For example, if the fire alarm fails, an FTA will use that as a top event. The diagram then explores potential causes whether the fire detection system failed or the heat sensors failed until the root cause is found. On the other hand, FMEA is an inductive method, which applies a general rule to a particular situation. These two very different approaches have their consequences when it comes to determining failure modes.
However, they have one thing in common: both approaches require someone with deep knowledge about the asset and its reliability. An FMEA analysis hinges on predicting all possible failure modes for each component. You can break them down into modes that cause a complete breakdown; partial failures and almost unnoticeable damage.
Unlike FTA, it will not take into account conditioning events, nor does it establish the relationship between multiple failures. An example is what happened at the nuclear power plant in Fukushima, Japan. Initially, the reactors survived the impact of the earthquake thanks to backup power generators. Given this, the selection of a Risk Management tool is exclusively depends upon the nature and the complexity of system or a process considered for analysis.
By Pavan Kishore Kota Subramanya. Leave a Comment. Save my name, email, and website in this browser for the next time I comment. FTA uses Boolean Logic to combine a series of lower-level events and its top-down approach to detect the component level failures basic events that cause the system level failure top-event to occur.
FTA consists of two elements: events and logic gates that connect the events to recognize the causes of the top events system-level failures.
In general, FTA is a more straightforward method than FMEA since it concentrates on all possible system failures of the undesirable top event. However, with FMEA, it analyzes to find all possible system failure modes regardless of their severity.
A side-by-side comparison of the steps of the FMEA process vs. Assemble the team. Define the system. List failure modes and effects. Define top-level faults. Rank severity. Identify causes for a top-level event. List the potential causes.
Identify the next level of events. Rank likelihood occurrence. Identify the root causes. List the process controls. Add probabilities to the events. Rank detection.
TWI is an Industrial Membership based organisation. TWI's experts can provide your company with an extension to your own resources as well as engineering consultancy services. Our experts are dedicated to helping industry improve safety, quality, efficiency and profitability in all aspects of materials joining technology. Industrial Membership of TWI currently extends to over companies worldwide, embracing all industrial sectors. The versatility of FMEA means that it is widely used for root cause analysis.
The failure is the fact that the machine is not printing, but the potential failure modes could be that the paper is jammed in the tray or that the printer ink has run out. So, one failure with two failure modes. FMEA not only highlights potential failure modes, but also assigns a value to the effect and impact of each failure.
This can be combined with a criticality analysis which demonstrates the different outcomes as a result of a failure, this is known as FMECA Failure Modes, Effects and Criticality Analysis.
FMEA works by thoroughly detailing a list of failure modes, causes and impacts. This information is usually presented as a table with seven columns that each detail a different step, as follows:. This is quite simply listing the potential causes of a given failure. For example, with a printer not working, the failure modes could include a paper jam, running out of paper, running out of ink, the power not being on, and so forth.
It is important not to forget any failure modes as this could compromise your risk assessments. This step time-consuming step can be sped up by cross-referencing failure modes for similar components or systems. The second step is to describe the effect of the failure, which can then be used to determine the severity of the failure in step three. Our broken printer may not have a big effect, depending on how often it needs to be used and for what tasks, or it could be deemed a critical item of equipment.
This third step involves determining the severity rating of your failure, based on the description in step two. The severity rating is scored on a scale of , as follows:. Each failure mode could have a number of root causes that need to be listed in step four.
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