FMEA means Failure Mode and Effect Analysis, whereas FMEC
A means Failure Mode
and Effect Criticality
Analysis, which is just a specific FMEA type.
During the last decades, many FMEA types have been established by
different sectors of industry. Some of them even have their own
FMEDA: D = Detectability
Design-FMEA, Process FMEA
HAZOP: Hazard and Operability Analysis
HACCP: Hazard Analysis and Critical Control Point
Despite the variety of FMEA types, the underlying principle is always
the same, and can be described as follows:
- Define the topic(s) / item(s) to be analysed (e.g. process, machine,
cold chain, etc.)
- Identify potential failure modes. It is important not focusing on
those failures that have already happened, but rather on those which
are imaginable to happen.
The way how potential failure modes are identified as well as all
downstream FMEA steps depend on FMEA type and FMEA goal, and can
therefore be very different.
The following two examples may outline the range of what is practically
encountered in the FMEA world:
1. A (moderated) group of 5 to 10 persons. The boundaries are
wide and there are only weak limits regarding thoughts. Every idea is
appreciated as long as there is a relationship with the FMEA goal.
Unexpected or surprising thoughts are even more appreciated. Goals of
such FMEAs are very often rather radical solutions than continual
improvement with small steps.
2. A single person performing a so called piece part FMEA. Piece part
FMEAs work according to established procedures. Results are often
foreseeable and almost never surprising. The main goal is to calculate
and document the failure rates of the failure modes of the FMEA item.
While the first example is focused on improvement, the second example
is rather used in reliability and safety analyses.
Depending on the FMEA type, one or more of the following topics will be
addressed in the FMEA:
- Identify the potential causes of the failure modes
- Identify the consequences (effects) of the failure modes (on
local component level, and/or assembly level, and/or system level)
- Qualitative classification of failure mode probabilities (e.g. on
a scale from 1 to 10)
- Quantitative calculation of failure mode probabilities (e.g. in
failures per million hours)
- Qualitative or quantitative assessment of failure severities
- Qualitative or quantitative assessment of failure detection
- Identify and authorize improvement or mitigation actions
- Due dates and responsibilities
The process of many FMEA types are live processes, and therefore the
FMEA documents are live documents. This means that they are updated and
reviewed on a regular basis. FMEAs focused on improvement are typical
live FMEAs: After each improvement/mitigation action, a re-assessment
is made until the results are conceived acceptable.
The basic toolset for FMEA is the FMEA table, also called FMEA
worksheet. Specific column headers of the FMEA worksheet and its
tabular structure define both FMEA type and FMEA methodology. In turn,
type of industry and applied FMEA standard can be easily concluded from
the column headers and the tabular structure of the FMEA worksheet.
The reader may expect here a list of established FMEA standards;
however, this is exactly what will not happen, because the core
principles of all these FMEA standards are almost the same. By
describing just three FMEA types of only two FMEA standards
(Mil-STD-1629 and IEC 60812), the following three paragraphs will
address all basic FMEA principles.
In practice there are also definitions like "Process FMEA", Design
FMEA", " Software FMEA" and so on. These definitions however have no
direct relationship with FMEA types, instead they only describe the
nature of the topic subject to FMEA.
The following page shows the "father" of all today's FMEA Standards,
the so called "task 101" of Mil-Std-1629, also called "component FMEA".
Mil-Std-1629 (Failure Mode and Effect Analysis) has been developed by
US department of defense as a requirement for army material suppliers.