Fault Tree AnalysisFault Tree Analysis

By Patrick AckersonBy Patrick Ackerson

OutlineOutline

• Why do we need fault tree analysis?Why do we need fault tree analysis?• What is it?What is it?• Why do we use it?Why do we use it?• Why this matters to youWhy this matters to you• How it worksHow it works• Bridgestone/FirestoneBridgestone/Firestone• Brief exerciseBrief exercise• SummarySummary

What Is Fault Tree What Is Fault Tree Analysis?Analysis?

• A common tool using graphics and A common tool using graphics and statistics to analyze an event and statistics to analyze an event and predict how and how often it will predict how and how often it will failfail

• Used in engineering and business Used in engineering and business to aid process and system to aid process and system developmentdevelopment

Why Do We Use Fault Tree Why Do We Use Fault Tree Analysis?Analysis?

• Very easy to understandVery easy to understand• Effective way to diagram problems Effective way to diagram problems

in a systemin a system• Helps to organize possible causes Helps to organize possible causes

of a problem in the systemof a problem in the system

Example Of Fault TreeExample Of Fault Tree

Is Fault Tree A Tool For Is Fault Tree A Tool For You?You?

• Does your company have problems Does your company have problems in your system or process flow?in your system or process flow?

• Does your system work under the Does your system work under the worst case scenario?worst case scenario?

• Do external forces effect your Do external forces effect your system?system?

Is Fault Tree A Tool For Is Fault Tree A Tool For You?You?

Yes!!Yes!!

How Does It Work?How Does It Work?

• Uses a variety of gates and events Uses a variety of gates and events to explain the systemto explain the system

• Uses a top-down approach to its Uses a top-down approach to its logiclogic

• End result is at the top of the tree End result is at the top of the tree and what leads to that result and what leads to that result follows under it follows under it

And GateAnd Gate

• One of main gates One of main gates usedused

• The output above The output above will occur if the will occur if the two events below two events below both occurboth occur

Or GateOr Gate

• The second main The second main gate usedgate used

• The output above The output above will occur if either will occur if either of one or more of one or more events happens events happens belowbelow

Three Main EventsThree Main Events

• Primary EventPrimary Event• Intermediate EventIntermediate Event• Expanded EventExpanded Event

Primary EventsPrimary Events

• Made up of basic, undeveloped, Made up of basic, undeveloped, and external eventsand external events

• A time in the event where the A time in the event where the process or system might failprocess or system might fail

Basic EventBasic Event

• Nothing is leading up to the eventNothing is leading up to the event• Can be like a machine breaking Can be like a machine breaking

unexpectedlyunexpectedly• A circle is used to represent the A circle is used to represent the

event in the fault treeevent in the fault tree

Undeveloped EventUndeveloped Event

• Events that don’t have a major Events that don’t have a major effect on the systemeffect on the system

• Also events that there is not Also events that there is not enough information aboutenough information about

• Represented by a diamond in the Represented by a diamond in the fault treefault tree

External EventExternal Event

• Expected to happenExpected to happen• Not considered a faultNot considered a fault• A house shape in a fault treeA house shape in a fault tree

Intermediate EventIntermediate Event

• A combination of multiple different A combination of multiple different faultsfaults

• Shown by rectangles in the fault Shown by rectangles in the fault treetree

• Sometimes linked by and/or gatesSometimes linked by and/or gates

Expanded EventExpanded Event

• Complex event that needs another Complex event that needs another fault tree to explainfault tree to explain

• The fault tree for the expanded The fault tree for the expanded event is not directly shown in event is not directly shown in current fault treecurrent fault tree

• Shown by a triangle on the fault Shown by a triangle on the fault treetree

Bridgestone Firestone tiresBridgestone Firestone tires

• Faulty tires on S.U.V.’s caused Faulty tires on S.U.V.’s caused numerous accidentsnumerous accidents

• Officially 148 deaths but estimates Officially 148 deaths but estimates up to 250up to 250

• Mostly involved with the Ford Mostly involved with the Ford ExplorerExplorer

Results Of Inquiry Results Of Inquiry

• Four events that led to faulty tiresFour events that led to faulty tires• Design problem in treadDesign problem in tread• Faulty process in Decatur, IllinoisFaulty process in Decatur, Illinois• Problem with Ford ExplorerProblem with Ford Explorer• Customers don’t take proper care Customers don’t take proper care

of tiresof tires

Values Of Fault Tree For Values Of Fault Tree For FirestoneFirestone

• Preventing the error in the first Preventing the error in the first placeplace

• After the error in the tire was After the error in the tire was found, finding all the things that found, finding all the things that caused itcaused it

• Preventing similar problems from Preventing similar problems from happening againhappening again

The New FirestoneThe New Firestone

• Firestone Firestone advertise that advertise that they are a they are a changed companychanged company

• Tries to get back Tries to get back old customersold customers

Test YourselfTest Yourself

• What are the two major kinds of What are the two major kinds of gates?gates?

• What are the three main events?What are the three main events?• A basic event is represented by a A basic event is represented by a

what?what?• True or False, an undeveloped True or False, an undeveloped

event has a major impact on the event has a major impact on the system?system?

Test YourselfTest Yourself

• What are the two major kinds of gates? What are the two major kinds of gates? And/Or gatesAnd/Or gates

• What are the three main events? What are the three main events? Primary, Primary, Independent, and Undeveloped Independent, and Undeveloped

• A basic event is represented by a what? A basic event is represented by a what? CircleCircle

• True or False, an undeveloped event has a True or False, an undeveloped event has a major impact on the system? major impact on the system? FalseFalse

Summary Of Fault Tree Summary Of Fault Tree AnalysisAnalysis

• An important toolAn important tool• Simple to useSimple to use• Graphics make it easy to Graphics make it easy to

understandunderstand• Each event is displayed by a Each event is displayed by a

unique shapeunique shape• Helps to prevent and correct errors Helps to prevent and correct errors

in the systemin the system

BibliographyBibliography

• Bridgestone/Firestone, “Firestone Homepage,” Bridgestone/Firestone, “Firestone Homepage,” 19992000, 19992000, www.firestone.comwww.firestone.com

• ““Firestone Facts,” Firestone Facts,” www.firestone-facts.comwww.firestone-facts.com• Foster, S. Thomas, Foster, S. Thomas, Managing Quality: An Integrated Managing Quality: An Integrated

ApproachApproach, (Upper Saddle River, NJ: Prentice-, (Upper Saddle River, NJ: Prentice- Hall Hall Inc. 2001) Inc. 2001)

• Garsten, Ed, “Bridgestone/Firestone says its found Garsten, Ed, “Bridgestone/Firestone says its found answers in its dig for cause of tire failure,”Dec answers in its dig for cause of tire failure,”Dec 12,2000, 12,2000, http://www.cnn.com/2000/US/12/20/http://www.cnn.com/2000/US/12/20/bridbridgestonegestone.firestone/index.html.firestone/index.html

• Relex Software Company, “Fault Tree Analysis,” Relex Software Company, “Fault Tree Analysis,” www.fault-tree.comwww.fault-tree.com