Experiences of accidents

The 30-year experience of accident-free rail shipment of SNF has brought out clearly that the used so far multi-purpose approach to solution of the challenges of safe shipment of nuclear materials is efficient and is capable of ensuring reliable and safe transportation of SNF under normal and emergency conditions. 

The symptoms of an illness might be around us, a desire to disregard past experience of accidents, which, if it should continue to grow, might really impair the safety of nuclear plants. On the one hand, a past WANO (World Association of Nuclear Operators) president has publicly declared, from his special observation point, that the interest in the lessons of experience is decreasing among operators. 

People have their own unique experience of specific tasks and the hazards which those tasks present. The experiences of accident victims, frequently recorded in accident reports, are an important source of information. Feedback from accidents is crucial in order to prevent repetition of them. 

At the workplace level, operators and supervisors have direct experience of accidents that are specific, concrete and rich in details. This type of information typically does not allow for generalisation and is unusable by anyone other than those who have generated it. Management at higher levels of the hierarchy, on the other hand, asks for coded summary data on accidents and quantified information on key performance indicators such as the accident... 

Hazard analysis does have limitations. First, there can never be a guarantee that the method has identified all of the hazards, accident scenarios, and consequences. Second, the method is very sensitive to the assumptions made by the analysts prior to beginning the procedure. A different set of analysts might well lead to a different result. Third, the procedure is sensitive to the experience of the participants. Finally, the results are sometimes difficult to interpret and manage. 

If sufficient experience does not exist, you should consider whether the consequence potential (Step 4) or the expected frequency of accidents (Step 5) is great. Consideration of consequence potential should include personnel exposure, public demographics, equipment density, and so forth in relation to the intrinsic hazard posed by the material of concern. In Step 5 you may perceive that the expected frequency of accidents alone is important enough to justify a QRA. However, even though your company may not have much relevant experience with the activity of interest, if the consequence potential of these accidents is not great, you may conclude that the expected frequency of the potential accidents is low enough for you to make your decisions comfortably using qualitative information alone. 

Many sophisticated models and correlations have been developed for consequence analysis. Millions of dollars have been spent researching the effects of exposure to toxic materials on the health of animals the effects are extrapolated to predict effects on human health. A considerable empirical database exists on the effects of fires and explosions on structures and equipment. And large, sophisticated experiments are sometimes performed to validate computer algorithms for predicting the atmospheric dispersion of toxic materials. All of these resources can be used to help predict the consequences of accidents. But, you should only perform those consequence analysis steps needed to provide the information required for decision making. 

The models you use to portray failures that lead to accidents, and the models you use to propagate their effects, are attempts to approximate reality. Models of accident sequences (although mathematically rigorous) cannot be demonstrated to be exact because you can never precisely identify all of the factors that contribute to an accident of interest. Likewise, most consequence models are at best correlations derived from limited experimental evidence. Even if the models are validated through field experiments for some specific situations, you can never validate them for all possibilities, and the question of model appropriateness will always exist. 

Chapters 8 and 9 presented computer codes that are available for computer hazardous material release and transport. Many of these codes have been tested using controlled experiments with varying agreement depending upon the code s applicability to the phenomena. In the author s opinion, the accuracy of the consequence calculation is not much better than the calculation of accident probabilities. 

Usually, experience of the past is used as the basis of failure scenarios, whereas one should look at a process each time again as if all unexpected events could occur. One has to keep in mind that accidents are often due to the highly unlikely coincidence or complex casual chains that seem improbable. It is necessary to examine all failure modes for all possible design alternatives in order to decrease the probability of an incident. 

After the Chernobyl accident the Academy of Sciences and KGB of Ukraine tested the household filters with fibroid sorbents and ten thousands filters were produced in the Institute of Nuclear Physics of Uzbekistan and given to Ukraine through "Isotope" Corp. (USSR). The experience of using the filters for purification of drinking water from radionuclides in Chernobyl region is described in the paper. 

The what-if/checklist analysis method combines the creative, brainstorming features of the what-if analysis with the systematic features of the checklist analysis. The PrHA team uses the what-if analysis method to brainstorm the types of accidents that can occur within a process. Then the team uses one or more checklists to help fill in any gaps. Finally, the team members suggest ways for reducing the risk of operating the process. The what-if analysis encourages the PrHA team to consider potential accident events and consequences that are beyond the experience of the authors of a good checklist and, thus, are not covered on the checklist. Conversely, the checklist lends a systematic nature to the what-if analysis. 

The hazards identification procedures presented in chapter 10 include some aspects of risk assessment. The Dow F EI includes a calculation of the maximum probable property damage (MPPD) and the maximum probable days outage (MPDO). This is a form of consequences analysis. However, these numbers are obtained by some rather simple calculations involving published correlations. Hazard and operability (HAZOP) studies provide information on how a particular accident occurs. This is a form of incident identification. No probabilities or numbers are used with the typical HAZOP study, although the experience of the review committee is used to decide on an appropriate course of action. 

The difficulty in utilizing accident reports lies in the lack of accident report standards. Reports vary a lot how they document the details of the accident itself, the path to the final event, the causes, and the consequences. Still the reports can tell much experience based information which can - and should be - utilized in designing new plants. In fact a major goal in improving the design of safe... 

The chemical and most process factors affecting the index are quite straightforward to estimate. More problematic are the equipment safety and the safety of process structure. The equipment safety subindex was developed based on evaluation of accident statistics and layout information. The evaluation of the safe process structure subindex is based on case-based reasoning, which requires experience based information on accident cases and on the operation characteristics of different process configurations. 

Moreover, while analysing the accidents and their precursors it was shown that often accidents are inadvertently caused by the higher control levels (i.e. the tactical and strategic level) in organizations, as had already been observed in the first experiment of the small company. The second experiment reconfirmed the strength of the developed 7-stage protocol. 

For all 17 accidents of this study, precursors could be identified. None of the 17 accidents could be classified as unforeseen . A total number of 39 precursors were identified in these 17 accidents which seems extremely low compared to normal accident analysis experience. Detailed accident analysis normally retrieves dozens of near misses and deviations leading to the final accident (e.g. van der Schaaf (Schaaf van der, 1992)), implying the existence of many more precursors. However, the limited amount of detailed information present in the FACTS database is the restricting factor here. The FACTS database reflects the kind of accident information companies and government agencies collect. It demonstrates clearly that detailed information about the period before the accident is not often collected. 

Qualitative reviews are studies base on the generic experience of personnel and do not involve mathematical estimations. Overall these reviews are essentially checklist reviews in which questions or process parameters are used to prompt discussions of the process design and operations and possible accident scenarios. 

Human factors and ergonomics play a key role in the prevention of accidents. Some theories attribute up to 90% of all accidents are caused by human factor features. It is therefore imperative that an examination of human factors and ergonomics be undertaken to prevent fire and explosions at petroleum facilities since historical experience have also shown it is a major contributor either as a primary or underlining cause. 

On February 6, 2005—a month after the Graniteville wreck—the three-man crew accused of failing to switch the railroad track back to the main line before disaster hit were fired by Norfolk Southern Railways. A railroad spokesman stated that the workers were terminated because they failed to perform their duties properly. Union officials said the three men will appeal, and each man had at least twenty-five years experience. The accident on January 6, 2005, killed nine people and injured hundreds more. 

Before beginning a new experiment, check the safety-related issues of the protocol as well as the chemicals involved. Take note of precautionary measures in case of accidents. Presumably all chemicals are harmful. 

It must be noted that the above four stages of development are not necessarily well defined in every experiment or accident. For example, in a situation in which the energy of initiation is supplied as a... 

Zack, J.A. Suskind. R.R. (1980) The mortality experience of workers exposed to tetrachloro-dibenzodioxin in a trichlorophenol process accident.. 7. occup. Med., 22. 11-14... 

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