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<C. Robert Nelms>

Hi Bill,

I thought I'd let you know that the "Why Tree" is a phrase coined and trademarked by Failsafe in 1985 in a specific attempt to distinguish it from the "Fault-Tree."

In 1985, Failsafe was doing a lot of work in northern Alberta, Canada and was using the phrase "Fault Tree" to describe the RCA team's diagram of the causal logic of a failure.  Several trainees correctly observed that Fault Trees are probabilitic in nature, are most-often used before a failure, and attempt to explain all possible causes of the "top event."  Although Failsafe was suggesting much of the same structure as the Fault Tree, there were enough differences that another phrase was needed.

The main differences between Fault Trees and Why Trees, by definition,  are:

1.  Why Trees are constructed AFTER the fact.
2.  Why Trees are NOT probabilistic.
3.  Why Trees have two symbols, the AND and OR.
4.  There are 2 types of WHY TREEs:  the EXPLORATORY and the EXPLANATORY.
5.  The phrase WHY TREE was suggested by the client in Northern Alberta in a specific attempt to get away from the phrase "FAULT."  (sounded like we were looking to blame someone).

There is a lot of history behind the WHY Tree, more than I have time to write.  Just as others have coined phrases to describe their own way of diagramming the causes of an incident (RCI's Logic Diagrams, Corcoran's Why Staircase, etc.) Failsafe has coined the phrase Why Tree to mean something specific.

Thanks for giving me the chance to comment, Bill.

Best wishes.

C. Robert Nelms

[ 2005.08.12 08:07 America/New_York ] [ E-mail ] [ WWW ]

<Bill>

Bob: Thanks for the info. I appreciate you pointing this out to me. I have revised the terminology I use in the article to make it more generic.

Anyone else that's interested: I highly recommend Bob's website to you for further information on Why Trees, and other root cause goodies. He can be found at Failsafe Network.

[ 2005.08.12 14:01 America/New_York ] [ E-mail ] [ WWW ]

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