Fault Tree Analysis

Applied to a tiny― Computer Startup ―

(2-3 people)

Introduction

• Fault Tree Analysis

– “Tree”: A hierarchical structure ... – “Faults”: ... depicting all potential faults ...– “Analyse”: ... which we can use to analyse risks.

Example(taken from IEC/FDIS 31010, p. 49)

TerminologyTop event“a specified undesired event”

Base event“...until further analysis becomes unproductive.In a hardware system, this may be at the component failure level.”

Chalkboard

Please pay attention and participate in the live example on the chalkboard.

Thank you!

Top event: server failureHuman errorsSoftware errorsHardware/Structural errors

Usage

• Qualitative vs Quantitativebacktracking failure vs calculating probabilities

• Design Stage // Operating Phase // Posthumous

before implementing the system //while the system is running //

in order to understand past failures

Application to Startup

Quantitative insights not terribly interesting...

Good way to assess Qualitative insights

– logically find vulnerabilities / weak spots(“disciplined approach, highly systematic”)

– Understand general system behaviour– Allow for all kinds of factors (system, human, ...)

Application to Startup

Can use in design phase, during runtime and in order to understand past issues.

Most ‘limitations’ are related to quantitative probability analysis

Application to Startup

Not a perfect method:Boolean model: possible to consider e.g. ‘low

performance’ instead of plain failure?

“Fault Tree is a static model; time interdependencies are not addressed.”

No built-in continuously recurring self-checks: danger of false sense of security(will this be reconsidered after system changes?)

Conclusion

Risk identification – goodRisk analysis – very goodRisk evaluation – satisfactory

Feasible method in terms of skills & time

Combine / complement with other methods?(e.g. Make part of PDCA cycle, recheck regularly ...)

For other domains: nice additional feature, but not to use alone