ISO 21927-5:2018

Smoke and heat control systems - Part 5: Powered smoke exhaust systems - Requirements and design

This document applies to powered smoke exhaust systems in spaces with a large area and with a ceiling height of minimum 3 m, in which smoke protection is required. It includes tables and calculation methods for the design of clear layers in order to comply, inter alia, with the requirements of various protection objectives. This document includes information and provisions concerning the requirements for powered smoke exhaust systems, their design and rules for their installation. NOTE The requirements for testing the ventilators are dealt with in ISO 21927‑3. Other parts of the ISO 21927 series of standards deal with the power supply (ISO 21927‑10), control equipment (ISO 21927‑9) and smoke control ducts and smoke control dampers (ISO 21927‑7 and ISO 21927-8 respectively). Design, as specified in this document, does not apply to: - spaces with fixed gas extinguishing systems; - storage facilities for hazardous materials; - spaces in which there is a risk of explosions; - corridors; - stairwells.

Installations pour l'extraction de fumée et de chaleur — Partie 5: Systèmes d'extraction de fumée mécaniques — Exigences et planification

General Information

• Status: Published
• Publication Date: 27-Nov-2018
• ICS: 13.220.20 - Fire protection
• Technical Committee: ISO/TC 21/SC 11 - Smoke and heat control systems and components
• Drafting Committee: ISO/TC 21/SC 11 - Smoke and heat control systems and components
• Current Stage: 9599 - Withdrawal of International Standard
• Start Date: 25-Jun-2025
• Completion Date: 13-Dec-2025

Overview

ISO 21927-5:2018 - "Smoke and heat control systems - Part 5: Powered smoke exhaust systems - Requirements and design" sets out requirements and design rules for powered smoke exhaust systems used to create and maintain a clear layer beneath a buoyant smoke layer in large spaces. The standard applies to spaces with a minimum ceiling height of 3 m where smoke protection is required, and it provides tables and calculation methods for designing clear layers to meet protection objectives. It also covers installation rules and system design assumptions (e.g., activation timing, air supply considerations). Certain spaces are excluded (see Key Topics).

Key topics and technical requirements

• Scope and exclusions: Applies to large-area spaces (ceiling ≥ 3 m). Design does not apply to spaces with fixed gas extinguishing systems, hazardous storage, explosion-risk areas, corridors or stairwells.
• Clear layer design: Defines the clear layer (distance from floor to smoke layer lower surface) with a minimum target height of 2.5 m; higher values may be required depending on occupancy or protected objects.
• Smoke reservoirs and barriers: Spaces must be divided into smoke reservoirs (maximum area guidance provided) using smoke barriers; maximum distance between barriers is 60 m.
• Air supply: Requires an immediate and sufficient replacement air supply near floor level when the system is activated; design limits include avoiding turbulence (replacement air velocity not greater than 1 m/s at the inlet point).
• Design assumptions: Typical design assumes early activation (automatic/manual), solid-fuel fires, a mean fire propagation rate around 10 minutes, and constraints on design fire area and smoke temperatures.
• Components and installation rules: Covers placement and types of ventilators (roof-, wall- or centrally mounted), smoke control ducts and dampers, and installation rules for reliable operation.
• Associated component standards: Ventilator testing, power supply and control equipment are covered in other parts of ISO 21927.

Practical applications

ISO 21927-5 is intended for use in the design and installation of smoke and heat exhaust ventilation systems (SHEVS) in large indoor environments, including:

• Warehouses and logistics hubs
• Shopping centres, exhibition halls and arenas
• Industrial production halls and large retail spaces The standard supports fire safety objectives such as enabling safe evacuation, improving firefighting access, limiting smoke spread, and protecting property and structure from heat and smoke damage.

Who uses this standard

• Fire safety engineers and smoke control designers
• HVAC and building services engineers
• Architects and structural designers specifying fire protection
• Contractors installing smoke exhaust systems
• Authorities having jurisdiction and code officials reviewing designs

Related standards

• ISO 21927-3 (ventilator specification/testing)
• ISO 21927-7 (smoke control ducts)
• ISO 21927-8 (smoke control dampers)
• ISO 21927-9 (control equipment)
• ISO 21927-10 (power supply)

Keywords: ISO 21927-5:2018, powered smoke exhaust systems, smoke and heat control, clear layer design, smoke reservoirs, smoke barriers, ventilators, smoke control ducts, SHEVS, fire safety design.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 21927-5
First edition
2018-11
Smoke and heat control systems —
Part 5:
Powered smoke exhaust systems —
Requirements and design
Installations pour l'extraction de fumée et de chaleur —
Partie 5: Systèmes d'extraction de fumée mécaniques — Exigences et
planification
Reference number
©
ISO 2018
© ISO 2018
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
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Phone: [phone]
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Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii © ISO 2018 – All rights reserved

Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Design principles . 2
4.1 General . 2
4.2 Height of space . 4
4.3 Target height of the clear layer, d, in a smoke reservoir, A . 4
R
4.4 Area of smoke reservoir, A . 4
R
4.5 Air supply . 4
4.5.1 General. 4
4.5.2 Natural air replacement. 5
4.5.3 Powered air replacement . 5
4.6 Duration of fire growth to be assumed in the design . 5
4.7 Design group . 5
5 Calculating the volume flow of the smoke gases to be exhausted . 6
5.1 Basis of the calculation . 6
5.2 Using the tables . 6
6 Component temperature classes . 8
7 Rules for installation . 9
8 Energy supply for powered smoke exhaust ventilators.13
9 Controlling powered smoke exhaust ventilators .13
10 Marking .13
Bibliography .14
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 11, Smoke and heat control systems and components.
A list of all parts in the ISO 21927 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.
iv © ISO 2018 – All rights reserved

Introduction
Smoke and heat control systems (SHCS) create and maintain smoke free areas in construction works by
controlling smoke flow, and thus improving the conditions for the safe escape and/or rescue of people
and animals and the protection of property, and permit the fire to be fought while still in its early
stages. The use of smoke and heat exhaust ventilation systems (SHEVS) to create smoke-free areas
beneath a buoyant smoke layer has become widespread. Their value in assisting in the evacuation of
people from construction works, reducing fire damage and financial loss by preventing smoke logging,
facilitating firefighting, reducing roof temperatures and retarding the lateral spread of fire is firmly
established. For these benefits to be obtained, it is essential that smoke and heat exhaust ventilators
operate fully and reliably whenever called upon to do so during their installed life. A heat and smoke
exhaust ventilation system is a scheme of safety equipment intended to play a positive role in a fire
emergency.
Components for any smoke and heat control system are installed as part of a properly designed system.
Smoke and heat control systems help to:
— keep escape and access routes free from smoke;
— facilitate firefighting operations;
— delay and/or prevent flashover and thus full development of a fire;
— protect equipment and furnishings;
— reduce thermal effects on structural components during a fire;
— reduce damage due to thermal decomposition products and hot gases.
Pressure differential systems are used either to positively pressurize spaces separated from the fire or
to depressurize the space containing the fire in order to limit or prevent the flow of smoke and heat into
adjacent spaces. A typical use would be to pressurize an escape stair well in order to protect vertical
means of escape.
Depending on the design of the system, natural or powered smoke and heat ventilators can be used in a
smoke and heat control system.
Control equipment is needed to control all components in a SHCS, such as:
— natural ventilators;
— powered ventilators;
— smoke barriers;
— smoke dampers;
— air inlets;
— duct sections;
— dampers.
SHCS control equipment can also provide control for day-to-day ventilation and signals to other fire
safety equipment under fire conditions.
SHCS control equipment can be for extra-low–voltage or low-voltage electrical systems or pneumatic
systems or any combination thereof.
INTERNATIONAL STANDARD ISO 21927-5:2018(E)
Smoke and heat control systems —
Part 5:
Powered smoke exhaust systems — Requirements and
design
1 Scope
This document applies to powered smoke exhaust systems in spaces with a large area and with a
ceiling height of minimum 3 m, in which smoke protection is required. It includes tables and calculation
methods for the design of clear layers in order to comply, inter alia, with the requirements of various
protection objectives.
This document includes information and provisions concerning the requirements for powered smoke
exhaust systems, their design and rules for their installation.
NOTE The requirements for testing the ventilators are dealt with in ISO 21927-3. Other parts of the
ISO 21927 series of standards deal with the power supply (ISO 21927-10), control equipment (ISO 21927-9) and
smoke control ducts and smoke control dampers (ISO 21927-7 and ISO 21927-8 respectively).
Design, as specified in this document, does not apply to:
— spaces with fixed gas extinguishing systems;
— storage facilities for hazardous materials;
— spaces in which there is a risk of explosions;
— corridors;
— stairwells.
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 21927-3, Smoke and heat control systems — Part 3: Specification for powered smoke and heat exhaust
ventilators
ISO 21927-8, Smoke and heat control systems — Part 8: Smoke control dampers
ISO 21927-9, Smoke and heat control systems — Part 9: Specification for control equipment
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21927-3 and the following apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— IEC Electropedia: available at https: //www .electropedia .org/
— ISO Online browsing platform: available at https: //www .iso .org/obp
3.1
roof-mounted ventilator
smoke exhaust ventilator designed to be mounted on a roof above a smoke reservoir and having exterior
weather protection
3.2
wall-mounted ventilator
smoke exhaust ventilator designed to be mounted in the upper part of an external wall
3.3
centrally installed ventilator
smoke exhaust ventilator to which smoke control ducts (3.7) from several smoke reservoirs can be
connected
3.5
area of smoke reservoir
A
a
area within a large space enclosed or bounded by smoke barriers or wall elements
3.6
design group
auxiliary design value that is used in the design of powered smoke exhaust systems and takes account
of the assumed duration of fire growth and the fire propagation rate
3.7
smoke control duct
duct through which smoke and heat are exhausted
3.8
single compartment smoke control damper
smoke control damper that is designed for use in a single smoke reservoir and can be connected to
single compartment smoke control ducts (3.7)
3.9
multi-compartment smoke control damper
fire-resistant smoke control damper designed for use in or on smoke control ducts (3.7) connecting
several smoke reservoirs, or in separating structural elements
4 Design principles
4.1 General
The design of powered smoke exhaust systems (see example in Figure 1) depends, inter alia, on the heat
release rate, the theoretical fire area of a building or the resulting design group, the target height of the
clear layer and the height of the space. Possible locations and designs of smoke exhaust ventilators are
described in ISO 21927-3.
2 © ISO 2018 – All rights reserved

Key
1 possible fire compartment
2 smoke layer in smoke reservoir
3 air inlet
4 smoke barrier (ISO 21927-1)
5 smoke exhaust ventilator (ISO 21927-3)
6 single compartment smoke control damper (ISO 21927-8)
7 smoke control duct for which there are no requirements for the duration of fire resistance (ISO 21927-7)
8 smoke control duct for which requirements for the duration of fire resistance apply (ISO 21927-7)
9 multi-compartment smoke control damper, installed in a wall or floor (ISO 21927-8)
10 multi-compartment smoke control damper, installed in a smoke control duct (ISO 21927-8)
11 electric cables
Figure 1 — Diagram showing possible powered smoke exhaust systems
The values to be used to determine the above parameters are auxiliary design values and they only
apply to designs in accordance with this document.
Design is based on the following:
— the powered smoke exhaust system is activated at an early stage, e.g. by an automatic fire alarm
system with smoke detectors, or immediately by trained personnel that are in attendance around
the clock;
— the mean fire propagation rate for an assumed duration of fire growth is around 10 min;
— there is a sufficiently large and evenly distributed air supply through inlets close to floor level;
the air supply needs to be effective from the time the powered smoke exhaust system is switched
on to avoid turbulence in the smoke (flow rate not greater than 1 m/s at the point at which the
replacement air enters the smoke reservoir; this can be achieved by using deflectors, for example);
— large spaces are divided into smoke reservoirs by means of smoke barriers;
— the fires are solid materials fires;
— the fire area does not exceed 80 m up to the time at which extinguishing measures commence;
— the smoke layer temperatures are below flash-over level.
4.2 Height of space
The height, h, of the space to be protected (as shown in Figure 2), shall be the distance from the floor
to the lower surface of the roof/floor in the case of horizontal roofs/floors. For pitched roofs or sloping
floors, it shall be the mean distance from the floor to the lower surface of the roof/floor. Floors with
smoke outlets are not regarded as floors in this context.
In the case of sawtooth roofs, the space height to be used for design purposes is the mean height of the
extraction point of the powered smoke exhaust system above floor level.
4.3 Target height of the clear layer, d, in a smoke reservoir, A
R
The clear layer, d, is defined as the distance between the surface of the floor assumed for design
purposes and the lower surface of the smoke layer.
Clear layers enable:
— the occupants of a building to escape to safety,
— the emergency services to rescue people, animals and property,
— fires to be fought effectively, and
— damage due to fire gases and products of thermal decomposition to be reduced.
The target height of the clear layer d (see Figure 2) should be not less than 2,50 m.
Design should be based on higher values of d if so required by the purpose for which the space is to be
used (e.g. spaces containing objects sensitive to smoke or flammable warehouse stock). The distance
between the objects to be protected and the smoke layer should not be less than 0,5 m.
For clear layers with a height d ≤ 4 m, the height of the smoke barrier shall protrude at least 0,5 m into
the clear layer. For clear layers with a height d > 4 m the smoke barrier shall at least equal to the height
of the smoke layer, z, but not less than 1,0 m in all cases.
4.4 Area of smoke reservoir, A
R
To enable powered smoke exhaust systems to be designed according to this document, spaces shall
either have a maximum area of 1 600 m or be divided into smoke reservoirs with a maximum area, A ,
R
of 1 600 m by
...