ISO 7240-32:2025

Fire detection and alarm systems - Part 32: Non-resettable line-type heat detectors

This document applies to non-resettable line-type heat detectors consisting of a sensing element distributed either continuously or discretely at close intervals along its length, which can be connected either directly or through a sensor control unit or an interface module to control and indicating equipment, and intended for use in fire detection and fire alarm systems installed in and around buildings and other civil engineering works. This document specifies requirements and performance criteria, and the corresponding test methods and provisions for assessment. This document also covers non-resettable line-type heat detectors intended for use in the local protection of plant (facility) and equipment. Non-resettable line-type heat detectors with special characteristics and developed for specific risks are not covered by this document.

Systèmes de détection et d'alarme incendie — Partie 32: Détecteurs de chaleur de type linéaire non-réenclenchables

General Information

• Status: Published
• Publication Date: 29-Sep-2025
• ICS: 13.220.20 - Fire protection
• Technical Committee: ISO/TC 21/SC 3 - Fire detection and alarm systems
• Drafting Committee: ISO/TC 21/SC 3 - Fire detection and alarm systems
• Current Stage: 6060 - International Standard published
• Start Date: 30-Sep-2025
• Due Date: 24-Aug-2025
• Completion Date: 30-Sep-2025

Overview

ISO 7240-32:2025 specifies requirements, performance criteria and test methods for non-resettable line-type heat detectors (NLTHD) used in fire detection and alarm systems. Published in 2025, this International Standard covers NLTHDs whose sensing element is distributed continuously or discretely along its length and which can be connected directly or via a sensor control unit or interface module to control and indicating equipment. The scope includes detectors for building and civil engineering fire protection and for local protection of plant and equipment, but excludes devices developed for very specific risks.

Key Topics and Technical Requirements

This standard sets out both design and verification topics, including:

• Conformance and performance type - definition of NLTHD performance classes and conformance requirements.
• Heat response characteristics - response behaviour for Class A applications and procedures for measuring response temperature.
• Environmental groups and endurance - operational and endurance tests such as dry heat, cold, damp heat (steady-state and cyclic), vibration, shock and impact, and sulphur dioxide corrosion.
• Individual alarm indication and signalling - requirements for alarm signalling, connection to control equipment and ancillary devices.
• Electrical and software integrity - requirements for supply variation, low-voltage faults, software design, storage of programs/data and sensing-element fault detection.
• On-site adjustment and commissioning - provisions for on-site adjustment of response behaviour and manufacturer’s adjustments.
• Performance under fire conditions - fire sensitivity assessments and optional Class A fire tests, plus a test schedule and tolerances.
• Test methods and procedures - specified atmospheric and mounting conditions, measurement procedures, and detailed test schedules for assessment and certification.

Applications and Who Uses This Standard

ISO 7240-32 is intended for professionals involved in the lifecycle of fire detection systems, including:

• Fire detector manufacturers and R&D teams - to design and validate NLTHD products.
• Testing and certification laboratories - to perform compliance testing and type approval.
• System designers and integrators - to specify detectors compatible with sensor control units and alarm systems.
• Building owners, facility managers and safety engineers - to select appropriate NLTHDs for building protection and local equipment safeguards.
• Regulators and certification bodies - to reference in procurement, compliance and inspection processes.

Using this standard helps ensure reliable detection performance, interoperability with control and indicating equipment, and repeatable test evidence for safety-critical installations.

Related Standards

• Other parts of the ISO 7240 series covering fire detection and alarm systems (general requirements, detector types and system integration).
• Relevant electromagnetic compatibility (EMC) and software safety guidelines referenced by ISO 7240-32 for immunity and software design.

Standards Content (Sample)

International
Standard
ISO 7240-32
First edition
Fire detection and alarm systems —
2025-09
Part 32:
Non-resettable line-type heat
detectors
Systèmes de détection et d'alarme incendie —
Partie 32: Détecteurs de chaleur de type linéaire non-
réenclenchables
Reference number
© ISO 2025
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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CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .vii
Introduction .viii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions and abbreviations . 1
3.1 Terms and definitions .2
3.2 Abbreviations .2
4 Requirements . 3
4.1 General .3
4.1.1 Conformance .3
4.1.2 NLTHD performance type .3
4.1.3 Heat response for Class A application .3
4.1.4 Environmental groups .3
4.2 Individual alarm indication .4
4.3 Signalling .4
4.4 Maximum ambient temperature.4
4.5 Connection of ancillary devices.4
4.6 Manufacturer's adjustments .4
4.7 Software .4
4.7.1 General .4
4.7.2 Software design .5
4.7.3 The storage of programs and data .5
4.8 Sensing element fault .5
4.9 On-site adjustment of response behaviour .5
4.10 Variation in supply parameters .5
4.11 Low voltage fault.5
4.12 Performance parameters under fire condition .6
4.13 Fire sensitivity for Class A application .6
4.14 Static response temperature test for Class A application .6
4.15 Dry heat (operational) for sensor control unit .6
4.16 Cold (operational) for sensing element .6
4.17 Cold (operational) for sensor control unit .6
4.18 Damp heat, steady-state (endurance) for sensor control unit and sensing element .6
4.19 Damp heat, cyclic (operational) for sensing element .6
4.20 Damp heat, cyclic (operational) for sensor control unit .6
4.21 Damp heat, steady-state (operational) for sensor control unit .6
4.22 Damp heat, cyclic (endurance) for sensor control unit and sensing element .6
4.23 Shock (operational) for sensor control unit .6
4.24 Impact (operational) for sensor control unit .7
4.25 Impact (operational) for sensing element .7
4.26 Vibration, sinusoidal (operational) for sensor control unit .7
4.27 Vibration, sinusoidal (operational) for sensing element .7
4.28 Vibration, sinusoidal (endurance) for sensor control unit .7
4.29 Vibration, sinusoidal (endurance) for sensing element .7
4.30 Sulphur dioxide (SO ) corrosion (endurance) for sensing element .7
4.31 Sulphur dioxide (SO ) corrosion (endurance) for sensor control unit .7
4.32 Electromagnetic compatibility (EMC), immunity (operational) .7
5 Test methods . 7
5.1 General .7
5.1.1 Atmospheric conditions for tests.7
5.1.2 Operating conditions for tests.8
5.1.3 Mounting arrangements .8
5.1.4 Tolerances .8

iii
5.1.5 Procedure for measurement of response temperature .8
5.1.6 Provision for tests .9
5.1.7 Test schedule .9
5.2 Individual alarm indication .11
5.3 Signalling .11
5.4 Maximum ambient temperature test (endurance) for sensing element .11
5.4.1 Objective of the test .11
5.4.2 Mounting of the sensing element .11
5.4.3 Test procedure. 12
5.4.4 Requirements . 12
5.5 Connection of ancillary devices. 12
5.6 Manufacturer's adjustments . 12
5.7 Requirements for software controlled detectors . 13
5.8 Sensing element fault . 13
5.8.1 Object of the test . 13
5.8.2 Test procedure. 13
5.8.3 Requirements . 13
5.9 On-site adjustment of response behaviour . 13
5.10 Variation in supply parameters . 13
5.10.1 Objective . 13
5.10.2 Test procedure. 13
5.10.3 Requirements . 13
5.11 Low voltage fault (sensor control unit with external power supply) .14
5.11.1 Objective .14
5.11.2 Test procedure.14
5.11.3 Requirements .14
5.12 Performance parameters under fire condition .14
5.12.1 Objective .14
5.12.2 Test procedure.14
5.12.3 Requirements .14
5.13 Fire sensitivity for Class A application (optional function) .14
5.13.1 Objective .14
5.13.2 Principle .14
5.13.3 Fire test room .14
5.13.4 Test fires for Class A application . 15
5.13.5 Mounting of the specimens . 15
5.13.6 Initial conditions . 15
5.13.7 Recording of the fire parameters and response times .16
5.13.8 Requirements .16
5.14 Static response temperature test for Class A application (optional function) .16
5.14.1 Object .16
5.14.2 Test procedure for NLTHD .16
5.14.3 Requirements .17
5.15 Dry heat (operational) for sensor control unit .17
5.15.1 Objective .17
5.15.2 Test procedure.17
5.15.3 Requirements .18
5.16 Cold (operational) for sensing element .18
5.16.1 Objective .18
5.16.2 Test procedure.18
5.16.3 Requirements .19
5.17 Cold (operational) for sensor control unit .19
5.17.1 Objective .19
5.17.2 Test procedure.19
5.17.3 Requirements . 20
5.18 Damp heat, steady-state (endurance) for sensor control unit and sensing element . 20
5.18.1 Objective . 20
5.18.2 Test procedure. 20
5.18.3 Requirements .21

iv
5.19 Damp heat, cyclic (operational) for sensing element .21
5.19.1 Objective of the test .21
5.19.2 Test procedure.21
5.19.3 Requirements . 22
5.20 Damp heat, cyclic (operational) for sensor control unit . 22
5.20.1 Objective of the test . 22
5.20.2 Test procedure. 22
5.20.3 Requirements . 23
5.21 Damp heat, steady-state (operational) for sensor control unit .24
5.21.1 Objective of the test .24
5.21.2 Test procedure.24
5.21.3 Requirements .24
5.22 Damp heat, cyclic (endurance) for sensor control unit and sensing element . 25
5.22.1 Objective . 25
5.22.2 Test procedure. 25
5.22.3 Requirements . 25
5.23 Shock (operational) for sensor control unit . 26
5.23.1 Objective . 26
5.23.2 Test procedure. 26
5.23.3 Requirements . 26
5.24 Impact (operational) for sensor control unit .27
5.24.1 Objective .27
5.24.2 Test procedure.27
5.24.3 Requirements .27
5.25 Impact (operational) for sensing element . 28
5.25.1 Objective . 28
5.25.2 Test procedure. 28
5.25.3 Requirements . 28
5.26 Vibration, sinusoidal (operational) for sensor control unit . 29
5.26.1 Objective . 29
5.26.2 Test procedure. 29
5.26.3 Requirements . 29
5.27 Vibration, sinusoidal (operational) for sensing element . 30
5.27.1 Objective . 30
5.27.2 Test procedure. 30
5.27.3 Requirements . 30
5.28 Vibration, sinusoidal (endurance) for sensor control unit .31
5.28.1 Objective .31
5.28.2 Test procedure.31
5.28.3 Requirements .31
5.29 Vibration, sinusoidal (endurance) for sensing element .31
5.29.1 Objective .31
5.29.2 Test procedure.31
5.29.3 Requirements .32
5.30 Sulfur dioxide (SO ) corrosion (endurance) for sensing element .32
5.30.1 Objective .32
5.30.2 Test procedure.32
5.30.3 Requirements . 33
5.31 Sulfur dioxide (SO ) corrosion (endurance) for sensor control unit . 33
5.31.1 Objective . 33
5.31.2 Test procedure. 33
5.31.3 Requirements . 34
5.32 Electromagnetic compatibility (EMC), immunity (operational) . 34
5.32.1 General . 34
5.32.2 State of the specimen during conditioning . 34
5.32.3 Final measurements . 34
5.32.4 Requirements . 35
6 Test report .35

v
7 Marking . .35
7.1 General . 35
7.2 Marking of sensor control unit . 35
7.3 Marking of sensing element . 36
7.4 Marking of functional units . 36
8 Data .36
8.1 Hardware documentation . 36
8.2 Software documentation .37
Annex A (normative) Arrangement of the sensing element in the fire test room .38
Annex B (normative) Flaming liquid test fires (TF6F, TF6 and TF6S) .40
Annex C (normative) Mounting of the sensing element of NLTHD in the heat tunnel .42
Annex D (normative) Heat tunnel for response temperature measurements .44
Annex E (informative) Construction of the heat tunnel .45
Annex F (normative) Test arrangement for vibration tests for sensing element . 47
Annex G (normative) Test apparatus for impact test on the sensing element .48

vi
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
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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).
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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
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Any trade name used in this document is information given for the convenience of users and does not
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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 3, Fire detection and alarm systems.
A list of all parts in the ISO 7240 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.

vii
Introduction
Non-resettable line-type heat detectors (NLTHD – also known in the market as "linear heat detectors" or
"digital detectors" have been used for many years. They are incorporated into fire detection systems and
in some countries even into fire alarm systems if accepted by the relevant authorities. These detectors are
typically used in areas where point type heat detectors are presented with challenging environmental
characteristics, and also where access to the detectors can significantly influence the fire alarm system design.
This document defines the minimum system functionality for NLTHD products.
Due to the various applications for NLTHD, it is necessary to devise separate environmental classification
tests for the sensing element and the sensor control units of these systems. This document is not intended to
specify applications or how NLTHD is used in applications.
Generally, NLTHD operate using the same basic principle. However, they can have different performance
with respect to their temperature response. Therefore, they have been differentiated by a type code which
reflects the nominal alarm temperature, the tolerance range and the maximum ambient temperature at
which they can be used. There are also options for room protection classes.

viii
International Standard ISO 7240-32:2025(en)
Fire detection and alarm systems —
Part 32:
Non-resettable line-type heat detectors
1 Scope
This document applies to non-resettable line-type heat detectors consisting of a sensing element distributed
either continuously or discretely at close intervals along its length, which can be connected either directly or
through a sensor control unit or an interface module to control and indicating equipment, and intended for use
in fire detection and fire alarm systems installed in and around buildings and other civil engineering works.
This document specifies requirements and performance criteria, and the corresponding test methods and
provisions for assessment.
This document also covers non-resettable line-type heat detectors intended for use in the local protection of
plant (facility) and equipment.
Non-resettable line-type heat detectors with special characteristics and developed for specific risks are not
covered by this document.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 7240-1, Fire detection and alarm systems — Part 1: General and definitions
IEC 60068-2-1, Environmental testing — Part 2-1: Tests — Test A: Cold
IEC 60068-2-2, Environmental testing — Part 2-2: Tests — Test B: Dry heat
IEC 60068-2-6, Environmental testing — Part 2-6: Tests — Test Fc: Vibration (sinusoidal)
IEC 60068-2-27, Environmental testing — Part 2-27: Tests — Test Ea and guidance: Shock
IEC 60068-2-42, Environmental testing — Part 2-42: Tests — Test Kc: Sulphur dioxide test for contacts and
connections
IEC 60068-2-75, Environmental testing — Part 2-75: Tests — Test Eh: Hammer tests
IEC 60068-2-78, Environmental testing — Part 2-78: Tests — Test Cab: Damp heat, steady state
IEC 62599-2, Alarm systems — Part 2: Electromagnetic compatibility — Immunity requirements for components
of fire and security alarm systems
3 Terms and definitions and abbreviations
For the purposes of this document, the terms and definitions given in ISO 7240-1 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 Terms and definitions
3.1.1
functional unit
part of a line-type heat detector in addition to the sensor control unit and the sensing element which is
essential for the function of the line-type heat detector
EXAMPLE Terminating device, filter, switch.
3.1.2
local protection application
application in which the sensing element is installed in relatively close proximity to the potential fire risk
EXAMPLE Pipelines, conveyor belts, combustion engines/turbines, rolling stock, transformers, process dryers,
cable trays, escalators, chemical process equipment, electrical equipment cabinets, ventilation systems (dust collector,
hood extractor, etc.), switch gear (e.g. printing press).
3.1.3
non-resettable line-type heat detectors
NLTHD
detector which responds to heat sensed in the vicinity of a continuous line or a series of discrete elements at
close interval along its length, and which can only respond once.
Note 1 to entry: A non-resettable line-type heat detector can consist of a sensor control unit, a sensing element and
functional units.
3.1.4
room protection application
application in which the sensing element is installed at a distance from the potential fire hazard close to the
ceiling or roof of the area to be protected
EXAMPLE car parks (open or closed), road/rail/metro tunnels, floor/ceiling voids, elevator shafts, cold stores,
warehouses, heritage buildings, aircraft hangars, spray shops, chemical storehouses, ammunition depots, refineries,
silos, etc.
3.1.5
sensing element
heat sensing part of the line-type heat detector which can be a fibre optic cable, a pneumatic tube or an
electrical cable
Note 1 to entry: A sensing element can consist of different segments separated, e.g. by functional units or splices.
Note 2 to entry: The sensing element can be connected directly to control and indicating equipment, an input/output
device or via a dedicated sensor control unit (see 3.1.6).
3.1.6
sensor control unit
unit
...