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Articles: SIL 101 | SIL 102 | SIL 103 | SIL 104
   
SIL 105

Calculating SIL Suitability Levels
Functional Safety Standards
Choosing a SIL System
LOPA: Layer of Protection Analysis



Functional Safety Standards
The ANSI/ISA-84.00.01-1996 was the first standard developed by the ISA SP84 committee to address the need to increase safety by systematically reducing process risk. The standards are updated approximately every 5 years and the most recent version was released in 2004. The new version adopts the IEC 61511 standard and adds the original 1996 version of ANSI/ISA 84 as a “grandfather clause”.

IEC 61508 is an umbrella standard released by the International Electrotechnical Committee in 1998 that is based on ANSI/ISA 84 and applies to all industries. The IEC 61508 standard is viewed as the document that vendors follow to receive certification for SIL suitability ratings for products and system components.

IEC 61511 was released in 2003 and was developed specifically to address functional safety in the process industry. This document is used by end-users to successfully implement system safety throughout the entire life-cycle of a system.

Please note, that if a system was implemented prior to the update of the standards in 2004 and has been operating in a safe manner without an increase in risks or safety incidents, then the system can be “grandfathered” and does not need to comply with the ANSI/ISA 84 2004 update. However, once significant changes are made to the system or if a safety issue arises, the system will have to comply with the most recent version of the standards.

It is important to note that none of the standards are prescriptive, but are performance based. The standards present guidelines for best practices, but do not identify procedures for specific implementation.

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General Monitors, Inc.
26776 Simpatica Circle
Lake Forest, CA 92630

Phone: 949-581-4464
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etech@generalmonitors.com

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