Fault Tree Analysis

[MohammadB84]

Hi,

I was wondering if anyone could help me out with a FT analysis that I am currently conducting.
My question is that in the tree if I have the basic events Failure Rates(#failure/10^6 hrs) instead of the Failure probability and that is the only information I have from my component(basic event) how does the calculations work out? How can I calculate the Failure Rate of the Top event? I have check many text books about FTAs and they all talk about probability calculations, I completely understand the calculations behind the FTA when you have probabilities but the story is different if you have FRs.
I am not sure how the results of the AND gates work out. with OR gates it is easy, a good estimate of the next level event is just the addition of FRs from basic events but for AND gate I am not sure what I need to do.

Is there any suggestions, my fault trees are not complicated at all and I don't have access to any software to do the calculations for me so I am just using Excel.

Any help is greatly appreciated

Mohammad

 

[tbuelna]

MohammadB84,

MIL-STD-1629 is obsolete, but it does give a good process for performing a FMEA/CIL analysis.

A FMEA analysis is different from a statistical reliability calculation. I'm by no means an expert, but basically a FMEA analysis is mostly concerned about whether a particular system failure mode is credible or not, what is the criticality of that failure mode, and how does the design provide the necessary level of fault tolerance to ensure safe operation of that particular system in the event of said failure mode.

Go here and search for MIL-STD-1629, to download a free copy:

http://www.assistdocs.com/search/search_basic.cfm

Good luck,
Terry

 

[HamishMcTavish]

Hi MohammadB84,

Look at reliability textbooks to see how failure rates and probability of failure on demand are linked.

You could also check out the following

http://www.openfta.com/

which is an open source Fault Tree program which you can download and use for free within the terms of the licence agreement.

Regards, HM

No more things should be presumed to exist than are absolutely necessary - William of Occam