Oxygen reduction systems for fire prevention -- Design, installation, planning and maintenance

This document specifies minimum requirements and defines the specifications governing the design, installation and maintenance of fixed oxygen reduction systems with oxygen reduced air for fire prevention in buildings and industrial production plants. It also applies to the extension and modification of existing systems. This document applies to oxygen reduction systems using nitrogen-enriched-air which are designed for continual oxygen reduction in enclosed spaces. NOTE Nitrogen is, today, the most suitable gas to be used for oxygen reduction. For other gases, this document can be used as a reference. This document does not apply to: — oxygen reduction systems that use water mist or combustion gases; — explosion suppression systems; — explosion prevention systems, in case of chemicals or materials containing their own supply of oxygen, such as cellulose nitrate; — fire extinguishing systems using gaseous extinguishing agents; — inertization of portable containers; — systems in which oxygen levels are reduced for reasons other than fire prevention (e.g. steel processing in the presence of inert gas to avoid the formation of oxide film); — inerting required during repair work on systems or equipment (e.g. welding) in order to eliminate the risk of fire or explosion. In addition to the conditions for the actual oxygen reduction system and its individual components, this document also covers certain structural specifications for the protected area. The space protected by an oxygen reduction system is a controlled and continuously monitored indoor climate for extended occupation. This document does not cover unventilated confined spaces that can contain hazardous gases.

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Status
Published
Publication Date
01-Sep-2019
Current Stage
6060 - International Standard published
Start Date
24-Jul-2019
Completion Date
02-Sep-2019
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INTERNATIONAL ISO
STANDARD 20338
First edition
2019-09
Oxygen reduction systems for fire
prevention — Design, installation,
planning and maintenance
Reference number
ISO 20338:2019(E)
ISO 2019
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ISO 20338:2019(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2019

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

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below or ISO’s member body in the country of the requester.
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Published in Switzerland
ii © ISO 2019 – All rights reserved
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ISO 20338:2019(E)
Contents Page

Foreword ..........................................................................................................................................................................................................................................v

Introduction ................................................................................................................................................................................................................................vi

1 Scope ................................................................................................................................................................................................................................. 1

2 Normative references ...................................................................................................................................................................................... 1

3 Terms and definitions ..................................................................................................................................................................................... 2

4 System requirements ....................................................................................................................................................................................... 3

4.1 General ........................................................................................................................................................................................................... 3

4.2 Personnel safety ..................................................................................................................................................................................... 3

4.3 Effectiveness and application ..................................................................................................................................................... 4

4.4 Alarm organization and emergency plan ......................................................................................................................... 4

5 Design .............................................................................................................................................................................................................................. 5

5.1 Qualification of the designer ....................................................................................................................................................... 5

5.2 Fire protection concept ................................................................................................................................................................... 5

5.3 Structural specifications for the protected area ......................................................................................................... 5

5.4 Oxygen concentration ....................................................................................................................................................................... 5

5.5 Oxygen reduction to prevent fire ............................................................................................................................................ 6

5.6 Safety margins ......................................................................................................................................................................................... 6

5.7 Oxygen reduced air quantity ....................................................................................................................................................... 9

5.7.1 Continuous oxygen reduction ............................................................................................................................... 9

5.7.2 Emergency plan ................................................................................................................................................................ 9

5.7.3 Oxygen reduced air .....................................................................................................................................................10

5.7.4 Fault signals ......................................................................................................................................................................10

5.8 Technical areas .....................................................................................................................................................................................11

5.8.1 Technical area for control panel ......................................................................................................................11

5.8.2 Technical area for reduced oxygen air generation...........................................................................11

6 Distribution pipework .................................................................................................................................................................................12

6.1 Pipework ...................................................................................................................................................................................................12

6.2 Pipe supports ........................................................................................................................................................................................12

6.3 Components in the pipework ..................................................................................................................................................12

7 Monitoring the oxygen concentration .........................................................................................................................................13

8 Alarms and notifications ...........................................................................................................................................................................14

9 Control equipment ..........................................................................................................................................................................................15

9.1 Function .....................................................................................................................................................................................................15

9.2 Requirements ........................................................................................................................................................................................16

9.3 Electrical power supply ................................................................................................................................................................16

9.4 Electrical cabling installations................................................................................................................................................16

9.5 Data recording ......................................................................................................................................................................................16

10 System operation...............................................................................................................................................................................................17

10.1 Instruction and training of personnel ..............................................................................................................................17

10.2 Inspections ..............................................................................................................................................................................................17

10.3 Operations log.......................................................................................................................................................................................17

10.4 Further obligations ...........................................................................................................................................................................17

11 Maintenance ...........................................................................................................................................................................................................18

12 Documentation ....................................................................................................................................................................................................18

13 Installation ..............................................................................................................................................................................................................19

13.1 Qualification of the installer .....................................................................................................................................................19

13.2 General specifications — Installation ..............................................................................................................................19

© ISO 2019 – All rights reserved iii
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ISO 20338:2019(E)

Annex A (normative) Ignition thresholds for oxygen reduction using nitrogen-enriched air

in fire prevention ..............................................................................................................................................................................................20

Bibliography .............................................................................................................................................................................................................................24

iv © ISO 2019 – All rights reserved
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ISO 20338:2019(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 fire

fighting, Subcommittee SC 8, Gaseous media and firefighting systems using gas.

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.
© ISO 2019 – All rights reserved v
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ISO 20338:2019(E)
Introduction

Oxygen reduction systems are designed to prevent fires from starting or spreading, by means of

the introduction of oxygen reduced air and creating an atmosphere in an area which is having lower

permanent oxygen concentration in respect to ambient conditions. Oxygen reduction systems are

not designed to extinguish fires. The design and installation are based on detailed knowledge of the

protected area, its occupancy and the materials in question. It is important to suit the fire protection

measures to the hazard as a whole.
vi © ISO 2019 – All rights reserved
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INTERNATIONAL STANDARD ISO 20338:2019(E)
Oxygen reduction systems for fire prevention — Design,
installation, planning and maintenance
1 Scope

This document specifies minimum requirements and defines the specifications governing the

design, installation and maintenance of fixed oxygen reduction systems with oxygen reduced air

for fire prevention in buildings and industrial production plants. It also applies to the extension and

modification of existing systems.

This document applies to oxygen reduction systems using nitrogen-enriched-air which are designed for

continual oxygen reduction in enclosed spaces.

NOTE Nitrogen is, today, the most suitable gas to be used for oxygen reduction. For other gases, this

document can be used as a reference.
This document does not apply to:
— oxygen reduction systems that use water mist or combustion gases;
— explosion suppression systems;

— explosion prevention systems, in case of chemicals or materials containing their own supply of oxygen,

such as cellulose nitrate;
— fire extinguishing systems using gaseous extinguishing agents;
— inertization of portable containers;

— systems in which oxygen levels are reduced for reasons other than fire prevention (e.g. steel

processing in the presence of inert gas to avoid the formation of oxide film);

— inerting required during repair work on systems or equipment (e.g. welding) in order to eliminate

the risk of fire or explosion.

In addition to the conditions for the actual oxygen reduction system and its individual components, this

document also covers certain structural specifications for the protected area.

The space protected by an oxygen reduction system is a controlled and continuously monitored indoor

climate for extended occupation. This document does not cover unventilated confined spaces that can

contain hazardous gases.
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 7240 (all parts), Fire detection and alarm systems

EN 12094-1, Fixed firefighting systems — Components for gas extinguishing systems — Part 1:

Requirements and test methods for electrical automatic control and delay devices

EN 50104, Electrical apparatus for the detection and measurement of oxygen — Performance requirements

and test methods
© ISO 2019 – All rights reserved 1
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ISO 20338:2019(E)
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:

— IEC Electropedia: available at http: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
alarm threshold

value of a process parameter which, when reached, triggers an alarm and, where necessary, initiates

automatic protection measures
3.2
design concentration

oxygen concentration level determined by subtraction of the safety margin from the ignition threshold

Note 1 to entry: See also Figure 1 and Table 2.

Note 2 to entry: The design concentration represents the maximum oxygen concentration which shall not be

exceeded at any time.
3.3
combustible material
material capable of combustion or being ignited

Note 1 to entry: For the purposes of this document, whether the quantity of a combustible material is to be regarded

as significant or not should be determined by means of a risk analysis as part of the fire protection design.

3.4
ignition threshold

maximum oxygen concentration in a mixture of a combustible material with air and inert gas, in which

there can be no ignition, determined under established test conditions

Note 1 to entry: This is a specific characteristic of combustible material and inert gas (see A.1).

3.5
detection and alarm installation

remote detection system for the reliable detection of risk to people and property

3.6
measuring zones
virtual separation of the protected volume for oxygen measuring
3.7
normal operation

situation in which the equipment, protection systems and components are able to carry out their

designated functions within their design parameters
3.8
oxygen reduced air

air with an oxygen concentration lower than that in normal atmospheric conditions

3.9
oxygen reduced air supply

nitrogen enriched air stream with an oxygen concentration lower than that in normal atmospheric

conditions, ready to be introduced into a protected volume
2 © ISO 2019 – All rights reserved
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ISO 20338:2019(E)
3.10
protected volume
space to be protected by oxygen reduction system
Note 1 to entry: Protected volume is measured in cubic meters.
3.11
system

combination of components whose function and compatibility guarantees the safety of the installation

3.12
technical area

area where the control panel, the nitrogen-enriched-air production unit and/or other relevant system

components are placed
3.13
control panel

electrical device for monitoring, controlling and operating the alarm and other functions of the oxygen

reduction system
4 System requirements
4.1 General
An oxygen reduction system shall consist at its minimum of:
a) a supply of oxygen reduced air;
b) a fixed pipework system with fittings, valves, nozzles, outlets;
c) oxygen sensors and control panel;
d) alarms.

Oxygen reduced air is produced by air separation or by injecting inert gas or gas mixture into the

protected area.

The oxygen concentration in the protected area shall be monitored by means of measuring equipment.

During operation, the supply of nitrogen-enriched air shall be controlled automatically according to

demand. Where necessary, as a result of a risk analysis, additional means shall be provided to operate

the supply manually or an additional supply operated manually or automatically.

The oxygen reduction system can be equipped with automatic equipment designed to shut down

machinery and to close fire doors and other equipment, with the aim of creating and maintaining the

required oxygen concentration.

The level of oxygen reduction is defined by the individual risks of these areas (see Annex A).

Individual components should comply with the relevant technical standards, if they exist.

Alternatively, for electrical/electronic/programmable electronic safety related systems,

IEC 61508 (all parts) should be used.
4.2 Personnel safety

Oxygen reduced air can be dangerous for personnel within protected volumes, technical areas housing

the oxygen reduction systems and adjacent areas.

Requirements for unventilated confined spaces do not necessarily apply to space protected by oxygen

reduction systems that control and continuously monitor indoor climate for extended occupation.

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ISO 20338:2019(E)

Personnel safety measures shall be made for the fact that neighbouring volumes can have a reduced

oxygen concentration. These areas may also need to be monitored and/or personnel safety measures

may need to be taken.

Technical or organizational measures shall be taken to prevent unauthorized people from entering

protected areas with permanently reduced oxygen levels.

The measurement system shall be designed in such a way that a loss of function or a measurement

error can in no event lead to the minimum oxygen threshold not being detected.

The spreading of the oxygen-reduced atmosphere to other areas not intended for this (e.g. through wall

openings, cable ducts, floor drainages, leaking doors, conveyor belts) shall be prevented.

4.3 Effectiveness and application

A fire risk assessment detailing the key fire protection factors shall be undertaken. The assessment

should take into account:
— the type and quantity of material/materials requiring protection;
— the area(s) requiring protection;

— the right dimension of the oxygen reduced air supply to maintain the reduced oxygen concentration

on its design value;
— a back-up oxygen reduced air supply, if provided;
— alarm equipment.

Oxygen reduction systems provide preventive fire protection. The introduction of nitrogen-enriched-

air reduces the oxygen concentration of the air, thereby preventing the ignition or spread of fire except

for the following:
— chemicals containing their own supply of oxygen (e.g. cellulose nitrate);

— mixtures containing oxidizing materials (e.g. sodium chlorate or sodium nitrate);

— chemicals capable of undergoing autothermal decomposition (e.g. some organic peroxides);

— reactive metals (e.g. sodium, potassium, magnesium, titanium and zirconium), reactive hydrides or

metal amides, some of which may react violently.

NOTE While oxygen reduction systems cannot prevent ignition of the fuels listed above, they can prevent

the spread of fire to other fuels which can offer protection to surrounding infrastructure (e.g. the building

structure).
4.4 Alarm organization and emergency plan
An alarm organization is required for the following purposes:
— to alert affected and responsible persons;
— to alert the permanently attended location;
— to initiate other necessary protective measures.
The responsibilities for the alarm organization shall be defined.

The emergency plan should cover key words to designate the basic measures that need to be taken in

case of emergency, too low oxygen levels or fire signal.
4 © ISO 2019 – All rights reserved
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ISO 20338:2019(E)
5 Design
5.1 Qualification of the designer

The designer shall be sufficiently technically qualified to ensure effective protection.

5.2 Fire protection concept
The system design shall be part of the fire safety concept of the building.

As part of the system design, a fire risk assessment may lead to further fire protection measures.

EXAMPLE Since the oxygen reduction system cannot prevent or detect smouldering or pyrolizing processes

(e.g. overheated cables), suitable smoke detection systems for the protected volume (e.g. highly sensitive smoke

detection systems according to ISO 7240-20 class A) are installable as part of the main fire alarm system of the

facility.

Where special circumstances deviate from what is covered in this document (e.g. spatial configuration,

structure, installations, combustible materials, altitude different from sea level, temperature different

from normal, fumes or gases, requiring special measures) the designer shall take these into account.

5.3 Structural specifications for the protected area

Structural partitions shall comply with the criteria governing the protection target, as shown in Table 1.

Building regulation specifications are unaffected by these measures.
Table 1 — Structural partitions
Protected
Level Protection target Specification Achieved by
volume
Enclosing elements (walls, floor and
The contents of a room
roof) shall be sufficiently air tight
1 shall be protected from Room —
over the life time to protect from
internal fires.
internal fires.
Enclosing elements (walls, floor
The contents of a room shall The construction of
and roof) shall be sufficiently air
be protected from internal fire compartments
2 Room tight over the lifetime and provide
fires and from fires spread- according to the rele-
protection against the spread of fire
ing from an external source. vant guidelines.
from the surrounding area.

Openings shall be constantly sealed or sealable; otherwise, the openings shall be reflected in the calculation of the

nitrogen-enriched-air production.

The user should be aware of the relationship between leakage, reduced oxygen air supply and the

system duty cycle.

In the case of oxygen reduction systems, all operational openings that are not included in the calculation

of the required levels of oxygen shall be provided with closing mechanisms or monitored via limit

switches. These operational openings include emergency exit doors and other doors, gates, etc.

5.4 Oxygen concentration

The following information should be used (where relevant) to determine the design concentration:

— combustible material present (in normal operation and in the case of maintenance work or faults);

— geometry of the combustible materials (e.g. hollow items, thin walls);

— volume of gas contained in combustible materials (e.g. hollow parts, densely packed storage items);

— temperatures and pressures in the protected area;
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ISO 20338:2019(E)

— safety margin between oxygen concentrations established experimentally and the oxygen

concentrations required for the design of the oxygen reduction system.
5.5 Oxygen reduction to prevent fire

NOTE 1 Ignition can only be prevented in protected areas if the oxygen concentration within the protected

area does not exceed the design concentration. If this level is exceeded, the protection objective of "fire

prevention" can no longer be guaranteed.

If different combustible materials are present in the protected area, the lowest ignition threshold (i.e.

the most ignitable material in its most ignitable geometry) shall be taken as the basis for determining

the design concentration. In individual cases, additional tests can be carried out to establish ignition

thresholds for combustible materials in the forms and geometry in which the materials are actually

present.
Testing shall be conducted according to Annex A.

NOTE 2 Authorities having jurisdiction can include requirements beyond this document.

The following are examples where the test described in A.2 may not be appropriate when the protected

volume contains:
— high voltage electrical equipment;
— toilet paper;
— clothing in bales;
— stored goods which may allow a large amount of oxygen to enter the warehouse.
In no case shall the oxygen concentration be higher than specified in Annex A.

Ignition thresholds for oxygen reduction using nitrogen-enriched-air for various applications are given

in A.1. Values obtained with mixtures of other gas components can differ from these figures. These

concentrations are determined under the specific test conditions described in A.2.

Concentrations other than those shown in Table A.1 can be achieved and allowed when the test is

validated by test reports in accordance with A.2. Materials not listed in Table A.1 should be tested

in accordance with the test in A.2 and validated by test reports. The design of oxygen reduction

systems shall take into account the ignition levels and the safety margins described in 5.6. This design

concentration shall not be exceeded anywhere in the protected area. In case of any fault arising, action

shall be taken according to the emergency plan (see 5.7.2).

WARNING — Where stored goods may allow a large amount of oxygen to enter the warehouse, the

test structure and the test described in A.2 may not be sufficient. In such cases, an appropriate

design concentration is the subject of agreement with the authority having jurisdiction. Such

cases may include, for example, warehouses containing toilet paper or clothing in bales.

5.6 Safety margins

The safety margin for oxygen reduction systems shall be set at 0,75 % oxygen by volume.

The difference between the design concentration and the warning threshold, or warning threshold

and operating range, is established according to the combustible materials, operation and fault related

fluctuations in time and place of the inert gas concentration, the time needed for protection measures

and emergency action to take effect, and the tolerance of the oxygen monitoring
...

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