ISO/FDIS 13785-1

• Abstract:

  ISO 13785-1:2002 specifies a screening method for determining the reaction to fire of materials and constructions of façades or claddings when exposed to heat from a simulated external fire with flames impinging directly upon a façade. It is intended for use by producers to reduce the burden of testing in ISO 13785-2:2002 by eliminating those systems that fail the tests described in ISO 13785-1:2002. The test method consists of observing the behaviour of the façade panel construction to fire and the resulting flame spread on or within the façade construction. This test method is applicable only to façades and claddings that are not free standing and that are used by adding to an existing external wall. This test method also is applicable only to vertical elements and is not applicable to determining the structural strength of the façade or cladding.

• Status: Not Published
• ICS: 13.220.50 - Fire-resistance of building materials and elements
• ICS: 91.060.10 - Walls. Partitions. Facades
• Technical Committee: ISO/TC 92/SC 1 - Fire initiation and growth
• Drafting Committee: ISO/TC 92/SC 1/WG 7 - Large and intermediate scale fire test methods
• Current Stage: 5020 - FDIS ballot initiated: 2 months. Proof sent to secretariat
• Start Date: 21-Aug-2026
• Completion Date: 21-Aug-2026

• Revises: ISO 13785-1:2002 - Reaction-to-fire tests for façades — Part 1: Intermediate-scale test
• Effective Date: 09-Mar-2024

Overview

ISO/FDIS 13785-1:2026 is the International Organization for Standardization's standard for Reaction-to-fire tests for façades – Part 1: Intermediate-scale test. This standard specifies a screening method to assess the reaction to fire of façade materials and claddings, particularly when exposed to external flames that impinge directly on the façade. The test is designed to observe how façade panels and constructions react to fire, focusing on flame spread either on or within the façade system. The method helps producers identify systems that are unsuitable for further evaluation under the large-scale test (ISO 13785-2), thus streamlining the overall testing process and reducing unnecessary investments in systems that do not meet initial fire safety requirements.

The test outlined in ISO 13785-1 applies to vertical façade elements and claddings added to existing external walls, excluding free-standing façades and does not assess structural strength. It emphasizes replicating real-world installation and construction details to ensure accurate representation of end-use scenarios.

Key Topics

• Intermediate-scale reaction-to-fire testing: Provides a controlled method for assessing flame spread over or within façade claddings when subjected to direct flames.
• Simulated external fire exposure: The test recreates scenarios such as fire venting from a window, which poses significant risk in real buildings.
• Test specimen configuration: Requires test panels to be constructed and fixed in accordance with actual installation practices, including the incorporation of joints, fixings, and cavity barriers as they would appear in finished buildings.
• Data collection and reporting: Involves surface and cavity thermocouple placement, optional measurements of heat release rate and heat flux, and detailed visual and instrumental monitoring.
• Health and safety precautions: Addressing the evolution of toxic gases and risk of specimen collapse, emphasizing thorough safety measures during testing.
• Comparative and screening function: Used primarily to eliminate façade systems unlikely to pass larger-scale fire tests, optimizing the evaluation process.

Applications

ISO 13785-1 serves a critical role in building safety by providing a cost-effective method for evaluating the fire performance of façade claddings and assemblies. Its main applications include:

• Building product development: Manufacturers can use this standard to screen façade systems in the early stages of product development and before investing in comprehensive large-scale tests.
• Regulatory compliance: The standard is relevant for meeting fire safety regulations by demonstrating the fire performance of façade products in line with national and international building codes.
• Comparative assessment: Enables objective performance comparison between different façade materials, assemblies, and configurations under fire exposure.
• Research and modeling: Provides a validated methodology to support fire safety engineering, computational modeling, and forensic investigations of building fire scenarios.
• Quality assurance: Ensures that façade claddings installed on buildings meet baseline fire reaction requirements, thereby reducing potential fire spread and improving occupant safety.

Related Standards

• ISO 13785-2: Reaction-to-fire tests for façades – Part 2: Large-scale test; for end-use performance evaluation of façade systems.
• ISO 9705-1: Reaction to fire tests – Room corner test for wall and ceiling lining products.
• ISO 24473: Fire tests – Open calorimetry – Measurement of heat and combustion product release.
• ISO 13943: Fire safety – Vocabulary; provides precise definitions for fire safety terms used in this standard.
• IEC 60584-1: Thermocouples – Specifications for temperature measurement instrumentation.
• ISO/TS 3814: Explains theory and background of reaction-to-fire tests.

Implementing ISO/FDIS 13785-1:2026 enhances fire safety for buildings utilizing exterior façade systems, offering a practical and efficient screening process in modern construction and safety management. For more information and the latest updates on the ISO 13785 series, visit the ISO website.

FINAL DRAFT
International
Standard
ISO/TC 92/SC 1
Reaction-to-fire tests for façades —
Secretariat: BSI
Part 1:
Voting begins on:
2026-08-21
Intermediate-scale test
Voting terminates on:
Essais de réaction au feu des façades —
2026-10-16
Partie 1: Essai à échelle intermédiaire
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 SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
FINAL DRAFT
International
Standard
ISO/TC 92/SC 1
Reaction-to-fire tests for façades —
Secretariat: BSI
Part 1:
Voting begins on:
Intermediate-scale test
Voting terminates on:
Essais de réaction au feu des façades —
Partie 1: Essai à échelle intermédiaire
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 SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Test facility . . 3
5.1 General .3
5.2 Specimen support frame .3
6 Test specimen . 7
7 Test specimen instrumentation . 8
7.1 Thermocouples .8
7.2 Heat release rate (optional) .9
7.3 Heat flux (optional) .9
7.4 Other equipment .10
7.4.1 Data acquisition . . .10
7.4.2 Timing device .10
8 Test specimen conditioning .11
9 Test environment .11
10 Procedure .11
10.1 Initial conditions .11
10.2 Test .11
11 Expression of results .12
12 Precision .12
13 Test report .12
Annex A (informative) Heat release rate measurement . 14
Annex B (informative) Repeatability and reproducibility . 17
Bibliography .18

iii
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 document 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 Technical Committee ISO/TC 92 Fire safety, Subcommittee SC 1, Fire
initiation and growth.
This second edition cancels and replaces the first edition (ISO 13785-1:2002), which has been technically
revised.
The main changes are as follows:
— modifications to accommodate thicker samples (Clause 6);
— introduction of heat release measurement option (subclause 7.2).
A list of all parts in the ISO 13785 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
Introduction
Fire is a complex phenomenon. Its behaviour and effects depend on a number of interrelated factors. The
behaviour of materials and products depends on the characteristics of the fire, the method of use of the
materials and the environment in which they are exposed. The theory of “reaction to fire tests” is explained
in ISO/TS 3814.
The need for improved thermal insulation of buildings both for single and multi-storey dwellings and for
industrial buildings has led to an increased use of insulated and often ventilated façades.
With these types of construction products, there are three primary fire threats to the walls and ceilings/
roofs of a building:
a) an interior compartment fire venting through an opening on to a façade;
b) an exterior fire in combustibles accumulated near a wall (e.g. rubbish, vegetation);
c) fire in an adjacent building.
Item a) is generally the most severe and substantially the most significant.
Fire can spread in several ways. The most significant is by spread over a combustible exterior surface or
the fire travelling vertically and horizontally through air cavities between external claddings or façades, or
through insulation or other layers.
The results may not, however, reflect the actual performance of exterior wall assemblies under all fire
exposure and end-use design conditions.
The test specified in this document covers a simple representation of one fire scenario with façade products,
typified by a fire within a building venting through a window and impinging directly on to a façade.
This document (ISO 13785-1) and ISO 13785-2 provide two test methods: an intermediate scale test specified
in this document, which is intended to be used for evaluation of sub-components or groups of products or as
a tool for extensions of applications, and a large scale test method such as the one specified in ISO 13785-2 is
used to provide the end-use evaluation of all aspects of the façade system. These test methods are intended
to evaluate assemblies that are not intended for use as an internal lining.
The test method of this document may be used as intermediate scale for validation of fire models in façade
[7] [8]
assessment studies or in fire investigations .
The test specified in this document may be used for comparative purposes between façade systems
or to ensure the existence of a certain level of performance considered. No other meaning is attached to
performance in this test. It is intended for use by producers to reduce the burden of testing in ISO 13785-2
by eliminating those systems that fail to reach a predefined performance level in the tests described in this
document. The large-scale test in ISO 13785-2should be used to give a more realistic end-use assessment of
performance.
v
FINAL DRAFT International Standard ISO/FDIS 13785-1:2026(en)
Reaction-to-fire tests for façades —
Part 1:
Intermediate-scale test
WARNING — So that suitable precautions may be taken to safeguard health, all persons involved
in the fire tests shall be aware of the possibility that toxic or harmful gases may be evolved during
exposure of test specimens.
Hazards are encountered when assessing the fire performance of any product on an intermediate-
scale and it is essential that adequate precautions be taken.
Particular attention shall be paid to the potential evolution of smoke and toxic gases and to the
fact that extensive flaming of specimens can occur sometimes with resultant mechanical failure of
fixings and joints and possible structural collapse.
An adequate means of extinguishing the specimen shall be provided.
1 Scope
This document specifies a test method for determining the reaction to fire performance of products and
constructions of façades claddings when exposed to heat from a simulated external fire with flames
impinging directly upon a façade.
This test method is applicable only to façades claddings that are not free standing and that are used as an
addition to an existing free-standing external wall.
This test method also is only applicable to vertical elements and is not applicable to determining the
structural strength of the façade cladding.
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 9705-1:2016, Reaction to fire tests — Room corner test for wall and ceiling lining products — Part 1: Test
method for a small room configuration
ISO 13943, Fire safety — Vocabulary
ISO 24473:2008, Fire tests — Open calorimetry — Measurement of the rate of production of heat and combustion
products for fires of up to 40 MW
IEC 60584-1, Thermocouples — Part 1: EMF specifications and tolerances
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 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
assembly
fabrication of materials (3.6), products (3.7) or composites (3.2)
EXAMPLE Sandwich panel.
Note 1 to entry: An assembly may include an air gap.
3.2
composite
combination of materials (3.6) that are generally recognized in building construction as discrete entities
EXAMPLE Coated or laminated product (3.7).
3.3
constant mass
state of a test specimen (3.8) when two successive weighing apparatus operations carried out at an interval
of 24 h do not differ by more than 0,1 % of the mass of the specimen or 0,1 g, whichever is greater
3.4
exposed surface
surface of a product (3.7) subjected to the heating conditions of the test
3.5
façade cladding
products (3.7) and constructions added to the external surface of an existing wall or frame
Note 1 to entry: The structure can be of concrete, lightweight concrete blockwork, masonry, timber, etc. The façade
cladding may be applied directly to the inner structure or may incorporate an air gap or an insulating layer.
3.6
material
single substance or uniformly dispersed mixture
EXAMPLE Substance made of metal, stone, timber, concrete, mineral fibre or polymers.
3.7
product
material (3.6), composite (3.2) or assembly (3.1) about which information is required
3.8
specimen
façade cladding (3.5) representing the material (3.6) of the end-use façade, including joints and fixings, and
mounting material/spacers where there is an air gap
Note 1 to entry: A substrate is not part of the specimen but is representative of the inner façade wall to which the
products (3.7) are mounted in end-use condition, including in terms of contribution to fire.
Note 2 to entry: The specimen may include an air gap.
4 Principle
The reaction to fire of a façade cladding is assessed when exposed to flames impinging directly on the edge
of the façade assembly in the intermediate scale. The specimen is constructed with a re-entrant angle of
90°, with the smaller wall parallel to the draught screens. This type of construction is common in end-use
condition and creates a worst-case situation.
The flame spread and mechanical behaviour of the specimen are assessed by indirect instrumental methods
within the internal cavity of the façade, or directly by observation of the front face of the façade.
Optionally, the heat release rate from the test assembly is measured during test.

5 Test facility
5.1 General
The test apparatus shall consist of a specimen support frame and an ignition source. A schematic
representation of the test apparatus is shown in Figure 1. The test apparatus shall be placed indoor and
influence of air entries and enclosure effects should be minimised as much as possible.
5.2 Specimen support frame
The specimen support frame (see Figure 1) shall consist of three walls, i.e. a three-part back wall and two
side walls. The side walls shall be positioned perpendicularly on both sides of the back wall and a small
perpendicular side wall of minimum 0,6 m wide. The test specimen shall be attached to a sample holder
that is the middle part of the back wall. The specimen support frame consists of a U-frame screen against
unwanted air currents in the laboratory environment and an L-frame specimen holder, both with a height of
2,8 m.
The U-frame screen wall (see Figure 1) consists of:
a) A back wall in three parts having a total width of 2 400 mm. The 1 200 mm wide central part consists
of a steel frame. The two other parts of the back wall consist of non-combustible board with a width of
600 mm on supporting frames.
b) Two 2 400 mm wide side walls consisting of non-combustible board on supporting frames shall be
positioned perpendicularly on both ends of the back wall.
The L-frame specimen holder (see Figure 1) consists of an L-shaped steel frame equipped at the front
with a substrate (a construction or boards) that represents well the construction to which the façade
product is mounted in end-use conditions. Measured from the inner corner line, the large wing has a
width of (1 750 ± 50) mm. The small wing, that is placed perpendicular to the large wing, has a width of
(1 150 ± 50) mm.
NOTE 1 The ‘construction to which the façade product is mounted in end-use conditions’ usually refers to the inner
wall.
NOTE 2 The specimen holder can consist of two separate steel frames with an appropriate substrate which are
placed in the test setup separately. Depending on type of specimen and the details and fixing of the corner construction
it can be possible to place the separate wing frames with a mounted specimen wing in the test setup.

Dimensions are in mm
a) U-frame b) L-frame
Figure 1 — Specimen holders
The L-frame is fixed inside U-frame with backwalls not separated by more than 20 mm. The lateral position
of the L-frame is conditioned by sample thickness (see Clause 7).
The screen wall and the specimen holder shall be located in an open laboratory environment below a smoke
extraction hood with adequate ventilation to catch all combustion products. The wall parts shall meet the
floor, with no air gaps formed. Care has to be taken so the exhaust flow does not affect the combustion.
3 -1
NOTE 3 A hood of 3 m × 3 m as proposed in ISO 9705-1 and a flow rate of more than 1 m ·s has been found suitable
to catch combustion products.
The test specimen shall be attached to the upper part of the sample holder so that the bottom edge of the
test specimen is 400 mm above the floor and that the front width of the specimen wings are 1 200 mm and
600 mm respectively. With the given dimensions of the L-frame specimen holder all specimens having up to
a thickness of 550 mm can be placed on the specimen holder (Figure 2).
NOTE 4 Due to the thickness of the specimen, the specimen holder is fitted with specimen wings having a width of
1 200 mm plus specimen thickness and 600 mm plus specimen thickness. The vertical centre line of the large wing is
centred between the two side walls of the U-frame screen wall.

a) Sample less than 100 mm b) Sample more than 100 mm (X = 500 mm)
Key
X tested sample thickness
burner position projection
Figure 2 — Specimen mounting, top view
WARNING — All equipment (tubes, couplings, flowmeters, etc.) shall be approved for propane. Be
aware of existing regulations regarding installation. The burner shall, for reasons of safety, be
equipped with a remote-control ignition device (e.g. a pilot flame or a glow wire). There shall be a
warning system for leaking gas and a valve for immediate and automatic cut-off of the gas supply in
case of extinction of the ignition flame.
The fire source shall be a propane gas burner. The size of the burner shall be
(1 200 ± 10) mm × (100 ± 2) mm × (150 ± 5) mm (length × width × height). To prevent deforming of the
burner by heating, the burner may be stiffened.
NOTE 5 Stiffening the burner can be achieved when the long edges of the burner are equipped with a steel L-profile
of (20 ± 1) mm × (20 ± 1) mm placed at the inside top edge of the burner. As an alternative, the top of the burner can be
reinforced with three steel clamps.
The burner filling consists of a minimum of 45 mm thick sand bed (particle size 1 mm to 2 mm) on a metal
mesh above a void with a height of 5 mm to 10 mm. The sand shall be clean, without debris from previous
test specimens. The top of the sand filling is flattened at less than 5 mm below the top of the burner.
NOTE 6 The objective of this requirement is an even propane flow over the entire opening area of the burner.
The burner shall be placed on the floor, lengthwise below the test specimen and with the ends of the burner
lined up with the edges of the test specimen. The long back side of the (100 mm wide) burner is only placed
on the specimen holder in case of a specimen thickness of not more than 100 mm. When the specimen
is thicker, the front of the burner shall be in the same vertical plane as the most protruding part of the
specimen bottom edge, and parallel to the specimen holder (see Figure 3).
NOTE 7 This position differs from previous versions of this document.

Key
A L-frame
B U-frame
C sample
D burner
X sample thickness
Figure 3 — Examples of burner positions depending on sample thickness, cut-view
The burner shall be supplied with natural grade propane (95 % minimum purity). The gas flow to the burner
shall be regulated using a mass flow controller with an accuracy of at least ±3 %. The heat output from
the burner shall be (100 ± 5) kW throughout the test. The burner heat release rate shall be calculated by
-1 -1
multiplying the gas flow by the heat of combustion of propane. A value of 46,4 kJ·g shall be used (2,16 g·s ).
Optionally, in case falling debris reduce the opening of the burner, the top of the burner may be provided
with a grid having an open to total area ratio of at least 90 % and a (45 ± 10)° angle sloping down to the front
of the burner as shown in Figure 4. The grid can be used to protect the burner against large fallen specimen
parts. The low side of the grid is directed to the open side of the U-frame screen wall.
Figure 4 — Burner protection grid

6 Test specimen
Both in construction and materials, the test specimen shall be representative of the system used in end-use
conditions. The application of the material to the test rig shall be as in end-use conditions. All constructional
details of joints, fixings, etc., shall be detailed and positioned in the test specimen as in end-use conditions.
The test specimen should be built by persons suitably qualified in the construction of this type of structure
in end-use conditions.
The specimen height is (2 400 ± 5) mm. After mounting on the specimen holder, the exposed surface width
of the large wing is (1 200 ± 5) mm, the exposed surface width of the small wing is (600 ± 5) mm, taken from
the inner corner line between the wings. The joints and fixings, where used in end-use conditions, shall be
installed as in end-use condition. The sample is fixed to the L-frame so that the large wing 1 200 mm width
is aligned with the 1 200 mm width of the opening of the U-frame. Therefore, the maximum width tested is
limited to 550 mm.
For façade systems with joints:
— The test specimen shall incorporate as stated in Figure 5 a):
— a central horizontal joint at mid-height [centre line at (1 200 ± 10) mm height] in both wings,
— a central vertical joint [centre line at (600 ± 10) mm from the corner line of the specimen wings] in
the large wing only, and
— a joint at the corner line between both wings.
— Alternatively, the horizontal joint in both wings may be positioned lower than at (1 200 ± 10) mm height.
...

ISO/TC 92/SC 1
Secretariat: BSI
Date: 2026-08-06
Reaction-to-fire tests for façades —
Part 1:
Intermediate-scale test
Essais de réaction au feu des façades —
Partie 1: Essai à échelle intermédiaire
FDIS stage
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
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Principle . 2
5 Test facility . 3
5.1 General. 3
5.2 Specimen support frame . 3
6 Test specimen . 7
7 Test specimen instrumentation . 8
7.1 Thermocouples . 8
7.2 Heat release rate (optional) . 9
7.3 Heat flux (optional) . 9
7.4 Other equipment . 10
8 Test specimen conditioning . 11
9 Test environment . 11
10 Procedure . 11
10.1 Initial conditions . 11
10.2 Test . 11
11 Expression of results . 12
12 Precision . 12
13 Test report . 12
Annex A (informative) Heat release rate measurement . 14
Annex B (informative) Repeatability and reproducibility . 18
Bibliography . 19

iii
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 document 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 Technical Committee ISO/TC 92 Fire safety, Subcommittee SC 1, Fire initiation
and growth.
This second edition cancels and replaces the first edition (ISO 13785-1:2002), which has been technically
revised.
The main changes are as follows:
— modifications to accommodate thicker samples (Clause 6);
— introduction of heat release measurement option (subclause 7.2).
A list of all parts in the ISO 13785 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
Introduction
Fire is a complex phenomenon. Its behaviour and effects depend on a number of interrelated factors. The
behaviour of materials and products depends on the characteristics of the fire, the method of use of the
materials and the environment in which they are exposed. The theory of “reaction to fire tests” is explained in
ISO/TS 3814.
The need for improved thermal insulation of buildings both for single and multi-storey dwellings and for
industrial buildings has led to an increased use of insulated and often ventilated façades.
With these types of construction products, there are three primary fire threats to the walls and ceilings/roofs
of a building:
a) an interior compartment fire venting through an opening on to a façade;
b) an exterior fire in combustibles accumulated near a wall (e.g. rubbish, vegetation);
c) fire in an adjacent building.
Item a) is generally the most severe and substantially the most significant.
Fire can spread in several ways. The most significant is by spread over a combustible exterior surface or the
fire travelling vertically and horizontally through air cavities between external claddings or façades, or
through insulation or other layers.
The results may not, however, reflect the actual performance of exterior wall assemblies under all fire
exposure and end-use design conditions.
The test specified in this document covers a simple representation of one fire scenario with façade products,
typified by a fire within a building venting through a window and impinging directly on to a façade.
This document (ISO 13785-1) and ISO 13785-2 provide two test methods: an intermediate scale test specified
in this document, which is intended to be used for evaluation of sub-components or groups of products or as
a tool for extensions of applications, and a large scale test method such as the one specified in ISO 13785-2 is
used to provide the end-use evaluation of all aspects of the façade system. These test methods are intended to
evaluate assemblies that are not intended for use as an internal lining.
The test method of this document may be used as intermediate scale for validation of fire models in façade
[7] [8]
assessment studies or in fire investigations .
The test specified in this document may be used for comparative purposes between façade systems or to
ensure the existence of a certain level of performance considered. No other meaning is attached to
performance in this test. It is intended for use by producers to reduce the burden of testing in ISO 13785-2 by
eliminating those systems that fail to reach a predefined performance level in the tests described in this
document. The large-scale test in ISO 13785-2 should be used to give a more realistic end-use assessment of
performance.
v
Reaction-to-fire tests for façades —
Part 1:
Intermediate-scale test
WARNING — So that suitable precautions may be taken to safeguard health, all persons involved in the
fire tests shall be aware of the possibility that toxic or harmful gases may be evolved during exposure
of test specimens.
Hazards are encountered when assessing the fire performance of any product on an intermediate-
scale and it is essential that adequate precautions be taken.
Particular attention shall be paid to the potential evolution of smoke and toxic gases and to the fact
that extensive flaming of specimens can occur sometimes with resultant mechanical failure of fixings
and joints and possible structural collapse.
An adequate means of extinguishing the specimen shall be provided.
1 Scope
This document specifies a test method for determining the reaction to fire performance of products and
constructions of façades claddings when exposed to heat from a simulated external fire with flames impinging
directly upon a façade.
This test method is applicable only to façades claddings that are not free standing and that are used as an
addition to an existing free-standing external wall.
This test method also is only applicable to vertical elements and is not applicable to determining the structural
strength of the façade cladding.
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 9705-1:2016, Reaction to fire tests — Room corner test for wall and ceiling lining products — Part 1: Test
method for a small room configuration
ISO 13943, Fire safety — Vocabulary
ISO 24473:2008, Fire tests — Open calorimetry — Measurement of the rate of production of heat and
combustion products for fires of up to 40 MW
IEC 60584-1, Thermocouples — Part 1: EMF specifications and tolerances
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 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
assembly
fabrication of materials (3.6), products (3.7) or composites (3.2)
EXAMPLE Sandwich panel.
Note 1 to entry: An assembly may include an air gap.
3.2
composite
combination of materials (3.6) that are generally recognized in building construction as discrete entities
EXAMPLE Coated or laminated product (3.7).
3.3
constant mass
state of a test specimen (3.8) when two successive weighing apparatus operations carried out at an interval of
24 h do not differ by more than 0,1 % of the mass of the specimen or 0,1 g, whichever is greater
3.4
exposed surface
surface of a product (3.7) subjected to the heating conditions of the test
3.5
façade cladding
products (3.7) and constructions added to the external surface of an existing wall or frame
Note 1 to entry: The structure can be of concrete, lightweight concrete blockwork, masonry, timber, etc. The façade
cladding may be applied directly to the inner structure or may incorporate an air gap or an insulating layer.
3.6
material
single substance or uniformly dispersed mixture
EXAMPLE Substance made of metal, stone, timber, concrete, mineral fibre or polymers.
3.7
product
material (3.6), composite (3.2) or assembly (3.1) about which information is required
3.8
specimen
façade cladding (3.5) representing the material (3.6) of the end-use façade, including joints and fixings, and
mounting material/spacers where there is an air gap
Note 1 to entry: A substrate is not part of the specimen but is representative of the inner façade wall to which the products
(3.7) are mounted in end-use condition, including in terms of contribution to fire.
Note 2 to entry: The specimen may include an air gap.
4 Principle
The reaction to fire of a façade cladding is assessed when exposed to flames impinging directly on the edge of
the façade assembly in the intermediate scale. The specimen is constructed with a re-entrant angle of 90°, with
the smaller wall parallel to the draught screens. This type of construction is common in end-use condition and
creates a worst-case situation.
The flame spread and mechanical behaviour of the specimen are assessed by indirect instrumental methods
within the internal cavity of the façade, or directly by observation of the front face of the façade.
Optionally, the heat release rate from the test assembly is measured during test.
5 Test facility
5.1 General
The test apparatus shall consist of a specimen support frame and an ignition source. A schematic
representation of the test apparatus is shown in Figure 1. The test apparatus shall be placed indoor and
influence of air entries and enclosure effects should be minimised as much as possible.
5.2 Specimen support frame
The specimen support frame (see Figure 1) shall consist of three walls, i.e. a three-part back wall and two side
walls. The side walls shall be positioned perpendicularly on both sides of the back wall and a small
perpendicular side wall of minimum 0,6 m wide. The test specimen shall be attached to a sample holder that
is the middle part of the back wall. The specimen support frame consists of a U-frame screen against unwanted
air currents in the laboratory environment and an L-frame specimen holder, both with a height of 2,8 m.
The U-frame screen wall (see Figure 1) consists of:
a) A back wall in three parts having a total width of 2 400 mm. The 1 200 mm wide central part consists of a
steel frame. The two other parts of the back wall consist of non-combustible board with a width of 600 mm
on supporting frames.
b) Two 2 400 mm wide side walls consisting of non-combustible board on supporting frames shall be
positioned perpendicularly on both ends of the back wall.
The L-frame specimen holder (see Figure 1) consists of an L-shaped steel frame equipped at the front with a
substrate (a construction or boards) that represents well the construction to which the façade product is
mounted in end-use conditions. Measured from the inner corner line, the large wing has a width of
(1 750 ± 50) mm. The small wing, that is placed perpendicular to the large wing, has a width of
(1 150 ± 50) mm.
NOTE 1 The ‘construction to which the façade product is mounted in end-use conditions’ usually refers to the inner
wall.
NOTE 2 The specimen holder can consist of two separate steel frames with an appropriate substrate which are placed
in the test setup separately. Depending on type of specimen and the details and fixing of the corner construction it can be
possible to place the separate wing frames with a mounted specimen wing in the test setup.
Dimensions are in mm
a) U-frame b) L-frame
Figure 1 — Specimen holders
The L-frame is fixed inside U-frame with backwalls not separated by more than 20 mm. The lateral position of
the L-frame is conditioned by sample thickness (see Clause 7).
The screen wall and the specimen holder shall be located in an open laboratory environment below a smoke
extraction hood with adequate ventilation to catch all combustion products. The wall parts shall meet the floor,
with no air gaps formed. Care has to be taken so the exhaust flow does not affect the combustion.
3 -1
NOTE 3 A hood of 3 m × 3 m as proposed in ISO 9705-1 and a flow rate of more than 1 m ·s has been found suitable
to catch combustion products.
The test specimen shall be attached to the upper part of the sample holder so that the bottom edge of the test
specimen is 400 mm above the floor and that the front width of the specimen wings are 1 200 mm and 600 mm
respectively. With the given dimensions of the L-frame specimen holder all specimens having up to a thickness
of 550 mm can be placed on the specimen holder (Figure 2).
NOTE 4 Due to the thickness of the specimen, the specimen holder is fitted with specimen wings having a width of
1 200 mm plus specimen thickness and 600 mm plus specimen thickness. The vertical centre line of the large wing is
centred between the two side walls of the U-frame screen wall.
a) Sample less than 100 mm b) Sample more than 100 mm (X = 500 mm)
Key
X tested sample thickness
burner position projection
Figure 2 — Specimen mounting, top view
WARNING — All equipment (tubes, couplings, flowmeters, etc.) shall be approved for propane. Be
aware of existing regulations regarding installation. The burner shall, for reasons of safety, be
equipped with a remote-control ignition device (e.g. a pilot flame or a glow wire). There shall be a
warning system for leaking gas and a valve for immediate and automatic cut-off of the gas supply in
case of extinction of the ignition flame.
The fire source shall be a propane gas burner. The size of the burner shall be
(1 200 ± 10) mm × (100 ± 2) mm × (150 ± 5) mm (length × width × height). To prevent deforming of the
burner by heating, the burner may be stiffened.
NOTE 5 Stiffening the burner can be achieved when the long edges of the burner are equipped with a steel L-profile
of (20 ± 1) mm × (20 ± 1) mm placed at the inside top edge of the burner. As an alternative, the top of the burner can be
reinforced with three steel clamps.
The burner filling consists of a minimum of 45 mm thick sand bed (particle size 1 mm to 2 mm) on a metal
mesh above a void with a height of 5 mm to 10 mm. The sand shall be clean, without debris from previous test
specimens. The top of the sand filling is flattened at less than 5 mm below the top of the burner.
NOTE 6 The objective of this requirement is an even propane flow over the entire opening area of the burner.
The burner shall be placed on the floor, lengthwise below the test specimen and with the ends of the burner
lined up with the edges of the test specimen. The long back side of the (100 mm wide) burner is only placed
on the specimen holder in case of a specimen thickness of not more than 100 mm. When the specimen is
thicker, the front of the burner shall be in the same vertical plane as the most protruding part of the specimen
bottom edge, and parallel to the specimen holder (see Figure 3).
NOTE 7 This position differs from previous versions of this document.
Key
A L-frame
B U-frame
C sample
D burner
X sample thickness
Figure 3 — Examples of burner positions depending on sample thickness, cut-view
The burner shall be supplied with natural grade propane (95 % minimum purity). The gas flow to the burner
shall be regulated using a mass flow controller with an accuracy of at least ±3 %. The heat output from the
burner shall be (100 ± 5) kW throughout the test. The burner heat release rate shall be calculated by
-1 -1
multiplying the gas flow by the heat of combustion of propane. A value of 46,4 kJ·g shall be used (2,16 g·s ).
Optionally, in case falling debris reduce the opening of the burner, the top of the burner may be provided with
a grid having an open to total area ratio of at least 90 % and a (45 ± 10)° angle sloping down to the front of the
burner as shown in Figure 4. The grid can be used to protect the burner against large fallen specimen parts.
The low side of the grid is directed to the open side of the U-frame screen wall.

Figure 4 — Burner protection grid
6 Test specimen
Both in construction and materials, the test specimen shall be representative of the system used in end-use
conditions. The application of the material to the test rig shall be as in end-use conditions. All constructional
details of joints, fixings, etc., shall be detailed and positioned in the test specimen as in end-use conditions.
The test specimen should be built by persons suitably qualified in the construction of this type of structure in
end-use conditions.
The specimen height is (2 400 ± 5) mm. After mounting on the specimen holder, the exposed surface width of
the large wing is (1 200 ± 5) mm, the exposed surface width of the small wing is (600 ± 5) mm, taken from the
inner corner line between the wings. The joints and fixings, where used in end-use conditions, shall be
installed as in end-use condition. The sample is fixed to the L-frame so that the large wing 1 200 mm width is
aligned with the 1 200 mm width of the opening of the U-frame. Therefore, the maximum width tested is
limited to 550 mm.
For façade systems with joints:
— The test specimen shall incorporate as stated in Figure 5 a):
— a central horizontal joint at mid-height [centre line at (1 200 ± 10) mm height] in both wings,
— a central vertical joint [centre line at (600 ± 10) mm from the corner line of the specimen wings] in the
large wing only, and
— a joint at the corner line between both wings.
— Alternatively, the horizontal joint in both wings may be positioned lower than at (1 200 ± 10) mm height.
The other parts of the specimen then consist of boards with a height of not more than (1 200 ± 10) mm
and equal joint configuration. As a consequence, two or more horizontal joints are present, as stated in
Figure 5 b).
a) Basis configuration for test specimens b) Alternative configuration for test specimens
incorporating joints, when panel heights exceed incorporating joints, when panel heights are less or
1 200 mm equal to 1 200 mm
Key
A vertical joint
B horizontal joint
C corner joint
D sealed vertical edges
Figure 5 — Details of sample mounting with joints
NOTE 1 Specimens of facades without joints, for example, continuous facades top layers applied in situ, are not
required to have joints. Rarely present joints having a specific deviating joint detail, for exmaple, like dilatations, are
basically not incorporated in a specimen.
NOTE 2 The positions of the vertical joints are also indicated using distances to the corner line to clarify the positions
of the joints as central positions after mounting of both large and small wing on the specimen holder (positions on the
‘open’ surfaces, without taking into account the parts of both wings that cover each other in the corner).
NOTE 3 A non-standard position of the joints in a specimen has no consequences for the position of the
thermocouples.
The vertical edges of both specimen wings are closed during the test, using a seal not more than 10 mm wider
than the initial thickness of the specimen. The top edge of the specimen wings is not sealed; therefore, a
possible cavity is open at the top. The top edge of
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