Required Safety Integrity Level Research Articles

Using layer of protection analysis to define safety integrity level requirements

AbstractThe 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

IEC 61508/61511—Pain or gain?

AbstractThe introduction of IEC 61508 provided safety system practitioners with the first internationally accepted generic benchmark policy for safety‐related systems. However, many practitioners find the way in which the standard is often presented and promoted quite intimidating. But, there is no need to be intimidated. The grassroots rationale of the standard is fundamental common sense, and there have been significant developments in practical software aids that remove the pain.An optimal design can lead to considerable capital cost savings from focused Safety Integrity Level (SIL) assessment, component selection, and logic simplification. Experience shows that up to 40% savings can be achieved with the aid of software tools at the design stage.Full life cycle considerations also require alignment of a design with appropriate maintenance and testing strategies. This can afford significant opportunities to reduce maintenance and testing costs, production deferment, and the avoidance of nuisance trips. These opportunities become very achievable with the aid of software tools.Software tools can help to achieve these not insignificant benefits by aiding design, and setting optimal testing and maintenance calculations to meet SIL requirements.

Determining the required safety integrity level for your process

A Safety integrity level (SIL) analysis is the initial step in the Safety system design process. Where the HAZOP process normally discovers potential hazards and provides general recommendations, the SIL is a specific analysis which defines the Safety criteria and mitigation of hazards which can lead to a significant economic, safety and environmental consequences. There are three SILs utilized by ISA S84 and four by IEC 1508/1511 for Risk Classification, as defined in terms of Probability of failure on demand (PFD). This paper provides a methodology to evaluate and classify risk in terms of consequences, and to determine the SIL for the process under consideration based on these consequences and the Process demand rate. The methodology can be customized to comply with existing company standards, and should satisfy many of the critical OSHA 29 CFR - 1910.119 requirements. In addition, the paper addresses the configuration of the Safety instrumented system (SIS) and the impact of field devices on the system SIL, including the necessity of redundancy and testing of field devices to achieve and maintain SILs of 2 or higher.