The 2010 Version of IEC 61508
The following is a brief summary of the main changes which brought about the 2010 version.
Architectural Constraints (Chapter 3)
An alternative route to the “safe failure fraction” (the so-called route 1H) requirements was introduced (known as Route 2H).
Route 2H allows the “safe failure fraction” requirements to lapse providing that amount of redundancy (so-called hardware fault tolerance) meets a minimum requirement AND there is adequate user-based information providing failure rate data.
The meaning of “safe” failures in the formula for safe failure fraction was emphasized as referring only to failures which force a “safe” state (e.g., spurious trip).
Security (Chapter 2)
Malevolent and unauthorized actions, as well as human error and equipment failure, can be involved in causing a hazard. They are to be taken account of, if relevant, in risk assessments.
Safety Specifications (Chapter 3)
There is more emphasis on the distinct safety requirements leading to separately defined design requirements.
Digital Communications (Chapter 3)
More detail in providing design and test requirements for “black box” and “white box” communications links.
ASICs and Integrated Circuits (Chapters 3 and 4)
Safety Manual (Chapters 3 and 4)
Producers are required to provide a safety manual (applies to hardware and to software) with all the relevant safety-related information. Headings are described in Annexes to the Standard.
Synthesis of Elements (Chapter 3)
In respect of systematic failures, the ability to claim an increment of one SIL for parallel elements.
Software Properties of Techniques (Chapter 4)
New guidance on justifying the properties which proposed alternative software techniques should achieve in order to be acceptable.
Element (Appendix 8)
The introduction of a new term (similar to a subsystem).
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