Functional Safety of Electrical/Electronic/Programmable Electronic Safety-Related Systems - Part 3: Software Requirements
|Publication Date:||1 April 1999|
|ICS Code (Industrial process measurement and control):||25.040.40|
This part of IEC 61 508
is intended to be utilised only after a thorough understanding of IEC 61508-1 and IEC 61 508-2;
applies to any software forming part of a safety-related system or used to develop a safety-related system within the scope of IEC 61508-1 and IEC 61508-2. Such software is termed safety-related software.
- Safety-related software includes operating systems,system software, software in communication networks, human-computer interface functions, support tools and firmware as well as application programs.
- Application programs include high level programs,low level programs and special purpose programs in limited variability languages (see 3.2.7 of IEC 61508-4).
requires that the software safety functions and software safety integrity levels are specified.
NOTE 1 - If this has already been done as part of the specification of the E/E/PE safety-related systems (see 7.2 of IEC 61508-2), then it does not have to be repeated in this part.
NOTE 2 - Specifying the software safety functions and software safety integrity levels is an iterative procedure; see figures 2 and 6.
NOTE 3 - See clause 5 and annex A of IEC 61508-1 for documentation structure. The documentation structure may take account of company procedures, and of the working practices of specific application sectors.
establishes requirements for safety lifecycle phases and activities which shall be applied during the design and development of the safety-related software (the software safety lifecycle model). These requirements include the application of measures and techniques, which are graded against the safety integrity level, for the avoidance of and control of faults and failures in the software.
provides requirements for information relating to the software safety validation to be passed to the organisation carrying out the E/E/PES integration.
provides requirements for the preparation of information and procedures concerning software needed by the user for the operation and maintenance of the E/E/PE safety-related system.
provides requirements to be met by the organisation carrying out modifications to safety-related software.
provides, in conjunction with IEC 61508-1 and IEC 61508-2, requirements for support tools such as development and design tools, language translators, testing and debugging tools, configuration management tools.
NOTE 4 - Figures 4 and 6 show the relationship between IEC 61508-2 and IEC 61508-3.
IEC 61508-1, IEC 61508-2, IEC 61508-3 and IEC 61508-4 are basic safety publications, although this status does not apply in the context of low complexity E/E/PE safety-related systems (see 3.4.4 of IEC 61508-4). As basic safety publications, they are intended for use by technical committees in the preparation of standards in accordance with the principles contained in IEC Guide 704 and ISO/IEC Guide 51. One of the responsibilities of a technical committee is, wherever applicable, to make use of basic safety publications in the preparation of its own publications. IEC 61508 is also intended for use as a stand-alone standard.
NOTE - In the USA and Canada, until the proposed process sector implementation of IEC 61508 (i.e. IEC 61511) is published as an international standard in the USA and Canada, existing national process safety standards based on IEC 61508 (i.e. ANSI/ISA S84.01-1996) can be applied to the process sector instead of IEC 61508.
Figure 1 shows the overall framework of parts 1 to 7 IEC 61508, and indicates the role that IEC 61508-3 plays in the achievement of functional safety for E/E/PE safety-related systems. Annex A of IEC 61508-6 describes the application of IEC 61508-2 and IEC 61508-3.