iSixSigma

Quick Guide to Failure Mode and Effects Analysis

Problems and defects are expensive. Customers understandably place high expectations on manufacturers and service providers to deliver quality and reliability.

Often, faults in products and services are detected through extensive testing and predictive modeling in the later stages of development. However, finding a problem at this point in the cycle can add significant cost and delays to schedules. The challenge is to design in quality and reliability at the beginning of the process and ensure that defects never arise in the first place. One way that Lean Six Sigma practitioners can achieve this is to use failure mode and effects analysis (FMEA), a tool for identifying potential problems and their impact.

FMEA: The Basics

FMEA is a qualitative and systematic tool, usually created within a spreadsheet, to help practitioners anticipate what might go wrong with a product or process. In addition to identifying how a product or process might fail and the effects of that failure, FMEA also helps find the possible causes of failures and the likelihood of failures being detected before occurrence.

Used across many industries, FMEA is one of the best ways of analyzing potential reliability problems early in the development cycle, making it easier for manufacturers to take quick action and mitigate failure. The ability to anticipate issues early allows practitioners to design out failures and design in reliable, safe and customer-pleasing features.

Finding Failure Modes

One of the first steps to take when completing an FMEA is to determine the participants. The right people with the right experience, such as process owners and designers, should be involved in order to catch potential failure modes. Practitioners also should consider inviting customers and suppliers to gather alternative viewpoints.

Once the participants are together, the brainstorming can begin. When completing an FMEA, it’s important to remember Murphy’s Law: “Anything that can go wrong, will go wrong.” Participants need to identify all the components, systems, processes and functions that could potentially fail to meet the required level of quality or reliability. The team should not only be able to describe the effects of the failure, but also the possible causes.

The sample shown in Figure 1 can be used as an example when learning how the FMEA works. The team in this case is analyzing the tire component of a car.

Figure 1: FMEA for Car Tire

Function or Process StepFailure TypePotential ImpactSEVPotential CausesOCCDetection ModeDETRPN
Briefly outline function, step or item being analyzedDescribe what has gone wrongWhat is the impact on the key output variables or internal requirements?How severe is the effect to the customer?What causes the key input to go wrong?How frequently is this likely to occur?What are the existing controls that either prevent the failure from occurring or detect it should it occur?How easy is it to detect?Risk priority number
Tire function: support weight of car, traction, comfortFlat tireStops car journey, driver and passengers stranded10Puncture2Tire checks before journey. While driving, steering pulls to one side, excess noise360
Recommended ActionsResponsibilityTarget DateAction TakenSEVOCCDETRPN
What are the actions for reducing the occurrence of the cause or improving the detection?Who is responsible for the recommended action?What is the target date for the recommended action?What were the actions implemented? Now recalculate the RPN to see if the action has reduced the risk.
Carry spare tire and appropriate tools to change tireCar ownerFrom immediate effectSpare tire and appropriate tools permanently carried in trunk42324

Criteria for Analysis

An FMEA uses three criteria to assess a problem: 1) the severity of the effect on the customer, 2) how frequently the problem is likely to occur and 3) how easily the problem can be detected. Participants must set and agree on a ranking between 1 and 10 (1 = low, 10 = high) for the severity, occurrence and detection level for each of the failure modes. Although FMEA is a qualitative process, it is important to use data (if available) to qualify the decisions the team makes regarding these ratings. A further explanation of the ratings is shown in Table 1.

Table 1: Severity, Occurrence and Detection Ratings

DescriptionLow NumberHigh Number
SeveritySeverity ranking encompasses what is important to the industry, company or customers (e.g., safety standards, environment, legal, production continuity, scrap, loss of business, damaged reputation)Low impactHigh impact
OccurenceRank the probability of a failure occuring during the expected lifetime of the product or serviceNot likely to occurInevitable
DetectionRank the probability of the problem being detected and acted upon before it has happenedVery likely to be detectedNot likely to be detected

After ranking the severity, occurrence and detection levels for each failure mode, the team will be able to calculate a risk priority number (RPN). The formula for the RPN is:

RPN = severity x occurrence x detection

In the FMEA in Figure 1, for example, a flat tire severely affects the customer driving the car (rating of 10), but has a low level of occurrence (2) and can be detected fairly easily (3). Therefore, the RPN for this failure mode is 10 x 2 x 3 = 60.

Setting Priorities

Once all the failure modes have been assessed, the team should adjust the FMEA to list failures in descending RPN order. This highlights the areas where corrective actions can be focused. If resources are limited, practitioners must set priorities on the biggest problems first.

There is no definitive RPN threshold to decide which areas should receive the most attention; this depends on many factors, including industry standards, legal or safety requirements, and quality control. However, a starting point for prioritization is to apply the Pareto rule: typically, 80 percent of issues are caused by 20 percent of the potential problems. As a rule of thumb, teams can focus their attention initially on the failures with the top 20 percent of the highest RPN scores.

Making Corrective Actions

When the priorities have been agreed upon, one of the team’s last steps is to generate appropriate corrective actions for reducing the occurrence of failure modes, or at least for improving their detection. The FMEA leader should assign responsibility for these actions and set target completion dates.

Once corrective actions have been completed, the team should meet again to reassess and rescore the severity, probability of occurrence and likelihood of detection for the top failure modes. This will enable them to determine the effectiveness of the corrective actions taken. These assessments may be helpful in case the team decides that it needs to enact new corrective actions.

The FMEA is a valuable tool that can be used to realize a number of benefits, including improved reliability of products and services, prevention of costly late design changes, and increased customer satisfaction.

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Comments 33

  1. Anthony San Mateo

    In the statement below:

    “Participants must set and agree on a ranking between 1 and 10 (1 = high, 10 = low) for the severity, occurrence and detection level for each of the failure modes.”

    Do we mean (1 = low, 10 = high)?

    Just clarifying.

    Thanks.

  2. George Forrest

    Hi Anthony,

    Yes…I can confirm ‘1= low’ and ’10 = high’.

    Regards,
    George

  3. Prashant Raut, Mumbai, INDIA

    Is FMEA must for each & every six sigma project?

  4. George Forrest

    Hi Prashant,

    In my opinion, FMEA is not a requirement for every six-sigma project. FMEA should be viewed as part of the your six-sigma ‘toolkit’. The skill is being able to pick the right tool(s) for your project requirements.

    Regards,
    George

  5. Geoffrey Melonhead

    A fine piece of work

  6. mrmetz101

    Depending on the number of potential risks being evaluated, and/or the level of discernment, a a 1-to-5 or even a 1-to-3 scale can be enough for a successful FMEA.

  7. George Forrest

    I agree with your comment.

    From my experience, the number of risks being considered is important to the scoring scale used. If the number of risks is high but a scale of ‘1 to 3’ or ‘1 to 5’ is used there is a tendency for the RPN scores to cluster hence making it more difficult to rank and prioritise individual risks within the clusters.

  8. Stewart

    Simple. Easy to understand. Useful.

    Overall a good article to introduce people to FMEA.

  9. Aravind

    The severity rating before and after(after implementing action) won’t change.After taking action,occurence will come down and detection will improve there by RPN will reduce.But severity will remain same

  10. Upendra

    In what basis we are giving Severity , POC & Detection values?

  11. Eric

    Note that for Detectability, 1 means very easily detectable and 10 means very difficult to detect. For Severity and Probability, 1 means low and 10 means high.

  12. Thamara

    Very good article to introduce FMEA. In general how do we reduce severity of given process step?

  13. Avinoam Moses

    Dear Sir or Madam.

    Is FMEA has an acceptable standart compliance with?
    I am using rating of 10 for RPN, but some are using the rating of 5, which one is correct and according which ISO std. or else?
    By using rating of 10, why it is acceptable to handle those with RPN>80?

    Please advise

    Thx

  14. Baldev singh

    Very nicely explained, can you just explain is it viable to do pfmea on individual part with eg; dimension 20 and told is +-0.05 how do we rate it under the sea, Occ
    Can you just give and example on this

  15. Robert Carter

    It is nice easy example to understand. From experience the severity measure remains consistent between the current and any future recommended action. You can only reduce severity by changing the basis of your assumptions via a change in design or function or a new process / technology. For instance, if I use a normal tyre that I can buy from a garage the use of a spare will not change the severity of a puncture it will remain a 10. I still have the chance that my spare will go flat(? ) If I change the type of tyre I use, say a “run-flat” tyre or similar then the severity will be less because I will not be driving on a “flat” tyre and can drive upon until such time as I can safely get a repair.

  16. Salvador Avalos Medina

    It Is an topic that not much school and enterprises use in the real life.
    That’s way some of those, not keep on growing up.

    Please not leave of give us more examples, for our pupils, they need our help.

  17. Subrata Sen

    I liked this. Well explained in simple language.
    Thanks

  18. Ravi Shingala

    Hi, I wanted to know. Can this tool be useful for finance (risk) projects? Like analyzing credit, market, operational and liquidity risk?

  19. geetha

    handy and excellent explanation

  20. Martin

    Hi,
    can anyone please explain the differences between FMEA and FMECA analysis? Most of the sources on thr internet describe FMEA including RPN number but that should only be within the FMECA analysis, right?
    Please correct me if I am wrong. Couldnt find a proper source to find out the true difference

  21. ANTON PERERA

    Short and sweat, very easily understandable, thank you very much

  22. Gnana Reuben A

    Hi
    I would like to know whether we rank every failure mode only in the perspective of impact to external customer. What about internal customer. This is in the perspective of a connected chain of processes where the internal external relationships are there before the actual end customer is affected/ impacted
    Any views from experts???

  23. Suradi

    Good guidelines to grow up my competencies

  24. chigozie

    nice one …..clear but need more

  25. Abraham Vidales

    Dear George:

    On the I industry I participate at, we use the RPN number only as a three digits value without multiplying, this allow us to assign priorities based on severity as our products reach final direct consumers. Personally I think this is a great way to customize the FMEA format and align this tool with company’s vision and mission. Let’s make sure that we we cuatomize the tools we kept the alignment with our company’s targets. Best regards.

  26. Mohamed Yusuf

    Hello George ,
    i have an inquiry , i just finished ISO 9001/2015 and one of the mandatory clauses is to make a risk assessment so i was thinking to use FMEA to make it but there is a little difference between RPN calculation that you mentioned is different from the calculation that we had into the training of ISO 9001/2015 as it was ( (S*O)/ detection ) , so what is the right answer to calculate the RPN ??
    Thanks
    Mohamed

  27. Andy

    Hello , I am interested to have more detail on the usage of FMEA. There are various stages we can use FMEA as below.
    1) When a process, product or service is being designed or redesigned, after quality function deployment.
    2) When an existing process, product or service is being applied in a new way.
    3) Before developing control plans for a new or modified process.
    4) When improvement goals are planned for an existing process, product or service.
    5) When analyzing failures of an existing process, product or service.
    6) Periodically throughout the life of the process, product or service

    Appreciate if anyone can provide an example how do we use FMEA in above situations no.1 – no.4.

    thanks

  28. Jack

    Under “Recommended Actions” – What are the actions for reducing the occurrence of the cause or improving the detection? The action was “Carry spare tire and appropriate tools to change tire”

    But this action reduces the “severity” ranking instead of occurrence of the cause or improving the detection. It contradicts the definition of “Recommended Actions.

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