Failure Modes and Effect Analysis

The Failure Mode and Effect Analysis (FMEA) is based on the systematic analysis of failure modes for each element of a system, by defining the failure mode and the consequences of this failure on the integrity of that system. It was first used in the 1960s in the field of aeronautics for the analysis of the safety of aircraft [15]. It is required by regulations in the USA and France for aircraft safety. It allows assessing the effects of each failure mode of a system s components and identifying the failure modes that may have a critical impact on the operability safety and maintenance of the system. It proceeds in four steps  

the system is to be defined with the function of each of its components, 

the failure modes of the components and their causes are established, 

One important point in this type of analysis is to define clearly the different states of the working system, to ensure that it is in normal operation, in a waiting state, in emergency operation, in testing, in maintenance, and so on. The depth 

In order to illustrate the method, we can take the example of a pump as a component. It may fail to start or to stop when requested, provide too low a flow rate or too low a pressure, or present an external leak. The internal causes for pump failure may be mechanical blockage, mechanical damage, or vibrations. The external causes may be power failure, human error, cavitation, or too high a head loss. Then the effect on the operation of the system and external systems must be identified. It is also useful to describe the ways for detecting the failure. This allows establishing the corrective actions and the desired frequency of checks and maintenance operations. 

There are basically two types of failure mode and effect analyses. They are distinguished more by the target of the analysis than the actual analysis itself. In fact, the steps required in the performance of each are very similar only the items being analyzed differ. Perhaps the fundamental difference between the two is in their approach. The first type, often referred to as the functional FMEA, utilizes the deductive reasoning approach (i.e., it begins by assuming a failure and focuses 

Basic Guide to System Safety, by Jeffrey W. Vincoli Copyright 2006 John Wiley Sons, Inc. 

The functional FMEA targets any subsystems that may exist within an entire system. The functional FMEA will evaluate each subsystem and attempt to identify the effect of any failures in these subsystems. The analyst not only looks for the possible effects of subsystem failures on the system as a whole but also examines the effect of such failures on other subsystems within the system. Although functional FMEAs are not as common as the hardware FMEA, their basic utility should not be dismissed. When a complex system (such as a nuclear reactor, an airliner, an overhead bridge crane, or a new robotic milling machine) consists of numerous secondary subsystems, each with its own set of supporting subsystems, the functional FMEA should be performed to ensure proper system safety evaluation at every level. 

The second and more common hardware FMEA examines actual system assemblies, subassemblies, individual components, and other related system hardware. This analysis should also be performed at the earliest possible phase in the product or system life cycle. Just as subsystems can fail with potentially disastrous effects, so can the individual hardware and components that make up those subsystems. As with the functional FMEA, the hardware FMEA evaluates the reliability of the system design. It attempts to identify single-point failures, as well as all other potential failures, within a system that could possibly result in failure of that system. Because the FMEA can accurately identify critical failure items within a system, it can also be useful in the development of the preliminary hazard analysis and the operating and support hazard analysis (Stephenson 1991). It should be noted that FMEA use in the development of the O SHA might be somewhat limited, depending on the system, because the FMEA does not typically consider the ergonomic element. Other possible disadvantages of the FMEA include its purposefiil omission of multiple-failure analysis within a system, as well as its failure to evaluate any operational interface. Also, in order to properly quantify the results, a FMEA requires consideration and evaluation of any known component failure rates and/or other similar data. These data often prove difficult to locate, obtain, and verify (Stephenson 1991). 

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Methods for performing hazard analysis and risk assessment include safety review, checkhsts, Dow Fire and Explosion Index, what-if analysis, hazard and operabihty analysis (HAZOP), failure modes and effects analysis (FMEA), fault tree analysis, and event tree analysis. Other methods are also available, but those given are used most often. 

Failure Mode and Effects Analysis. The system design activity usually emphasizes the attainment of performance objectives in a timely and cost-efficient fashion. The failure mode and effects analysis (FMEA) procedure considers the system from a failure point of view to determine how the product might fail. The terms design failure mode and effects analysis (DFMEA) and failure mode effects and criticaUty analysis (EMECA) also are used. This EMEA technique is used to identify and eliminate potential failure modes early in the design cycle, and its success is well documented (3,4). 

Chrysler Corporation, Ford Motors, General Motors Corporation 1995 Potential Failure Mode and Effects Analysis (FMEA) - Reference Manual, 2nd Edition. 

A risk assessment analyses systems at two levels. The first level defines the functions the system must perform to respond successfully to an accident. The second level identifies the hardware for the systems use. The hardware identification (in the top event statement) describes minimum system operability and system boundaries (interfaces). Experience shows that the interfaces between a frontline system and its support systems are important to the system cs aluaiion and require a formal search to document the interactions. Such is facilitated by a failure modes and effect analysis (FMEA). Table S.4.4-2 is an example of an interaction FMEA for the interlace and support requirements for system operation. 

A failure modes and effects analysis delineates components, their interaction.s ith each other, and the effects of their failures on their system. A key element of fault tree analysis is the identification of related fault events that can contribute to the top event. For a quantitative evaluation, the failure modes must be clearly defined and related to a numerical database. Component failure modes should be realistically and consistently postulated within the context of system operational requirements and environmental factors. 

How do you then design an effective system There are several techniques you can use. Failure Modes and Effect Analysis (FMEA), Fault Tree Analysis (FTA), and Theory of Constraints (TOC) are but three. The FMEA is a bottom-up approach, the FTA a top-down approach, and TOC a holistic approach. 

There is one technique widely used in the automotive industry for detecting and analyzing potential nonconformities Failure Modes and Effects Analysis (FMEA). There are Design FMEAs and Process FMEAs. The technique is the same - it is only the focus that is different. As clause 4.14 addresses potential nonconformities, the subject of FMEAs is treated in Part 2 Chapter 14. 

The lists of critical items that were described under Identifying controls in Part 2 Chapter 2, together with Failure Modes and Effects Analysis and Hazard Analysis, are techniques that aid the identification of characteristics crucial to the safe and proper functioning of the product. 

A failure modes and effects analysis is a systematic analytical technique for identifying potential failures in a design or a process, assessing the probability of occurrence and likely effect, and determining the measures needed to eliminate, contain, or control the effects. Action taken on the basis of an FMEA will improve safety, performance, reliability, maintainability and reduce costs. The outputs are essential to balanced and effective quality plans for both development and production as it will help focus the controls upon those products, processes, and characteristics that are at risk. It is not the intention here to give a full appreciation of the FMEA technique and readers are advised to consult other texts. 

Guidelines to failure modes and effects analysis (SMMT)... 

Potential failure mode and effects analysis (FMEA) (GM, Ford, Chrysler)... 

This paper describes a reliability analysis of dual - diaphragm pumps in uranium solution service. It is part of the output from a failure modes and effects analysis of the design for a system to be installed at the Oak Ridge Y-12 plant. The study involved collecting data on pumps with Viton and Teflon diaphragms at 10 gpm and 15 gpm. 

Failure Modes and Effects Analysis (FMEA) A hazard identification technique in which all known failure modes of components or features of a system are considered in turn and undesired outcomes are noted. 

Hazard Analysis Report - Hazard and Operability Study (HAZOP), failure mode and effect analysis, quantitative fault tree analysis or what/if check list (sec Part IV for details in theses subjects)... 

The what-if analysis is a creative, brainstorming examination of a process or operation conducted by a group of experienced individuals able to ask questions or voice concerns about undesired events. It is not as inherently structured as some other methods, such as the hazard and operability (HAZOP) study or a failure mode and effects analysis (FMEA). 

Table 4.21. Time Estimates for Using the Failure Mode and Effects Analysis Method...

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