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.

What if Analysis

“WHATIF” HAZARD ANALYSIS

                   “What–If” Hazard Analysis is a structured brainstorming method of determining what things can go wrong and judging the likelihood and severity of those situations occurring. The answers to these questions form the basis for making judgments regarding the acceptability of those risks and determining a recommended course of action for those risks judged to be unacceptable.

                   Assembling an experienced, knowledgeable team is probably the single most important element in conducting a successful “WhatIf” analysis. Individuals experienced in the design, operation, and servicing of similar equipment or facilities are essential. Their knowledge of design standards, regulatory codes, past and potential operational errors as well as maintenance difficulties brings a practical reality to the review. Team members may include the P.I., Laboratory Manager, RM&S representative(s), and representatives with specific skills, as needed (maintenance rep., compressed gas rep., manufacturer rep. etc.).

                The next most important step is gathering the needed information. The operation or process must be understood by the review team. If these documents are not available, the first recommendation for the review team becomes clear. Develop the supporting documentation! Effective reviews cannot be conducted without updated reliable documentation. An experienced team can provide an overview analysis, but not without proper documentation. 

“WhatIf” questions can be formulated around human errors, process upsets, and equipment failures.

The questions could address any of the following situations:

• Failure to follow procedures or procedures followed incorrectly
• Procedures incorrect or latest procedures not used
• Operator inattentive or operator not trained
• Procedures modified due to upset
• Process conditions upsets
• Equipment failure
• Instrumentation miscalibrated
• Debugging errors
• Utility failures such as power, steam, gas
• External influences such as weather, vandalism, fire
• Combination of events such as multiple equipment failures

             To minimize the chances that potential problems are not overlooked, moving to recommendations is held until all of the potential hazards are identified.

           The review team then makes judgments regarding the likelihood (e.g., unlikely, possible, quite possible) and severity (e.g., minor, serious, very serious) of the “WhatIf” answers. If the risk indicated by those judgments is unacceptable then a recommendation is made by the team for further action. The completed analysis is then summarized and prioritized, and responsibilities are assigned.

Measures of Flammability

MEASURES OF FLAMMABILITY

             Several terms are important when evaluating the flammability of a material.The flash point is the temperature at which a liquid gives off sufficient vapors for an external ignition source to cause a flame to flash across the surface of the liquid.

However, if the ignition source is removed, the flame will go out because self sustained combustion is not possible at this temperature. Several methods are available for testing flash point; Tag Closed Cup ASTM D-56, Tag Open Cup ASTM D-1310, Cleveland Open Cup ASTM D-92, and Pensky-Martens Closed Cup ASTM D-93.



The ignition temperature or fire point is the temperature at which the material will begin self-sustained combustion if an external ignition source is used to initiate the process. This temperature is usually only slightly higher than the flash point. The auto-ignition temperature is the point at which the material has been sufficiently heated for combustion to occur without an external ignition source.

The flammable or explosive range identifies the percentage mixture of flammable vapor or gas in air that can be ignited. The flammable range is the area between the upper (UFL) and lower (LFL) flammable limits, also referred to as explosive limits (UEL and LEL). Gasoline, for example, has a lower flammable limit of approximately 1.5 and an upper flammable limit of approximately 7.5. This means that if its vapors are mixed in the surrounding air between 1.5 and 7.5%, and an ignition source is introduced, it will burn or explode. If the percent of vapors in air were 1%, the mixture would be too lean to burn because sufficient fuel would not be present. If the percent of vapors in air were 10%, the mixture would be too rich to burn because there would be too much fuel relative to the oxygen.


Figure illustrates a comparison of flammable ranges for several common substances. A solid material’s contribution to a fire is most commonly measured by its ease of ignition, flame spread, and smoke production. For testing and evaluation, solid materials are usually grouped into two primary categories: flexible solids, which include upholstery, furniture cushions, and clothing, and structural solids, which include solid building materials whether they are used in the structure or the contents.


Ease of ignition is tested to provide information about how much and how long heat must be applied to ignite the material under consideration. Flame spread addresses the speed at which a fire, once ignited, will travel across the surface of the material. Flame spread testing is typically done in a Steiner Tunnel. One example of a test standard is NFPA 255 Standard Method of Test of Surface Burning Characteristics of Building Materials. Smoke production has traditionally been evaluated based on the amount of visible smoke and not on the chemical composition of the smoke. The current trend is toward more accurate measurement of the smoke’s toxic components that may produce detrimental effects on people in a fire situation.