SRC Forum - Message Replies
Forum: Reliability & Maintainability Questions and Answers
Topic: Reliability & Maintainability Questions and Answers
Topic Posted by: Reliability & Maintainability Forum
Organization: System Reliability Center
Date Posted: Mon Aug 31 12:47:36 US/Eastern 1998
Posted by: SP
Date posted: Mon Apr 19 9:13:57 US/Eastern 2004
I am undetaking a FMECA and am trying to determine as to whether or not the criticality analysis (Severity of failure v. Probability of failure matrix)takes into account equipment that has redundancy or does it look at the failure of the item as a stand alone item and does not take into account the item having redundancy?
I hope this makes sense!
Thanks for any advice.
Reply Posted by: Jean-Marie Cloarec
Date Posted: Mon Apr 19 21:07:03 US/Eastern 2004
If you take a look to MIL STD 1629, BluePrint, you will see that severity levels are generic (deals mostly with safety). But you can tailor the severity class. For example, in a study I made, I take 2 severity indicators:
- first which represent the "raw" severity without detection/mitigation/redundancy/...
- second which represent the "corrected" severity taking into account detectio/mitigation/redundancy/...
This allows me to show the efficiency of the detection/mitigation/redundancy/...
The problem in doing this is that you must defined your own criticality matrix that will be different from the standard.
In fact, you can do what you want, but you have to defined your proper rules
Reply Posted by: Satish Subramanian
Organization: Proton Energy Systems
Date Posted: Tue Apr 20 8:28:25 US/Eastern 2004
After finishing the FMECA do a FMES(Failure Mode Effects Summary). Please refer to APR4761 for guidance.
This should help as I have been through this before.
Reply Posted by: A. Rowland
Date Posted: Wed Apr 28 17:24:28 US/Eastern 2004
By definition, the FMEA considers single item failures as the only failure in the system. Thus, if the system under consideration employees redundancy, this redundancy should be captured in a less severe end-effect. Given this, it follows that the severity term in the criticality analysis would be reduced accordingly.