The IEC 61508 standard is a generic standard, created in European version by CENELEC in 2002 as EN 61508, and todayis used as reference by all major industrial sectors.
Since its creation, several derivatives of this standard (called child standards) were created. Each time, these child standards have been established with the objective of making applicable the EN 61508 for different sectors.
These child standards are the following :
- The CEI 61511 standard, introduced in 2003, is the standard adapted from the IEC 61508 standard for industrial processes.
- The CEI 61513 standard, introduced in 2001, is the standard adapted from the IEC 61508 standard for the nuclear sector.
- The CEI 62061 standard, introduced in 2005, is the standard adapted from the IEC 61508 standard for the safety of machines.
- The EN 50126/EN 50128/EN 50129 standards, established respectively for the latest versions, in 1999/2001/2003, are standards adapted from the 61508 standard for the railway sector.
- The ISO 26262 standard is being developed and its release is foreseen for 2009,and it is the adaptation of the IEC 61508 standard for the automotive sector.
In this article, we will only talk about the standards represented by an orange square in the picture above.
The main lines of IEC 61508:
The IEC 61508 standard deals with the functional safety of electrical/electronic systems and programmable electronic (E/E/EP). This standard approach is very generic to enable the integration of all security systems E/E/PE.
This standard is decomposed in 7 parts :
- Part 1 : General Requirements,
- Part 2 : Requirements for systems E/E/PES safety related ,
- Part 3 : Software requirements,
- Part 4 : Definitions et abreviations,
- Part 5 : Example of Methods to determinate the SIL (Safet Inegrity Level) ,
- Part 6 : Guidelines for the application of the parts 2 and 3,
- Part 7 : Presentation of techniques and measures.
This standard has revolutionized the world of the operational safety because despite its aspect generic, it brings novelties in the way to integrate and achieve the activities of operational safety in the developement cycle of a system E/E/PE.
The standard has helped to define the levels of integrity for systems E/E/PE which take into account, in the risk management, as well the quantitative and qualitative aspects.
In addition, the standard integrates the safety activities, in parallel to the life cycle of the system E/E/EP, and these are adapted according to Safety Integrity Level (known as the name of “SIL:”) desired.
By its generic aspect, the IEC 61508 standard breafly describes tools, methods and techniques of implementation.
EN 50126/EN 50128/EN 50129 Standards:
In the purpose of be able to implement the approaches described in the IEC 61508 standard, in the railway field , three standards have been established:
EN 50126 – « Specification and demonstration of the reliability, availability, maintainability and safety»:
This standard allows to implement a consistent approach to management of the reliability, availability, maintainability and safety called RAMS. This standard can be applied in the rail industry throughout the life cycle because it integrates the requirements RAMS specific to this field.
EN 50128 – « Signalling Systems, telecommunications and treatment »:
This standard deals, in particular, with methods that are necessary to be used to provide software that can satisfy the requirements of safety integrity level for the railway field. The integrity of a software is distributed on five levels SIL, ranging from SIL 0 to SIL 4. These levels SIL are defined by association, in the risk management, to the frequency and the result of a hazardous event.
To be able to define the SIL level for this software, the technical and messurement needs are defined in this standard.
EN 50129 – « Railway applications – Safety electronics systems for signaling»:
This standard addresses all the issues related to the approval process ofindividual systems, that can be software or hardware, and which may exist in the framework of a global system. This standard defines the evidence to provide for the acceptance of each individual system in the light of its SIL integrity level.
ISO 26262 Standard
The ISO 26262 standard, also called ISO/CD 26262, is currently being written, and it should be released during 2009. This new standard redefines the five SIL levels (Safety Integrity Level) of the IEC 61508 standard in four levels, called ASIL (Automotive Safety Integrity Level) ranging from ASIL A to ASIL D. The level of ASIL is determined by a risk analysis taking into account the evaluation of the severity, controllability and the exhibition on events.
This standard focuses largely on the software. It deals with the safety , the design of the product, the system analysis, the development software and hardware and production managment.
The french version of this standard should be released during 2011.