ITEM TOOLKIT

6 ITEM ToolKit Getting Started Guide
Using Fault Tree’s detailed information, efforts to improve system safety and reliability can be highly focused, and tailored
to your individual system. Possible design changes and other risk-mitigating actions can be evaluated for their impact on
safety and reliability, allowing for a better-informed decision making process and improved system reliability. This type of
analysis is especially useful when analyzing large and complex systems where manual methods of fault isolation and
analysis are not viable.
• Markov
The Markov module is a powerful modeling and analysis technique with strong applications in time-based reliability and
availability analysis. The reliability behavior of a system is represented using a state-transition diagram, which consists of a
set of discrete states that the system can be in, and defines the speed at which transitions between those states take place. As
such, Markov models consist of comprehensive representations of possible chains of events, i.e., transitions, within systems,
which, in the case of reliability and availability analysis, correspond to sequences of failures and repair.
• Maintain
The Maintain module provides an integrated environment for predicting the expected number of hours that a system or a
device will be inoperative or "down" while it undergoes maintenance. A comprehensive design tool for calculating MTTR,
Maintain conforms to maintenance standards established in MIL-HDBK-472, Procedure V, Method A.
• SpareCost
The SpareCost module Calculates spares required for equipment supported at Sites (First and Second line maintenance by
replacement) and Bases (Third line maintenance to support Sites and the repair of returned defective spares). It optimizes
scale of spares at Sites for minimum cost. SpareCost produces full information of spares holding by replaceable item at both
Site and Base. Expected number of failures for each component over a defined period is also output. SpareCost generates
spares holding required at sites against a stock-out risk at the Site. This scale of spares is optimized against the cost of the
spares held.
• Event Tree Analysis
Event tree analysis is based on binary logic, in which an event either has or has not happened or a component has or has not
failed. It is valuable in analyzing the consequences arising from a failure or undesired event.
Event tree analysis is generally applicable for almost any type of risk assessment application, but used most effectively to
model accidents where multiple safeguards are in place as protective features. Event tree analysis is highly effective in
determining how various initiating events can result in accidents of interest.
An event tree begins with an initiating event, such as a component failure, increase in temperature/pressure or a release of a
hazardous substance. The consequences of the event are followed through a series of possible paths. Each path is assigned a
probability of occurrence and the probability of the various possible outcomes can be calculated.
The module also includes the BDD analysis method as an alternative to the Rare Event and Esary-Proschan quantification
options. It uses the Binary Decision Diagram algorithm to obtain cut-sets and quantification results. BDD algorithms
distinguish themselves from conventional quantification methods by returning results that do not involve approximations.
Instead, BDD algorithms produce results that are in accordance with the basic rules of probability theory.