Fault Tree Analysis

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Fault Tree Analysis

• By Patrick Ackerson

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Outline

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

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What Is Fault Tree Analysis?

• A common tool using graphics and statistics to
  analyze an event and predict how and how often it
  will fail
• Used in engineering and business to aid process
  and system development

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Why Do We Use Fault Tree Analysis?

• Very easy to understand
• Effective way to diagram problems in a system
• Helps to organize possible causes of a problem in
  the system

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

• Does your company have problems in your system or
  process flow?
• Does your system work under the worst case
  scenario?
• Do external forces effect your system?

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Is Fault Tree A Tool For You?

• Yes!!

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How Does It Work?

• Uses a variety of gates and events to explain the
  system
• Uses a top-down approach to its logic
• End result is at the top of the tree and what
  leads to that result follows under it

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And Gate

• One of main gates used
• The output above will occur if the two events
  below both occur

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Or Gate

• The second main gate used
• The output above will occur if either of one or
  more events happens below

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Three Main Events

• Primary Event
• Intermediate Event
• Expanded Event

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Primary Events

• Made up of basic, undeveloped, and external
  events
• A time in the event where the process or system
  might fail

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Basic Event

• Nothing is leading up to the event
• Can be like a machine breaking unexpectedly
• A circle is used to represent the event in the
  fault tree

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Undeveloped Event

• Events that dont have a major effect on the
  system
• Also events that there is not enough information
  about
• Represented by a diamond in the fault tree

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External Event

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

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Intermediate Event

• A combination of multiple different faults
• Shown by rectangles in the fault tree
• Sometimes linked by and/or gates

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Expanded Event

• Complex event that needs another fault tree to
  explain
• The fault tree for the expanded event is not
  directly shown in current fault tree
• Shown by a triangle on the fault tree

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Bridgestone Firestone tires

• Faulty tires on S.U.V.s caused numerous
  accidents
• Officially 148 deaths but estimates up to 250
• Mostly involved with the Ford Explorer

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Results Of Inquiry

• Four events that led to faulty tires
• Design problem in tread
• Faulty process in Decatur, Illinois
• Problem with Ford Explorer
• Customers dont take proper care of tires

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Values Of Fault Tree For Firestone

• Preventing the error in the first place
• After the error in the tire was found, finding
  all the things that caused it
• Preventing similar problems from happening again

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The New Firestone

• Firestone advertise that they are a changed
  company
• Tries to get back old customers

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Test Yourself

• What are the two major kinds of gates?
• What are the three main events?
• A basic event is represented by a what?
• True or False, an undeveloped event has a major
  impact on the system?

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Test Yourself

• What are the two major kinds of gates? And/Or
  gates
• What are the three main events? Primary,
  Independent, and Undeveloped
• A basic event is represented by a what? Circle
• True or False, an undeveloped event has a major
  impact on the system? False

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Summary Of Fault Tree Analysis

• An important tool
• Simple to use
• Graphics make it easy to understand
• Each event is displayed by a unique shape
• Helps to prevent and correct errors in the system

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Bibliography

• Bridgestone/Firestone, Firestone Homepage,
  19992000, www.firestone.com
• Firestone Facts, www.firestone-facts.com
• Foster, S. Thomas, Managing Quality An
  Integrated Approach, (Upper Saddle River, NJ
  Prentice- Hall Inc. 2001)
• Garsten, Ed, Bridgestone/Firestone says its
  found answers in its dig for cause of tire
  failure,Dec 12,2000, http//www.cnn.com/2000/US/
  12/20/brid gestone.firestone/index.html
• Relex Software Company, Fault Tree Analysis,
  www.fault-tree.com