Human error major accidents

A valuable QRA result is the importance of various components, human errors, and accident scenarios contributing to the total risk. The risk importance values highlight the major sources of risk and give the decision maker a clear target(s) for redesign or other loss prevention efforts. For example, two accident scenarios may contribute 90% of the total risk once you realize that, it is obvious that you should first focus... 

The analysis of accidents and disasters in real systems makes it clear that it is not sufficient to consider error and its effects purely from the perspective of individual human failures. Major accidents are almost always the result of multiple errors or combinations of single errors with preexisting vulnerable conditions (Wagenaar et al., 1990). Another perspective from which to define errors is in terms of when in the system life cycle they occur. In the following discussion of the definitions of human error, the initial focus will be from the engineering and the accident analysis perspective. More detailed consideration of the definitions of error will be deferred to later sections in this chapter where the various error models will be described in detail (see Sections 5 and 6). 

R. B. Whittingham s The Blame Machine Why Human Error Causes Accidents, a 2004 publication, is also referenced and recommended in Chapter 3, Serious Injury Prevention. Its emphasis is on human errors and defective management systems as causal factors for major accidents. From the Preface ... 

Human error remains a causal factor in the majority of serious aircraft accidents. Human error causes accidents of fail-safe, fully functional designs. 

In addition to these formal studies of human error in the CPI, almost all the major accident investigations in recent years, for example, Texas City, Piper Alpha, Phillips 66, Feyzin, Mexico City, have shown human error as a significant causal factors in design, operations, maintenance or the management of the process. Figures 4.4-1 and 4.4-2 show the effects of human error on nuclear plant operation. 

The application of the science of human factors to eliminating error in all aspects of process design, management, operation, and maintenance is the focus of this work. Human error has been a major cause of almost all of the catastrophic accidents that have occurred in the chemical process industries (CPI). If one adopts the broad view of human error as being the result of a mismatch between human capabilities and process demands, then clearly management s role is critical in the following areas ... 

Garrison (1989) Human error accounted for 563 million of major chemical accidents up to 1984... 

Human error has often been used as an excuse for deficiencies in the overall management of a plant. It may be convenient for an organization to attribute the blame for a major disaster to a single error made by a faUible process worker. As will be discussed in subsequent sections of this book, the individual who makes the final error leading to an accident may simply be the final straw that breaks a system already made vulnerable by poor management. 

From the organizational view of accident causation presented in the previous section, it will be apparent that the traditional approach to human error, which assumes that errors are primarily the result of inadequate knowledge or motivation, is inadequate to represent the various levels of causation involved. These contrasting views of error and accident causation have major implications for the way in which human error is assessed and the preventative measures that are adopted. 

Analysis of accidents and major losses in the CPI indicates that they rarely arise from a single human error or component failure. Often there is a combination of some triggering event (hardware or human) together with preexisting conditions such as design errors, maintenance failures or hardware deficiencies. 

The first area focuses on the cultural and organizational factors that will have a major influence on the effectiveness of a human error data collection system and how well the information derived from such a system is translated into successful error reduction strategies. Regardless of how effectively the technical issues are dealt with, the system will not be successful imless there is a culture in the organization which provides support for the data gathering process. No data collection system aimed at identifying human error causes of accidents will be workable without the active cooperation of the workforce. 

Three major themes have been emphasized in this chapter. The first is that an effective data collection system is one of the most powerful tools available to minimize human error. Second, data collection systems must adequately address underlying causes. Merely tabulating accidents in terms of their surface similarities, or using inadequate causal descriptions such as "process worker failed to follow procedures" is not sufficient to develop effective remedial strategies. Finally, a successful data collection and incident investigation system requires an enlightened, systems oriented view of human error to be held by management, and participation and commitment from the workforce. 

The DOE technical team that went to Japan after the accident concluded that, in spite of a relatively strict regulatory regime, human error - a lack of training and adherence to procedure - was the major cause of the accident. The industry must redouble its efforts to train workers and make certain that the rules and regulations are followed. 

Rasmussen, Jens. Approaches to the control of the effects of human error on chemical plant safety. In International Symposium on Preventing Major Chemical Accidents, American Inst, of Chemical Engineers, February 1987. 

No discussion of aew error is complete without considering the hazard Loss of Situational Awareness , which studies have shown to be a leading causal factor in a review of 175 military aviation nfishaps (Hartel et al., 1991) and a major causal factor in 88% of accidents associated with human error in a review of major aircraft accidents between 1989 and 1992 (Endsley, 2001). 

People and the jobs they do play an important safety role. Nowhere is this made more clear than in the study of aviation disasters, where, in more than two out of three cases, accident investigators are driven to conclude that human error played a major role (Edwards, 1988). These errors are not usually due to sudden illness, suicidal tendencies, wilful neglect or lack of basic abilities. More typically, they arise from temporary breakdown in skilled performance because, in many instances, system designers and managers have paid insufficient attention to human characteristics and skills, or not properly accounted for enviromnental stressors, workload and other reasonably foreseeable distractions. 

Literature has many theories and concepts discussing human reliability and associated human error causal factors that always trigger incidents and accidents within safety-critical systems. The main - by definition - characteristics of such safety occurrences are their randonmess, rare predictability, sophisticated, yet vague sequence of propagation. Such characteristics can basically allow for the retrospective analysis of these occurrences and their causes at various sectors and levels within industry such that re-occurrence margins are reduced if not totally eliminated. The major drawback of such reactive treatment... 

Aas, A. L. (2009). Probing Human Error as Causal Factor in Incidents with Major Accident Potential. The Third International Conference on Digital Society (ICDS). Y. Taka-hashi, L. Bemtzen and A. Smedbetg. Cancun, Mexico, IEEE Computer Society 272-276. 

According to the major incident/accident reports of nuclear power plants in Korea, the contribution of human errors takes up about 22% of the total events (KINS). The previous study presents that most of the human-related unplanned reactor trip events during the normal power operation are associated with the test and maintenance activities (63%), which are comprised of the plant maintenance activities such as a periodic preventive maintenance , a plannedmaintenance and a corrective maintenance (Kim Park 2008). This means that the test and maintenance activities should be a major subject that needs to be focused on. The hiunan errors intervened during a periodic preventive maintenance and a corrective maintenance mostly lead directly to a trip event, while the hmnan errors during a planned maintenance , which are performed during the period of a plant overhaul, are mostly dormant imtil a triggering event occurs. 

Turning to the hazards and the impact of industrial processes. Many disasters such as Flixborough, Seveso and Bhopal (see section 1.6) have ably illustrated the environmental impact of human errors and the need for rigorous safety controls. The capacities and productivity of chemical plants are driven upwards as are the magnitudes of losses in terms of economic cost and fatalities. Analysis of the major causes of accidents in the U.S. chemical industry in the 1978-1980 period highlighted that ... 

One of the major contributory factors in road accidents is human error (for example violation of speed limits). The type, size and frequency of these human errors depend on the whole road system and traffic regulations, which must be designed in a way to be safe and protective of such human errors. 

By doing this, I rely on earlier studies that indicate accidents caused by a combination of five main dimensions (human-vehicle-environment-road-system). One of the major contributory factors in road accidents is human error. The size of this human error depends on the whole road system and traffic regulations. Rumar (1999) has shown that the major contributory factor in road accidents is the human factor. The results are taken from two in-depth studies and analyses carried out in the UK and USA. Both studies indicate that the hmnan factor (road users), overlapping with other factors, is the major contributory factor in 94/95 % of accidents as shown in Figure 5.6. 

This theory is based on the assumption that accidents occur due to a chain of events caused by human error. It consists of the following major factors that lead to human error [1,2,20] ... 

We used to think that individual human error was a major cause of medical accidents. We learned that this is rarely the case. The human tendency to assign error as cause and place blame is universal and cross-cultural, a tremendous barrier to safety. When an accident does occur, aU the victims—the patient, the family, and the providers need support, disclosure, and accountable leadership. The focus of investigating accidents is on system breakdowns, not on individual error. 

The design of the plant should be tolerant of human error. To the extent practicable, any inappropriate human actions should be rendered ineffective. For this purpose, the priority between operator action and safety system actuation should be carefully chosen. On the one hand, the operator should not be allowed to override reactor protection system actuation as long as the initiation aiteria for actuation apply. On the other hand, there are simations where operator interventions into the protection system are necessary. Examples are manual bypasses for testing purposes or for adoption of acmation criteria for modifications to the operational state. Furthermore, the operator should have an ultimate possibility, under strict administrative control, to intervene in the protection system for the purposes of managing beyond design basis accidents in the event of major failures within the reactor protection system. 

Human reliability analysis is an important component of risk analysis. Reviews of past accidents show that human error accounts for the vast majority of these events. The technique most widely used for estimating human error probabilities is called THERP (Swain and Guttman, 1983). The method uses event trees drawn in a different format to arrive at a human error probability. See Fig. 10.15 for an example. In these event trees, failure paths branch right and success paths branch left. 

Almost aU the major accident investigations in recent years. have shown that human error was a significant causal factor at the level of design, operations, maintenance, or the management process. 

Another of James Reason s books—Managing the Risks of Organizational Accidents—is a must read for safety professionals who want an education in human error reduction. It was published in 1997 and has been reprinted five times. Reason writes about how the effects of decisions accumulate over time and become the causal factors for incidents resulting in serious injuries or damage when all the circumstances necessary for the occurrence of a major event come together. This book was referenced in Chapter 3, Serious Injury Prevention, because it stresses the need to focus on decision making above the worker level to prevent major accidents. Reason writes this ... 

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