ISO 26262

IEC 61511 - ISO 26262 - ANSI/ISA S84.01

Safety Instrumented Systems for the Process Industry

IEC 61511 is a technical standard developed by the International Electrochemical Commission (IEC) that sets out practices in the engineering of systems that ensure the safety of an industrial process through the use of instrumentation. Such systems are referred to as Safety Instrumented Systems (SIS), and essentially they are the ‘emergency-stop valve’ for a system within a process facility.

 

IEC 61508 is a generic functional safety standard that sets the standard for safety-related system design of hardware and software. Sector-specific standards have been released using the IEC 61508 framework, IEC 61511 (process), IEC 61513 (nuclear) and IEC 62061 (machinery). ISO 26262 uses the same framework, but refers to Safety Integrity Levels as applied to the automotive industry. IEC 61511 provides good engineering practices for the application of safety instrumented systems in the process sector.

ANSI/ISA S84.01 (the Application of Safety Instrumented Systems for the Process Industry), is superseded by the IEC 61511 standard.

 

Impact

IEC 61511 covers the design and management requirements for Safety Instrumented Systems (SISs) from cradle to grave, outlining the requirements for ensuring that systems are designed, implemented, operated and maintained to provide the required safety integrity level (SIL). Three SILs are defined according to the risks involved in the system application, with SIL3 being used to protect against the highest risks. There are three major components to compliance with the standard:

 

  1. Conducting a Target Safety Integrity Level (SIL) assessment to determine what level SIL the Safety Instrumented System should be
  2. Designing, building and implementing the SIS
  3. Verifying that the SIS is as designed and can safely meet the target SIL

 

Typically, the process facility will conduct a Process Hazard Analysis study to assess potential risk, then determine the Target SIL in one of a number of ways (Layer of Protection Analysis, Risk Matrix, Risk Graph, Hazard and Operability Analysis with SIL), design the Safety Instrumented System, and then verify that the built system really does correspond with the required SIL level.

 

Challenge

Determining the target SIL can be complex and time-consuming, but it is essential to get it right. Many process facilities mistakenly assume that a Safety Instrumented System that can handle a SIL3 is inherently the safest and thus the most likely to not fail when needed. However, this can be overkill in certain situations. The higher SIL a Safety Instrumented System can handle, the more expensive and complex it is. In addition to viewing all potential risk and determining where more complex SIS are needed, compliance with IEC 61511 requires looking carefully at all systems and analyzing the target SIL level that best fits with that particular process.

 

The Dyadem Solution

In order to effectively comply with IEC 61511 and ensure that Safety Instrumented Systems are designed, built and implemented properly, process facilities need tools that can assist in both the initial risk assessment, the target SIL and the verification of the SIS. Organizations are typically looking for a tool that:

 

  • can help in determining how good the safety system should be (target SIL);
  • can utilize multiple ways to determine that target SIL (Risk Matrix, Risk Graph, LOPA); and
  • can help them determine this in conjunction with a HAZOP

 

The Stature enterprise risk management solution has modules that can assist with all aspects of IEC 61511. Industry-leading templates for LOPA, SIL and HAZOP can help determine what type of SIS is needed. With the addition of an FTA (Fault Tree Analysis) application, Stature can aid in SIL verification after an SIS has been implemented. Its Risk Assessment, Management of Change and Incident Management modules support multiple workflows that can be configured to any corporate standard and provide a global risk register of all hazards across the organization. By allowing you to view risk holistically from the start, Stature can help ensure potential risk is addressed efficiently and effectively.