Project evaluation tree analysis

Analytical trees are also very useful as feeder documents for several hazard analysis techniques, for example, failure mode and effects analysis (Chapter 14), fault tree analysis (Chapter 15), energy trace and barrier analysis (Chapter 13), and project evaluation tree analysis (Chapter 16), the primary hazard analysis tools for many projects. Virtually any analytical technique or any type of analysis can be simplified by starting with the analytical tree as a base document. 

The operating hazard analysis (OHA) is normally started and sometimes completed during this phase, even though, if adequate information is available, the OHA may be initiated in the design phase. Hazards associated with the human interface and with operating and maintenance procedures should be identified at this time. Project evaluation tree (PET) analysis is the preferred technique for performing OHAs. 

In all cases, a very important analysis and control effort should be initiated and, if sufficient data are available, completed during the production phase. The operating hazard analysis (OHA) focuses on the human interface with the end product. It examines the adequacy of maintenance and operating procedures and instructions and, if appropriate, the adequacy of the organization and training of maintenance and operations personnel. The recommended technique for completing the OHA is the project evaluation tree (PET) analysis. 

Project evaluation tree (PET) analysis is recommended as the primary evaluation technique. 

As soon as practical, consistent with SSPP guidance, an OHA is prepared by the SSWG. Project evaluation tree (PET) analysis is the recommended technique. 

The management oversight and risk tree (MORT) chart is a large, complex, negative tree (see Chapter 18). Even though the project evaluation tree (PET) is depicted as a positive tree, it is mentally converted and used as a fault tree for accident analysis applications (see Chapter 16). 

The purpose of the project evaluation tree is to provide a relatively simple, straightforward, and efficient method of performing an in-depth evaluation or analysis of a project or operation. It is best suited for performing operating hazard analysis and accident analysis. It can also be a valuable review and inspection tool. If adequate information is available, PET analysis may be helpful in performing preliminary hazard analysis, subsystem hazard analysis, and system hazard analysis. 

Project Evaluation Tree A system safety analytical technique which was developed from the more extensive management oversight and risk tree (MORT) method of analysis. A simplified and efifieient method to evaluate a project or operation. Especially usefiil in the analysis of accidents and hazards. 

In a tiny fraction of cases, a quick formula can be used. For most cases, the analysis uses an options tree, with one leaf per possible outcome. However, this falls prey to the curse of dimensionality —the number of leaves on the tree grows exponentially in the number of risk and decision dimensions considered. Thus only a limited, simple set of situations can be optimized in this way because one has to severely limit the decisions and risks that are considered. Tools available to help automate and simplify options analysis, widely used in pharmaceutical project evaluation, include Excel addons such as R1SK [11] and more graphically based solutions such as DPL [12]. Both of these support the creation and evaluation of decision trees and of influence diagrams Figure 11.2 shows a simple example of each of these. A primer in applied decision theory is Clemen s book Making Hard Decisions, other sources may be found in the website of James Vornov, Director of Clinical Research at Guildford Pharmaceuticals, a recent convert to decision theory for options analysis [13]. 

The digital I C considered for the project is new with respect to what is used in previous NPPs in Slovakia. For this reason there is no relevant operational experience from operating Slovak NPPs and the assessment of its reliability is based on the detailed reliability data from relevant suppliers. The reliability of the I C is assessed based on standard FMEA analysis, followed by a fault tree analysis for reliabihty estimation. The potential common failure modes are accounted for with suitable common cause factors substantiated with detailed analysis. Input data used for its evaluation are taken from the operational experience of the digital systems operating in other NPPs. Several conservative assumptions (e.g., input reliability data) are considered to ensure that the final result is a bounding estimation. 

In this study detailed fault trees with probability and failure rate calculations were generated for the events (1) Fatality due to Explosion, Fire, Toxic Release or Asphyxiation at the Process Development Unit (PDU) Coal Gasification Process and (2) Loss of Availability of the PDU. The fault trees for the PDU were synthesized by Design Sciences, Inc., and then subjected to multiple reviews by Combustion Engineering. The steps involved in hazard identification and evaluation, fault tree generation, probability assessment, and design alteration are presented in the main body of this report. The fault trees, cut sets, failure rate data and unavailability calculations are included as attachments to this report. Although both safety and reliability trees have been constructed for the PDU, the verification and analysis of these trees were not completed as a result of the curtailment of the demonstration plant project. Certain items not completed for the PDU risk and reliability assessment are listed. 

In 1985, the American Institute of Chemical Engineers (AIChE) initiated a project to produce the Guidelines for Hazard Evaluation Procedures. This document, prepared by Battelle, includes many system safety analysis tools. Even though frequently identified as hazard and operability (HazOp) programs, the methods being developed by the petrochemical industry to use preliminary hazard analyses, fault trees, failure modes, effects, and criticality analyses, as well as similar techniques to identify, analyze, and control risks systematically, look very much like system safety efforts tailored for the petrochemical industry (Goldwaite 1985). 

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