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Risk Analysis Techniques 83

Figure 12.6 Electronic thermometer.
The benefits of this technique are multifold:
1. Parallel work—Let’s consider the example in Fig. 12.6, which describes an elec-
tronic thermometer decomposed into the electronics and the mechanical casing. It
would be possible for the electronic team to be working on the FMEA of the elec-
tronics, while the mechanical team works on the casing FMEA. Later, the results of
their work are integrated in the DFMEA of the Electronic Thermometer System.
2. Modularity and reuse—If in the example of Fig. 12.6 the manufacturer decides
to update the thermometer casing for a fresh look, but keeps the electronics
the same, the hierarchical multilevel FMEA technique allows the reuse of the
electronic DFMEA, while refreshing only the Casing DFMEA/PFMEA.
Specifically, the DFMEAs lend themselves to modular reusability. PFMEAs can be
reused in the ordinary sense of basing a new analysis on old work and making revi-
sions thereto. UMFMEAs are unique to each System and any reuse depends on the
degree of similarity between the current System and the previous System.
For DFMEAs to be modularly reusable, strict adherence to the scope, and bound-
ary of analysis is required. In the DFMEAs, for Failure Modes that have a safety
impact, Severity and Detectability ratings depend on the context of use. Therefore
during reuse of DFMEAs, for Failure Modes with safety impact, Severity and
Detectability ratings need to be reexamined within the context of use.
For more details on the integration of DFMEAs see Section 16.1.

12.4.3 Failure theory
In the context of FMEA the End Effect is the outcome of a chain of events. Fig. 12.7
shows a model of this concept.

Figure 12.7 Failure theory.