Page 141 - Safety Risk Management for Medical Devices

120 Safety Risk Management for Medical Devices

FTA is a top-down deductive analysis tool that starts with the top event, e.g., a
Hazardous Situation, and works backwards toward the root cause(s). It seeks to answer
the question: “How can this Hazardous Situation occur?”
FMEA is a bottom-up inductive analysis tool that starts at the basic elemental level
and works forward toward the top event to answer the question: “what is the End
Effect of the failure of the item in question?”
The FTA is more suitable for:
• Early in the product development process, when only high-level knowledge
of the device is available.
• When there are few top events of interest, e.g., for derivative products
when the predicate device is already well analyzed and understood, and the
derivative only adds a few new top events.
• When a top event can be caused by multiple initiating Causes, or where
there are many interactions and relationships among the components.
• Detection of CCFs.
• Systems with redundancies in the design.

The FMEA is more suitable for:
• Systems that are novel, or complex, and not well understood.
• When there are a large number of top events that can result from bottom
events.
• Where occurrence of the top events do not require multiple faults.
• When there is a need for fail-safe operation.

First-order cut sets in the FTA, should also appear in FMEAs as single-point fail-
ures that can result in the top event.

Tip Use FTA to prioritize FMEA work for complex products. FTA can more efficiently identify
safety-critical parts of the System. Use this knowledge to prioritize the FMEA work.