Comparison of safety integrity level selection methods and utilization of risk baed approaches

Abstract

The method wedfor the selection ofa Safety Integrity Level (SIL) for a Sa ety Instrumented System (SIS) o a hazardous consequences and likelihood, as well as the effectiveness of process safeguard. Process Sajty Management, under OSHA 29 CFR Part 191 0, requires an assurance of mechanical integrity for all emergency shutdown systems andsajty critical controls. The International Society for Measurement and romulgated an industy standard S84.01, to States, and the International Electrochemical Commission (IEC) created a similar standard for Europe. These standard specifi that all electrical electronic, and rogrammable electhat thg, achieve a spec$ed SIL. These standard arepe@rmance baed givingguidunce on how to select and achieve an appropriate SIL for a given SIS, but are not prescriptive to any particular method or equipment. The SIL selection is critical since in many cases the SIS is the h t hyer ofprotection for the prevention of hazardous events. The probability offailure on demand of a SIS are quantitatively categorized into discrete integrity h e h (i.e. SIL) by both indwty standard. Since neither standard spec$es re uirements for intep;ty level selection, ing the risk ofa process to a levelacceptable or tolerable to each individual company. In this pa er, current indw practicesfor the selection of estimation of risk reduction that the SIS willprovide for a given process. The level of effort, required expertise, and accuracy of the methods are also compared to assist the reader in choosing the appropriate SIL selection methodology. process shou d we a risk based approach to eva Ir uate potential assist Contra in l(ISA)f comp iance with the PSM regulation in the United tronic system, used in SISs, are require a! to be desiped such the determination of a s4 IL for a SIS is based solely on reduc-SILs are eva P uated to illustrate x ow each methodprovides an _ _ ~ * The authou, Edward M. Marszal, I? E., can be reached via

Safety integrity level requirements in deepwater drilling — Where safety meets reliability

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Using the ISA 84/HAZOP/LOPA procedure to design a safety instrumented system for a fumed silica burner

“… An Example Risk Matrix Showing the Impact of SIL Designs on Risk Reduction Approach. Risk Reduction Approaches: (1) Reduce Consequence with inherently safer design; (2) Reduce Likelihood with engineering and administrative controls; and (3) Define SILs to reach tolerable risk region, as needed [18]. [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]…”

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