Failure Modes, Effects, and Criticality

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].)... 

Failure modes and effects analysis (FMEA) A systematic, methodical analysis performed to identify and document all identifiable failure modes at a prescribed level and to specify the resultant effect of the failure mode at various levels of assembly (NSTS 22254) the failure or malfunction of each system component is identified, along with the mode of failure (e.g., switch jammed in the on position). The effects of the failure are traced through the system and the ultimate effect on task performance is evaluated. Also called failure mode and effect criticality analysis (ASSE) a basic system safety technique wherein the kinds of failures that might occur and their effect on the overall product or system are considered. Example The effect on a system by the failure of a single component, such as a register or a hydraulic valve (SSDC). 

FMECA Failure Mode and Effects Criticality Analysis... 

Failure Mode and Effect Criticality Analysis (FMECA)... 

MODEL 7.4 Failure mode and effect criticality analysis. 

Consultants ABS have carried out a detailed FMECA of blowout preventers Blowout preventer (BOP) failure mode and effect criticality analysis (FMECA) for the Bureau of Safety and Environmental Enforcement, Final Report, 2650788-DFMECA-3-D2, June 28, 2013. 

In (Andrawus et al., 2008) a hybrid of Failure Modes and Effect Criticality Andysis (FMECA) and Delay-Time Maintenance Model (DTMM) is used to find optimal inspection intervals for selected critical components. The failure modes of the turbines are determined by FMECA approach and then mean delay time are derived by DTMM approach. 

Functional Flow Diagrams, which model sequences of interactions within and external to the system. These diagrams will help to create the PHA and the Failure Modes and Effects Criticality Analysis (FMECA)... 

Hazard Analyses have been generated to identify and resolve potentially hazardous conditions, and these analyses are compatible with the associated Failure Modes and Effects Analysis/Failure Modes and Effects Criticality Analysis (FMEA/EMECA) as applicable... 

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. 

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. 

All of these factors determine the stress experienced by the workers and the extent to which operational errors will be recovered before disastrous consequences have ensued. In this context, hazard identification techniques, such as hazard and operability studies (HAZOP), failure modes and effects and criticality analysis (FMECA), fault trees, and others are useful in making the process environment more forgiving. 

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. 

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 ... 

Cichocki, T. and J. Gorski, Failure Mode and Effect Analysis for Safety-Critical Systems with Software Components, in Floor Koomneef, Meine van der Meulen (eds.) Computer Safety, Reliability and Security, Proceedings of 19th International Conference SAFECOMP 2000, Rotterdam (The Netherlands), October 24—27, 2000, Springer Lecture Notes in Computer Science 1943, p. 382-394. 

A failure mode and effects analysis (also known as failure mode and criticality analysis) examines a high-risk process in advance of an error to detect potential problems. The problems can then be fixed before an error occurs. It is used to discover the potential risk in a product or system. It involves examining a product or system to identify all the ways in which it might fail and allows for a proactive approach to fixing problems before they occur. 

It is critical to spend early development time using failure mode and effects analysis (FMEA) and establishing a design plan that minimizes or eliminates the potential failure modes identified as part of the design FMEA. Using multiple tests to evaluate failure modes is also a key component to success. 

Since diagnostics are such a critical variable in the calculations, the ability to measure and evaluate the effectiveness of the diagnostics is important. This is done using an extended failure modes and effects analysis technique (Ref. 9) and verified with fault injection testing (Ref. 10 and 11). The techniques were refined to include multiple failure modes (Ref. 12) and today are commonly used to evaluate diagnostic capability and failure mode split (Ref. 13). 

Instructions for preparation of failure modes and effects analyses and critical items list Methodology for conduct of NSTS hazard analyses... 

Common techniques for hazard analysis are the failure modes and effects analysis (FMEA) and fault tree analysis (FTA). Many of the other techniques listed in Chapter 17 are also used. TTie FMEA is considered a reliability tool and used, in most NASA and NASA contractor organizations, by a separate reliability division or branch. The FMEA is used to generate another popular NASA tool, the critical items list (CIL). 

Based on the results of the PHA, recommendations made by 30% review boards, and guidance provided in the system safety program plan, detailed hazard analyses are made of specified (critical) subsystems. The techniques for these SSHAs are as outlined in the system safety program plan or as selected by the SSWG. Failure modes and effects analysis (FMEA) and/or fault tree analysis (FTA) are generally the techniques of choice. Software hazard analysis, common cause analysis, and/or sneak circuit analysis may also be appropriate. 

Fault tree analysis is used primarily as a tool for conducting system or subsystem hazard analyses, even though qualitative or top-level (that is, limited number of tiers or detail) analyses may be used in performing preliminary hazard analyses. Generally, FTA is used to analyze failure of critical items (as determined by a failure mode and effects analysis or other hazard analysis) and other undesirable events capable of producing catastrophic (or otherwise unacceptable) losses. 

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). 

The PHA (Figure 6.2) is perhaps the most critical analysis that will be performed because it is usually the first in-depth attempt to isolate the hazards of a new or, in some cases, modified system. The PHA will also provide rationale for hazard control and indicate the need for further, more detailed analyses, such as the subsystem hazard analysis (SSHA) and the system hazard analysis (SHA). The PHA is usually developed using the system safety techniques known as failure mode and effect analysis (FMEA) (Chapter 9) and/or the ETBA. Data required to complete... 

In the failure mode and effects described above, one failure mode has been assessed as critical. The analyst should now provide either acceptance or rejection rational so that management can evaluate all aspects of this failure mode and effect before making a decision. Remember that one of the primary underlying purposes of the system safety effort is to provide management with choices in their evaluation of system risk. 

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