IEC TR 61508-3-3:2025
(Main)Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 3-3: Object-oriented software in safety-related systems
Functional safety of electrical/electronic/programmable electronic safety-related systems - Part 3-3: Object-oriented software in safety-related systems
IEC TR 61508-3-3:2025 makes a proposal as to which topics to consider and which methods and techniques to use when designing object-oriented software to ensure suitable quality for use in functional safety applications.
Object-oriented languages are perceived as "state-of-the-art" nowadays. Such languages seem to be excluded from use by several statements in IEC 61508-3. However there are additions in some tables such as in IEC 61508-3:2010, Table B.1, where notes are added under which their use might be justified. Such exceptions that would allow, for example, dynamic objects, name the main concerns such as memory allocation and predictable timing issues and guide the user to safe use of object-oriented languages. These considerations are taken up in this document to specify methods and techniques that allow the reduction of systematic faults to the levels required by the respective systematic capabilities.
This document is not intended to replace any part of IEC 61508-3. Rules that exist in IEC 61508‑3 are valid here as well and are not repeated, including rules that concern:
• the software life cycle,
• involvement of the assessor,
• modularization,
• principle of information hiding,
• proving and conventional testing,
• basic aspects of documentation,
• low coupling and high cohesion,
• responsibilities and training of people,
• operational experience as described in IEC 61508-4 and IEC 61508-7
This TR is a supplement to the IEC 61508 standard series. It has to be read in conjunction with IEC 61508-3 and proposes a way how the use of object-oriented software in safety relevant applications can be justified.
General Information
Standards Content (Sample)
IEC TR 61508-3-3 ®
Edition 1.0 2025-07
TECHNICAL
REPORT
Functional safety of electrical/electronic/programmable electronic safety-related
systems –
Part 3-3: Object-oriented software in safety-related systems
ICS 13.110; 25.040.40 ISBN 978-2-8327-0556-8
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CONTENTS
FOREWORD . 2
INTRODUCTION . 4
1 Scope . 5
2 Normative references . 5
3 Terms, definitions and abbreviated terms . 5
4 Structure of this document . 9
5 Initial consideration at the project start . 10
6 Contract-oriented programming . 12
7 Encapsulation . 15
8 Inheritance . 21
9 Polymorphism . 27
10 Dynamic objects . 31
11 Cross issue considerations during the project . 39
12 Maintenance . 43
13 Exception handling . 46
Bibliography . 52
Figure 1 – Class hierarchy – inheritance tree . 27
Table 1 – Tailoring in proposal tables . 10
Table 2 – Initial consideration at the project start . 12
Table 3 – Contract-oriented programming . 14
Table 4 – Encapsulation . 18
Table 5 – Inheritance . 23
Table 6 – Polymorphism . 29
Table 7 – Dynamic objects . 33
Table 8 – Cross issue considerations during the project. 40
Table 9 – Maintenance . 44
Table 10 – Exception handling . 49
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
Functional safety of electrical/electronic/programmable
electronic safety-related systems -
Part 3-3: Object-oriented software in safety-related systems
FOREWORD
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shall not be held responsible for identifying any or all such patent rights.
IEC TR 61508 has been prepared by subcommittee 65A: System aspects, of IEC technical
committee 65: Industrial-process measurement, control and automation. It is a Technical Report.
This TR is a supplement to the IEC 61508 standard series. It has to be read in conjunction with
IEC 61508-3 and proposes a way how the use of object-oriented software in safety relevant
applications can be justified.
The text of this Technical Report is based on the following documents:
Draft Report on voting
65A/1176/DTR 65A/1181/RVDTR
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 Report 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
This document addresses specific concepts associated with object-oriented (OO) software. It
deals only with OO software in general without referencing any specific language. Each of the
concepts is discussed under separate clauses, one addressing fundamentals – i.e. benefits,
disadvantages and counter-measures to the disadvantages, the others detailing guidance on
the attributes to be satisfied in safety-related systems, according to the systematic capability to
be achieved.
It is useful to consider addressing the language-specific best practice contained in guidelines,
coding rules, handbooks etc. for each OO language. If an object-oriented module is modified,
it is proposed that the entire module conform to the guidance within this document. Further, it
is useful to consider assessing the interfaces, interactions and side effects on unchanged
modules to determine that there is no impact on other unchanged modules and their integration.
See also IEC 61508-3:2010, Annex D.
This document is intended as a supplement to the existing requirements in the IEC 61508 series
which continue to apply.
1 Scope
This part of IEC 61508, which is a Technical Report, makes a proposal as to which topics to
consider and which methods and techniques to use when designing object-oriented software to
ensure suitable quality for use in functional safety applications.
Object-oriented languages are perceived as "state-of-the-art" nowadays. Such languages seem
to be excluded from use by several statements in IEC 61508-3. However there are additions in
some tables such as in IEC 61508-3:2010, Table B.1, where notes are added under which their
use might be justified. Such exceptions that would allow, for example, dynamic objects, name
the main concerns such as memory allocation and predictable timing issues and guide the user
to safe use of object-oriented languages. These considerations are taken up in this document
to specify methods and techniques that allow the reduction of systematic faults to the levels
required by the respective systematic capabilities.
This document is not intended to replace any part of IEC 61508-3. Rules that exist in
IEC 61508-3 are valid here as well and are not repeated, including rules that concern:
• the software life cycle,
• involvement of the assessor,
• modularization,
• principle of information hiding,
• proving and conventional testing,
• basic aspects of documentation,
• low coupling and high cohesion,
• responsibilities and training of people,
• operational experience as described in IEC 61508-4 and IEC 61508-7.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes
...
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