Fault Tree Analysis
By Patrick Ackerson
Outline
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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
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
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
Example Of Fault Tree
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?
Is Fault Tree A Tool For
You?
Yes!!
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
And Gate
• One of main
gates used
• The output
above will occur
if the two events
below both
occur
Or Gate
• The second
main gate used
• The output
above will occur
if either of one
or more events
happens below
Three Main Events
• Primary Event
• Intermediate Event
• Expanded Event
Primary Events
• Made up of basic, undeveloped,
and external events
• A time in the event where the
process or system might fail
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
Undeveloped Event
• Events that don’t have a major
effect on the system
• Also events that there is not
enough information about
• Represented by a diamond in the
fault tree
External Event
• Expected to happen
• Not considered a fault
• A house shape in a fault tree
Intermediate Event
• A combination of multiple
different faults
• Shown by rectangles in the fault
tree
• Sometimes linked by and/or
gates
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
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
Results Of Inquiry
• Four events that led to faulty
tires
• Design problem in tread
• Faulty process in Decatur,
Illinois
• Problem with Ford Explorer
• Customers don’t take proper
care of tires
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
The New Firestone
• Firestone
advertise that
they are a
changed
company
• Tries to get back
old customers
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?
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
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
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: PrenticeHall 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