IEC TS 61508-3-2:2024

IEC TS 61508-3-2 ®
Edition 1.0 2024-08
TECHNICAL
SPECIFICATION
Functional safety of electrical/electronic/programmable electronic safety-related
systems –
Part 3-2: Requirements and guidance in the use of mathematical and logical
techniques for establishing exact properties of software and its documentation

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IEC TS 61508-3-2 ®
Edition 1.0 2024-08
TECHNICAL
SPECIFICATION
Functional safety of electrical/electronic/programmable electronic safety-related

systems –
Part 3-2: Requirements and guidance in the use of mathematical and logical

techniques for establishing exact properties of software and its documentation

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 25.040.40  ISBN 978-2-8322-9565-6

– 2 – IEC TS 61508-3-2:2024 © IEC 2024
CONTENTS
FOREWORD . 3
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms, definitions and abbreviations . 6
3.1 Terms and definitions . 6
3.2 Abbreviations . 15
4 Conformance to this document . 15
5 Formal safety requirements specification . 16
6 Formal software architecture / Design specification . 16
7 Higher-level programming languages: Selection of ESCL . 17
8 Compilation to object code . 17
9 Run-time errors and exceptions . 17
10 Applicable techniques . 18
Annex A (normative) Applicable Mathematical and Logical Techniques . 19
Annex B (informative) Specific Mathematical and Logical Techniques . 21
Annex C (informative) Properties assured by application of specific M< techniques . 24
Annex D (informative) Software refinement from safety specification to Code . 26
D.1 Transformation . 26
D.2 Refinement . 26
Bibliography . 27

Table A.1 – M< Techniques . 19
Table B.1 – Specific M< Techniques/Tools . 21
Table C.1 – Properties Assured by M< Techniques . 24

INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
FUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/PROGRAMMABLE
ELECTRONIC SAFETY-RELATED SYSTEMS –

Part 3-2: Requirements and guidance in the use of mathematical
and logical techniques for establishing exact properties
of software and its documentation

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and
in addition to other activities, IEC publishes International Standards, Technical Specifications, Technical Reports,
Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC Publication(s)”). Their
preparation is entrusted to technical committees; any IEC National Committee interested in the subject dealt with
may participate in this preparatory work. International, governmental and non-governmental organizations liaising
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Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) IEC draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). IEC 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, IEC had not received notice of (a) patent(s), which
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the latest information, which may be obtained from the patent database available at https://patents.iec.ch. IEC
shall not be held responsible for identifying any or all such patent rights.
IEC TS 61508-3-2 has been prepared by subcommittee 65A: System aspects, of IEC technical
committee 65: Industrial-process measurement, control and automation. It is a Technical
Specification.
– 4 – IEC TS 61508-3-2:2024 © IEC 2024
The text of this Technical Specification is based on the following documents:
Draft Report on voting
65A/1113/DTS 65A/1143/RVDTS
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this Technical Specification is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/publications.
A list of all parts in the IEC 61508 series, published under the general title Functional safety of
electrical/electronic/programmable electronic safety-related systems, can be found on the IEC
website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn, or
• revised.
INTRODUCTION
IEC 61508-1:2010 through IEC 61508-7:2010 forms the series of basic standards for the
functional safety of electric, electronic and programmable electronic systems (E/E/PE systems).
It covers the life cycle of these systems. The major part of the functionality of such systems is
often implemented in software. IEC 61508-3:2010 sets software requirements.
IEC 61508-3:2010 Annex A (normative) and Annexes B and C (informative) contain tables
listing various techniques and measures, and provide some guidance to the selection of such
techniques for different safety integrity levels (SIL). It lists general categories and gives different
levels of recommendation for these, such as "not recommended", "recommended" or "highly
recommended", as well as more specific techniques for various phases of software
development.
These techniques and measures are a mix of generic and specific. The phrase "Formal
Methods" as used in IEC 61508-3 refers to the use of mathematical and logical techniques for
specifying, assessing, designing and verifying software. Today, such methods are available for
specifying requirements, for the assessment of the design, for checking source code and object
code and for the derivation of test suites, and for monitoring the correct operation of software
at runtime. In this document, we refer to these methods by using the description as
mathematical and logical techniques (M< sometimes doubled as M< techniques). Some
of the M< techniques in this document are not restricted to software development, being
equally applicable to other digital-system-based engineering technologies. None of the M<
techniques are limited to the domain of safety-related software systems, although in this
document only safety-related applications of M< techniques are explicitly addressed.
Use of the recommended methods of IEC 61508-3:2010, Annexes A, B and C do not rule out,
for example, susceptibility of the software to run-time failure. State of the art in software
development enables various types of run-time failures to be ruled out through rigorous
development of the software. It is possible using techniques identified here to assure freedom
from many types of software run-time failures.

– 6 – IEC TS 61508-3-2:2024 © IEC 2024
FUNCTIONAL SAFETY OF ELECTRICAL/ELECTRONIC/PROGRAMMABLE
ELECTRONIC SAFETY-RELATED SYSTEMS –

Part 3-2: Requirements and guidance in the use of mathematical
and logical techniques for establishing exact properties
of software and its documentation

1 Scope
This Technical Specification, part of the IEC 61508 series, covers the general assurance of
dependable software used in critical operation
...