The Failure Mode and Effects Analysis (FMEA)

What is an FMEA?

Also called: potential failure modes and effects analysis; failure modes, effects, and criticality analysis (FMECA)

• "Failure modes" means the ways, or modes, in which something might fail. Failures are any errors or defects, especially ones that affect the customer and can be potential or actual.
• "Effects analysis" refers to studying the consequences of those failures.

When to Use FMEA?

• When a process, product, or service is being designed or redesigned, after deployment.
• When an existing process, product, or service is being applied in a new way.
• Before developing control plans for a new or modified process.
• When improvement goals are planned for an existing process, product, or service.
• When analyzing failures of an existing process, product, or service.
• Periodically throughout the life of the process, product, or service.

Process

• Assemble a cross-functional team of people with diverse knowledge about the process, product or service, and customer needs.
• Identify the scope of the FMEA. 
• "Is it for the concept, system, design, process, or service?"
• "What are the boundaries?"
• "How detailed should we be?"
• Use flowcharts to identify the scope and to make sure everybody understands it in detail.
• Fill in the identifying information at the top of your FMEA form. 
• The remaining steps ask for information that will go into the columns of the form.
• Identify the functions of your scope. Ask:
• "What is the purpose of this system, design, process, or service?"
• "What do our customers expect it to do?" 
• Name it with a verb followed by a noun. Usually, one will break the scope into separate subsystems, items, parts, assemblies, or process steps and identify the function of each.
• For each function, identify all the ways failure could happen. 
• These are potential failure modes. If necessary, go back and rewrite the function with more detail to be sure the failure modes show a loss of that function.
• For each failure mode, identify all the consequences on the system, related systems, process, related processes, product, service, customer, or regulations. 
• These are potential effects of failure. Ask,
• "What does the customer experience because of this failure?" 
• "What happens when this failure occurs?"
• Determine how serious each effect is. 
• This is the severity rating or S. Severity is usually rated on a scale from 1 to 10, where 1 is insignificant and 10 is catastrophic. 
• If a failure mode has more than one effect, write on the FMEA table only the highest severity rating for that failure mode.
• For each failure mode, determine all the potential root causes. 
• Use tools classified as cause analysis tools, as well as the best knowledge and experience of the team. 
• List all possible causes for each failure mode on the FMEA form.
• For each cause, determine the occurrence rating, or O. 
• This rating estimates the probability of failure occurring for that reason during the lifetime of your scope. 
• Occurrence is usually rated on a scale from 1 to 10, where 1 is extremely unlikely and 10 is inevitable. 
• On the FMEA table, list the occurrence rating for each cause.
• For each cause, identify current process controls. 
• These are tests, procedures, or mechanisms that you now have in place to keep failures from reaching the customer.
• These controls might prevent the cause from happening, reduce the likelihood that it will happen, or detect failure after the cause has already happened but before the customer is affected.
• For each control, determine the detection rating, or D. 
• This rating estimates how well the controls can detect either the cause or its failure mode after they have happened but before the customer is affected. 
• Detection is usually rated on a scale from 1 to 10, where 1 means the control is absolutely certain to detect the problem and 10 means the control is certain not to detect the problem (or no control exists). 
• On the FMEA table, list the detection rating for each cause.
• Optional for most industries: Ask
• "Is this failure mode associated with a critical characteristic?" (Critical characteristics are measurements or indicators that reflect safety or compliance with government regulations and need special controls.) 
• If so, a column labeled "Classification" receives a Y or N to show whether special controls are needed. Usually, critical characteristics have a severity of 9 or 10 and occurrence and detection ratings above 3.
• Calculate the risk priority number, or RPN, which equals S × O × D. 
• Also calculate Criticality by multiplying severity by occurrence, S × O. 
• These numbers provide guidance for ranking potential failures in the order they should be addressed.
• Identify recommended actions. 
• These actions may be design or process changes to lower severity or occurrence. 
• They may be additional controls to improve detection. 
• Note who is responsible for the actions and target completion dates.
• As actions are completed, note the results and the date on the FMEA form. 
• Note new S, O, or D ratings and new RPNs.

Notes

• This is a general procedure. 
• Specific details may vary with the standards of your organization or industry. 
• Before undertaking an FMEA process, learn more about standards and specific methods in your organization and industry through other references and training.

References

•  What is FMEA? Failure Mode & Effects Analysis | ASQ