ISO 21927-6:2026

International
Standard
ISO 21927-6
First edition
Smoke and heat control systems —
2026-01
Part 6:
Specification for pressure
differential systems
Systèmes pour le contrôle des fumées et de la chaleur —
Partie 6: Spécifications relatives aux systèmes à différentiel de
pression
Reference number
© ISO 2026
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Published in Switzerland
ii
Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms, definitions, symbols and abbreviated terms . 1
3.1 Terms, definitions and abbreviated terms .1
3.2 Symbols .2
4 Characteristics . 3
4.1 General .3
4.2 Nominal activation conditions/sensitivity .4
4.2.1 Kit .4
4.2.2 Components .4
4.3 Response delay (response time) .5
4.3.1 Kit .5
4.3.2 Components .6
4.4 Operational reliability .6
4.4.1 Kit . .6
4.4.2 Components .7
4.5 Effectiveness of smoke/hot gas extraction (air release/powered air release) .7
4.5.1 Kit .7
4.5.2 Components .7
4.6 Performance parameters under fire conditions .8
4.6.1 Kit .8
4.6.2 Components .8
4.7 Pressurization performance .9
4.7.1 Kit .9
4.7.2 Components .9
4.8 Fire resistance – Integrity (E) .10
4.8.1 Kit .10
4.8.2 Components .10
4.9 Fire resistance – Insulation (I) .11
4.9.1 Kit .11
4.9.2 Components .11
4.10 Fire resistance – Smoke leakage (S) .11
4.10.1 Kit . .11
4.10.2 Components . 12
4.11 Fire resistance – Mechanical stability . 12
4.11.1 Kit . 12
4.11.2 Components . 12
4.12 Fire resistance – Maintenance of cross section. 13
4.12.1 Kit . . 13
4.12.2 Components . 13
4.13 Durability .14
4.13.1 Kit .14
4.13.2 Components .14
5 Test methods .15
5.1 General . 15
5.1.1 Kits . 15
5.1.2 Families . 15
5.1.3 Substitution of components from different families .16
5.2 Nominal activation conditions/sensitivity .16
5.2.1 Kit . .16
5.2.2 Components .16

iii
5.3 Response delay (response time) .17
5.3.1 Kit .17
5.3.2 Components .17
5.4 Operational reliability .17
5.4.1 Kit .17
5.4.2 Components . 29
5.5 Effectiveness of smoke/hot gas extraction . 29
5.5.1 Kit . . 29
5.5.2 Components . 29
5.6 Performance parameters under fire conditions . 30
5.6.1 Kit . . 30
5.6.2 Components . 30
5.7 Pressurization performance .31
5.7.1 Kit . .31
5.7.2 Components .31
5.8 Fire resistance – Integrity (E) .31
5.8.1 Kit . .31
5.8.2 Components .32
5.9 Fire resistance – Insulation (I) .32
5.9.1 Kit . .32
5.9.2 Components .32
5.10 Fire resistance – Smoke leakage (S) . 33
5.10.1 Kit . . 33
5.10.2 Components . 33
5.11 Fire resistance – Mechanical stability . 34
5.11.1 Kit . . 34
5.11.2 Components . 34
5.12 Fire resistance – Maintenance of cross section. 34
5.12.1 Kit . 34
5.12.2 Components . 34
5.13 Durability . 35
5.13.1 Kit . . 35
5.13.2 Components . 35
6 Verification of performance .36
6.1 Type testing . 36
6.1.1 General . 36
6.1.2 Test samples, testing and compliance criteria .37
6.1.3 Test reports .37
6.2 Factory production control (FPC) .37
6.2.1 General .37
6.2.2 Requirements . 38
6.2.3 Product specific requirements . 40
7 Marking, labelling and packaging .40
Annex A (normative) Pressure differential kit types (pressurization) .42
Annex B (normative) Test method for hot gas control damper at elevated temperature .53
Annex C (normative) Test required for powered smoke and heat exhaust ventilators with
frequency inverter and operated with variable speed at elevated temperature .57
Annex D (normative) Installation and maintenance document.59
Bibliography .60

iv
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).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by the European Committee for Standardization (CEN), CEN/TC 191, Fixed
firefighting systems (as EN 12101-6:2022) and was adopted, without modification other than those given
below by Technical Committee ISO/TC 21, Equipment for fire protection and fire fighting, Subcommittee
SC 11, Smoke and heat control systems and components.
— Editorial changes in 3.2, Symbols: the subscript elements are not written in italics.
— Normative references: the normative references were changed from the European Standard of the series
EN 12101-xx into the ISO standard of the series ISO 21927-xx.
— Clause 7: Headline "Table 3" was added and the sentence above the table was rephrased.
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.

v
Introduction
0.1  Objectives of pressure differential systems
Pressure differential systems offer the facility of maintaining tenable conditions in protected spaces, for
example: escape routes, firefighting access routes, firefighting lift shafts, lobbies, staircases, and other
spaces that require being kept free of smoke. It is necessary to determine not only where the fresh air
supply for pressurization is to be introduced into a building, but also where that air and smoke will leave the
building and what paths it will follow in the process.
The aim therefore is to establish a pressure gradient from the protected space to the unprotected space (fire
room) while the doors are closed, and an airflow while the doors are open.
0.2  Smoke control methods
The effect of the air movement forces, described above, are to create pressure differentials across the
partitions, walls and floors and can cause smoke to spread to spaces remote from the fire source. The
technique most commonly used to limit the degree of smoke spread, or to control its effects, is pressurization.
0.3  System components
A typical pressure differential system will comprise three basic components:
a) components for providing supply air and to extract air;
b) components for controlling the pressure difference between the space with higher pressure and the
adjoining space with lower pressure;
c) components for releasing air flowing through the door between the space with higher pressure to those
with lower pressure (to prevent unwanted pressure build up in this space).
Installations of pressure differential systems (PDS) may comprise:
— fans (temperature rated) if necessary;
— air or smoke control ducts to provide a passageway for the transmission of air or smoke;
— ventilation openings to provide leakage of air (including dampers, active or passive controlled);
— power supply;
— connecting cables;
— means of activation;
— means of pressure control;
— control panel;
— smoke control dampers in branches from the ductwork where the ductwork is situated outside the
protected enclosure;
— grilles and diffusers;
— door closers.
1)
The design of pressure differential systems is covered in ISO 21927-13 .
1)  Under preparation. Stage at the time of publication ISO/DIS 21927-13:2025.

vi
International Standard ISO 21927-6:2026(en)
Smoke and heat control systems —
Part 6:
Specification for pressure differential systems
1 Scope
This document applies to pressure differential system kits and components, positioned on the market and
intended to operate as part of a pressure differential system. The purpose of a pressure differential system
is to prevent protected spaces from smoke spread by using pressure difference and airflow. This document
specifies characteristics and test methods for components and kits for pressure differential systems to
produce and control the required pressure differential and airflow between protected and unprotected
space.
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 21927-2, Smoke and heat control systems — Part 2: Specifications for natural smoke and heat exhaust
ventilators
ISO 21927-3, Smoke and heat control systems — Part 3: Specifications for powered smoke and heat exhaust
ventilators
ISO 21927-8, Smoke and heat control systems — Part 8: Smoke control dampers
EN 1363-1, Fire resistance tests — Part 1: General requirements
EN 1366-8, Fire resistance tests for service installations — Part 8: Smoke extraction ducts
EN 1366-9, Fire resistance tests for service installations — Part 9: Single compartment smoke extraction ducts
EN 1366-10, Fire resistance tests for service installations — Part 10: Smoke control dampers
EN 1751, Ventilation for buildings — Air terminal devices — Aerodynamic testing of damper and valves
EN 13501-4, Fire classification of construction products and building elements — Part 4: Classification using
data from fire resistance tests on components of smoke control systems
3 Terms, definitions, symbols and abbreviated terms
3.1 Terms, definitions and abbreviated terms
For the purposes of this document, the terms and definitions given in ISO 13943 and the following apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp

— IEC Electropedia: available at https:// www .electropedia .org/
3.1.1
air release
means by which pressurizing air or a mixture of pressurizing air and smoke is able to escape from the
accommodation or other unpressurized space to outside the building
3.1.2
control panel
multi-operational device to activate and/or control a PDS
3.1.3
depressurization
smoke control using pressure differentials between the protected space and the unprotected space with a
lower pressure in the unprotected space
3.1.4
pressure differential system
PDS
combination of at least one kit and additional components intended to produce pressure differential and
airflow between protected and unprotected spaces
3.1.5
pressurization
smoke control using pressure differentials between the protected space and the unprotected space with a
higher pressure in the protected space
3.1.6
pressure differential system
PDS
combination of at least two components which are necessary to produce and control the required pressure
differential and airflow-between protected and unprotected space
Note 1 to entry: The type of kit is dictated by the PDS design and objectives. Schematic overviews of different types
are given in Annex A.
3.1.7
active control
pressure control actuated from measured pressure and using external energy (e.g. motor driven damper,
frequency inverter-controlled fans, etc.)
3.1.8
barometric relief damper
damper activated by local pressure difference that opens to permit airflow and therefore controls the
pressure
3.1.9
activation signal
signal to initiate from stand-by to the active mode of the pressure differential system
3.2 Symbols
The symbols and abbreviations below are used in the document:

Symbol Unit Description
measured air release volume flow rate from space 1 (representing the protected space in
 3
m /h the building) to space 2 (representing the unprotected space in the building) via open air
V
ar
release path during the test (nominal value given by the manufacturer)
required leakage flow rate if necessary for the function of the PDS kit. If the building leakages
 3
V m /h (always present) are at the same rate or larger, during the test (nominal value given by the
RL
manufacturer), the component to produce the defined leakage is part of the PDS kit under test
m /h volume flow rate through temporary openings (e.g. open doors from staircases on differ-

V
ent levels from fire level, open escape/exit door) in case of pressurization during the test
TO
ps
(nominal value given by the manufacturer)
m /h volume flow rate through temporary openings (e.g. open doors from staircases on different

V
levels from fire level, open escape/exit door) in case of depressurization during the test
TO
dp
(nominal value given by the manufacturer)

m /h
exhaust volume flow rate out of space 2 for combined systems
V
ex

m /h
V required minimum leakage volume flow rate at nominal pressure difference ∆p
Nom
rl
m /h lower limit of volume flow rate through air release

V
ar,ll 
VV09,
ar,ll ar

m /h
supply air volume flow rate measured at inlet nozzle
V
sa

m /h
total controlled volume flow rate of the PDS kit as sum of flow rate air release V + flow
ar

V
TC

rate through temporary openings V (nominal value given by the manufacturer)
TC

m /h
bypass air volume flow rate
V
BP
Pa
∆p pressure differential between space 1 and reference pressure (static pressure in test hall)
tr1
Pa
∆p pressure differential between space 2 and reference pressure (static pressure in test hall)
tr2
Pa nominal pressure differential to be maintained by the PDS kit with closed air release opening
∆p
nom
and closed temporary openings (static conditions)
∆p Pa pressure difference across the open-air release path
ar
Pa
∆p Upper limit of nominal pressure differential pP12,
Nom,ul Nom,ul Nom

s
∆t Time period needed to establish volume flow rate V (flow criteria – see Figure 6)
V ar,ll
s
∆t
Pressure stabilizing time period (pressure criteria – see 5.7)
p
∆t s
time to establish volume flow rate in TCS cycle i
V ,i
s
∆t
pressure stabilizing time in TCS cycle i
pi,
−1
f s frequency of the frequency inverter from the PDS kit where equipped
−1
s minimal frequency of the frequency inverter at the passed test with all openings closed and
f
min
at lowest required leakage – shall be stated in the test report
−1
s highest frequency of the frequency inverter at the passed test with air release path and
f
max
temporary opening open and at highest required leakage – shall be stated in the test report
I A absorbed current of the fan (motor)
fan
TCS test cycle sequence
4 Characteristics
4.1 General
This clause gives details of the characteristics and additional test details. The structure of this clause is
mirrored in Clause 5. The characteristics are listed here, with the corresponding test reference in Clause 5.
NOTE 1 This structure was used as it mirrors the requirements for harmonized product standards to ensure all the
relevant subjects are covered.

For example, in 4.2.2.1 the characteristics for natural smoke and heat exhaust dampers are shown and the
matching 5.2.2.1 provides the test method. This is continued throughout these two clauses.
The kit shall be shown to be able to fulfil the specific pressure differential application that it is designed to
provide. To demonstrate this, certain components have their own requirements and will need to fulfil these.
Any component with no specific characteristics shown below shall be listed as part of the kit and included in
the kit testing.
— Where there is a need for air or smoke release (cold or hot) to the outside through an opening fitted with
a natural smoke and heat exhaust ventilator shall be used.
— Where air volume and pressure are to be controlled using mechanical pressure relief a barometric
damper or controlled damper in accordance with this document shall be used.
— Where ambient air is to be supplied using fans, the fans shall be further shown to be in accordance with
this document.
— Where air or smoke is to be extracted by the pressure differential systems (cold or hot) this shall be done
using powered heat exhaust ventilators (smoke control fans).
— Where air or smoke is to be extracted (cold or hot) using ductwork, the ductwork shall be smoke control
duct (Builders work shafts may be used as an option and this is not within the scope of this document).
— Where dampers are needed to open and close to provide a path for air or smoke (cold or hot) to the
outside and maintain compartmentation, these shall be smoke control dampers.
— Where volume control around high temperature fans is to be provided using motorized control dampers
these shall be hot gas control dampers in accordance with this document.
NOTE 2 Fans/shafts/ductwork used to balance stack effects in the staircase do not need to have a temperature
rating.
4.2 Nominal activation conditions/sensitivity
4.2.1 Kit
The PDS kit shall be activated automatically by smoke detectors and it shall be possible to trigger it manually
by an external switch.
The following proxy characteristics shall be taken into account
a) the response time – see 4.3, and
b) the operational reliability – see 4.4.
In addition, the following components shall have their own characteristics when functioning as a part of the
kit.
4.2.2 Components
4.2.2.1 Natural smoke and heat exhaust ventilators
The characteristics for nominal activation conditions/sensitivity in ISO 21927-2 shall be met – see 5.2.2.1.
4.2.2.2 Pressure control dampers (e.g. barometric dampers, motorized control dampers)
The following proxy characteristics shall be taken into account
a) the response time – see 4.3, and
b) the operational reliability – see 4.4.

4.2.2.3 Fans
4.2.2.3.1 Ambient air supply fans
The following proxy characteristics shall be taken into account
a) the response time – see 4.3, and
b) the operational reliability – see 4.4.
4.2.2.3.2 Smoke control fans (powered smoke and heat exhaust ventilators)
In addition to any response time required by the kit (4.3.1), the characteristics for nominal activation
conditions/sensitivity in ISO 21927-3 shall be met – see 5.2.2.3.2.
See also Annex C for additional tests with smoke fans controlled by frequency inverters.
4.2.2.4 Smoke control ducts
Smoke control ducts have no nominal activation conditions/sensitivity requirements as they have no moving
parts.
4.2.2.5 Smoke control dampers
The characteristics for nominal activation conditions/sensitivity in ISO 21927-8 shall be met – see 5.2.2.5.
4.2.2.6 Hot gas control dampers
The following proxy characteristics shall be taken into account
a) the response time – see 4.3,
b) the operational reliability – see 4.4, and
c) characteristics as determined in Annex B.
4.3 Response delay (response time)
4.3.1 Kit
4.3.1.1 General
The proxy characteristics in 4.3.1.2 and 4.3.1.3 shall be taken into account.
4.3.1.2 Initial response time
The kit shall achieve operating status within a time period of less than 60 s after the activation signal. This
shall be tested in accordance with 5.4.1.
4.3.1.3 Response time of door opening and door closing
The kit shall achieve at least 90 % of the nominal airflow rate within 3 s of a door being fully opened (opening
angle 90°) in accordance with test method in 5.4.1.2.
The kit shall reach the nominal pressure differential in the protected space Δp ±20 % within 3 s after a
nom
door to the unprotected space or a temporary opening is closed completely. The pressure differential shall
not exceed Δp = Δp ⋅ 1,2 for a time period of more than 3 s. This shall be demonstrated in accordance
nom,ul nom
with the test method in 5.4.1.

The kit shall re-establish behaviour under the conditions of the oscillating test in 5.4.1.11 even in the case of
several door closing/opening cycles in accordance with test method in 5.4.1.11.
4.3.2 Components
4.3.2.1 General
In addition, the following components shall have their own requirements when functioning as a part of the
kit.
4.3.2.2 Natural smoke and heat exhaust ventilators
The characteristics for response delay (response time) in ISO 21927-2 shall be met – see 5.3.2.1.
4.3.2.3 Pressure control dampers (e.g. barometric dampers, motorized control dampers)
The pressure control dampers shall meet the response time characteristics as shown in 4.3.1 when tested as
part of the kit – see 5.3.2.2.
4.3.2.4 Fans
4.3.2.4.1 Ambient air supply fans
The ambient supply fans shall meet the response time characteristics as shown in 4.3.1 when tested as part
of the kit – see 5.3.2.3.1.
4.3.2.4.2 Smoke control fans (powered smoke and heat exhaust ventilators)
In addition to any response time required by the kit (4.3.1), if the product requires it, the characteristics for
nominal activation conditions/sensitivity in ISO 21927-3 shall be met – see 5.3.2.3.2.
4.3.2.5 Smoke control ducts
Smoke control ducts have no response delay requirements as they have no moving parts.
4.3.2.6 Smoke control dampers
The characteristics for response delay (response time) in ISO 21927-8 shall be met – see 5.3.2.5.
4.3.2.7 Hot gas control dampers
The characteristics shown in Annex B shall be reported against the listed classifications. The dampers shall
meet the requirements in 4.3.1 and move to the required position in less than 3 s (4.3.1) and it shall be
proven that the average operation time as determined in Annex B under elevated temperature conditions is
no more than plus 20 % of that determined at ambient temperature.
4.4 Operational reliability
4.4.1 Kit
The following proxy characteristics shall be taken into account: the ability of the kit to fulfil the volume flow
rate and pressurization values as part of the functionality test – see 5.4.1.
Complete the 10 000 cycles requirement.
In addition, the following components shall have their own requirements when functioning as a part of the
kit.
4.4.2 Components
4.4.2.1 Natural smoke and heat exhaust ventilators
The characteristics for operational reliability in ISO 21927-2 shall be met – see 5.4.2.1.
4.4.2.2 Pressure control dampers (e.g. barometric dampers, motorized control dampers)
The pressure control dampers shall meet the operational reliability as shown in 4.4.1 when tested as part of
the kit – see 5.4.2.2.
4.4.2.3 Fans
4.4.2.3.1 Ambient air supply fans
The ambient supply fans shall meet the operational reliability characteristics as shown in 4.4.1 when tested
as part of the kit – see 5.4.2.3.1.
4.4.2.3.2 Smoke control fans (Powered smoke and heat exhaust ventilators)
In addition to any operational reliability required by the kit test (4.4.1), the smoke control fans shall meet
the operational reliability requirements of ISO 21927-3 – see 5.4.2.3.2.
See also Annex C for additional tests with smoke fans controlled by frequency inverters.
4.4.2.4 Smoke control ducts
Smoke control ducts have no operational reliability requirements as they have no moving parts.
4.4.2.5 Smoke control dampers
The characteristics for operational reliability in ISO 21927-8 shall be met – see 5.4.2.5.
4.4.2.6 Hot gas control dampers
The 10 operations at ambient and 10 operations at elevated temperature (see Annex B) shall be met before
being part of the kit test – see 4.4.1.
4.5 Effectiveness of smoke/hot gas extraction (air release/powered air release)
4.5.1 Kit
The following proxy characteristic shall be taken into account
— the ability of the kit to fulfil the operational reliability requirements – see 4.4.
4.5.2 Components
4.5.2.1 Natural smoke and heat exhaust ventilators
The aerodynamic free area and relevant loading reliability requirements of ISO 21927-2 shall be met – see
5.5.2.1.
4.5.2.2 Pressure control dampers (e.g. barometric dampers, motorized control dampers)
As a proxy characteristic the pressure control dampers shall meet the response time (4.3.1) and operational
reliability (4.4.1) when tested as part of the kit – see 5.5.2.2.

4.5.2.3 Fans
4.5.2.3.1 Ambient air supply fans
The ambient supply fans shall meet the operational reliability characteristics as shown in 4.4.1 when tested
as part of the kit – see 5.5.2.3.1.
4.5.2.3.2 Smoke control fans (Powered smoke and heat exhaust ventilators)
In addition to any operational reliability required by the kit test (see 4.4.1)
...