Fault tree analysis gates

Fault Tree Analysis Faiilt tree analysis permits the hazardous incident (called the top event) frequency to be estimated from a logic model of the failure mechanisms of a system. The top event is traced downward to more basic failures using logic gates to determine its causes and hkelihood. The model is based on the combinations of fail-... 

Comptete all gate inputs. Beginning a new gate before completing a previous gate leads to confusion and incompleteness. These rules are made concrete by an example of fault tree analysis. 

The term near miss —which may better be called near hit —describes an incident that did not result in an actual loss but that had the potential to do so. For example, if an object is dropped from a crane but no one is hurt then the incident is a near miss. In terms of fault tree analysis, a near miss is an event in which one or more of the inputs to an AND gate was negative. 

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). 

NFPA has developed a Fire Safety Concepts Tree At the top of the tree are fire safety objectives, followed by actions to achieve the objectives. Elements of the tree connect using AND and OR gates, similar to fault tree analysis (Figure 36-10). A Fire Safety Concepts Tree can help analyze buildings and designs using qualitative and quantitative procedures. 

Fault Tree Analysis (FTA) is a well known and widely used safety tool, implementing a deductive, top down approach. It starts with a top level hazard, which has to be known in advance and "works the way down" through all causal factors of this hazard, combined with Boolean Logic (mainly AND and OR gates). It can consider hardware, software and human errors and identifies both single and multiple points of failure. Both a quantitative and qualitative analysis is possible. 

Temporal (relationship) gate in software fault tree analysis. 

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. 

---