ISO 21927-4:2019

INTERNATIONAL ISO
STANDARD 21927-4
First edition
2019-04
Smoke and heat control systems —
Part 4:
Natural smoke and heat exhaust
ventilators — Design, requirements
and installation
Systèmes pour le contrôle des fumées et de la chaleur —
Partie 4: Exutoires de fumées et de chaleur naturels —
Dimensionnement, exigences et mise en place
Reference number
©
ISO 2019
© ISO 2019
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Published in Switzerland
ii © ISO 2019 – All rights reserved

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 Design principles . 2
5.1 General . 2
5.2 Height of space . 3
5.3 Target height of the clear layer, height of smoke barrier . 3
5.4 Area of smoke reservoir . 4
5.5 Air inlets . 4
5.6 Duration of fire growth . 5
5.7 Theoretical fire area, design groups . 5
5.8 Aerodynamic effectiveness of NSHEVs . 6
6 Design . 6
6.1 General . 6
6.2 Smoke exhaust openings in roofs . 6
6.3 Smoke exhaust openings in walls .12
7 Installation .13
7.1 General .13
7.2 Rules for installation .13
8 NSHEVs combined with fire extinguishing equipment .14
9 Testing, maintenance and repair .15
9.1 Testing .15
9.2 Maintenance .15
9.3 Repair .15
Bibliography .16
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
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electrotechnical standardization.
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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
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.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
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iv © ISO 2019 – All rights reserved

Introduction
Smoke and heat control systems (SHCS) create and maintain smoke free areas in a construction works
by controlling smoke flow and thus improve 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 perform 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 in order 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.
Power output devices for control equipment are dealt with in ISO 21927-10.
INTERNATIONAL STANDARD ISO 21927-4:2019(E)
Smoke and heat control systems —
Part 4:
Natural smoke and heat exhaust ventilators — Design,
requirements and installation
1 Scope
This document applies to the design and installation of natural smoke and heat exhaust ventilators
(NSHEVs) for spaces from which smoke is extracted vertically by thermal buoyancy via the roof in the
case of single-storey buildings and via the uppermost storey in the case of multi-storey buildings. It
also applies to spaces in which NSHEVs are installed in external walls.
This document includes tables and calculation methods for the design of clear layers in order to comply
with the requirements of various protection objectives.
This document includes information and provisions to be taken into account when applying the design
rules set out herein and when installing NSHEVs.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 13943, Fire safety — Vocabulary
ISO 21927-1, Smoke and heat control systems — Part 1: Specification for smoke barriers
ISO 21927-2, Smoke and heat control systems — Part 2: Specification for natural smoke and heat exhaust
ventilators
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply.
ISO and IEC maintain 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
aerodynamic free area
measure of smoke and heat exhaust area of the ventilator
Note 1 to entry: It is the geometric area multiplied by the coefficient of discharge.
3.2
automatic activation
initiation of operation without direct human intervention
3.3
coefficient of discharge
aerodynamic efficiency
c
v
ratio of actual flow rate, measured under specified conditions, to the theoretical flow rate through the
ventilator
Note 1 to entry: The coefficient takes into account any obstructions in the ventilator, such as controls, louvres
and vanes, and the effect of external side winds.
3.4
exhaust ventilator
device for the movement of gases out of the construction works
3.5
initiation device
device that activates the operating mechanism of the component, e.g. of a damper or a ventilator, on
receipt of information from a fire detection system or thermal device
3.6
smoke and heat exha
...