Hazard analysis basic causes

CONSTRUCTING THE FAULT TREE. Fault tree construction begins at the top event and proceeds, level by level, until all fault events have been traced to their basic contributing events or basic events. The analysis starts with a review of system requirements, function, design, environment, and other factors to determine the conditions, events, and failures that could contribute to an occurrence of the undesired top event. The top event is then defined in terms of sub-top events, i.e., events that describe the specific "whens and wheres" of the hazard in the top event. Next, the analysts examine the sub-top events and determine the immediate, necessary, and sufficient causes that result in each of these events. Normally, these are not basic causes, but are intermediate faults that require further development. For each intermediate fault, the causes are determined and shown on the fault tree with the appropriate logic gate. The analysts follow this process until all intermediate faults have... 

For the analysis of accidents and incidents in aviation, roughly two streams can be distinguished in the literature, namely accident analysis and risk analysis. Whilst the former has the goal to determine the cause of an accident that actually took place, the latter aims to assess the likelihood of the occurrence of future accidents. Hence, although both streams have similar purposes, a main difference is that accident analysis attempts to identify one specific combination of hazardous factors, whereas risk analysis basically explores a whole range of such factors, and the associated risks. Nevertheless, most of the existing approaches are used for both streams. 

Three hazard analysis techniques are currently used widely Fault Tree Analysis, Event Tree Analysis, and HAZOP. Variants that combine aspects of these three techniques, such as Cause-Consequence Analysis (combining top-down fault trees and forward analysis Event Trees) and Bowtie Analysis (combining forward and backward chaining techniques) are also sometimes used. Safeware and other basic textbooks contain more information about these techniques for those unfamiliar with them. FMEA (Failure Modes and Effects Analysis) is sometimes used as a hazard analysis technique, but it is a bottom-up reliability analysis technique and has very limited applicability for safety analysis. 

Chapter 3 presents introductory aspects of safety and human factors. Chapter 4 is devoted to methods considered useful to perform patient safety analysis. These methods include failure modes and effect analysis (FMEA), fault tree analysis (FTA), root cause analysis (RCA), hazard and operability analysis (HAZOP), six sigma methodology, preliminary hazard analysis (PFfA), interface safety analysis (ISA), and job safety analysis (JSA). Patient safety basics are presented in Chapter 5. This chapter covers such topics as patient safety goals, causes of patient injuries, patient safety culture, factors contributing to pahent safety culture, safe practices for better health care, and patient safety indicators and their selection. 

Accidents are usually complex and are the result of multiple causes. A detailed analysis of an accident will normally reveal three cause levels basic, indirect, and direct. At the lowest level, an accident results only when a person or object receives the release of an amount of energy or exposure to hazardous material that cannot be absorbed safely. This energy or hazardous material is the direct cause of the accident. The second causal areas are usually the result of one or more unsafe acts or unsafe conditions, or both. Unsafe acts and conditions are the indirect causes or symptoms. In turn, indirect causes are usually traceable to poor management policies and decisions, or to personal or environmental factors. These are the basic causes. 

FTA is somewhat similar to fish-bone analysis another hazard analysis method (Fig. V/3.0-4). When compared with fishbone analysis shown and discussed in Fig. V/3.0-3 and Fig. V/3.0-4 respectively, FTA is more formal and specific, that is, it resolves basic causes for the accidental event or consequences. 

Initiating event In hazard analysis, an event could be the occurrence of a deviation which may lead to an accident. So, the initiating events are the causes for which there is the process deviation. The initiating events may be or may not be the most basic underlying root-causes, but are the results of the root causes. According to CCPS there are three types of initiating events or causes ... 

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-... 

Loss-of-Containment Causes The list in Table 23-30 indicates four basic ways in which containment can be lost. These cause cate-ories can be used both as a checklist of considerations during the esign process and as a starting point for evaluating the adequacy of safeguards as part of a process hazard and risk analysis. 

The chance of an incident is generally a function of the distance traveled. Thus, the frequency of an accident is often expressed as an accident rate per mile. Contributions from non-accident-initiated events are typically expressed on a frequency-per-hour or per-year basis. Thus, the duration of the hazardous materials movement is a key parameter. Figure 5.3 illustrates the basic calculation sequence for one trip or movement. If multiple trips are made, the total risk is equal to the number of trips times the risk per trip. The basic calculation sequence will have minor variations for each mode of transport and can be broken down into greater detail as needed. Increased detail might include different accident rates and lengths for each segment of a route or might explicitly address the accident rates and release probabilities for different accident causes. Inputs to the analysis that may be altered or may influence the calculation include ... 

Fig. H/3.2.5 1 is an important record-keeping document for HAZID analysis. This hazard register is same as the risk register discussed in Clause 3.2 of Chapter I, and details of the risk register are shown in Fig. 1/3.2.1-1. Since details of the risk register are already available, it will not be repeated here. Fig. 11/3.2.5-1 shows the basic structure. In the case of HAZID, hazard register is the popular term, hence it is used here. These hazard registers are available for each section of the facility. For each section, all hazards and major incidents/accidents are listed along with the probable cause. The register also contains the control measure, assumptions, etc. This will become the main document for subsequent use.

Fault tree analysis (FTA) provides a logical representation of many events and component failures that may combine to cause one critical event (e.g., pipeline explosion). It uses logic gates to show how basic events may combine to cause the critical top event. The top event would normally be a major hazard such as "pipeline SCC" as in the example shown in Fig. 12.10. The most commonly used tree symbols and gates used in the construction of fault trees are illustrated in Fig. 12.11 and briefly described here [12] ... 

Systems analysis. - Although it is useful to consider behavior in hazardous situations when trying to understand danger and its consequences, it is not sufficient this approach to viewing hazards makes research on accident causes too person-oriented and fails to consider other important factors. This situational approach to viewing hazards must be supplemented by a systems approach. In man-machine-environment systems, man and machines are, as indicated by the term, the basic components which are connected by means of an... 

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