Symbols fault tree analysis

This section describes the most commonly used method for complex systems analysis - fault tree analysis. The previous section introduced cutsets as physically cutting through an RED, here, cuiscis. ire presented mathematically. The symbols of fault trees are introduced and a heuristic... 

Bums and Hazzan demonstrated tlie use of event tree and fault tree analysis in tlie study of a potential accident sequence leading to a toxic vapor release at an industrial chemical process plant. The initiator of tlie accident sequence studied is event P, the failure of a plant programmable automatic controller. Tliis event, in conjunction willi the success or failure of a process water system (a glycol cooling system) mid an operator-manual shutdown of tlie distillation system produced minor, moderate, or major release of toxic material as indicated in Fig. 21.4.1. The symbols W, G, O represent tlie events listed ... 

Other tools Information from any of the methods for gathering information can be summarized using a tree diagram. A tree diagram is similar to a cause-and-effect diagram when causes of an event are being evaluated. Standard symbols are used with tree diagrams for applications like fault tree analysis or failure mode and effects antilysis (FMEA). 

The above layout would be cumbersome to construct for each fault tree generated, so many fault tree analysis programs allow CCF groups to be created. Basic events are added to the group and a Beta factor between 0 and 1 specified. This is normally represented visually on the fault tree by displaying a p symbol next to the included events, as shown in Fig. 4A-4A 4 below. 

Even though the basic symbols are the same, there are vety distinct differences between the fault trees discussed in this chapter and fault tree analysis, the analytical technique discussed in Chapter 15. 

Fault tree analysis is a very detailed analytical technique for determining the various ways in which a particular type of failure could occur. Fault tree analysis is based on the negative analytical trees discussed in Chapter 10 and uses the same event and gate symbols (Fig. 15-1). 

The symbols used on the MORT chart are basically those used for other analytical trees (Chapter 10) and fault tree analysis (Chapter 15). They include the rectangle as the general event symbol, the circle as the base event symbol, the diamond as an undeveloped terminal event, the and gate, the or gate, and the ellipse as a constraint symbol (Rgs. 18-1 and 18-2). 

Common Fault Tree Symbols and Fault Tree Analysis Steps... 

Define the four commonly used symbols to perform fault tree analysis. What are the main advantages and disadvantages of fault tree... 

Figure 12.4 Sample fault tree analysis (FTA) showing structure, event, symbol placement, and aitset identification.

In general, the remainder of this chapter focuses on the explanation of the various MORT event tree symbols and their use and meaning. Since the tree is an analytical model, the information presented in the previous chapter (on fault tree analysis) will be helpful and should be reviewed. 

Fault tree analysis uses a particular set of symbols. Figure 36-4 illustrates commonly used symbols. There are some variations in symbology among practitioners. 

Figure 36-4. Symbols commonly used in fault tree analysis.

What symbol represents each of the following fault tree analysis factors ... 

A Fault Tree Analysis (FTA) is a top-down, deductive logic model that traces the failure pathways for a predetermined, undesirable condition or event, called the TOP Event. An FTA can be carried out either quantitatively or subjectively. The FTA generates a fault tree (a symbolic logic model) entering failure probabilities for the combinations of equipment failures and human errors that can result in the accident. Each immediate causal factor is examined to determine its subordinate causal factors until the root causal factors are identified. 

Event tree analysis follows a process from inputs to outputs. Each situation or condition is the result of previous events. They may have to happen together to produce the condition (i.e. both 1 and 2) or either one may produce the condition (i.e. either 1 or 2). As all possible situations are ejqrlored, an event tree begins to unfold. Mathematical probabihties can often be assigned to each condition and a quantitative analysis performed. Symbols, boxes and lines join the events and conditions to produce a visual representation of the event tree. Unwanted outcomes can be traced back in a reversal of the analysis above to determine which factors contributed to the unwanted outcomes. This is called fault tree analysis . Faults differ from events in that faults are viewed as being a result of controllable human error. Events can include such faults. 

In addition to these, the MORT chart also uses a rounded rectangle, or elongated circle, to represent a satisfactory event (an event that may have contributed to an accident or incident but whose existence is essential for normal system operation). Also, instead of the house symbol common to fault tree analysis to represent those events that are considered normal and expected in a typical system, MORT uses a scroll symbol. Figure 13.2 shows the MORT symbols as described here. 

Logic Gate As pertains to fault tree analysis (FTA) and/or the Management Oversight and Risk Tree (MORT), a symbol used to idenhly the association between events on a logic tree. 

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