Slide 1 May 8th, 2007Compliance EngineeringUltratech Internal Use Only Introduction to FBD and FTA Functional Block Diagrams Fault Tree Analysis

Slide 2 May 8th, 2007Compliance EngineeringUltratech Internal Use Only Fault Tree Analysis - Review n What ? n A structured team analysis of the possible underlying causes of a known equipment failure. n When ? n root cause analysis of a failure is needed n Why? - (outcomes) n A better understanding of the root causes of a failure (Step 3: Root cause) n A better set of action plans to eliminate those root causes (Step 4: Solution) CONFIRM RESULTS THEME STANDARDIZE DATA ROOT CAUSE SOLUTIONREFLECT No Yes

Slide 3 May 8th, 2007Compliance EngineeringUltratech Internal Use Only Fault Tree Analysis… n 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. n 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.

Slide 4 May 8th, 2007Compliance EngineeringUltratech Internal Use Only FTA Example: Smoke Detector n 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. CONFIRM RESULTS THEME STANDARDIZE ROOT CAUSE SOLUTIONREFLECT No Yes DATA

Slide 5 May 8th, 2007Compliance EngineeringUltratech Internal Use Only FBD Example: Smoke Detector Inputs Presence of smoke Process Detection of smoke Outputs Alarm signaling Smoke enters through vent Battery powers control box, indicator light, and smoke detector Smoke is ionized and causes increase in voltage Signal sent from smoke detector triggers control box circuit Signal/power to siren turns motor Smoke enters ionization chamber Control Box sends signal/power to siren Motor causes siren to sound Alarm signals

Slide 6 May 8th, 2007Compliance EngineeringUltratech Internal Use Only FAILURE Smoke Detector does not detect smoke Smoke not present in chamber Vent is blocked Dust blockage Ionization chamber blocked Dust blockage Paint blockage Smoke not detected Defective Control box No power at control box Defective ionization chamber Ionization chamber cracked Broken wire Defective solder joint Alarm not sounding Defective alarm No power at alarm Broken wire Defective solder joint No power at ionization chamber CONFIRM RESULTS THEME STANDARDIZE ROOT CAUSE SOLUTIONREFLECT No Yes DATA Sample solution ( incomplete )

Slide 7 May 8th, 2007Compliance EngineeringUltratech Internal Use Only Typical use for an FTA: n 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. n Began brainstorming and building a functional block diagram to fully understand how the smoke detector functions. n Continued brainstorming on possible causes for the smoke detector failure resulting in the alarm not signaling. n Probable causes were identified: n The team constructed the FTA around the three major categories in the functional block diagram, inputs, process, and outputs. n The team continued to build the FTA and completed it by adding lower levels of detail under appropriate causes of failure. n 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. n The leading causes of failure and solutions were identified. n A design project was started to correct the problem.

Slide 8 May 8th, 2007Compliance EngineeringUltratech Internal Use Only Fault Tree n Symbols Review n Square Describes the top and lower level failures n Or GateProduces output (failure) if one or more inputs exist n And GateProduces output (failure) if and only if all inputs exist n Circle Potential root failure which cannot be broken down into lesser failures n DiamondPotential failure which is not analyzed for various reasons

Slide 9 May 8th, 2007Compliance EngineeringUltratech Internal Use Only How to build a Fault Tree 1) Identify a top failure 2) Brainstorm basic contributors to failure 3) Link contributors to the top failure n 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? ) n Link the contributors to the top failure with the correct gate. (And/Or) Ask: Can we determine contributors for this lower failure ? n Yes - repeat cycle making each contributor a top failure, assign gates, etc... n No - we are finished - We may also end our fault tree when we reach all indeterminable, basics, or causes which require further research etc...

Slide 10 May 8th, 2007Compliance EngineeringUltratech Internal Use Only Understanding the symbols (Gates Review) And gate means For this upper failure to occur All of these failures must occur Or gate means that For this upper failure to occur Only one of these failures must occur Failure

Slide 11 May 8th, 2007Compliance EngineeringUltratech Internal Use Only Step 1 Identify Top Level Fault Step 2 Brainstorm first level contributors Step 3 Link contributors to top by logic gates Step 4 Brainstorm second level contributors basic event cannot be broken down any further event that is not analyzed for various reasons Step 5 Link contributors to upper level by logic gates Step 6 Repeat / continue for each lower level failure (This page is taken from SVERDROP MANUAL - FTA and Risk Management by P.L. Clemens, 1992/1993, pg. 10 )

Slide 12 May 8th, 2007Compliance EngineeringUltratech Internal Use Only FTA Do’s & Don'ts n Do’s n Start at the Top n Think Categories n Brainstorm, then organize n Facilitate proper brainstorming n Know when to stop n Have action plans for all circles n Check that branches terminate with a circle or diamond n Revisit the FBD or FTA when new data is found n Use yellow stickies to capture the brainstormed causes n Don'ts n Don’t get bogged down n Don’t jump to solutions!