Probabilistic Risk Assessment

1. Probabilistic Risk Assessment Workshop on Best Practices for Reducing Transfusion Errors • John Grout • jgrout@campbell.berry.edu • www.mistakeproofing.com • 706-238-7877 • David Marx • david@davidmarx.com • www.causationtrainer.com • (952) 443-5009

2. Designing Processes to Fail? “We rely on failure of all kinds being designed into many of the products we use every day, and we have come to depend upon things failing at the right time to protect our health and safety...” “We often thus encourage one mode of failure to obviate a less desirable mode.” (Petroski, 1997, page 415) John Grout

3. Design in Benign Failures. "Failure is a relative concept, and we encounter it daily in more frequent and broad-ranging ways than is generally realized. And that is a good thing, for certain types of desirable failures, those designed to happen, are ones that engineers want to succeed at effecting." (Petroski, 1997, page 416) John Grout

4. Money Well Spent... ...Creating a Failure • Audi 5000 • Jeep Grand Cherokee John Grout

5. Fault Tree Basics Top Event P(top event)= P(F1F2)+ P(F3)+P(F4)=.11 OR P(F1F2)= P(F1)*P(F2)=.01 AND Basic Failure #1 P(F1)=.1 Basic Failure #2 P(F2)=.1 Basic Failure #3 P(F3)=.05 Basic Failure #4 P(F4)=.05 John Grout MCS 2 MCS 3 Minimal Cut Set 1

6. Converting Undesired Failures to Benign Failures (before) benign failure (aggravation only) Table saw motor will not operate Undesired failure (operator injury) Or table saw turned on prematurely Electricity not reaching motor motor unable to turn properly Or Or And anti-kickback blade guard not mounted blade insert not mounted properly wrench left on spindle nut broken wire in electric cord not plugged in excessive friction inadequate lubrication Basic 3 Basic 4 Basic 5 Basic 6 Basic 7 Basic 1 Basic 2 John Grout tie wrench to electric cord near plug install limit switch in insert cavity

7. B3 Converting Undesired Failures to Benign Failures (after) Table saw motor will not operate Benign failure Or Electricity not reaching motor motor unable to turn properly Undesired failure Or And table saw turned on prematurely break in electrical connection not plugged in excessive friction inadequate lubrication B2 B1 Or Or Or broken wire in electric cord blade insert not mounted properly Operator forgets to plug in wrench left on spindle nut anti-kickback blade guard not mounted B4 B3A B4A B5 John Grout

8. Multiple Fault Tree Analysis • Stopping the process is a failure (albeit benign) • Causing harm is a failure (undesirable) • Mistake-proofing converts undesirable failures to benign ones John Grout

9. Thank You!