pressure estimates (both positive and negative) based on data obtained for each agent are given in Table 1.
Caution: It is physically possible to develop pressures greater than those covered by this document
during system discharges.
Table 1 — Summary of equation application limits
Agent Minimum Maximum Minimum Maximum Maximum Maximum
agent agent discharge discharge over-pres- under pres-
time time sure pfs (Pa) sure pfs (Pa)
Conc Conc
% vol % vol
FK-5–1-12 4,2 6 6 10 5 (239) 25 (1 197)
HFC-23 18 30 6 10 30 (1 437) n/a
HFC-125 8 10,5 6 10 10 (479) 10 (479)
HFC-227ea 6,25 10,5 6 10 8 (383) 20 (958)
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oSIST prEN ISO 21805:2021
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6 Safety
6.1 Structural safety
The provision of correctly designed and engineered pressure venting of enclosures protected by gaseous
fire-extinguishing systems is essential to prevent the possibility of failure of structural integrity. This is
essential to mitigate forces exerted by the changes in enclosure pressure when gaseous fighting media
are discharged into an enclosure.
6.2 Personnel safety
The operation of pressure-relief vents or extract systems requires the displacement of mixtures
of air/gaseous media from a protected enclosure to the atmosphere or another area not necessarily
protected. The safety issue may arise due to exposures to the extinguishants themselves or products of
combustion and/or extinguishant breakdown products. Also, any hazards arising from the operation of
the over/under pressurization vents themselves should be considered.
7 System design — Pressure-relief venting
7.1 General
The basic design principle is to limit the pressure excursions imposed on the structure of the protected
enclosure by the discharge of gaseous extinguishant to that within the limits the enclosure can
withstand.
A room integrity test can be used to determine the equivalent leakage area, or simply the” vent” area
that exists at the time of evaluation. The methods of this document can use the known or estimated
pressure-relief vent area to estimate the maximum pressure that will be developed on the discharge
of a clean agent system. If the estim
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