Failure Mode and Effects Criticality Analysis (FMECA)

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About this lesson

The FMECA is a special form of FMEA that accentuates the focus on finding and controlling critical characteristics. It simplifies the FMEA process, but loses fidelity in the analysis.

Quick reference

Failure Mode and Effects Criticality Analysis (FMECA)

Failure Mode Effects Criticality Analysis (FMECA) is a quick method for determining if a failure requires mitigation effort.  The analysis relies only on the Severity and Probability ratings from the FMEA analysis.

When to use

The FMECA approach is often used to conduct a quick analysis of an existing product or process to determine if mitigation of failure modes is required.  It is not as rigorous as FMEA, but provides helpful insight in small design projects.

Instructions

The FMECA approach is used to determine if mitigation is required.  It can also be used to identify critical characteristics that require monitoring in a quality control plan.  When doing a FMECA analysis, each failure mode is assessed for severity and probability.  Based upon that assessment, the FMECA criticality matrix is used to decide whether mitigation is needed.

Many organizations create their own FMECA criticality matrix that is based upon internal processes or other management systems.  The matrix shown in this program is the one found in IEC 60812, and is a good generic standard that can be used as a basis for a custom matrix.

Severity ratings – I - IV

The IEC 60812 standard identifies four severity rating categories:

  • IV – Catastrophic: A failure mode which could potentially result in the failure of the system's primary functions and therefore cause serious damage to the system and its environment and/or personal injury.
  • III – Critical: A failure mode which could potentially result in the failure of the system's primary functions and therefore cause considerable damage to the system and its environment, but which does not constitute a serious threat to life or injury.
  • II – Marginal: A failure mode which could potentially degrade system performance function(s) without appreciable damage to system or threat to life or injury.
  • I – Insignificant: A failure mode which could potentially degrade the system's functions but will cause no damage to the system and does not constitute a threat to life or injury.

Probability ratings – A - E

The IEC 60812 standard identifies five probability rating categories:

  • A – Frequent:  Occurrence is greater than 20%
  • B – Probable:  Occurrence is 10% to 20%
  • C – Occasional:  Occurrence is less than 10%
  • D – Remote:  Occurrence is less than 1%
  • E – Improbable:  Occurrence is less than 0.1%

Hints & tips

  • FMECA is faster than FMEA, but not as rigorous.  Also, since there are fewer categories for severity and probability, it is less precise. 
  • If the product or process is new, there is no experience to use when setting the probability rating.  In that case, either use a similar product or process or switch to FMEA.
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  • 00:04 Hi, I'm Ray Sheen.
  • 00:06 There's a special case of FMEA, and it's a failure mode effects and
  • 00:10 criticality analysis, known as a FMECA.
  • 00:14 Let's explore this for a moment.
  • 00:15 You may be wondering what we mean by criticality.
  • 00:20 Well, the purpose of a FMECA is to put emphasis on critical failure modes so
  • 00:24 that they will receive special attention.
  • 00:27 And the FMEA methodology is a great way
  • 00:29 to put some analytical rigor into determining what is critical.
  • 00:34 There is no universal definition of what is critical.
  • 00:36 It varies by industry and even by companies within an industry.
  • 00:40 But when using the FMEA methodology to determine criticality,
  • 00:44 it normally would be based upon a combination of the severity and
  • 00:48 probability of occurrence scores.
  • 00:50 In many organizations, a full FMEA is not done,
  • 00:54 just an abbreviated one that looks at criticality.
  • 00:57 When that is the case, the severity and probability are evaluated.
  • 01:01 And if the failure mode is critical then the detection method is determined and
  • 01:05 mitigation methods are applied.
  • 01:07 If the failure mode is not critical, no further analysis is done.
  • 01:11 To explain how this works, we'll create a critcality matrix.
  • 01:15 The vertical scale of the matrix is probability of occurrence, and
  • 01:19 the horizontal scale is severity of the failure.
  • 01:22 As you can see, the higher the severity and
  • 01:24 the higher the probability, the greater the criticality of the failure mode.
  • 01:29 The matrix I'm showing you is the one found in IEC standard 60812.
  • 01:34 Your organization may have a custom one used for your business of industry.
  • 01:39 The advantage of the matrix is that it provides a simple,
  • 01:41 straightforward representation of criticality,
  • 01:44 which is very helpful when explaining why something is classified as critical.
  • 01:48 In the next lesson, we'll discuss in more detail how design and
  • 01:51 operational management must treat critical characteristics.
  • 01:55 The criticality scales for probability has five levels and
  • 01:58 the severity has four levels.
  • 02:00 This is less than the scales used in a full FMEA which have ten levels.
  • 02:05 This reduced discrimination,
  • 02:07 makes it a little bit easier to determine the appropriate levels for each scale.
  • 02:11 When considering criticality, set the score for
  • 02:14 each of the two sides of the matrix.
  • 02:16 If the result is classified as intolerable, then a product or
  • 02:19 process design change is needed to reduce the risk of failure.
  • 02:23 If the result is undesirable, check the methodology used for detection.
  • 02:28 If it is robust, you can use that.
  • 02:31 But make sure that mechanism is marked as critical in product or
  • 02:34 process documentation.
  • 02:36 If the result is tolerable, typically, no design action is required but
  • 02:40 the failure mode should be monitored.
  • 02:42 And if the result is negligible, then don't worry about it.
  • 02:46 Let's go a little deeper into the criticality scale of severity.
  • 02:50 Severity has four levels.
  • 02:53 The highest level is level IV for catastrophic failures.
  • 02:57 A failure mode which could potentially result in the failure of the system's
  • 03:01 primary functions.
  • 03:02 And therefore, cause serious damage to the system and
  • 03:05 its environment and/or personal injury.
  • 03:08 This level is used for the case where someone gets hurt or
  • 03:12 the equipment is significantly damaged.
  • 03:14 The next level is level III, which is for
  • 03:17 failure modes that create a critical condition.
  • 03:20 A failure mode which could potentially result in the failure of the system's
  • 03:23 primary functions, and therefore cause considerable damage to the system and
  • 03:27 it's environment.
  • 03:29 But which does not constitute a serious threat to life or injury.
  • 03:32 So, people don't get hurt, but the system may be damaged or broken.
  • 03:38 On to level II, which is the marginal level.
  • 03:41 A failure mode, which can potentially degrade the system performance functions
  • 03:45 without appreciable damage of the system or a threat to life or injury.
  • 03:50 So, the system's still working partially.
  • 03:52 It performs some of the functions but is not able to perform all functions.
  • 03:57 Finally, we get to level I, which is the insignificant level.
  • 04:01 A failure mode which could potentially degrade the systems functions but will
  • 04:05 cause no damage to the system and does not constitute a threat to life or injury.
  • 04:10 Notice, now it has a potential for degraded system performance.
  • 04:14 All of these are subjective assessments, which is why you need an FMEA team or
  • 04:18 subject matter experts.
  • 04:20 Now, let's look at the probability scale.
  • 04:23 In this case, we will use objective percentages for our probability ratings.
  • 04:27 However, if this is a new product, there is no data to calculate probability.
  • 04:32 So the FMEA team will need to consider data from other similar products or
  • 04:36 processes and then extrapolate that data to this item.
  • 04:40 The five rating levels are really quite simple to use.
  • 04:44 If the probability is greater than 20%, it's considered frequent and
  • 04:48 classified as level A.
  • 04:49 Between 10% and 20%, the classification is probable and it's called level B.
  • 04:56 From 1% to 10%, it's considered occasional and classified with the letter C.
  • 05:01 From one-tenth of 1% to 1%, it's considered remote and
  • 05:06 classified as letter D.
  • 05:08 And finally, that the probability is less than one-tenth of 1%,
  • 05:12 it's considered improbable and classified as letter E.
  • 05:16 Now, these are the probability ratings that are found in the IEC standard.
  • 05:20 Many companies have their own ratings that are slightly different.
  • 05:23 And of course, if your company uses a different scale,
  • 05:26 that's the one you should work with.
  • 05:28 So the FMEA methodology can help to determine the criticality of failure
  • 05:33 modes, by using the severity and the probability of occurrence.
  • 05:38 But be sure to use the scales that your organization has adopted.

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