Failure Modes and Effects Analysis (FMEA)

FMEA / FMECA Overview

In general, Failure Modes, Effects and Criticality Analysis (FMEA / FMECA) requires the identification of the following basic information:

• Item(s)
• Function(s)
• Failure(s)
• Effect(s) of Failure
• Cause(s) of Failure
• Current Control(s)
• Recommended Action(s)
• Plus other relevant details

Most analyses of this type also include some method to assess the risk associated with the issues identified during the analysis and to prioritize corrective actions. Two common methods include:

• Risk Priority Numbers (RPNs)
• Criticality Analysis (FMEA with Criticality Analysis = FMECA)

Basic Analysis Procedure for FMEA or FMECA

The basic steps for performing an Failure Mode and Effects Analysis (FMEA) or Failure Modes, Effects and Criticality Analysis (FMECA) include:

• Assemble the team.
• Establish the ground rules.
• Gather and review relevant information.
• Identify the item(s) or process(es) to be analyzed.
• Identify the function(s), failure(s), effect(s), cause(s) and control(s) for each item or process to be analyzed.
• Evaluate the risk associated with the issues identified by the analysis.
• Prioritize and assign corrective actions.
• Perform corrective actions and re-evaluate risk.
• Distribute, review and update the analysis, as appropriate.

Risk Evaluation Methods

A typical failure modes and effects analysis incorporates some method to evaluate the risk associated with the potential problems identified through the analysis. The two most common methods, Risk Priority Numbers and Criticality Analysis, are described next.

Risk Priority Numbers

To use the Risk Priority Number (RPN) method to assess risk, the analysis team must:

• Rate the severity of each effect of failure.
• Rate the likelihood of occurrence for each cause of failure.
• Rate the likelihood of prior detection for each cause of failure (i.e. the likelihood of detecting the problem before it reaches the end user or customer).
• Calculate the RPN by obtaining the product of the three ratings:

RPN = Severity x Occurrence x Detection

The RPN can then be used to compare issues within the analysis and to prioritize problems for corrective action. This risk assessment method is commonly associated with Failure Mode and Effects Analysis (FMEA).

Criticality Analysis

The MIL-STD-1629A document describes two types of criticality analysis: quantitative and qualitative. To use the quantitative criticality analysis method, the analysis team must:

• Define the reliability/unreliability for each item and use it to estimate the expected number of failures at a given operating time.
• Identify the portion of the item’s unreliability that can be attributed to each potential failure mode.
• Rate the probability of loss (or severity) that will result from each failure mode that may occur.
• Calculate the criticality for each potential failure mode by obtaining the product of the three factors:

  Mode Criticality = Expected Failures x Mode Ratio of Unreliability x Probability of Loss
  

• Calculate the criticality for each item by obtaining the sum of the criticalities for each failure mode that has been identified for the item.

  Item Criticality = SUM of Mode Criticalities

To use the qualitative criticality analysis method to evaluate risk and prioritize corrective actions, the analysis team must:

• Rate the severity of the potential effects of failure.
• Rate the likelihood of occurrence for each potential failure mode.
• Compare failure modes via a Criticality Matrix, which identifies severity on the horizontal axis and occurrence on the vertical axis.

These risk assessment methods are commonly associated with Failure Modes, Effects and Criticality Analysis (FMECA).

Applications and Benefits for FMEA and FMECA

The Failure Modes, Effects and Criticality Analysis (FMEA / FMECA) procedure is a tool that has been adapted in many different ways for many different purposes. It can contribute to improved designs for products and processes, resulting in higher reliability, better quality, increased safety, enhanced customer satisfaction and reduced costs. The tool can also be used to establish and optimize maintenance plans for repairable systems and/or contribute to control plans and other quality assurance procedures. It provides a knowledge base of failure mode and corrective action information that can be used as a resource in future troubleshooting efforts and as a training tool for new engineers. In addition, an FMEA or FMECA is often required to comply with safety and quality requirements, such as ISO 9001, QS 9000, ISO/TS 16949, Six Sigma, FDA Good Manufacturing Practices (GMPs), Process Safety Management Act (PSM), etc.

You can use something as simple as a paper form or an Excel spreadsheet to record your FMEA / FMECA analyses. However, if you want to establish consistency among your organization's FMEAs, build a "knowledge base" of lessons learned from past FMEAs, generate other types of reports for FMEA data (e.g. Top 10 Failure Modes by RPN, Actions by Due Date, etc.) and/or track the progress and completion of recommended actions, you may want to use a software tool, such as ReliaSoft's Xfmea, to facilitate analysis, data management and reporting for your failure modes and effects analyses