Honeywell HC900 - The IEC 61508 and IEC 61511 Standards; Table 1 - IEC 61508 Versus IEC 61511 Terminology

The Safety Manual - The IEC 61508 and IEC 61511 Standards
2 HC900 Process & Safety Controller Safety Manual Revision 1.9
01/14
Safety Integrity Level (SIL)
The IEC 61508 standard specifies 4 levels of safety performance for safety functions. These are called
safety integrity levels. Safety integrity level 1 (SIL1) is the lowest level of safety integrity, and safety
integrity level 4 (SIL4) the highest level. If the level is below SIL1, the IEC 61508 and IEC 61511 do not
apply. HC900 can be used for processing multiple SIFs simultaneously demanding a SIL1 and SIL2.
The IEC 61508 and IEC 61511 Standards
SISs have been used for many years to perform safety instrumented functions e.g. in chemical,
petrochemical and gas plants. In order for instrumentation to be effectively used for safety instrumented
functions, it is essential that the instrumentation meets certain minimum standards and performance levels.
To define the characteristics, main concepts and required performance levels, standards IEC 61508 and IEC
61511 have been developed. The introduction of Safety Integrity level (SIL) is one of the results of these
standards.
This brief provides a short explanation of each standard. Detailed information regarding IEC 61508 and
61511 can be found on the IEC web site, http://www.iec.org.
What standard to use?
• If you are in the process sector and you are an owner/user, it is strongly recommended that you pay
attention to the IEC 61511 (ANSI/ISA 84.00.01).
• If you are in the process sector and you are a manufacturer, it is strongly recommended that you pay
attention to the IEC 61508.
• If you are in another sector, it is strongly recommended that you look for, and use, your sector specific
IEC standard for functional safety (if there is one). If none exists, you can use the IEC 61508 instead.
IEC 61508 and IEC 61511 terminology
This guide contains both IEC 61508 and IEC 61511 related terminology. As the IEC 61511 sits within the
framework of IEC 61508 most of the terminology used may be interchanged. Table 1 below provides an
overview of the most common interchangeable terminology.
Table 1 – IEC 61508 versus IEC 61511 terminology
IEC 61508 terminology IEC 61511 terminology
safety function safety instrumented function
electrical/electronic/programmable electronic
(E/E/PE) safety-related system
safety instrumented system (SIS)
IEC 61508, the standard for all E/E/PE safety-related systems
The IEC 61508 is called “Functional safety of electrical/electronic/programmable electronic safety-related
systems” IEC 61508 covers all safety-related systems that are electrotechnical in nature (i.e. Electrical,
Electronic and Programmable Electronic systems (E/E/PE) ).