9 ssgb amity bsi faul tree

Module-9

Fault Tree Analysis (FTA)

At the end of this section delegates will be able to:

• Understand the role of Fault Tree Analysis within

the DMAIC Improvement Process

• Construct a Fault Tree from “Top Event” down to

actionable “Basic Events”

• Identify appropriate actions to “close” a branch of

the tree

• Recognise that Fault Tree can be used both as a

prevention tool and a diagnostic tool

Fault Tree Analysis Learning Objectives

1. Fault Tree Analysis Within DMAIC

2. Fault Tree Analysis Roadmap:

• Define Top Event

• Define scope of system

• Understand system

• Construct Fault Tree

• Analyse the Tree

• Closing Actions

3. Workshop

4. Summary

Fault Tree Analysis – Agenda

15 20 25 30 35

LSL USL

� Define Measures (y’s)

� Check Data Integrity

� Determine Process Stability

� Determine Process Capability

� Set Targets for Measures

Phase Review

� Control Critical x’s

� Monitor y’s

� Validate Control Plan

� Identify further opportunities

� Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

y

Phase Review

� Develop Detailed Process Maps

� Identify Critical Process Steps (x’s) by looking for:

– Process Bottlenecks

– Rework / Repetition

– Non-value Added Steps

– Sources of Error / Mistake

� Map the Ideal Process

� Identify gaps between current and ideal

START

PROCESSSTEPS

DECISION

STOP

Phase Review

� Brainstorm Potential Improvement Strategies

� Select Improvement Strategy

� Plan and Implement Pilot

� Verify Improvement

� Implement Countermeasures

Criteria A B C D

Time + s - +

Cost + - + s

Service - + - +

Etc s s - +

15 20 25 30 35

LSL USL

Phase Review

Analyse Improve ControlMeasureDefine� Select Project

� Define Project

Objective

� Form the Team

� Map the Process

� Identify Customer Requirements

� Identify Priorities

� Update Project File

Phase Review

Define

Six Sigma Transactional Improvement Process

• Fault Tree Analysis (FTA) is a graphical tool for analysing

possible causes of a failure.

• Can be used as a Prevention Tool - Prevent the failure

mode from occurring.

• Or can be used as a Diagnostic Tool - Identify what caused

the failure

• Focuses on a single failure mode (as opposed to FMEA

that looks at all failures)

• In Six Sigma it can be used to help identify the Critical

Inputs or Process Steps (x’s) (Analyse), and develop

improvements and controls for the Critical Inputs or

Process Steps (x’s) (Improve/Control)

Introduction to Fault Tree Analysis

Step 2:

Define Scope of System

Step 3:

Understand System.

Step 1:

Define Top Event.

Step 4:

Construct Fault Tree

Step 5:

Analyse the Tree

Step 6:

Closing Action.

Fault Tree Analysis Roadmap

• The ‘Top Event’ is the major failure to be analysed in

the fault tree.

• Within Six Sigma DMAIC this typically will be the

issue(s) identified in the Measure Phase e.g. Delay in

invoice payment, Incomplete order shipment etc.

• When identifying, consider main functions of

processes, major “customer” effects, historical

failures…

• A separate fault tree should be generated for each Top

Event that is a fundamental concern.

Step 1 – Define Top Event

Step 2 – Define Scope of System

What comprises the ‘system’ (transactional

process) to be analysed:

• Which parts/process steps will be considered ?

• Which parts/process steps will be outside the

scope (responsibility of supplier or third party)?

• What level of detail ?

(macro/micro process steps)

• ‘System’ can consist of manual steps and / or

automated steps (e.g. IT system).

Step 3 – Understand the System

• The relevant experts (IT, Process “Operators” etc.) explain the function of each part/process step to the team.

• Supported by:

• Process Maps

• Specification Documents

• “Walking the process”

• Customer Feedback data

Dark

Room

Bulb Blown

Switch Failed

To Close

No PowerFuse Blown

Power Cut

AND OR

AND Gate OR Gate

OR OR

ANDBattery failureLoss of

Power

Step 4 – Construct Fault Tree

Top Event Intermediate Events

Basic

EventClosing

Action

Specification

Supplier

Quality

Process

OR OR OR

AND



Basic Events

Events leading to (causing) top event. Sequenced from high level to lower level (“Macro” process step to “micro” step).

Lowest level events within scope of FTA. Actionable level of detail. Three types of basic events should be considered (although not all may be present).

Main failure to be investigated Top Event

Intermediate

Events

Basic Event Types

Event relates to inadequate or

incorrect processing, e.g.

information entered incorrectly.

Specification

Related

Supplier Quality

Related

Process Related

Event relates to incorrect

specification e.g. information

not specified as required

Event relates to supplier not

meeting specification, e.g.

incorrect information provided.


Top Event

Incorrect

labeling of

product

Wrong label

fixed to

product

No label

Wrong label

printed

Basic Events Closing

Actions

Intermediate

Events

Incorrect part

number entered

Error in

database

Information on

label incorrect

OROR OR

Labels mixed

up on line

Stock of Labels

held

on line

Multiple Product

Types on

Production Line

AND

FTA Example: Labelling Example

Pricing

information

incorrect

Top Event

Delay in

Invoice

payment

Missing/

Incorrect

Information

Bankruptcy

Missing order

number

Basic Events Closing

Actions

Intermediate

Events

Lack of

authorisation

Not supplied

by Sales

Sent to wrong

person/place

OROR OR

FTA Example: Invoicing Example

Method 1

• Brainstorm all possible events (causes) that might lead to Top Event.

• Transfer to Post-Its or cards.

• Sort into groups of events for related parts.

• Organise into a tree structure with Top Event on left side, branching

to the Basic Events on the right.

Method 2

• Starting from the top event and ask the question “how could this

happen ?”

• Work on each branch in turn, repeating the question “how could

this happen?”

In practice a combination of both methods can be used.


Step 5 – Analyse Tree

Check:

• All known (historical) failures shown.

• Sequence of events from left to right.

• All branches have been developed to an

actionable level.

• Optional step :

• Prioritize the basic events in terms of their

probability of occurrence. (ref. FMEA

Occurrence Rating).

• ALL Basic Events should have a closing action.

• ‘Level / depth’ of action dependent upon the level of concern (occurrence).

• Three areas of focus:

• Specification Validation– to ensure that the transactional process has been correctly specified

• Supplier Quality- to ensure that any process inputs are correct

• Process Control – to ensure that the transactional process is operated correctly

• Action not closed (signed off) until completed.

Step 6 – Closing Action

Typical closing actions include:

• Standard Operating Procedures, SOP’s

• Operator Training

• Mistake Proofing

• Statistical Process Control, SPC

• Control Plan

Step 6 – Closing Action

Step 2:

Define Scope of System

Step 3:

Understand System.

Step 1:

Define Top Event.

Step 4:

Construct Fault Tree

Step 5:

Analyse the Tree

Step 6:

Closing Action.

Fault Tree Analysis Roadmap

15 20 25 30 35

LSL USL

� Define Measures (y’s)

� Check Data Integrity

� Determine Process Stability

� Determine Process Capability

� Set Targets for Measures

Phase Review

� Control Critical x’s

� Monitor y’s

� Validate Control Plan

� Identify further opportunities

� Close Project

1 5 10 15 20

10.2

10.0

9.8

9.6

Upper Control Limit

Lower Control Limit

y

Phase Review

� Develop Detailed Process Maps

� Identify Critical Process Steps (x’s) by looking for:

– Process Bottlenecks

– Rework / Repetition

– Non-value Added Steps

– Sources of Error / Mistake

� Map the Ideal Process

� Identify gaps between current and ideal

START

PROCESSSTEPS

DECISION

STOP

Phase Review

� Brainstorm Potential Improvement Strategies

� Select Improvement Strategy

� Plan and Implement Pilot

� Verify Improvement

� Implement Countermeasures

Criteria A B C D

Time + s - +

Cost + - + s

Service - + - +

Etc s s - +

15 20 25 30 35

LSL USL

Phase Review

Analyse Improve ControlMeasureDefine� Select Project

� Define Project

Objective

� Form the Team

� Map the Process

� Identify Customer Requirements

� Identify Priorities

� Update Project File

Phase Review

Define

Six Sigma Transactional Improvement Process

• Analyse - Fault Tree can be used to identify possible Critical

Inputs or Process Steps (x’s) that are causing the poor

performance in Process Outputs (y’s)

• Improve - Fault Tree can be used to help identify how the Critical

Inputs or Process Steps (x’s) might be changed / eliminated /

controlled to improve the Process Output (y)

• Control - Fault Tree can be used to identify appropriate controls

for the Critical Inputs or Process Steps (x’s)

• Control - Fault Tree can be used as a diagnostic tool to identify

corrective action when a failure occurs

Summary Fault Tree Analysis

Workshop Time:

Develop a Fault Tree Analysis for the given “Top Event” and Transactional Process scope:

1. Understand the “System” (for a transactional process application, develop/review the process flow).

2. Brainstorm “How could top event happen?”. Put each idea onto a post-it as it is generated.

3. Organise the post-its into the tree structure, starting with the top event on the left, working towards the root causes (basic events) on the right.

4. Analyse the tree to check that the branches are logical and identify any missing causes.

5. Identify closing actions for the five most likely causes (use the FMEA Occurrence rating if required).

6. Prepare a short presentation on your team's findings.

Workshop – Construct a Fault Tree Analysis