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We face two difficulties when applying ISO 26262[1] in the concept phase. ISO 26262 is the functional safety standard in the automobile field and requires strict safety requirements. Usually, it is not easy to divide requirements into safety parts and non-safety parts because they are closely connected with each other. That is, we have to perform two activities, functional development and functional safety activity, simultaneously. Other difficulty is a term item. From the definition, the item is a 'system 1.129 or array of systems to implement a function at the vehicle level'. In concept phase, we apply hazard analysis to an item, not system. The system definition comes after item definition and hazard analysis and risk assessment. So, it is hard to use the conventional methods e.g. Failure Mode and Effect Analysis FMEA and Fault Tree Analysis FTA.

This article presents a practical implementation of a safety verification framework for nuclear power plants (NPPs) based on fuzzy logic where hazard scenarios are identified in view of safety and control limits in different plant process values. Risk is estimated quantitatively and compared with safety limits in real time so that safety verification can be achieved. Fuzzy logic is used to define safety rules that map hazard condition with required safety protection in view of risk estimate. Case studies are analyzed from NPP to realize the proposed real-time safety verification framework. An automated system is developed to demonstrate the safety limit for different hazard scenarios.

With the recently approved IEC 61511 and ANSI/ISA-84.00.01 standards, process industry companies are being challenged to determine the level of performance required from their safety instrumented functions (SIF) and to verify that the design, installation, operation, and maintenance employed is sufficient to ensure that the required performance is sustained until the SIF is decommissioned. As a practical matter, user companies must self-certify or user approve their SIF equipment, since they are responsible for the correct operation of the SIF in the operating environment, not just individual components as manufactured. To accomplish this, user companies need lifecycle assistance from equipment manufacturers, irrespective of hardware or software certification status related to IEC 61508. One of the best means to communicate the necessary information is via a safety manual for those involved in instrument system design installation and operation. IEC 61508 requires that equipment manufacturers provide a safety manual with any product claimed to comply with IEC 61508. Although required for product certification, it is the authors' current experience that quality and consistency in safety manuals is lacking. Part of this is due to IEC 61508 not providing a clear concise template with minimum requirements. The safety manual requirements are scattered throughout the rather complex standard. This article seeks to provide a user's perspective of what essential information is needed from equipment manufacturers to not only comply with IEC 61508, but also to provide enough information to the user of the product to allow the essential balance of reliability and safety in both SIF and instrumented protective function applications. © 2007 American Institute of Chemical Engineers Process Saf Prog 2007

The recent publication of ANSI/ISA standard S84.01 – 2004 defines the life safety cycle for the design and installation of safety instrumented functions (SIFs) using safety instrumented systems (SISs). However, the determination of the required safety integrity level (SIL) is an activity that the process designers need to complete prior to detailed design. This article outlines an approach for the determination of the required SIL using the layer of protection analysis (LOPA) method. An example is presented along with a suggested format for documenting the LOPA, SIL, and SIF requirements in a manner that can be transferred to the detailed design team for implementation. © 2007 American Institute of Chemical Engineers Process Saf Prog, 2007

Two complementary standards are compared, both of which are concerned with the production of quality software. One, IEC 61508, is concerned with the safety of software intensive systems and the other, ISO/IEC TR 15504, takes a process view of software capability assessment. The standards are independent, though both standards build on ISO/IEC 12207. The paper proposes a correspondence between the safety integrity levels (SILs) of 61508 and the capability levels (CLs) of 15504, and considers the appropriateness of the 15504 reference model as a framework for assessing safety critical software processes. Empirical work from the SPICE trials and COCOMO II is used to support the arguments of the paper as well as to investigate their consequences. The development of a 15504 compatible assessment model for software in safety critical systems is proposed.

The performance based ANSI/ISA S84.01 and IEC 61508 standards provide overall risk based safety life cycle models for industrial processes. Among other guidance, they provide the basic methodology and guidelines for the identification of safety instrumented systems necessary for a process to meet the established target risk levels. In order to arrive at risk based solutions, many practical issues need to be addressed. Such issues include identification of target risk levels, identification of hazardous events associated with the process under consideration, establishing the existing risk associated with the process, and selection of appropriate non-instrumented and instrumented safety systems to meet the target risk. This paper outlines the basic methodology, and discusses some of the related issues mentioned above. Further, it provides a few methodologies to establish the requirements of the safety instrumented systems and their safety integrity levels.