Logic trees analysis

Logic tree analysis to identify the most effective maintenance procedures for preventing failure in the most critical parts... 

Fault Tree Analysis. Fault trees represent a deductive approach to determining the causes contributing to a designated failure. The approach begins with the definition of a top or undesired event, and branches backward through intermediate events until the top event is defined in terms of basic events. A basic event is an event for which further development would not be useful for the purpose at hand. For example, for a quantitative fault tree, if a frequency or probabiUty for a failure can be deterrnined without further development of the failure logic, then there is no point to further development, and the event is regarded as basic. 

Eault tree analysis (ETA) is a widely used computer-aided tool for plant and process safety analysis (69). One of the primary strengths of the method is the systematic, logical development of the many contributing factors that might result ia an accident. This type of analysis requires that the analyst have a complete understanding of the system and plant operations and the various equipment failure modes. 

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-... 

Fault tree analysis of mitigating systems to develop logic models of how system failure may occur ... 

Fault Tree Analysis (FTA) A method for logical development of the many contributing failures that might result in an incident. 

Logic Diagram Methods (Fault Tree Analysis, Event Tree Analysis, Cause-Consequence Analysis, Human Reliability Analysis, Success and Failure Trees, etc,)... 

Three hazard evaluation procedures using logic diagrams are (1) fault-tree analysis (FTA), (2) event-tree analysis (ETA), and (3) cause-consequence analysis (CCA). Appropriate references are [2,3,251,261]. 

Event tree (analysis) a graphical logic diagram which identifies and sometimes quantifies the frequencies of possible outcomes following an initiating event. 

Fault tree (analysis) a method for the logical estimation of the many contributing failures that might lead to a particular outcome (top event). 

Fault tree analysis is based on a graphical, logical description of the failure mechanisms of a system. Before construction of a fault tree can begin, a specific definition of the top event is required for example the release of propylene from a refrigeration system. A detailed understanding of the operation of the system, its component parts, and the role of operators and possible human errors is required. Refer to Guidelines for Hazard Evaluation (CCPS, 1992) and Guidelines for Chemical Process Quantitative Risk Assessment (CCPS, 2000). 

Event trees are used to perform postrelease frequency analysis. Event trees are pictorial representations of logic models or truth tables. Their foundation is based on logic theory. The frequency of n outcomes is defined as the product of the initiating event frequency and all succeeding conditional event probabilities leading to that outcome. The process is similar to fault tree analysis, but in reverse. 

Fault Tree Analysis (ETA)—Estimation of the hazardous incident (top event) frequency from a logic model of the failure mechanisms of a system. 

The disciplines of engineering and quality control have long recognized the principles of root cause analysis. Some process safety tools for root cause analysis have been borrowed from these disciplines. For example, fault tree analysis was developed as an engineering tool, but its logic tree structure has been adapted to meet process safety requirements. 

Checklists may also be used to supplement other tools for example, checklists on human factors may be used in conjunction with logic trees. Similarly, checklists may be used in combination with structured brainstorming tools such as What If/Checklist and Hazard and Operability (HAZOP) Analysis.(P It is also a good practice to apply a tool like the 5-Whys to the root causes identified from the checklist to verify whether they are truly root causes. 

The earliest logic trees were based on engineering fault tree analysis methods. Today, companies use a number of variations or combinations of logic trees and call them by different names, such as Why Tree,< 9) Causal Tree,(20,21) Cause and Effect Logic Diagram (CELD),<22) and Multiple-Cause, Systems-Oriented Incident Investigation (MCS011).<23,24) tools have more similarities than differences. 

Another type of logic tree, the event tree, is an inductive technique. Event Tree Analysis (ETA) also provides a structured method to aid in understanding and determining the causes of an incident.(i) While the fault tree starts at the undesired event and works backward to identify root causes, the event tree looks forward to display the progression of various combinations of equipment failures and human errors that result in the incident graphically. 

In addition, the team should also update the in-progress analysis of the occurrence. For example, update the fact list, logic tree, or fact hypothesis matrix. Finally, the information from the interview must he communicated to the remainder of the investigation team. 

AVhile some methods use checklists as the logic analysis step, an understanding of the logic tree approach is still helpful because checklists are developed from logic trees. Checklists are especially helpful when related to human factor issues. A sample checklist is included in Chapter 6 as Figure 6-6 (page 94). 

Many deductive investigation techniques use logic tree diagrams. A partial list of these methods includes fault tree analysis (FTA), causal tree... 

Predefined trees are relatively easy to use and generally require less training and effort to conduct root cause analysis tban logic trees. 

The use of checklists to supplement another root cause analysis method can be a very powerful technique, for example, human factors checklist(s) may be used in conjunction with logic trees. The checklist may be used as a guide during development of a logic tree, or as a check after the tree has been developed. The checklist essentially acts as a memory jogger to direct the investigation team. This is especially helpful if the team lacks previous experience in the subject matter. 

---