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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 . Designing Processes to Fail?.

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Probabilistic risk assessment
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


Designing processes to fail
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


Design in benign failures
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


Money well spent creating a failure
Money Well Spent... ...Creating a Failure

  • Audi 5000

  • Jeep Grand Cherokee

John

Grout


Fault tree basics
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


Converting undesired failures to benign failures before
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


Converting undesired failures to benign failures after

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


Multiple fault tree analysis
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