Fault Tree Analysis Slides 5n3ya
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Introduction to FBD and FTA Functional Block Diagrams Fault Tree Analysis
Compliance Engineering
Ultratech Internal Use Only
Slide 1 May 8th, 2007
Fault Tree Analysis - Review
What ?
When ?
A structured team analysis of the possible underlying causes of a known equipment failure. root cause analysis of a failure is needed
Why? - (outcomes)
A better understanding of the root causes of a failure (Step 3: Root cause)
A better set of action plans to eliminate those root causes (Step 4: Solution)
1 THEME
2 DATA
3
4
5
ROOT CAUSE
SOLUTION
CONFIRM RESULTS No
Compliance Engineering
Ultratech Internal Use Only
6
Yes
STANDARDIZE
7 REFLECT
Slide 2 May 8th, 2007
Fault Tree Analysis…
Fault tree analysis is an effect and cause diagram that uses standard symbols developed in the defense industry and is used heavily in safety engineering. FTA is a structured approach for analyzing the root causes of a failure mode not yet fully understood.
Note: FTA is an alternative to Ishikawa (Fish Bone) Diagrams. Many feel that FTA is better suited to understanding layers and relationships of causes of equipment failures. However, if you still prefer fish bones after trying FTA, there is no reason not to use them. The goal always remains to use the most efficient method for solving problems.
Compliance Engineering
Ultratech Internal Use Only
Slide 3 May 8th, 2007
FTA Example: Smoke Detector Failure: The indicator light is on… yet even with sufficient amounts of smoke directly below the detector vents the alarm does not signal.
Before we begin either a Fault Tree Analysis or Failure Modes and Effects Analysis, our first step should be to construct a Functional Block Diagram.
1
THEME
2
DATA
3
4
5
ROOT CAUSE
SOLUTION
CONFIRM RESULTS No
Compliance Engineering
Ultratech Internal Use Only
6
Yes
STANDARDIZE
7
REFLECT
Slide 4 May 8th, 2007
FBD Example: Smoke Detector Inputs
Process
Presence of smoke
Detection of smoke
Smoke enters through vent Smoke enters ionization chamber
Battery powers control box, indicator light, and smoke detector
Outputs Alarm signaling Signal/power to siren turns motor Motor causes siren to sound
Smoke is ionized and causes increase in voltage
Alarm signals
Signal sent from smoke detector triggers control box circuit Control Box sends signal/power to siren
Compliance Engineering
Ultratech Internal Use Only
Slide 5 May 8th, 2007
Sample solution (incomplete)
FAILURE Smoke Detector does not detect smoke
Smoke not present in chamber
Vent is blocked Dust blockage
Smoke not detected
Ionization chamber blocked
Defective Control box
No power at control box
Alarm not sounding
Defective ionization chamber
No power at ionization chamber
Defective alarm
No power at alarm
Dust blockage
Paint blockage Broken wire
1 THEME
2 DATA
Defective solder t
Ionization chamber cracked
3
4
5
ROOT CAUSE
SOLUTION
CONFIRM RESULTS No
Compliance Engineering
Ultratech Internal Use Only
Broken wire
6 Yes
STANDARDIZE
Defective solder t 7 REFLECT
Slide 6 May 8th, 2007
Typical use for an FTA:
Began by clearly identifying the failure as: The indicator light is on … yet even with sufficient amounts of smoke directly below the detector vents the alarm does not signal. Began brainstorming and building a functional block diagram to fully understand how the smoke detector functions. Continued brainstorming on possible causes for the smoke detector failure resulting in the alarm not signaling. Probable causes were identified:
The team constructed the FTA around the three major categories in the functional block diagram, inputs, process, and outputs. The team continued to build the FTA and completed it by adding lower levels of detail under appropriate causes of failure. The team identified the types of failure where it did not have the expertise to analyze possible root causes. If deemed necessary, the team would seek help from suppliers or consultants to further analyze these area. The leading causes of failure and solutions were identified.
A design project was started to correct the problem.
Compliance Engineering
Ultratech Internal Use Only
Slide 7 May 8th, 2007
Fault Tree
Symbols Review
Compliance Engineering
Square
Describes the top and lower level failures
Or Gate
Produces output (failure) if one or more inputs exist
And Gate
Produces output (failure) if and only if all inputs exist
Circle
Potential root failure which cannot be broken down into lesser failures
Diamond
Potential failure which is not analyzed for various reasons Ultratech Internal Use Only
Slide 8 May 8th, 2007
How to build a Fault Tree 1) Identify a top failure 2) Brainstorm basic contributors to failure 3) Link contributors to the top failure
Determine which combination of contributors is needed to cause the top failure. (Ask: How many of the inputs are needed to cause the top failure? ) Link the contributors to the top failure with the correct gate. (And/Or)
Ask: Can we determine contributors for this lower failure ?
Compliance Engineering
Yes - repeat cycle making each contributor a top failure, assign gates, etc... No - we are finished - We may also end our fault tree when we reach all indeterminable, basics, or causes which require further research etc... Ultratech Internal Use Only
Slide 9 May 8th, 2007
Understanding the symbols (Gates Review) And gate means For this upper failure
Failure
to occur
All of these failures must occur
Or gate means that For this upper failure
Failure
to occur
Only one of these failures must occur
Compliance Engineering
Ultratech Internal Use Only
Slide 10 May 8th, 2007
Step 1 Identify Top Level Fault Step 3 Link contributors to top by logic gates Step 2 Brainstorm first level contributors Step 5 Link contributors to upper level by logic gates Step 4 Brainstorm second level contributors
Step 6 Repeat / continue for each lower level failure
basic event cannot be broken down any further
event that is not analyzed for various reasons
(This page is taken from SVERDROP MANUAL - FTA and Risk Management by P.L. Clemens, 1992/1993, pg. 10 ) Compliance Engineering
Ultratech Internal Use Only
Slide 11 May 8th, 2007
FTA Do’s & Don'ts
Do’s
Start at the Top Think Categories Brainstorm, then organize Facilitate proper brainstorming Know when to stop Have action plans for all circles Check that branches terminate with a circle or diamond Revisit the FBD or FTA when new data is found Use yellow stickies to capture the brainstormed causes
Don'ts
Don’t get bogged down Don’t jump to solutions!
Compliance Engineering
Ultratech Internal Use Only
Slide 12 May 8th, 2007
Compliance Engineering
Ultratech Internal Use Only
Slide 1 May 8th, 2007
Fault Tree Analysis - Review
What ?
When ?
A structured team analysis of the possible underlying causes of a known equipment failure. root cause analysis of a failure is needed
Why? - (outcomes)
A better understanding of the root causes of a failure (Step 3: Root cause)
A better set of action plans to eliminate those root causes (Step 4: Solution)
1 THEME
2 DATA
3
4
5
ROOT CAUSE
SOLUTION
CONFIRM RESULTS No
Compliance Engineering
Ultratech Internal Use Only
6
Yes
STANDARDIZE
7 REFLECT
Slide 2 May 8th, 2007
Fault Tree Analysis…
Fault tree analysis is an effect and cause diagram that uses standard symbols developed in the defense industry and is used heavily in safety engineering. FTA is a structured approach for analyzing the root causes of a failure mode not yet fully understood.
Note: FTA is an alternative to Ishikawa (Fish Bone) Diagrams. Many feel that FTA is better suited to understanding layers and relationships of causes of equipment failures. However, if you still prefer fish bones after trying FTA, there is no reason not to use them. The goal always remains to use the most efficient method for solving problems.
Compliance Engineering
Ultratech Internal Use Only
Slide 3 May 8th, 2007
FTA Example: Smoke Detector Failure: The indicator light is on… yet even with sufficient amounts of smoke directly below the detector vents the alarm does not signal.
Before we begin either a Fault Tree Analysis or Failure Modes and Effects Analysis, our first step should be to construct a Functional Block Diagram.
1
THEME
2
DATA
3
4
5
ROOT CAUSE
SOLUTION
CONFIRM RESULTS No
Compliance Engineering
Ultratech Internal Use Only
6
Yes
STANDARDIZE
7
REFLECT
Slide 4 May 8th, 2007
FBD Example: Smoke Detector Inputs
Process
Presence of smoke
Detection of smoke
Smoke enters through vent Smoke enters ionization chamber
Battery powers control box, indicator light, and smoke detector
Outputs Alarm signaling Signal/power to siren turns motor Motor causes siren to sound
Smoke is ionized and causes increase in voltage
Alarm signals
Signal sent from smoke detector triggers control box circuit Control Box sends signal/power to siren
Compliance Engineering
Ultratech Internal Use Only
Slide 5 May 8th, 2007
Sample solution (incomplete)
FAILURE Smoke Detector does not detect smoke
Smoke not present in chamber
Vent is blocked Dust blockage
Smoke not detected
Ionization chamber blocked
Defective Control box
No power at control box
Alarm not sounding
Defective ionization chamber
No power at ionization chamber
Defective alarm
No power at alarm
Dust blockage
Paint blockage Broken wire
1 THEME
2 DATA
Defective solder t
Ionization chamber cracked
3
4
5
ROOT CAUSE
SOLUTION
CONFIRM RESULTS No
Compliance Engineering
Ultratech Internal Use Only
Broken wire
6 Yes
STANDARDIZE
Defective solder t 7 REFLECT
Slide 6 May 8th, 2007
Typical use for an FTA:
Began by clearly identifying the failure as: The indicator light is on … yet even with sufficient amounts of smoke directly below the detector vents the alarm does not signal. Began brainstorming and building a functional block diagram to fully understand how the smoke detector functions. Continued brainstorming on possible causes for the smoke detector failure resulting in the alarm not signaling. Probable causes were identified:
The team constructed the FTA around the three major categories in the functional block diagram, inputs, process, and outputs. The team continued to build the FTA and completed it by adding lower levels of detail under appropriate causes of failure. The team identified the types of failure where it did not have the expertise to analyze possible root causes. If deemed necessary, the team would seek help from suppliers or consultants to further analyze these area. The leading causes of failure and solutions were identified.
A design project was started to correct the problem.
Compliance Engineering
Ultratech Internal Use Only
Slide 7 May 8th, 2007
Fault Tree
Symbols Review
Compliance Engineering
Square
Describes the top and lower level failures
Or Gate
Produces output (failure) if one or more inputs exist
And Gate
Produces output (failure) if and only if all inputs exist
Circle
Potential root failure which cannot be broken down into lesser failures
Diamond
Potential failure which is not analyzed for various reasons Ultratech Internal Use Only
Slide 8 May 8th, 2007
How to build a Fault Tree 1) Identify a top failure 2) Brainstorm basic contributors to failure 3) Link contributors to the top failure
Determine which combination of contributors is needed to cause the top failure. (Ask: How many of the inputs are needed to cause the top failure? ) Link the contributors to the top failure with the correct gate. (And/Or)
Ask: Can we determine contributors for this lower failure ?
Compliance Engineering
Yes - repeat cycle making each contributor a top failure, assign gates, etc... No - we are finished - We may also end our fault tree when we reach all indeterminable, basics, or causes which require further research etc... Ultratech Internal Use Only
Slide 9 May 8th, 2007
Understanding the symbols (Gates Review) And gate means For this upper failure
Failure
to occur
All of these failures must occur
Or gate means that For this upper failure
Failure
to occur
Only one of these failures must occur
Compliance Engineering
Ultratech Internal Use Only
Slide 10 May 8th, 2007
Step 1 Identify Top Level Fault Step 3 Link contributors to top by logic gates Step 2 Brainstorm first level contributors Step 5 Link contributors to upper level by logic gates Step 4 Brainstorm second level contributors
Step 6 Repeat / continue for each lower level failure
basic event cannot be broken down any further
event that is not analyzed for various reasons
(This page is taken from SVERDROP MANUAL - FTA and Risk Management by P.L. Clemens, 1992/1993, pg. 10 ) Compliance Engineering
Ultratech Internal Use Only
Slide 11 May 8th, 2007
FTA Do’s & Don'ts
Do’s
Start at the Top Think Categories Brainstorm, then organize Facilitate proper brainstorming Know when to stop Have action plans for all circles Check that branches terminate with a circle or diamond Revisit the FBD or FTA when new data is found Use yellow stickies to capture the brainstormed causes
Don'ts
Don’t get bogged down Don’t jump to solutions!
Compliance Engineering
Ultratech Internal Use Only
Slide 12 May 8th, 2007
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