Safety engineering fault tree analysis

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. 

Simplified equations and fault tree analysis will be used to determine the PFDavg of the SIF shown in Figure 13-3. One advantage in using the fault tree approach for the PFDavg calculation for this SIF is that most engineering personnel are familiar with the development and analysis of fault trees. This enables them to better understand the operation of complex safety instrumented functions by reviewing its associated fault tree. 

Rauzy, A., 1993. New Algorithms for Fault Tree Analysis, Reliability Engineering and System Safety, vol. 40. 

Huang, H. Z., Tong, X. Zuo M. (2004) Posbist fault tree analysis of coherent systems. Reliability Engineering and System Safety 84 153-16. 

Volkanovski, A., M. Cepin, and B. Mavko (2009). Application of the fault tree analysis for assessment of power system reliability. Reliability Engineering and System Safety 94, 1116-1127. 

Analytical trees can be used in a variety of ways in the system safety effort. The most common application of analytical trees in current system safety programs is probably the use of fault trees for fault tree analysis (FTA). However, analytical trees can also be used as planning tools, project description documents, status charts, and feeder documents for several hazard analysis techniques (including fault tree analysis). Analytical trees can be multipurpose, life cycle documents and represent one of the most useful tools available to managers, engineers, and safety professionals. 

Fault tree analysis is a technique by which the system safety engineer can rigorously evaluate specific hazardous events. It is a type of logic tree that is developed by deductive logic from a top undesired event to all subevents that must occur to cause it. It is primarily used as a qualitative technique for studying hazardous events in systems, subsystems, components, or operations involving command paths. It can also be used for quantitatively evaluating the probability of the top event and all subevent occurrences when sufficient and accurate data are available. Quantitative analyses shall be performed only when it is reasonably certain that the data for part/component failures and human errors for the operational environment exist. 

Much of the functional safety practitioner s work involves random hardware failure modes and failure rates as a way of providing quantitative information to support claims that a SIL specification has been met. This is accompanied by rehabihty engineering calculations, as described in detail in lEC 61508. Standard software packages have eased the calculation burden, particularly with fault tree analysis and probabihty of failure estimates. 

Over the years professionals working in the area of reliability and safety engineering have identified many benefits and drawbacks of fault tree analysis. Some of its main benefits are as follows [9,23] ... 

The engineering methods and techniques used for demonstrating the satisfaction of equipment safety requirements (e.g Fault Tree Analysis, Event Tree Analysis, Zonal Hazard Analysis etc.) are relatively well understood by the wider safety engineering community compared with those for people and procedures and will therefore not be discussed further here. The remainder of this paper will discuss how the above approach to safety requirements specification and realisation can be developed in the case of human-based subsystems, using Human Factors methods and techniques. 

K.A. Dejmek, Fault Tree Analysis as a Tool for Safety Instrumented System (SIS) Performance Evaluation, Wilfred Baker Engineering, Inc. 

HAZOP and wAat-iJ/safety checklists, two of the most common safety methods in the chemical industry, are explained. Sample process problems, which engineers face every day at work, are shown. Other safety tools, such as fault tree analysis, failure modes and effects analysis, human factors safety analysis, and software safety, are explained. Examples of the use of these tools are also presented. 

Our approach solely consists of 8 different process steps which are all not new in the area of safety engineering. Thus, established safety analysis techniques (such as Hazard and Operability Studies (HAZOP), Failure Mode and Effects Analysis (FMEA), Fault Tree Analysis (FTA), etc.) can be applied and no new safety analysis methodologies need to be developed. 

System safety engineers require FMECA in order to complete the FTA (Fault Tree Analysis) of the system and use the FR (Failure Rate) data,... 

The term engineering RA is mainly introduced to highlight differences to the IT RA concept. The framework is well defined in the (outdated) (ISO/ IECGuide73 2002). The basic approaches and concepts as, e.g., FMEA, Fault Tree Analysis and Probabilistic Safety Analysis, are supposed to be known to the reader. Major goals are hazard identification and its impact on environment. Typical fields of application are chemical industry and nuclear power generation. 

Vaurio, J.K. 2001. Fault tree analysis of phased mission systems with repairable and non-repairable components. Reliability Engineering and System Safety 74 169-180. 

According to the survey results, the fault tree analysis is the most applied method by safety engineers. Based on this result and the applicability of this method, a demonstrator for data exchange among tools using PREMISE system model was realized. The presentation of this work would exceed this paper and will be presented in an additional publication. 

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