MORT chart symbols used

Figure 18-3 Transfers In addition to the triangle commonly used as the transfer symbol for analytical trees, the MORT chart also uses large capital letters as drafting break transfers and small ellipses as transfer symbols for assumed risks.

Figure 18-6 Management system factors. The alphanumeric notations near the lower left of each event symbol were originally used as a cross reference to the MORT User s Manual. Later versions of the MORT chart now use page numbers for cross reference purposes.

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. 

The project evaluation tree is an analytical tree to be used primarily as a graphic check in basically the same manner as the management oversight and risk tree (see Chapter 18). The PET chart, however, contains fewer than 200 event symbols and no transfers the MORT chart contains approximately 1,500 events symbols, multiple transfers, transfers within transfers, and drafting breaks. The PET chart is divided into three branches procedures, personnel, and plant and hardware. 

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). 

In addition, Bill Johnson used a scroll as a normally expected event and an oval as a satisfactory event. The normally expected event distinguishes events that are typically a part of any system, such as change and normal variability. The satisfactory event describes events that may be accident causal factors but are a necessary part of the operation, like functional (part of the system) people or objects in the energy channel. Also, in addition to using the traditional transfer symbol (a triangle), the MORT chart includes capital letters as drafting breaks and small ellipses as risk transfers (Fig. 18-3). 

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.

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