Microsoft PowerPoint - Summers Hearn - Risk Criteria Protection Layers and Conditional Modifiers.ppt [Compatibility Mode]1 www.sis-tech.com
Risk Criteria, Protection Layers d C diti l M difiand Conditional Modifiers
Angela E. Summers, PhD, PE, President William H Hearn PE FellowWilliam H Hearn, PE, Fellow
SIS-TECH Solutions, LP
Dr. Angela Summers President
2010 PPSS Best Paper Active participant in many CCPS books 1 of 5 US Experts to the IEC 61508/IEC 61511 committee Working Group Chair, TR84.00.02 (SIL Verification) and TR84.00.04 (Guidance on
SIS-TECH
g p , ( ) ( ISA 84.00.01-2004) Member of more than 20 industrial committees and forums Ph.D. and Engineering Fellow, The University of Alabama Licensed Professional Engineer in the State of Texas
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Risk and Loss Prevention
Risk Result of deviations from expected operation– Result of deviations from expected operation
– Related to process design and site safety culture – Function of frequency of deviations and consequence
of deviation Loss Prevention – Seeks to identify the deviations and reduce theirSeeks to identify the deviations and reduce their
frequency of occurrence or impact should they occur
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Risk Criteria
Purpose Comparison value used to determine whether an– Comparison value used to determine whether an identified risk is tolerable
– Maximum risk tolerable per company standard
Company Goal is Zero Loss of Containment E ents
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Zero Injuries and Fatalities
• PHA, LOPA, QRA – Intent
– Boundaryy • Assessing hazardous event or harmful event
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Hazardous Event Process deviation exceeds safe operating limit of the process resulting in loss of containment or equipment damage
Initiating Cause – Control Failure – Operating Error
Enabling Condition – Coincident failure
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Hazardous Situation A hazardous event that exposes people, property or the environment, etc. to one or more hazards
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Act to prevent hazardous event
hazardous situation and harm
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CCPS IPS Book, CCPS HEP, and CCPS ISD Onion Skin Graphic
Proactive IPLs Proactive IPLs act to prevent the hazardous event
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Reactive IPLs Reactive IPLs act to reduce the hazardous situation
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Response IPL Response IPL acts to address harm caused by the event
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Focus: Preventing releases or– Preventing releases or loss of containment
Factors Considered: – Initiating Causes – Enabling Conditions – Proactive LayersProactive Layers – (No conditional
modifiers)
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Validation: – Operational records
• Upsets • Trip Reports
– Mechanical Integrity records
– Near miss – Incident reports
Reactive Layers reduce the hazardous situation caused by releaseby release – Contain spill – Extinguish fire
Conditional Modifiers model the hazardous situation – Particular to each scenario
• Characteristics of material released • Surrounding environment • Presence of workers and/or public
– Justified by analysis and controls
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Factors Considered: – Hazardous Event Factors – Reactive Layers – Conditional Modifiers
• Probability of ignition• Probability of ignition • Probability of occupancy • Probability of impact (fatality)
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• Consequence Severity • Conditional Modifiers • Reactive Layers
Validation: – Near Miss/Incident reports
Factors Considered: – All Harmful Events – Harmful Event Factors
Ti i k– Time at risk
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• Startup • Shutdown • Normal • Maintenance
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Validation: – Near Miss/Incident reports – Illness/Injury Rate
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Summary
Table 1: Example Risk Criteria (3) C it i W k P bliCriteria Worker Public
Maximum Individual Risk - All events 10-3 fatality/yr 10-4 fatality/yr
Maximum Individual Risk - Each event 10-5 fatality/yr 10-6 fatality/yr
Maximum Hazardous Event Frequency – Each event 10-4 event/yr 10-5 event/yr
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Layers and Conditional Modifiers