How to Use and Calculate an FMEA For Six Sigma

By the time a Six Sigma DMAIC project team is ready to implement improvements, they have already worked through the Define, Measure and Analyze phases of the project. They have identified the customer requirements and the performance of the process relative to those requirements. They have established a clear understanding of how the process is performed and of any common cause and special cause variation that affects performance. And they have established the root cause(s) of the problem being addressed. Six Sigma principles for improvement of management of processes include verifying assumptions with data, so the root causes have actually been validated empirically.

In the Improve phase, the team designs process improvements aimed at countering the root cause(s). Prior to implementing the changes in a pilot or full roll-out, they conduct a Failure Modes and Effects Analysis (FMEA) to assess potential risks. This technique allows groups to systematically identify potential risks, evaluate how much effort should be put into minimizing or preventing each one, and create a mitigation plan.

To design an FMEA for your Six Sigma project, first bring together a group consisting of some of the DMAIC team members and some of the individuals who perform the process being modified. Begin the exercise by brainstorming a list of problems that could occur with the new process. Do not judge at this stage whether they are severe enough to worry about or likely enough to occur, just list them all. The goal is to identify all potential risks.

Next, create a scale from 1-10 to rate each potential risk on its severity should it occur. Groups usually find it helpful to have descriptions associated with each rating or at least for the minimum and maximum. For some processes, such as those in health care environments, maximum severity might represent patient death or infection of other patients and staff. For most business processes, maximum severity is not a matter of life or death but of financial loss, customer dissatisfaction, or product or process failure.

Using your scale, assign ratings of severity for each of the potential risks you have identified. Note that the relative numbers are more important than the absolute ratings, so do not let the group get too hung up on selecting exact ratings.

Then create another scale from 1-10 to rate each of the identified risks on the likelihood of occurrence. As with the severity scale, establish descriptions for at least the ratings of 1 and 10. Assign a likelihood rating for each potential risk.

Finally, create a third scale to estimate the likelihood that a risk could come to fruition and not be discovered in time to mitigate its impact. A rating of 1 would indicate that is is extremely likely that the problem would be identified in time to prevent any negative consequences. A rating of 10 indicates that it is highly likely that by the time the problem is detected it would be too late to prevent the consequences in their fullest severity. Do not confuse the detection rating with the severity rating, however. A risk could have a detection rating of 9 but a severity rating of only 2. These ratings are independent.

Once all three ratings have been assigned for each potential risk, multiply them together to obtain a single number, called the Risk Priority Number (RPN), for each risk. The higher this number, the higher the priority the project team should give to creating a plan for eliminating or mitigating the risk. Identify the risks with the top priorities and create a plan to address them before implementing your improvements. Your FMEA is now complete.