Severity Reduction in a Design FMEA (DFMEA)

[Matt_B]

I am having a disagreement with the person who is training me to teach FMEA classes. I wrote a blog post in which I used an example FMEA that had a severity of 10. The actions taken involved a design change that eliminated the potential failure effect so I made a new estimate for the severity.

My trainer told me that I was wrong to do this. He said that in the revised metrics section of the FMEA I should have kept the severity at 10 and re-estimated the occurrence and detection based upon the improvements. This particular failure can?t occur due to the listed failure mode so I believe a new severity is appropriate.

We are in agreement that the new design should also be evaluated as a new point in the FMEA; however, I am convinced that the severity can be reduced with a proper design change. The AIAG manual concurs; however, my trainer believes that this new severity is used in a new line and not as part of the revised metrics.

I disagree with my trainer, but have agreed to teach things his way until such time as I can provide concrete evidence that I am correct.
Can anybody please provide that evidence? Or, explain to me why I am wrong.

Thanks!

 

[somashekar]

Re: Severity reduction in a design FMEA

Is the design change something like making the 10000 V shock to say 1000 v shock in the unlikely chance of a shock delivery ...
Change the severity rating.
Is the design change something like making the probability of the 10000 V shock delivery much more unlikely ...
No change in the severity rating as still a 10000 V shock can be delivered.

 

[Matt_B]

Re: Severity reduction in a design FMEA

My change is like making the 10000v shock only 1000v. In the example, I had systems connected in such a way that damage to an external area was transferred directly to a critical system that led to a catastrophic loss of the entire unit. The design change was to remove the interlinks so surface damage is not directly transmitted inside of the unit.
Unfortunately, I need evidence that I can present to my trainer.

 

[somashekar]

Re: Severity reduction in a design FMEA

You are doing stuff only on the occurrence. However if in any case, it is still directly transmitted inside to the critical system., the catastrophic loss of the entire unit still exists. The severity exists .... Right ?

 

[Matt_B]

Re: Severity reduction in a design FMEA

In the example, the catastrophic loss was no longer possible; hence, the severity reduction.
Regardless of my example, I say a severity reduction is possible with a design change and the new severity can be listed with the new RPZ on the right side of the FMEA form. I just can?t find any evidence to prove this.

 

[Matt_B]

Re: Severity reduction in a design FMEA

Here is the blog post that started the disagreement:

https://blog.minitab.com/blog/statistics-in-the-field/for-want-of-an-fmea-the-empire-fell

 

[somashekar]

Re: Severity reduction in a design FMEA

In the example, the catastrophic loss was no longer possible; hence, the severity reduction.
Regardless of my example, I say a severity reduction is possible with a design change and the new severity can be listed with the new RPZ on the right side of the FMEA form. I just can?t find any evidence to prove this.

In the example, if you can say the catastrophic loss is now a minor loss, and such a catastrophic loss will no longer manifest, then your design had addressed the severity and you are good to reduce it...

 

[Matt_B]

Re: Severity reduction in a design FMEA

In the example, if you can say the catastrophic loss is now a minor loss, and such a catastrophic loss will no longer manifest, then your design had addressed the severity and you are good to reduce it...

I know; but my trainer and I agreed that I will do things his way until I can provide evidence or an example from a standard to prove that I was right.
He insists that the severity remain the same regardless of actions and the severity is only lowered by a new entry in the FMEA. He said the severity in the revaluation of the RPZ after corrective actions must remain the same.

 

[adamsjm]

Re: Severity reduction in a design FMEA

What Design Requirement change was made to eliminate the Failure Mode (anti-function)?
Reduction of Occurrence to a 1 (Failure Eliminated) and/or a Detection of 1 (Error [Cause] prevention as a result of part design.) will NOT reduce severity, only a Design Requirement elimination will.

 

[somashekar]

Re: Severity reduction in a design FMEA

Your design solution can be mitigating the severity or occurrence. So depending on the solution you are good to change whichever without a new entry in the dFMEA.