Integrity management
Introduction
The Safety Integrity Level, abbreviated SIL, in Spanish "Security Integrity Level" is defined as a relative level of risk reduction provided by a safety function"), or to specify the objective level for risk reduction. SIL could be defined simply as a measure of the performance required for a safety instrumented function") (SIF).
The requirements for a given SIL are not consistent across all functional safety standards. In European safety standards, 4 SILs are defined, level 4 being the most severe and 1 being the lowest. SIL is determined from a number of quantitative factors in combination with qualitative factors such as the development process and security lifecycle management.
SIL assignment
There are several methods for assigning SIL. These are often used in combination and include:.
Assignment can be verified using pragmatic and controllability approaches, applying the SIL assignment guideline published by the UK HSE.[1] Processes for assigning SIL that use the HSE guideline to ratify assignments developed from risk matrices have been certified to comply with IEC EN 61508.
Problems with the use of SIL
There are several problems inherent to the use of Safety Integrity Levels that can be summarized as follows:.
All of this leads to erroneous reasoning such as: "This system has a SIL N because the process followed during its development was that corresponding to a SIL N system", or the use of the SIL concept out of context, such as: "This is a SIL 3 heat exchanger". According to IEC 61508, the concept of SIL has to be related to the catastrophic failure rate of a system, and not simply to its failure rate. The definition of catastrophic failure modes, through some safety analysis, is intrinsic to the appropriate determination of the failure rate.[2].
Certification to a SIL
The International Electrotechnical Commission (IEC) standard IEC 61508", now IEC EN 61508, defines SIL using requirements grouped into two broad categories: hardware safety integrity and systematic safety integrity. A device or system must meet the requirements of both categories to achieve a given SIL.