*Safety Instrumented SystemsANGELA E. SUMMERS, PH.D., P.E.SIS-TECH Solutions, LLCWere Proven-in-Use.

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TerminologyCritical Control SystemsSafety Shutdown SystemsProtective Instrumented SystemsEquipment Protection SystemsEmergency Shutdown SystemsSafety Critical SystemsInterlocksSafety Instrumented Systems

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What is a Safety Instrumented System (SIS)?An SIS is designed to:

respond to conditions in the plant which may be hazardous in themselves or, if no action was taken, could eventually give rise to a hazard, and to respond to these conditions by taking defined actions that either prevent the hazard or mitigate the hazard consequences.

Input ---- Logic Solver ---- Output

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Examples of Safety Instrumented SystemsHigh fuel gas pressure furnace initiates shutdown of main fuel gas valves.High reactor temperature initiates fail open action of coolant valve.High column pressure initiates fail open action of pressure vent valve.

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OSHA & EPAProcess Safety ManagementGOOD ENGINEERING PRACTICEWritten Internal GuidelinesMentor/Engineering PracticesIndustry Codes & Standards

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Standards Bodies that Define Good Engineering Practice for Safety Instrumented SystemsISA, Instrumentation Systems and Automation SocietyIEC, International Electrotechnical Commission

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Other standards and guidelines must be integrated with SIS standards!ASMENFPAAPIISOAICHE BooksBoiler Codes

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Safety Instrumented System StandardsISA 84.01-2003 - Functional Safety: Safety Instrumented Systems for the Process Industry SectorIdentical to IEC 61511 with inclusion of grandfather clauseTo be published October 2003IEC 61508 - Functional Safety: Safety Related SystemsCurrent version released 1999Under revision for next release 2005IEC 61511 - Functional Safety: Safety Instrumented Systems for the Process Industry SectorPublished 2003

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Front End EngineeringEngineering DesignCommissioningManagement of ChangeSafety LifecyclePlanningOperations & Maintenance

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Manage risk - PeopleIdentify role of individual or departmentsWho is assigned to project?What are their roles?Document competency of individuals and departmentsDoes anyone need more training?Who will mentor inexperienced engineers?Who will review and approve?

This is good project management.

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Manage risk ProceduresDefine when the following will take place:Verifications, Audits, and Validation.Require procedures for evaluating the performance of the SIS after it has been installedPerformance audits andTracking failures rates.

This is good quality control.

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Assess risk and mitigate itWill talk about the how to laterThe assessment results in the assignment of Safety Integrity Level

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Safety Integrity Level

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Lets talk about Risk.What is your wager?How many times do you place the wager each year?What are your odds of losing your wager?

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Design SIFJustify selection of devicesDocument the safety requirements specificationDesign SIFs to achieve Safety Integrity Level.

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Prove itVerifySafety Integrity LevelFault toleranceCommissioningInstall SIFs per design documentsFunctional safety assessmentMake sure all documents are in place and all hazards analysis items are addressed.ValidationTest SIFs to ensure that they have desired functionality

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Maintain itOperation, maintenance and testingUse diagnostics and testing to maintain performanceCreate and maintain procedure to support these activitiesTrain personnel on procedures

Management of changeMonitor changes to SIS that might affect SIL

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Audit itIncludes design and proceduresDefine frequency of auditsDetermine the degree of independence of auditing activityDocument auditDefine follow-up activities

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Front End EngineeringEngineering DesignCommissioningManagement of ChangeSafety LifecyclePlanningOperations & Maintenance

****The regulations required industry to examine their risks and to minimize them. Most of the regulations were not prescriptive. They simply required that something be done. The industrial community responded by issuing industry standards concerning the evaluation of risk and the design of corresponding safety instrumented systems. Examples of the industry standards are as follows:**