Hello,

Currently I am trying to make a PFMEA Guidelines for our company (automotive microelectronics).
Here is my suggestion about how to give priorities of the corrective actions:

Recommended actions

Prioritize recommended/ corrective actions in the following order:

A. Actions are mandatory for ALL Failure modes resulting in a Severity of 9 or 10
B. By the “Seriousness” = Severity x Occurrence
High Severity values, coupled with high Occurrence values merit special attention (require Recommended actions). Actions are recommended for any Severity of 5 or higher with an Occurrence of 4 or higher
C. Actions recommended for any failure modes resulting in a high RPN regardless of Severity X Occurrence combination (Use Pareto technique to prioritize the highest RPNs).
Apply Pareto principle 30/70 which means:
30% of causes produce 70% of the troubles.

You should work towards RPN reductions until RPN became to be lower than 32. If RPN < 32, and A and B cases are not valid, then Corrective actions are not required anymore.

So, my question is regarding this RPN limit (<32) from which applying corrective actions is not feasible anymore.

How this number was obtained:
8x2x2 = 32 => Severity 8 combined with Occurrence 2 and Detection 2 I consider to be no more danger. The other variant is 8x1x2 = 16.

What is your opinion? What is the practice in your companies? Although PFMEA is continual improvement process it is not feasible to try to reduce the RPNs at any cost. We should stop at certain point.

Thank you,
:)

Brutas,

Keep it simple.

For sure,maintain "A" & "B".

"B" is also known as "criticality" in the auto industry.

If criticality >/= 18 , a mandatory redesign (or plans for) is needed.

Since "A" feeds "B",you can pareto within this group.

Other than that, simply state that you need to work on the top 5 RPNs
at any given time.

As one is resolved, another one is moved up onto the list. This supports the "continuous improvement process".

Brutas,

If criticality >/= 18 , a mandatory redesign (or plans for) is needed.
Why 18?

Brutas,
As one is resolved, another one is moved up onto the list. This supports the "continuous improvement process".
I agree but we need a point/ level at which to stop improving because it wouldn't be feasible.

18 = Sev 9 X Occ 2.
NHTSA is operating on a safety defect rate of 1/800,000 over the product life for new products (to begin inquiries that could potentially lead to recalls). This figure was obtained several years ago when I called their Chicago office. It was reinforced when I visited them in Washington to promote Electronic stability control with a group from Bosch.



Daimler Chrysler , Ford and GM have provided the Top 5 argument.
If you think about it, the FMEA is meant to be a dynamic document.
eg, continually upgraded.


ps I have a tool that might be helpful to you if you have some basic background in Reliability.

It provides a means to add a cost to the issue (so that you have half of the cost benefit done).

If you want a copy of it e-mail me at michael[DOT]walmsley[DOT]b[AT]bayer[DOT]com.

Thank you very much Michael,
but I need a limit. This is what our management wants and what some of the Customer require.
I know that this is a living document and continual improvement philosophy should be in place but I also know that many of the companies use such limit (arround 50~60).

You will agree with me thah RPN < 16 is not needed to be decrease (or < 32).

I just want to know your practice and your arguments but I need a limit :)

Thank you.
:rolleyes:

36 = Sev X Occ X Det = 6 X 3 X 2.


In the auto industry, safety issues / concerns initiate with severity level >/= 7.

Occ level of 4 is associated with a Ppk process of 1.33.


I would use the 36 level from my perspective as a cutoff point.

Thank you Michael.
It will be interesting to see other opinions also...

Hello Brutas

A different approach in setting priorities:cool:

Prepare a second FMEA document and align the failure modes with the cost of occurance instead of the severity. The failure mode may not injure or cause annoyance to the customer/user, but if it occurs once, the cost of correction may be significant. Both internal and external costs should be used.

This new FMEA will give you more benefit to your business by prioritizing the higher failure costs. The decision to "fix or monitor" can be made more clearly, especially if the return on investment is low.

Why have mandatory action for severity 9 or 10? If OCC is 1 and DET is 1 it is likely that you cannot reduce risk further.

Do not work to thresholds (max rpn) as engineers whom are good at math will modify the numbers to reach the threshold. Instead work on reducing the high risk numbers that can be reduced with given available resources.

Do not work to thresholds (max rpn) as engineers whom are good at math will modify the numbers to reach the threshold. Instead work on reducing the high risk numbers that can be reduced with given available resources.

I agree with you but this process is not endless. The reducing of the RPNs should stop at certain level.

Why have mandatory action for severity 9 or 10? If OCC is 1 and DET is 1 it is likely that you cannot reduce risk further.

Do not work to thresholds (max rpn) as engineers whom are good at math will modify the numbers to reach the threshold. Instead work on reducing the high risk numbers that can be reduced with given available resources.

Why have mandatory action for 9 or 10?
Because it is required in the auto industry regardless of the Occ or Det level.
Reason : Historical product safety recalls , product liability lawsuits and NTHSA levels for investigation kickoff.

In the Pharma where I work now , we elected to maintain that logic.

NOTE that mandatory does not mean immediate action. IT IS subject to resource availability. The actions must be on your planning horizon.

Outside of these required issues,What Brutas is looking for is when can he feasibly stop.

For continous improvement the risk reduction process should never end but for financial reason it may no longer make sense to reduce RPN further.

Why have mandatory action for 9 or 10?
Because it is required in the auto industry regardless of the Occ or Det level.
Reason : Historical product safety recalls , product liability lawsuits and NTHSA levels for investigation kickoff.

In the Pharma where I work now , we elected to maintain that logic.

NOTE that mandatory does not mean immediate action. IT IS subject to resource availability. The actions must be on your planning horizon.

Outside of these required issues,What Brutas is looking for is when can he feasibly stop.

What action can you take reduce risk further in the case where severity is 10 and Occ and Det is 1?

As an example if a seatbelt breaks you have a sever effect. How can you reduce this RPN further? Sev 10 Occ 1, Det 1.

Redesign the mode out.

Redesign the mode out.

I was expecting that answer. Another answer I've heard was to stop making seat belts and start making cup holders.

For any items in which the sole function is safety related you have to remove the functional requirement for the item in order to reduce the severity or perhaps add redundancy.

And another would be to consider implementing auxiliary systems such as air bags in conjunction with the safety belts.

I have not personally noted a seat belt system with S=10 , O=D=1.

More in the line of S=9 , O=2 and D=1.
The seat belt alarm/buzzer accounts for the reduction in severity.

The controllers they are putting into the vehicles today monitor the status of many critical systems in an effort to enhance safety and reduce OEM liability.

If someone does not wish to use the belt,it is duly recorded. The FMEA then
conveys that it is not controllable at your level. You can pursue no further action. It should be mentioned in your FMEA as such.

Another would be to consider the level at which the belts were qualified to w/r to vehicle impacts.

If the impact was outside of the range qualified against (exceeds), there is nothing you can do. Again,it should be mentioned in your FMEA as such.

What action can you take reduce risk further in the case where severity is 10 and Occ and Det is 1?

As an example if a seatbelt breaks you have a sever effect. How can you reduce this RPN further? Sev 10 Occ 1, Det 1.


I don't recall a requirement that further action must be taken. Perhaps I'm wrong (gosh, as an auditor I would hate to have THAT happen!), but I believe the requirement is that further action be considered.

It might well be, in this example, there is no further action possible.

Also, a seatbelt breaking would be a product failure, and belongs on the DFMEA. It is not a process failure and would not likely be on the PFMEA. Unless of course the failure mode is that the process damaged or cut the seatbelt, which could have the impact that it would break.

See the attached. I also conducted a stint as an ISO/QS/TS auditor.

As you may recall all shoulds are now shalls which mean mandatory.

The customer specific requirements (not mentioned by the original poster) would also have an impact and further enhance on the content of the guideline.

See the attached. I also conducted a stint as an ISO/QS/TS auditor.

As you may recall all shoulds are now shalls which mean mandatory.

The customer specific requirements (not mentioned by the original poster) would also have an impact and further enhance on the content of the guideline.


Thanks for the scan, I was recalling the same text, pretty much. But, to the original OP, when they have done all they can, there is nothing else one can require of them. If there is a seatbelt, the risk remains. But, at an RPN of 10-20, they have done all they can do.

Thank you all for your posts.
Attached is what I finally decided to include in my PFMEA Guidelines.

:)

Very good discussions here!
Per my experence, if you require mandatory actions for S>=9, after several updating, you will find that no more actions you can put there unless there is some new technologies because what your guys know have been put in "Current control" already.:biglaugh: