Failure Modes and Effects Analysis (FMEA)

Failure Modes and Effects Analysis (FMEA) is a form of risk analysis that should be applied when designing or changing products and processes.  FMEA is a methodical seven step approach to analyzing a product or process for ways that it can fail, and then taking appropriate actions based on this information.   We will explain the application of this approach using the example of preparing microwave popcorn.
Step One – List what is required of the product or process and what actions are planned to change the process.  Alternatively, list each step in the process and then the requirements.
Example – the requirement is that the popcorn be fully popped without being burned.
Step Two – List the failure modes – how could the product or process fail to meet its requirements?
Example – the popcorn could be left in the microwave for too long a period of time.
Step Three – List the failure effects – what happens if the failure occurs?  What is the impact on the output?
Example – If the popcorn is left in the microwave for too long a period of time, it will be burned and the batch will need to be discarded.
Step Four – Assign values for Probability of Occurrence (O), Severity of Failure (S), and Difficulty of Detection (D).  Suggested values are shown next.  The values and the words that go along with them may be modified as you see fit for a specific set of circumstances.
Probability of Occurrence (O)
1 – Very unlikely
2 – Unlikely
4 – Low probability
6 – Likely
8 – Highly likely
10 – Certain
Severity of Failure (S)
1 – No effect on customer
2 – Minor defect
4 – Slight inconvenience
6 – Moderate inconvenience
8 – Major inconvenience
10 – Threat to health and safety
Difficulty of Detection (D)
1 – Immediately detectable
2 – Easy to detect
4 – Highly likely to be detected
6 – Likely to be detected
8 – Unlikely to be detected
10 – Extremely unlikely to be detected
Example – We consider it to be likely that the popcorn will be popped for too long a time, resulting in an O value of 6.  We consider it to be a major inconvenience if the popcorn is burned and thrown out, resulting in an S value of 8.  We consider the difficulty of detection to be highly likely to be detected, resulting in a D value of 4.
Step Five – Calculate the Risk Priority Number (RPN) for each item.  The RPN = O x S x D.  The worst situation is one where the failure is certain to occur, the failure has drastic consequences, and the failure is extremely unlikely to be detected.  This situation will result in the highest possible Risk Priority Number of 1000.
Example – The RPN for our popcorn is 6 x 8 x 4 = 192.
Step Six – List the root causes of each of the failure modes.
Example – the root cause of popcorn being popped for too long is the lack of knowledge of how long it should be left in the microwave oven.
Step Seven – For items with the highest RPN’s, take action to:

  • Prevent the failure from happening at all
  • Reduce the probability of the failure occurring
  • Reduce the impact of the failure
  • Increase the chance of detection of the failure.

Example – determine the optimum popping time for the popcorn through experimentation, then use a timer to maintain strict control of the time that the popcorn is heated in the microwave.
Your comments or questions about this article are welcome, as are suggestions for future articles.  Feel free to contact me by email at
About the author:  Mr. Roger C. Ellis is an industrial engineer by training and profession.  He is a Six Sigma Master Black Belt with over 48 years of business experience in a wide range of fields.  Mr. Ellis develops and instructs Six Sigma professional certification courses for Key Performance LLC.   For a more detailed biography, please refer to