Page 102 - Safety Risk Management for Medical Devices

Risk Analysis Techniques 81

four types of FMEA: Design Failure Modes and Effects Analysis (DFMEA), Software
Failure Modes and Effects Analysis (SFMEA), Process Failure Modes and Effects
Analysis (PFMEA) and Use-Misuse Failure Modes and Effects Analysis (UMFMEA).
At the service risk management, FMEAs are to identify Hazards, and estimate the
likelihood of their occurrence.
It is important to distinguish two terms: Fault and Failure. A fault is an anomalous
condition for a part. A failure is the inability of an entity to achieve its purpose.
• A fault could result in a failure, but not necessarily
• A failure may occur with no faults
With respect to risk management, FMEAs are used to identify Failure Modes
which can result in Hazards or Hazardous Situations. It is important to realize
that occurrence of faults and failures can result in Hazards, but not necessarily.
And Hazards or Hazardous Situations can occur in the absence of any fault/fail-
ure. To elucidate—a medical device that is designed for adults, if used on children
may create a Hazardous Situation, even though the device is working perfectly
according to its design. Or, a medical device may have a fault that doesn’t create a
Hazard.
In the FMEA, the subject of analysis is decomposed into elements. The granularity
of this decomposition is subjective and is called the level of indenture. During the
course of the analysis, the Failure Modes of each element and consequences on the
subject of analysis is considered. In general, the identification of Failure Modes and
the resulting effects is based on experience with similar products and processes, or on
knowledge of the applicable science.
The subject of the FMEA analysis may be the entire medical device, a subsystem,
a component, a process, or anything that the analyst chooses.

Tip When choosing the granularity of decomposition of the subject of FMEA (level of inden-
ture) save time and resources by not going deep into the parts of the System that are understood
and have a well-known history.

It is important that the scope of analysis be clearly defined and understood.
That is, the boundary of analysis, and what is included in the analysis should be
clearly defined. Interfaces to the subject of the analysis should also be clearly
identified.
Context of operation is important. The same Failure Mode could have starkly dif-
ferent severities, depending on the context of operation. For example, the failure of a
jet engine on an aircraft has very different consequences whether the aircraft is in
flight, or on the ground.