FMEA/FMECA criticality analysis

We previously encountered failure modes and effects (FMEA) and failure modes effects and criticality analysis (FMECA) as qualitative methods for accident analysis. These tabular methods for reliability analysis may be made quantitative by associating failure rates with the parts in a systems model to estimate the system reliability. FMEA/FMECA may be applied in design or operational phases (ANSI/IEEE Std 352-1975, MIL-STD-1543 and MIL-STD-1629A). Typical headings in the F.Mld. A identify the system and component under analysis, failure modes, the ef fect i>f failure, an estimale of how critical apart is, the estimated probability of the failure, mitigaturs and IHissihiy die support systems. The style and contents of a FMEA are flexible and depend upon the. ilitcLiives of the analyst. 

In the FMECA procedure [2,3,256], an exhaustive list of the equipment is first made. Every item on the list is then reviewed for possible ways in which it can fail (the failure modes are open, closed, leaks, plugged, on, off, etc.). The effects of each failure mode are then recorded and a criticality ranking of every item of equipment is calculated. A limitation of this procedure is that combinations of failures which may cause an incident are not really identified. Failure modes and effects analysis (FMEA) is the same procedure without the criticality analysis. 

FMEA is a prospective hazard analysis technique which is widely used in many domains and increasingly in the service industries [4]. The methodology has its origins in military systems and the aerospace industry in the 1960s. Subsequently the automotive and chemical engineering sectors adopted the tool - indeed in some regulated industries application of the technique is now mandatory. The objective of the tool is to identify what in a product can fail, how it can fail, whether failure can be detected and the impact that will have. The technique can be supplanented with a Criticality Analysis which takes into account the severity of the failure. When this extension is employed, the technique is often called FMECA. 

In this chapter we explore the Failure Modes Effects Analysis (FMEA) and the Failure Modes Effects Criticality Analysis (FMECA) which, as the name suggests, simply is an extension of the FMEA.i This chapter will use the acronym EMEA and highlight those instances where is extended to include EMECA. 

BS5760, 1991. Reliability of Systems, Equipment and Components Part 5 Guide to Failure Modes, Effects and Criticality Analysis (FMEA and FMECA). British Standards Institute. 

In most organizations that have a reliability effort separate from the safety or system safety effort, an FMEA is considered a reliability tool. The safety version is called a failure modes and effects criticality analysis (FMECA). 

Used originally as a reliability tool, the FMEA is now often used to identify and prioritize safety problems associated with hardware failures. This is usually done by including a risk assessment code (RAC) in the analysis (Table 14-1). (Note When a RAC or other method of quantifying is used to identify critical safety items, some organizations and analysts call the technique failure mode and effects criticality analysis [FMECA].)... 

A system design or condition such that the failure of a component, subsystem, or system, or input to it, will automatically revert to a predetermined safe static condition or state of least critical consequence. The opposite of fail-safe is fail to danger. See also Failure Mode Failure Mode and Effects Analysis (FMEA/FMECA). 

FMEA is a method widely used in the industrial sector to perform reliability and safety analyses of engineering systems. It is a powerful tool used to perform analysis of each potential failure mode in a system to determine the effects of such failure modes on the total system [1,2]. When FMEA is extended to classify the effect of each potential failure according to its severity, it is called failure mode effects and criticality analysis (FMECA). 

Reliability of systems, equipment and components. Guide to failure modes, effects and criticality analysis (FMEA and FMECA)... 

Failure Modes and Effects Analysis (FMEA) is a hazards analysis technique used to analyze equipment items. The method examines the ways in which an equipment item can fail (its failure modes), and examines the effects or consequences of such failures. If the criticality of each failure is to be considered, then the method becomes a Failure Modes, Effects, and Criticality Analysis (FMECA). The consequences have to do with safety, reliability, or environmental performance. 

FMEA is an analytical method used to identify potential problems in the product and in its process of development. It is an inductive method used for identification of hazards of a system with single point failure. When criticality analysis is added with FMEA it is known as failure mode effect and criticality analysis (FMECA). It was used as early as 1950 in reliability engineering. FMEA/FMECA is mainly used for manufacturing, product development, etc. 

When criticality analysis is also done it is referred to as FMECA. In fact, prioritization is done mainly based on criticality analysis so that the most critical issue is addressed first. FMEA reduction may be in terms of reducing severity or lowering the occurrence, or both. When the root cause is addressed, then it will be almost impossible to occur. So, in a nutshell, FMEA could be used as a guiding tool to the complete set of actions in product development process so that risks are either avoided or mitigated in the systems, subsystems, or components (to an acceptable limit). 

FAILURE MODES AND EEEECTS ANALYSIS (FMEA) also called Failure Modes, Effects, and Criticality Analysis (FMECA)... 

Fault trees, failure modes and effects analysis (FMEA), failure modes effects and criticality analysis (FMECA) and event trees use logic, reliability data (component failure rates), and assessed system failure rates, combined with human error failure rates (using methodologies such as HEART or THERP) and other methodologies such as software reliability assessment, to develop estimates of system failure frequencies, and hence plant accident frequencies. 

Failure Mode and Effects Analysis (FEMA)—FEMA is a tabulation of facility equipment items, their potential failure modes, and the effects of these failures on the equipment or facility. Failure mode is simply a description of what caused the equipment to fail. The effect is the incident, consequence, or system response to the failure. It is usually depicted in tabular format and expresses failures in an annual estimation. A FEMA is not useful for identifying combinations of failures that can lead to incidents. It may be used in conjunction with other hazard identification techniques such as HAZOP for special investigations such as critical or complex instrumentation systems. There is also a Failure Modes, Effects, and Criticality Analysis (FMECA), which is a variation of FMEA that includes a quantitative estimate of the significance of the consequence of a failure mode. 

A failure modes, effects and criticality analysis (FMECA) (or its simpler form, FMEA) is a systematic method of identif5dng a system failure modes. FMEA is implemented by considering each equipment item and associated systems in the plant, detailing the possible failure modes (e.g. leak or break in the case of pressure equipment), and determining their resulting effect on the rest of the system. The analysis is more concerned with specif5ung the likely effects and criticality of different modes of failure rather than the mechanisms or events leading to a specific failure [11]. 

Failure Mode and Effects (and Criticality) Analysis (FMEA/FMECA) are structured methodologies for the identification and analysis of the effects of latent equipment failure modes on system performance. This is a bottom-up process starting with the failure of a constituent/subsystem and investigating the effect of this on the system. It should be conducted by a team of experts with cross-functional knowledge of the analysed system, process or product. The methodology consists of the following steps ... 

Failure mode effects and criticality analysis (FMECA) is an extended version of FMEA. More clearly, when FMEA is extended to group or categorize each failure effect with respect to its level of severity (this includes documenting catastrophic and critical failures), then it (i.e., FMEA) is called FMECA. It was developed by the National Aeronautics and Astronautics Administration (NASA) for assuring the required reliability of space systems. A military standard titled "Procedures for Performing a Failure Mode, Effects, and Criticality Analysis" was developed by the U.S. Department of Defense in the 1970s [20]. 

The CIL is a list of items that is considered critical for reliable and/or safe operation of the system. The list is generated from the FMEA and the failure modes and effects and criticality analysis (FMECA). Although it is primarily a rehabihty product, it can be used for system safety purposes. 

In this section, the qualitative analysis aimed at identifying the hazards and failure mechanisms associated to the operation of a system is exemplified by way of a very common method known as failure mode and effects analysis (FMEA). Actually in practice, a FMECA (failure mode, effects, and criticality analysis) is typically performed to arrive at also assigning a criticality class to each failure mode, for example, according to the following ranking ... 

The process of conducting a Failure Mode, Effects and Critical Analysis (FMECA) can be examined in two levels of detail. Failure Mode and Effects Analysis (FMEA) is the first level of... 

The general process of FMECA and criticality analysis has been described in Chapter 3. In an FMEA, Risk Priority Number (RPN) can also be used to model each failure mode in order to rank all the failure modes. Such a process can be divided into several steps as seen in Figure 7.1. These steps are briefly explained as follows ... 

Process analysis A prerequisite for other processes (FMEA/FMECA, PRA, HACCP) in order to describe an activity that brings together all the functional constraints (flows, resources etc.) in order to identify critical points and improve the steps in its functions, particularly with regard to interfaces between services Requires a knowledge of the need that has to be met in relation to the available resources... 

FMECA adds Criticality Analysis (CA) to the FMEA. The difference between these two safety techniques is best understood in terms of the following equation ... 

General considerations, preliminary tasks, FMECA, and report analysis. Major issues involved shall include but not limited to Basic background rule, FMEA with relevant worksheet, reporting and updating. It also provides detailed flow diagram for FMEA. Critical matrix and FMECA are also included. 

---