Failure Mode And Effect Analysis (FMEA)

FAILURE MODE AND EFFECT ANALYSIS (FMEA)

            This is an analytic technique, which explores the effects of failures or malfunctions of individual components in a system – i.e., “if this part fails, in this manner, what will be the result?”. First the system under the consideration must be defines, so that system boundaries are established. Thereafter the essential questions are:

1. How can each component / part fail?
2. What might cause these modes of failure?
3. What could the effects be if the failures did occur?
4. How serious are these failure modes?
5. How is each failure mode detected?

An example FMEA worksheet:

Component / part	Potential failure mode	Potential effects of failure	Severity	Potential causes of failure	How will failure be detected	Action to control risk
Bulb	Filament break	No illumination	/	Voltage too high	Human visual	Regulate voltage
Bulb	implosion	Etc.,

NOTE: There are many software's available for FEMA, the format of one differs to another.

The level of risk determined by Risk Matrix

Or         RISK = PROBABILITY OF FAILURE X SEVERITY CATEGORY

Where severity may be categorized thus:

Category	Degree	Description
I	Minor	Functional failure of part of machine or process – No potential injury
II	Critical	Failure will probably occur without major damage to system or serious injury
III	Major	Major damage to system another potential serious injury to personnel
IV	Catastrophic	Failure causes complete system loss and / or potential or fatal injury

And probability may be categorized thus:

Level	Probability	Individual Failure Mode
A	Frequent	Likely to occur frequently.
B	Probable	Likely to occur several times in the life of an item.
C	Occasional	Likely to occur sometime in the life of an item.
D	Remote	Unlikely to occur but possible.
E	Improbable	So unlikely that occurrence may not be experienced.

Application:

                     A practical application of the FEMA technique would involve the completion of a worksheet in which the failure modes of individual components, such as relays and switches, are identified, evaluated and risk priority codes identifies. A summary sheet can then be prepared in which failure modes are listed in declining order or risk priority codes. The summary should also list the corrective measures required to reduce the frequency of failure or to mitigate the consequences. Corrective actions could include changes in design, procedures organizational arrangements e.g. the additional of redundant features and detection methods or a change in maintenance policy may be suggested.

                   FMEA can be used for single point failures but can be extended to cover concurrent failure modes. It can be a costly and time consuming process but once completed and documented it is available for future reviews and as a basis for other risk assessment techniques such as Fault Tree Analysis and Event Tree Analysis.