Home �   ITIL�  Index

Fault Tree Analysis in 6 Steps

Dec 21, 2006

Hank Marquis


5. Continue identifying causes for each fault until you reach a root cause (reactive FTA), or one that you can do something about (proactive FTA). For example, the root cause of “power supply failure” might be “filter clogged;" the root cause of “battery backup exhausted” might be “battery backup too small."

6. Consider countermeasures. A root cause is one you can do something about; so now you need to think of the countermeasures you might apply to each root cause. List countermeasures for each root cause in a box under the root cause. For example, for “filter clogged” a countermeasure might be “clean filter monthly.” Link the countermeasure to the root cause by drawing a line.

FTA is useful alone on paper and as a group exercise on a media board. When your diagram is complete, you have a fault tree. Fault trees show how an event can occur and what you can about it from a design or change perspective. For Problems, you also have a possible root cause and a solution.

FTA is actually pretty simple, but don’t let its simplicity fool you. If you want to get fancy, you can play with probability statistics to try and get even more precise – determining the “chance” that a fault or cause could occur. Applying probabilities derived from CI metrics like mean time to repair and mean time between can produce some very precise calculations.

Even if you don’t get fancy with FTA you will have taken a powerful step toward preventing problems in the first place, or resolving tough problems. Often just the act of creating a fault tree as a group generates excellent ideas and possible solutions where before there were none.

FTA can be used by technical observation post (TOP) teams, problem managers, availability manager, and even IT service continuity management teams with a minimum of training. The graphical nature of FTA makes it easy to understand and easy to maintain in the face of changes.

Hank Marquis is a managing partner and CTO at itSM Solutions . You can contact Hank at hank.marquis@itsmsolutions.com.