Chapter 3 Using the Risk Assessment Matrix

Chapter 3 Using the Risk Assessment Matrix - WORKING WITH...

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Sverdrup 1 WORKING WITH THE RISK ASSESSMENT MATRIX P. L. Clemens June 1993 2 nd Edition REVISED for UC System Safety I
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2 THE RISK ASSESSMENT MATRIX… Guides subjective Risk Assessments for Hazard Analyses. Is based on the Definition of Risk and the Principle of the Isorisk Contour. Is widely described in the literature, standards, and regulations. The Matrix can only be used for Identified Hazards . The Matrix DOES NOT identify the hazards.
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3 THE RISK DEFINITION… The EXPECTATION of LOSS An Expression of the combined SEVERITY and PROBABILITY of LOSS The long-term RATE of LOSS…i.e., the LOSS RATE VALUE PROBABILITY ( ) LOSS EVENTS UNIT TIME or ACTIVITY SEVERITY ( ) x LOSS LOSS EVENT • RISK ( ) = EXPECTED LOSS UNIT TIME or ACTIVITY PROBABILITY must be attached to an Exposure Interval! For a given Hazard, i.e. an activity or condition posing threat of Harm, Risk is…
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THE RISK PLANE… 4 PROBABILITY SEVERITY LIKELY 0 NEVER CATACLYSMIC Increasing Risk Iso-risk Contours R = P x S = K 1 R = K 2 > K 1 R = K 3 > K 2 The two variables that constitute risk define a RISK PLANE. SEVERITY and PROBABILITY axes shown here have linear scales. Logarithmic scales produce linear iso-risk plots for R = P x S = K
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5 ISO-RISK CONTOURS… A USEFUL CONVENTION: When assessing a hazard’s risk, consider the WORST CREDIBLE OUTCOME. Show range of SEVERITY vs PROBABILITY combinations for which risk is constant. Characterize risk for many hazards. (Be wary of exceptions! … usually, high-energy cases.) Can guide setting RISK ACCEPTANCE LIMITS. Are useful as “thought tools” in assessing risk.
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AN ISO-RISK CONTOUR IN REAL LIFE… 6 Minor Misstep — no medical attention required (“nuisance”). $1 5 x 10 –4 Minor Injury — Dr’s Office or Emergency Room visit. $30 1.7 x 10 –5 Major Fall — Injury re- sults in Hospitalization. $1500 3.3 x 10 –7 Fatality $1M 1.7 x 10 –9 OUTCOME SEVERITY PROBABILITY* *DATA SOURCE : Templer, John; “The Staircase;” Vol. 2 “Studies of Hazards, Falls, and Safer Design;” MIT Press. SLIPS / TRIPS / FALLS DURING STAIRWAY ASCENTS AND DESCENTS… more
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THE STAIRWAY RISK PLOT… 7 SEVERITY ( $ ) PROBABILITY ( per stair use ) 1x10 -1 1x10 0 1x10 1 1x10 2 1x10 3 1x10 4 1x10 5 1x10 6 1x10 7 1x10 -10 1x10 -9 1x10 -8 1x10 -7 1x10 -6 1x10 -5 1x10 -4 1x10 -3 1x10 -2 Data Curve Fit Severity x Probability = 10 –3
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PROBABILITY SEVERITY 0 0 ISO-RISK CONTOUR USES… 8 RISK ASSESSMENT
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Chapter 3 Using the Risk Assessment Matrix - WORKING WITH...

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