I am often asked about the application of detection in FMEAs. When and how to assess for the risk of detection can be confusing. Here are some pointers for when and how to use detection in an FMEA.
We’ll start with a definition. The Oxford English dictionary defines “detection” as “the action or process of identifying the presence of something concealed.”
What is Detection in FMEA?
Here is an excerpt from one of my articles posted as part of the “Inside FMEA” series, called “Understanding FMEA Detection: Part 1.”
Detection is a ranking number associated with currently planned detection-type controls, based on the criteria from the Detection scale. The detection ranking considers the likelihood of detection of the failure mode/cause, according to defined criteria.
Simply put, detection is an assessment of the risk that the currently planned detection controls will not detect the failure mode and associated cause in a timely manner. The article goes on to describe the application of detection in Design and Process FMEAs.
One word . . . two different applications
Unfortunately, the same word “detection” can be used in two very different scenarios. Some FMEA practitioners are immersed in one of the scenarios, not realizing the other scenario exists. Let’s examine both of them.
Scenario One: Detection during product development
One of the roles of detection in Design and Process FMEAs is to identify risk from inadequate tests or analyses during product development. Although the primary objective of Design and Process FMEA is to improve the product or process design, an important secondary objective is to improve testing. It is not always possible to reduce risk to an acceptable level by design improvements only. Often it takes improving the ability of tests and analyses to detect failure modes and associated causes so they can be remedied before product launch.
In automotive applications, and certain other industries, you will be using detection ratings as part of risk prioritization in the FMEA, along with Severity and Occurrence. In Automotive standards, such as SAE J1739:2021, and AIAG/VDA:2019, the detection scale is used to assess risk related to detection of a given failure mode and associated cause during product development.
Chapter 5, 6, and 7 of Effective FMEAs covers this type of detection, and supports the application of detection risk during product development.
Scenario Two: Detection during product usage?
Many complex systems monitor performance during customer usage and are designed to detect when system response is needed. Failure to detect system malfunction in a timely manner is a risk.
According to MIL-STD 1629A, a Failure Detection Method is a “description of the methods by which occurrence of the failure mode is detected by the operator. The failure detection means, such as visual or audible warning devices, automatic sensing devices, sensing instrumentation, other unique indications, or none shall be identified.”
Defense industry projects often use MIL-STD 1629A as their FMEA standard, and typically consider Failure Detection Method, as defined above, in their analysis. They typically do not assess and manage Detection risk during product development. This is an opportunity for improvement.
If you are part of the defense industry, or if your company uses one of the defense-related FMEA standards, such as MIL-STD 1629A, you will be considering Detection as part of operational risk. In this case, the ability of the system to detect performance or safety issues is assessed during operation, and improvements to risk mitigation can be recommended.
Chapter 12 of Effective FMEAs is dedicated to FMECA, provides an overview of Criticality Assessment (CA), and aligns with MIL-STD 1629A and its applications. The earlier chapters are also applicable for FMEA fundamentals.
What about Supportability FMEAs?
If you are doing Supportability FMEAs, you are not as concerned about potential test deficiencies during product development, and your detection risk is focused on operations.
According to the presentation from JC Leverette at the recent RAMS FMEA Panel, the objective of Supportability FMEA is to identify those failures that need to be corrected after they occur. It should be used to influence design for improved support (reduce resources required), and as an input for Reliability Centered Maintenance (RCM) analysis.
What is this new extension of FMEA called “Supplemental FMEA-MSR”?
Referencing SAE J1739:2021, “Supplemental FMEA for Monitoring and System Response (FMEA-MSR) is an extension of the Design FMEA. It provides a means of assessing risk reduction due to diagnostic detection with a subsequent response during customer operation.” Supplemental FMEA-MSR will determine whether or not the currently planned diagnostic detection can allow a reduction in Severity rating. The “M” part of FMEA-MSR is Diagnostic Monitoring, and it is the detection of an abnormal condition that leads to an undesired state of operation. I will write about Supplemental FMEA-MSR in a future Inside FMEA article.
What are common misunderstandings about Detection?
As covered in “Understanding FMEA Detection: Part 1”, one of the common misunderstandings or misapplications of the detection scale is to confuse or co-mingle three factors of detection risk:
- Likelihood of detection by the identified controls – specifically, what is the likelihood that the current detection-type control will be able to discover the failure mode or its cause (remote, low, moderate, high, etc.)
- Timing of the opportunity for detection – specifically, what is the timing of the current detection-type control (prior to design freeze, post design freeze, in service, etc.)
- Type of test used to detect the cause of the problem – specifically, what is the quality of test method used to detect the failure mode or its cause (degradation test, test to failure, pass/fail test, etc.)
Depending on the Detection scale you are using, you can consider all three of these factors when assessing Detection in an FMEA.
Whether you are doing FMEAs in support of automotive industry, defense industry or any other industry or application, there is risk related to detection both during product development, and in operation. If you are considering Severity and Occurrence for your risk prioritization (without Detection), you still have risk related to Detection.
My personal view is if you are doing Design or Process FMEAs, you should use all three risk rating scales, Severity, Occurrence, and Detection. That way you can assess risk from potential design deficiencies, as well as risk from potential test deficiencies, and take action to reduce risk. You also need to understand and assess risk related to detection in-service, using either Supplemental FMEA-MSR or analysis of Failure Detection Method.
There is a new FMEA standard that is in progress that will integrate the approaches. It will replace MIL-STD 1629A and attempt to integrate the best practices from all FMEA applications. I will be writing a future article in the Inside FMEA series on this new FMEA standard.
In the next Inside FMEA article I will take up another set of reader questions, concerning Occurrence ratings, and whether they should be objective or subjective. Lots to share on this important topic.
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