Failure mode and effects analysis (FMEA)
What is FMEA?
FMEA stands for failure mode and effects analysis and is a step-by-step risk management, process analysis tool for identifying where and how failures might occur in a design, manufacturing, or assembly process for a product or service. It assesses the relative impact of different failures in order to identify the parts of the process that need to change.
FMEA is also referred to as potential failure modes and effects analysis, or failure modes, effects and criticality analysis (FMECA).
"Failure modes" refers to the ways, or modes, in which something might fail within a process. Failures are any potential or actual errors or defects.
"Effects analysis" refers to studying the consequences of those failures.
Failures are prioritized according to how severe their consequences are, how frequently they occur, and how easily they can be detected. Severity describes the seriousness of failure consequences. Frequency describes how often failures can occur. Detectability refers to the degree of difficulty in detecting failures. The overall goal of FMEA is to provide insight into what actions need to be taken to eliminate or reduce failures, starting with the highest-priority ones.
Failure modes and effects analysis is also used for continuous improvement. For example, FMEA is used during design to prevent failures before systems are built. It’s also used for quality control by assessing ongoing operations and processes. Ideally, effective FMEA begins during the earliest conceptual stages of design and continues throughout the life of the product or service.
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What are the 5 steps of the FMEA process?
The five most basic steps when conducting FMEA include identifying potential failures and effects, determining the severity of each, gauging the likelihood of each failure occurring, failure detection, and assigning a risk priority number. Each step is described in greater detail below.
Step 1: Identify potential failures and effects
The first FMEA step is to analyze functional requirements and their effects and identify all potential areas of failure. It’s important to consider that failure modes in one component can induce failure in others. List all failure modes per function and consider the ultimate effect(s) of each failure mode. Examples of failure effects include overheating, noise, abnormal shutdown, or user injury.
Step 2: Determine severity
Severity refers to how serious the consequences and effects are of a failure. A number of severity is assigned to each failure, with one being the lowest severity and 10 being the highest. Typical FMEA severity ratings are as follows:
1 - No effect, no danger
2 - Very minor – usually noticed only by very observant users
3 - Minor – only a minor part of the system is affected; the failure is noticed by average users
4-6 - Moderate – most users are merely inconvenienced and/or annoyed
7-8 - High – there is a loss of primary function; users are dissatisfied
9-10 - Very high – failure constitutes a safety hazard and can cause injury or death, or the product becomes inoperative ,and customers become angry
Step 3: Gauge likelihood of occurrence
Examine and document the cause(s) of each failure mode and how often failure occurs. Look at similar processes or products and their documented failure modes. Examples of causes can include incorrect algorithms, insufficient or excess voltage, the temperature or humidity of the operating environment. Failure modes are also assigned a number based on occurrence, with 1 being the lowest and 10 being the highest.
1 - No documented failures on similar products or processes
2-3 - Low - relatively few failures occur
4-6 - Moderate - there are some occasional failures
7-8 - High - repeated failures are experienced
9-10 - Very high - failure is almost certain ,and the results in a hazard
Step 4: Failure detection
Determine corrective actions and when they should be tested for efficacy and efficiency. Verify and inspect procedures within the design of the system or process. A detection value is assigned to each failure indicating how likely the failure will be detected, and ranks the ability of identified actions to remedy or remove defects or detect failures. The higher the value of D, the more likely the failure will not be detected.
1 - Fault is certain to be detected by testing
2 - Fault is almost certain to be detected by testing
3 - High probability that testing will detect the fault
4-6 - Moderate probability that tests will detect the fault
7-8 - Low probability that testing will detect the fault
9-10 - Fault will be passed undetected to the end-user/customer
Step 5: Calculate the risk priority number (RPN)
Risk priority numbers (RPNs) influence which actions will be taken against failure modes. RPN is calculated from the values of severity, occurrence, and detection as follows:
RPN = Severity * Occurrence * Detection (or RPN = S x O x D)
RPN should be calculated for the entire design and/or process and documented in the FMEA. The highest RPNs should get the highest priority for corrective measures. These measures can include a variety of actions including new inspections, tests or procedures, design changes, different components, added redundancy, modified limits, etc.
The goals of corrective measures are to eliminate failure modes, minimize the severity of failure modes, reduce the failure rate, and improve the detection of failure modes. When corrective measures are implemented, RPN is calculated again and the results are documented in the FMEA.