Fault trees symbols used

Figure 18-1 Event Symbols. The General Event symbol, Basic Event symbol, and Undeveloped Terminal event symbol are the same as commonly used for other fault trees. The use of the stretched circle for a Satisfactory Event and the scroll for a Normally Expected Event are unique to the MORT chart.

Step 3 Determine all types of possible potential causes that can result in the occurrence of the top fault event by using fault tree symbols, such as shown in Figure 4.4, and the logic tree format. 

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

Fault tree symbols are divided into four categories primary event, intermediate event, gate, and transfer. Figure 7.1 defines each of the symbols used in fault tree generation. 

In order to demonstrate the application of fault-tree analysis in the area of rail safety, using the fault-tree symbols defined in Chapter 4, a simple fault tree for fhe fop evenf—release of liquefied chlorine from a rail tank shell— is shown in Figure 7.1 [25]. The capital letters in the circles and rectangles of the fault-tree diagram in Figure 7.1 denote, respectively, basic and intermediate fault events associated with the rail tank shell. Each of these capital letters is defined below [25]. 

For a particular event called the top event (usually a failure of a system to perform some intended function), a fault tree is used to identify the combinations of base events (usually component failures or operator errors) that could lead to the top event. An example is shown in Figure 2.6-5, which is a fault tree for a hypothetical, one-pump injection system. The symbols used in fault trees origin ate from the logical operations OR (+) and AND ( ). For the example, insufficient system flow could result from a failure to actuate the injection system OR from insufficient flow from the pump. The actuation failure requires both that the automatic actuation signal fail AND that the operator fail to actuate the system manually. Insufficient flow from the pump can be caused by any of the failure events listed under the corresponding OR gate. Note that one of these events, failure of power to the pump, is based on another fault tree for the power system, which is a support system for the injectiop system. 

The foUowiag symbols are used ia fault tree constmction to display the iaterrelationships between equipment failures and a specific accident ... 

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 ... 

With the view that a KBS interpreter is a method for mapping from input data in the form of intermediate symbolic state descriptions to labels of interest, four families of approaches are described here, each offering inference mechanisms and related knowledge representations that can be used to solve interpretation problems namely, model-based approaches, digraphs, fault trees, and tables. These methods have been heavily used... 

The fault tree is a graphic representation of the relationships between basic events and the selected top event. Table 4.24 presents the standard symbols used in fault tree construction to show these relationships. 

TRANSFER OUT symbol. Transfer symbols are used to transfer off-page or to avoid repeating identical logic (with identical events) in several places in a fault tree. 

The flat tire example is pictured using a fault tree logic diagram, shown in Figure 11-12. The circles denote basic events and the rectangles denote intermediate events. The fishlike symbol represents the OR logic function. It means that either of the input events will cause the output state to occur. As shown in Figure 11 -12, the flat tire is caused by either debris on the road or tire failure. Similarly, the tire failure is caused by either a defective tire or a worn tire. 

TRANSFER Symbols Used to transfer the fault tree... 

In the opening segment the facilitator should discuss the importance of and methods for choosing the top event and any preestablished and existing boundaries of the investigation. If multiple events are involved, it is best to start with the last event in the time sequence. It may be appropriate, depending on the nature of the occurrence, to formally review the rules and symbols used in logic tree or fault tree development or whichever other formal method will be used. 

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 second type of logical gate used in fault trees is the and cate, the symbol for which is shown in Figure 15.6. All inputs to an and cate need to be positive for the output to be positive. 

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). 

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

Numerous symbols are used in the construction of a basic fault tree. These symbols, sometimes referred to as fundamental logic symbols, provide the analyst with a pictorial representation of the event and how it interacts with other events on the tree. Figure 12.2 shows the basic symbols used during the FTA process. Once the reader has a general understanding of these symbols and their use, as described below, fault tree construction will be greatly facilitated. 

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