Emphasizing Severity more than Occurrence and Detection vs. Overall RPN

S

someshvar

#11
Jim,

To an extent, I would agree with you.The example you just gave of an Automobile Airbag will have same severity rating for risk of injury in pre an post airbag scenario, isn't it?

Moreover when we talk of DFMEA, we might give example you just gave even though I totally don't agree with you.

But what in case of a process FMEA?
__________________

Hardik
 
Elsmar Forum Sponsor

Jim Wynne

Staff member
Admin
#12
Jim,

To an extent, I would agree with you.The example you just gave of an Automobile Airbag will have same severity rating for risk of injury in pre an post airbag scenario, isn't it?
It depends on how the potential failure mode is defined. If it's defined as "serious injury due to violent contact with the steering apparatus," then introduction of the airbag will lessen the severity, no?

Moreover when we talk of DFMEA, we might give example you just gave even though I totally don't agree with you.

But what in case of a process FMEA?
Again, it depends on how failure modes are characterized. If you're talking about failures in the process, as opposed to manifestations of process failures in the product (part defects) then risk may be mitigated by a change in the design of the process. This is one reason that I recommend using process failures as failure modes.
 
R

ralphsulser

#13
Has anyone heard about the auto industry (or specific auto manufacturers) placing emphasis on the Severity score and not the overall Risk Priority Number (severity x occurrence x detection)?

It was suggested to our organization to determine action plans based on severity only and not the overall RPN.

Thank you,

Dirk
Yes, I have been informed to place more emphasis on Severity and Occurence by a big 4 OEM SQE.
We have not needed to do an FMEA since, but will be soon, plus using their requirements. There have been mixed comments in the past about RPN numbers min or max. We will find out more when the info is prepared for review.
 

Al Rosen

Staff member
Super Moderator
#14
Can anyone tell me how would you reduce severity for a said failure mode?

As per best of my knowledge even if you improve the design, you can reduce occurrence and not severity.

I am looking forward to serious discussion as to how would you reduce the severity.

Thanks and regards,
Hardik Someshvar
I agree, the severity of a failure wouldn't change, but the frequency of occurrence could be reduced or the frequency of detection increased.
 

Miner

Forum Moderator
Staff member
Admin
#15
You can change a design to eliminate the failure mode entirely, or by adding a backup.

An example would be a bonded metal to rubber engine mount. Most modern designs include a mechanical interlock such that if the rubber fails (e.g., tears, delaminates from metal, etc.) the metal components keep the engine from dropping.

The severity changes from engine falls to pavement to harsh vibration and noise. A clear drop in severity.
After reading this a second time, I was not clear on how this related to a Process FMEA.

The process is the application of an adhesive to a metal substrate to bond rubber to metal. The potential failure mode is for the bond to fail. The potential effect of the failure is for the engine to drop, which is a high severity.

A change in the process cannot reduce this severity. However, changing the design of the part to add a mechanical interlock will eliminate the effect of engine dropping. A new effect is created, which is metal to metal contact without rubber damping resulting in noise and vibration. The severity of noise and vibration is lower than the previous severity.
 

Al Rosen

Staff member
Super Moderator
#16
After reading this a second time, I was not clear on how this related to a Process FMEA.

The process is the application of an adhesive to a metal substrate to bond rubber to metal. The potential failure mode is for the bond to fail. The potential effect of the failure is for the engine to drop, which is a high severity.

A change in the process cannot reduce this severity. However, changing the design of the part to add a mechanical interlock will eliminate the effect of engine dropping. A new effect is created, which is metal to metal contact without rubber damping resulting in noise and vibration. The severity of noise and vibration is lower than the previous severity.
The way I see it, the probability of the engine dropping was reduced by adding the mechanical interlock, and the severity remains the same if the engine drops to the ground.
 

Jim Wynne

Staff member
Admin
#17
The way I see it, the probability of the engine dropping was reduced by adding the mechanical interlock, and the severity remains the same if the engine drops to the ground.
I agree in this instance, but like I said earlier, a lot depends on how the failure mode (and effect) are characterized.
 
G

Geoff Withnell

#18
It depends on how the potential failure mode is defined. If it's defined as "serious injury due to violent contact with the steering apparatus," then introduction of the airbag will lessen the severity, no?
Actually, serious injury due to violent contact with the steering apparatus is NOT a failure mode. It is a failure effect. The failure mode that the airbag is in place to mitigate is "frontal impact while seat belt is not fastened", which has the effect above. Oddly enough, the airbag increases the severity of the failure of "frontal impact while seat belt is fastened", since it provides no protection the seat belt does not, and may actually cause injury.

Geoff Withnell
 

Jim Wynne

Staff member
Admin
#19
It depends on how the potential failure mode is defined. If it's defined as "serious injury due to violent contact with the steering apparatus," then introduction of the airbag will lessen the severity, no?
Actually, serious injury due to violent contact with the steering apparatus is NOT a failure mode. It is a failure effect. The failure mode that the airbag is in place to mitigate is "frontal impact while seat belt is not fastened", which has the effect above. Oddly enough, the airbag increases the severity of the failure of "frontal impact while seat belt is fastened", since it provides no protection the seat belt does not, and may actually cause injury.

Geoff Withnell
Once again, how we characterize modes, effects and causes will influence how severity is rated and whether or not the severity factor can be reduced. In another thread, someone asked,
Severity relates to consequence of error/failure. How can a design change change this?
My response was,
If you're filling the balloons at a children's birthday party with methane, the consequences of popping a balloon using a match can be made less severe by using helium.:cool:
 
M

Mrs. PPAP MKM

#20
We have considered both the customer and the end user when evaluating severity. In our process FMEA we consider the effect on the part that we manufacture as well as the effect on the vehicle. It has proved to be very useful to us and our customers really like it.
 
Thread starter Similar threads Forum Replies Date
R DFMEA/PFMEA mitigation of high severity (9-10) in low volume products IATF 16949 - Automotive Quality Systems Standard 1
silentmonkey How to measure severity if my product is designed for emergency use and failure would result in death? ISO 14971 - Medical Device Risk Management 9
J On PFMEA for danger labels - Label always should be assigned severity 10 ? FMEA and Control Plans 3
S The Severity of a Medical Device Hazard - Risk Analysis Clarification ISO 14971 - Medical Device Risk Management 6
MrTetris Informational Risk Register - Same hazardous situation, different severity of harms ISO 14971 - Medical Device Risk Management 7
A PFMEA severity score different applications FMEA and Control Plans 11
X Customer Service FMEA - Specifically Customer Care / Severity Rankings Service Industry Specific Topics 3
D How to fill a Process FMEA - Three columns - Severity, occurrence and Detection FMEA and Control Plans 16
R DFMEA Severity 9-10 with Occurrence 3 and Detection 3 - Actions FMEA and Control Plans 3
S What should the FMEA Severity for SC & CC Characteristics be? FMEA and Control Plans 4
N AIAG 4th ed. FMEA Manual "Fit" Changed to "Appearance" - Fit severity? FMEA and Control Plans 2
G Severity in Process FMEA for Rework Process FMEA and Control Plans 1
O PFMEA - Reducing Severity (S) Ranking - Manufacturing Process Design Changes FMEA and Control Plans 4
S FMEA's - Severity and Classification of Print Characteristics FMEA and Control Plans 1
N Risk Severity Estimation for Medical Devices as per ISO 14971 ISO 14971 - Medical Device Risk Management 12
C Determining PFMEA Severity for Armored Parts FMEA and Control Plans 5
C FMEA DOGMA about Severity - Am I right or Wrong? FMEA and Control Plans 2
K 4th Edition AIAG FMEA Occurrence, Severity and Detection Criteria for Plastics FMEA and Control Plans 1
F Risk = Likelihood * Severity - Can we mitigate the Severity? Occupational Health & Safety Management Standards 44
M Severity Reduction in a Design FMEA (DFMEA) FMEA and Control Plans 25
E Risk Management selection Probability of Occurrence and Severity ISO 14971 - Medical Device Risk Management 24
S Severity of 9 or 10 should be identified as Special characteristic? FMEA and Control Plans 10
G Internal vs. External PFMEA Severity Rankings FMEA and Control Plans 12
R Risks which must be Distinctly Identified - Harm, Hazard, Severity ISO 14971 - Medical Device Risk Management 7
C Severity of Effect on Process (Manufacturing/Assembly Effect) Scrap or Reworking FMEA and Control Plans 3
W Severity Rating CORRECTIVE ACTIONS - Opinions Wanted Please Nonconformance and Corrective Action 15
H DFMEA Severity Ranking of Non-Compliance to EMC Standards FMEA and Control Plans 2
P Chemical Purity Testing - FMEA Severity Scale FMEA and Control Plans 2
T FMEA Severity 9 &10 - Example of "with warning?" FMEA and Control Plans 6
E Harms Severity Scoring - Combination of Hazards ISO 14971 - Medical Device Risk Management 4
B The Distribution that represents the Severity of Nonconformances Nonconformance and Corrective Action 2
A AIAG Design FMEA Severity Rankings - Noncompliance Government Regulation? FMEA and Control Plans 9
D Severity or Occurrence? Performing an FMEA on Motorcycle Operation FMEA and Control Plans 9
L FMEA Occurrence, Severity and Detection Criteria FMEA and Control Plans 3
I Ford FMEA requirements for Severity and Occurrence Rankings Customer and Company Specific Requirements 1
G FMEA Severity Ranking for an Automotive Audio System FMEA and Control Plans 9
Chennaiite FMEA Severity Rating for Potential Manufacturing Effect mentioned in the FMEA manual FMEA and Control Plans 9
kedarg6500 FMEA Severity Scale - Higher for Failure at Customer's or End-Customer's place? FMEA and Control Plans 19
M FMEA Severity Ratings for Health Care Information System FMEA and Control Plans 10
C Does the PFMEA Severity have to match the DFMEA Severity? FMEA and Control Plans 3
P Measuring Severity of Construction Nonconformance Report Nonconformance and Corrective Action 3
L Standard for process control level depending on gravity (severity)? FMEA and Control Plans 7
I Defining a Severity Level of a non-conformance Nonconformance and Corrective Action 13
Y Severity, Occurrence and Detection FMEA Ranking Tables - Guidelines? FMEA and Control Plans 8
L FMEA - Should a severity of 9 or 10 be always followed by recommended actions? FMEA and Control Plans 2
J Severity of Finding for "Past Due Gage" found on the shop floor General Measurement Device and Calibration Topics 40
S FMEA Severity of 9 or 10 - Shower does not operate FMEA and Control Plans 13
J Ranking Severity of Non-Conforming Material Defects Nonconformance and Corrective Action 5
R Severity, Occurance and Detection ratings seem qualitative FMEA and Control Plans 14
M FMEA: Which Severity, Occurrance, Detection scale in healthcare? FMEA and Control Plans 3

Similar threads

Top Bottom