Failure Modes and Effects Analysis Process
The process for conducting a Failure Modes and Effects Analysis (FMEA) is presented here. This process is shown in a flowchart.
Assembling the Team and Establishing a Rating System
It is important to assemble a team that has comprehensive knowledge of the process — from design through operation — to perform the analysis. The team must first establish a method of rating occurrence, severity, and detection of failure modes. For example, a team could use a scale of 1 through 10 to rank occurrence, severity, and detection. Any system can be developed provided it is applied consistently.
The team must then establish a threshold for acceptable risk relative to the rating scale. In general, the established factors (rating values of severity, occurrence, and detection) are multiplied. The result is the Risk Priority Number (RPN). The threshold of tolerance is then established relative to the RPN.
Identifying and Ranking Failure Modes
The team identifies possible failure modes, along with the measures (both design and administrative) used to control hazards. This is done for each failure mode and is documented in a table format. The team then rates each failure mode and calculates the RPN. The analysis continues for each failure mode.
Mitigating Risk
After calculating the RPN for each failure mode, the team assesses risk that falls beyond acceptable levels. Based on the nature of the risk, appropriate prevention and mitigation measures are identified.
Risks can be mitigated, or made less severe, in three ways:
- Detection of risk and taking corrective action before negative consequences occur
- Prevention of risk by minimizing the probability of occurrence
- Control of risk by implementing process parameters to increase margins and minimize severity or frequency.
The following are examples of detection, prevention and control for hydrogen fueling stations:
Detection: Sensors can be used to measure process parameters, identify deviations in normal operating conditions, detect mechanical yielding, and spot leaks.
Prevention: Hydrogen systems can be redesigned to eliminate potential risks. Typical methods include reducing potential leak paths and component failures.
Control: Control valves with automatic shutdown features can isolate hydrogen in the event of a single component failure or leak. Controls can help perform regular safety checks on system components as well.
After all risks are deemed acceptable, the FMEA is included as part of the design documentation. The FMEA is considered a working document that does not end at this step. As operational data are obtained, the FMEA should be reevaluated. Any changes to risk level that result in an unacceptable outcome need to be reevaluated to reduce risk levels. While the FMEA is effective, it does have limitations.