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CHAPTER 12

Risk Analysis Techniques

Abstract
Identification of hazards for risk analysis can be done using various tools. Two of the most common
tools are Fault Tree Analysis (FTA) and Failure Modes and Effects Analysis (FMEA). In this chapter
three types of FMEA are discussed: DFMEA, PFMEA, and UMFMEA. Additionally, two other tools are
presented: Mind Map Analysis and P-Diagram. Ultimately it is the analyst's choice on how many
tools to use. While extra analyses consume more resources, they also reduce the likelihood of miss-
ing some Hazards and their causal chains.
Keywords: Fault Tree Analysis; FTA; Failure Modes and Effects Analysis; FMEA; DFMEA; PFMEA; UMFMEA;
Mind Map Analysis; P-Diagram

12.1 FAULT TREE ANALYSIS
12.1.1 Introduction
The Fault Tree Analysis (FTA) technique was developed by Bell Labs in 1962 for use
on the Minuteman missile system. Later it gained wide use in civil aviation, space,
and military applications. MIL-HDBK-338B published in 1998 provides a reference
for this technique. After the 1979 incident at Three Mile Island, the Nuclear
Regulatory Commission expanded the use of FTA and published NUREG-0492—
Fault Tree Handbook in 1981. This handbook was later updated by NASA in 2002
with the title Fault Tree Handbook with Aerospace Applications [24].
FTA is a deductive top-down reasoning process that starts from the undesired sys-
tem outcomes and attempts to find out all the credible sequences of events that could
result in the undesired system outcomes. The fault tree is a graphical model that
depicts the logical relationships among the parallel and sequential combination of
events that could lead into the event at the top of the tree.
FTA can model both normal and fault conditions, under various environmental
and operational scenarios. FTA can also identify and model fault dependencies, and
common cause failures (CCFs).
Fault Trees (FTs) are constructed using logic gates, such as AND and OR gates.
As such, FTs lend themselves to logical simplification and reduction. Therefore there
is not just one correct FT to describe a system, but potentially multiple logically
equivalent FTs.

Safety Risk Management for Medical Devices r 2018 Elsevier Ltd.
DOI: https://doi.org/10.1016/B978-0-12-813098-8.00012-X All rights reserved. 67