Severity, Occurance and Detection ratings seem qualitative

P

Pazuzu - 2009

#11
Ok, obviously something as been taken the wrong way.

Never did I mention that the RPN# is the bible and that there should be a hard and fast point at which something should or should not be evaluated. Yes it is relative, yes there are other parameters to review before making a decision (as there always should be). What I did mention is that both the RPN and the individual numbers (S/O/D) should be reviewed. If the RPN is higher than acceptable look at the individuals to see where the culprit is. If the RPN is low, review the individuals as well just in case there is one errantly high number. The question is...what number is acceptable in terms of both RPN and individual? That is something that should be decided from the get go.
 
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#12
Never did I mention that the RPN# is the bible and that there should be a hard and fast point at which something should or should not be evaluated.
Well, you said,
The important thing to remember is to set a standard for re-evaluation of the process. Not being from the auto industry I'm not 100% positive but I think the generally accepted RPN number is 100.
Yes it is relative, yes there are other parameters to review before making a decision (as there always should be). What I did mention is that both the RPN and the individual numbers (S/O/D) should be reviewed. If the RPN is higher than acceptable look at the individuals to see where the culprit is. If the RPN is low, review the individuals as well just in case there is one errantly high number.
Sorry, Pazuzu, but what you're saying is that the S-O-D numbers should be evaluated regardless of their RPN product, which is absolutely correct, but also absolutely contradicts your threshold premise.

The question is...what number is acceptable in terms of both RPN and individual? That is something that should be decided from the get go.
No, it's not. The purpose of performing the analysis is to discover and evaluate potential sources of risk, so the purpose is at least partially defeated if you make up your mind "from the get go" that any RPN with a value greater than x requires special action.
 
P

Pazuzu - 2009

#13
I never said that 100 is THE threshold. I never said that any number in paricular is THE threshold. In fact, I never even said there should be a "threshold" until you mentioned it. What I did say is that I have been told by a few people from inside the auto industry that 100 is generally used. Whether or not this is the same parameter for other industries I have no idea. I also stated that the SOD numbers are equally assessed and that 7 is generally used by those same individuals.

Use whatever numbers you want...dont use whatever numbers you want...just do whatever works best for your application.

Sorry if my initial choice of words were interpreted wrong...that's the difficulty with forums.
 
#14
Just to pass along another twist on the FMEA philosophy, I was trained in an earlier life to a "FEMCA" philosophy (the Shanin Risk ReduXtion philosophy) and "D-FEMCA" for design projects. When you approach an FMEA with this different spin, you are looking first at the "Effects" then the "Modes" and potential "Causes" as opposed to the "Modes" then "Effects". In other words, you look at the "Y" (effect) before you look for the "X" (root cause).

Using this approach, you still use the Severity, Occurrence and Detection numbers; however, setting "Bogeys" (as they were called to us) by setting an arbitrary RPN threshold was frowned upon. Instead, the approach was to rank the failures and systematically analyze them from worst to least.

The other "key" to not setting bogeys was so you didn't "stop" analyzing the data when you reached that magic threshold. The plan was to set a reasonable length of time within the project framework and then knock down the potential failure effects one by one until you run out of time. Of course, a lot of thought needs to go into this approach as well since you don't want to give yourself a month to fix a year's worth of problems - but it's merely a different perspective on a time honored risk analysis tool.

Just my :2cents: ... :bigwave:
-Steve
 
T

tac123

#15
Agreed that it should be taken as reference because of the possible situations you mentioned...but is there not typically a limit as which point it should be evaluated? The threshold I'm referring to is a generic number...not an absolute. Understood that sometimes things cannot be done...and understood that sometimes you can improve it when it "seems" there is no need to...but if there is no threshold then what's the point of putting a numbering system against it?
Stay away from Thresholds or else all of a sudden you will find all the RPNs will magically come out below this threshold. Instead work on top 5, 10 or 20 items until you feel all risk is at an acceptable level or keep doing the continuous improvment thing.

Engineers are great at selecting three numbers that will come in below your threshold. Whoever first came up with the idea of a threshold on a subjective ranking scheme should be locked away.
 
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