  Event Tree (ET) analysis is a widely used forward deductive safety analysis
technique for decision-making at a system design stage. Existing ET tools
usually provide Graphical Users Interfaces (GUI) for users to manually draw
system-level ET diagrams, which consist of nodes and branches, describing all
possible success and failure scenarios. However, these tools do not include
some important ET analysis steps, e.g., the automatic generation and reduction
of a complete system ET diagram. In this paper, we present a new Event Trees
Modeling and Analysis (ETMA) tool to facilitate users to conduct a complete ET
analysis of a given system. Some key features of ETMA include: (i) automatic
construction of a complete ET model of real-world systems; (ii)
deletion/reduction of unnecessary ET nodes and branches; (iii) partitioning of
ET paths; and (iv) probabilistic analysis of the occurrence of a certain event.
For illustration purposes, we utilize our ETMA tool to conduct the ET analysis
of a protective fault trip circuit in power grid transmission lines. We also
compared the ETMA results with Isograph, which is a well-known commercial tool
for ET analysis.
