This article is an introductory look at what exactly is a pFMEA or Process Failure Modes and Effects Analysis, and some ideas on how to use them as part of a living breathing risk management system.
I recently had someone ask for help understanding the
process FMEA a little better. I can’t blame them because I was lost the first
time I tried to fill out a form for one. It can be a confusing and overwhelming
if you have never seen one before.
First things first, what is a pFMEA-
FMEA= Failure Modes and Effects Analysis
A lower-case letter will come before the FMEA, and that denotes the ‘what’, of what the failure is that is being analyzed. A pFMEA will often be examining process failures where a dFMEA might evaluate design failures. (dFMEA’s can be confusing as well, Robert Packard created a training on how to document risk management activities without using one in his Death of the dFMEA Webinar)
Some systems capitalize all the letters. Some capitalize
none. That is not what is important as long as it is consistent throughout your
system. Everyone should be able to easily understand that whatever variation of
pfmea is used it means “process failure modes and effects analysis”.
What does a pFMEA do?-
A pFMEA will break down your manufacturing process into its individual steps and methodically examine them for potential risks or failures. For companies that utilize our Turn-Key Quality Management System, FRM-025 process Failure Modes and Effects Analysis can be used as a template.
For this example, we will look at receiving inspection of
injection molded casing parts for a medical device. This receiving inspection
includes a manual inspection of 10 randomly selected parts out of each delivery
of 100 using an optical overlay.
This area as the section title suggests is the process step. When looking at the process as a whole the pFMEA will break it down into each and every step included in that process. This area is simply that individual step that is going to be examined.
The Process Step, or item function depending on what your form uses for this scenario is going to be part of the random sampling for manual inspection of the received parts using an optical overlay. Our example is going to be the backlighting element of the optical overlay display. The backlighting element will illuminate the inspected part against the template to verify that the part is within specific dimension criteria.
Potential Failure Modes-
A failure mode is a way in which that process step might fail. since it is failure modeS, it needs to be considered that there may be more than one way for the process step to fail. Do not be fooled that because this box on the form has been filled in that the pFMEA will be complete. A thorough examination of all of the possible failures should be investigated.
Our example in this process requires the backlighting element to illuminate a visual template over the parts. The light not illuminating properly is a potential failure mode of this process.
Potential Effects of Failure-
the potential effects of the failure is a look into what the ramifications would be if that failure for that process step actually happened.
In our scenario one of the potential effects of the lighting not functioning properly is that parts outside of the designated sizing acceptance criteria may be accepted rather than rejected as non-conforming parts.
The next area is the first area that requires an estimated grading of the failure. That is ‘Severity’ which is abbreviated as S. There is a scale provided in the ratings section of FRM-025 that outlines the numbering system that Medical Device Academy uses.
Below is a snippet of the rating scale used, this is included with purchase of SYS-010 Risk Management Procedure.
|Severity of the effect||Scale||Definition|
|Business Risk||0||No potential harm to patient or user|
|Superficial||2||Little potential for harm to patient or user|
In this case our example is using molded plastic pieces of the outside casing of a medical device. Pieces that are too large or too small will not fit when making the final assembly of the device. These plastic pieces do not happen to be patient contacting, and do not affect the function of the device.
The evaluation of this failure is determined to have no
potential affect on patient safety or increase any potential for risk of harm,
therefore the severity is assigned as a ‘business risk’ meaning that it bears
no risk for the user or the patient. This makes the Severity Score 0.
Causes of Failure-
This column is exactly that. What might cause this identified failure to happen? In our example might be the light bulbs in the overlay machine may slowly burn out over time with use. This burnout causes the potential failure.
If the bulb is expected to only have a lifetime of 100 hours,
then the more hours the bulb is used the more dim the light may become. A
slowly dimming light decreases the sharpness of the overlay template and our
parts that are supposed to have a + or – size criteria of 10% now have a fuzzy
template that in reality changes the overlay to show closer to + or – 13%. Now
parts that are too small or too large may be accepted.
This grading criteria is also found in the Ratings section
of FRM-025. This is how often the failure is expected to occur. How often will
the lighting element of our optical overlay fail to function in the appropriate
manner for this cause?
Hopefully not very often. In fact, regularly scheduled
maintenance and calibration of the overlay machine could prevent this from ever
happening in the best-case scenario. Our evaluations determine that the
probability of this happening is low. However, since we cannot be certain it
will never happen the potential for this risk exists and makes the Occurrence
score a 4.
Current Process Controls-
What is currently being done to control this risk? Our
example uses regularly scheduled maintenance and calibration to prevent bulb
burnout effecting the overlay.
Our current process is based off of routine maintenance and
visual inspection. This means that the bulb burnout is something that is
visually inspected for and visual inspections for detectability on the rating
scale are graded as 8. This chart is found in the Ratings Section of FRM-025.
RPN (Risk Priority Number)-
This is a number that is found by multiplying the Severity,
by the Probability, by the Detectability. In our example the numbers RPN
is 0X4X8=32 for an RPN of 32 which is
Below is a short video explaining the math behind calculating the Risk Priority Number
What if anything can be done to improve this process? In our
example a recommended action may be to transfer from visual only inspections to
verification of light output by meter. This makes the Detectability of the
failure measurable by meter or gage which is a detectability score of 4.
This changes the RPN now to 0X4X4=16
The pFMEA shouldn’t be a solo thing-
If it can be avoided this type of analyisis should be done by a multidisciplinary team. Sometimes in smaller companies people end up having to wear more than one hat. There are many entrepreneurs that have to function as the CEO/CFO/Design Engineer/RA/QA manager.
Ideally a team approach should be used if feasable. Have the management level staff who have ownership of the processes participating in this analysis. They should know the process more intimately than anyone else in the company and should have more insight into the possible failure modes of the processes as they have likely seen them first hand. They are also the type of employee who would know the types of recomended actions to control the risk of those failures as well.
The pFMEA should also be a living document-
As new failure modes are discovered they should be added to your pFMEA. A new failure mode might be discovered through a CAPA because the process had an actual failure that was not originally analyzed. Take an instance like that as an opportunity for improvement and to update your pFMEA as part of a living breathing risk management system. Also use this as a time to re-brainstorm potentially similar failure modes that may not have been considered previously so that they can be controlled before they happen.
If you took the time to watch the video above it is also mentioned that in some instances the very first FMEA must be based off of estimates because there is no data. Managers, and engineers may be forced to estimate the probability of occurence. If that is the case the FMEA should be updated in the future to adjust the (O) score to reflect what is occuring in actuality based off of real data and not the theoretical data that was used for the initial estimate.