Causes Of Severe Accidents Research Articles

Analysis of Severe Accident in Complex System Reactor Using Moving Particle Semi-Implicit (MPS) Method

The very complex structure of nuclear reactors is one aspect of the cause of severe accidents in nuclear reactors. To prevent serious accidents, analysis is needed on the reactor design before the reactor is built. Reactor accident analysis can be done using the Moving Particle Semi-Implicit method. The Moving Particle Semi-Implicit method is excellent in simulating the movement of liquid fuel in a reactor because it can analyze the free surface flow of an incompressible liquid without using a mesh grid. Simulations were carried out using three types of fluids with different viscosities and densities such as water, oil, and wax. The simulation results show that the water takes the fastest time to drain all the particles and the oil takes the longest time. From the simulation results, it can be determined that the kinematic viscosity of a liquid affects its flow velocity.

Application of an Enhanced Version of Recursive Operability Analysis for Combustible Dusts Risk Assessment.

Organic dust explosions were and are still today a critical issue in the food, pharmaceutical, and fine chemical industry. Materials such as flour, corn starch, sugar and APIs represent a cause of severe accidents. In this framework, we investigated a modified version of Recursive Operability Analysis−Incidental Sequence Diagrams (ROA–ISD), called ROA Plus−ISD, specifically tailored to describe industrial processes involving organic combustible dusts. Compared to more classical techniques such as Hazard and Operability (HazOp), ROA−ISD allows for a direct generation of fault trees, providing a useful tool to connect Qualitative with Quantitative Risk Analysis (QRA). ROA Plus−ISD is very similar to ROA−Cause Consequence Diagrams (CCD), which has already proven to be an effective tool to perform both risk assessment on existing plants and reconstructing already occurred accidents, given its logical structure and width of the application fields. In this work, we modified specific parts of the standard ROA−CCD method: (1) the Failure Mode and Operability Analysis (FMEA) database has been structured in order to retrieve the well-known explosion pentagon (for dusts) and all the instruments, devices, apparatuses and controllers typical of industries which process organic dusts; (2) a new comprehensive list of process variables has been compiled. In this way, it is possible to tailor the information required for the generation of the fault trees concerning top events involving mainly dust explosions and fires. This method has been implemented in order to reconstruct the dynamics of the February 2008 Imperial Sugar refinery plant accident (Port Wentworth, GA, USA). Results demonstrated the applicability of the enhanced method by highlighting the criticalities of the process already showed by a previously detailed reconstruction performed by the Chemical Safety Board.

A Bayesian network-based approach for the assessment and management of ageing in major hazard establishments

Currently, there is an increasing attention towards ageing of industrial equipment, as the phenomenon has been recognised as a cause of severe accidents, recorded in the last years in many process establishments. Recent studies described ageing through a number of key-factors affecting the phenomenon by accelerating or slowing it down. The Italian Competent Authority for the prevention of chemical accidents (Seveso III Directive) adopted a short-cut method, accounting for the assessment of these factors, to evaluate the adequateness of ageing management during inspections at Seveso sites. In this paper, a Bayesian Network was developed, by using the data gathered during the first application of the short-cut method, with the aim to verify the robustness of the approach for ageing assessment and the validity of the a priori assumptions used in assessing the key-factors. The structure of the Bayesian network was established by using experts’ knowledge, whereas the Counting Learning algorithm was adopted to execute the parameter learning by means of the software Netica. The results showed that this network could effectively explore the complex logical and uncertain relationships amongst factors affecting equipment ageing. Results of the present study were exploited to improve the short-cut method.

Facing the Challenges of Supercooled Large Droplet Icing: Results of a Flight Test Based Joint DLR-Embraer Research Project

<div class="section abstract"><div class="htmlview paragraph">Today’s airplanes are well equipped to cope with most common icing conditions. However, some atmospheric conditions consisting of supercooled large droplets (SLD) have been identified as cause of severe accidents over the last decades as existing countermeasures even on modern aircraft are not necessarily effective against SLD-ice. In 2014, the new Appendix O to the certification regulations (FAR Part 25 / CS-25) had been issued to guarantee the safe operation of future airplane when encountering SLD conditions. But as the SLD topic is quite new for the majority of aircraft manufacturers and research institutes in a same way, DLR (German Aerospace Center) and Embraer established a joint research cooperation in 2012 to obtain a better understanding of the distinct influences of SLD-ice shapes on aircraft characteristics and to evaluate proper ways for future airplane certification under App. O. Furthermore, one additional scientific goal of the cooperation was to develop and test new tools for the in-flight monitoring of aircraft characteristics as well as the on-board identification of simulation models. During the 4 years of the project, a distinct way to better understand icing-induced degradations on a specific aircraft was followed: first, data of the clean aircraft was gathered in flight test to identify a dynamic simulation model as base for the subsequent evaluations. Second, data of test flights with artificial App. C ice configurations were analyzed and used for the development of distinct modifications of the base aircraft simulation model; a first evaluation of the icing-induced changes of aircraft characteristics was conducted. Third, after the generation of SLD-ice shapes, wind tunnel testing and flight clearance, a second flight test campaign with these artificial SLD-ice shapes delivered the data for an additional model modification and identification. The results of the final data and model evaluation provide the observable degradation of SLD-ice in flight, which is well comparable to results obtained from the App. C ice configurations.</div></div>

A Technique for the Retrospective and Predictive Analysis of Cognitive Errors for the Oil and Gas Industry (TRACEr-OGI)

Human error remains a major cause of several accidents in the oil and gas (O&G) industry. While human error has been analysed in several industries and has been at the centre of many debates and commentaries, a detailed, systematic and comprehensive analysis of human error in the O&G industry has not yet been conducted. Hence, this report aims to use the Technique for Retrospective and Predictive Analysis of Cognitive Errors (TRACEr) to analyse historical accidents in the O&G industry. The study has reviewed 163 major and/or fatal O&G industry accidents that occurred between 2000 and 2014. The results obtained have shown that the predominant context for errors was internal communication, mostly influenced by factors of perception. Major accident events were crane accidents and falling objects, relating to the most dominant accident type: ‘Struck by’. The main actors in these events were drillers and operators. Generally, TRACEr proved very useful in identifying major task errors. However, the taxonomy was less useful in identifying both equipment errors and errors due to failures in safety critical control barriers and recovery measures. Therefore, a modified version of the tool named Technique for the Retrospective and Predictive Analysis of Cognitive Errors for the Oil and Gas Industry (TRACEr-OGI) was proposed and used. This modified analytical tool was consequently found to be more effective for accident analysis in the O&G industry.

An energy analysis of parametric roll for application to the second generation intact stability criteria

Parametric roll is an amplification of the roll motion due to the periodic variation of the restoring moment in waves. This phenomenon is mostly observed in head and following seas and is the cause of several accidents occurred on container vessels during recent decades. One of the second generation intact stability criteria, currently under finalization and validation by the IMO, requires computing the maximum roll angle with regard to parametric roll. Both proposed methods are relatively complex to implement and require tools that naval architects are not accustomed to. In this paper, we propose an easier alternative method providing the amplitude of parametric roll for any loading condition at any speed, based on energy considerations and assuming a linear GZ. The implementation of this easy method in the corresponding second generation intact stability criterion provides almost the same value of KGmax than the on-degree-of-freedom time simulation proposed by the future regulation.

Pooling knowledge and improving safety for contracted works at a large industrial park.

At a large chemical park maintenance is contracted by the major companies operating the plants to many small firms. The cultural and psychological isolation of contractor workers was recognized a root cause of severe accidents in the recent years. That problem is common in chemical industry. The knowledge sharing has been assumed a good key to involve contractors and sub contractors in safety culture and contributing to injuries prevention. The selection of personal protective equipment PPE for the maintenance works has been taken as benchmark to demonstrate the adequateness of the proposed approach. To support plant operators, contractors and subcontractors in PPE discussion, a method has been developed. Its core is a knowledge-base, organized in an Ontology, as suitable for inferring decisions. By means of this tool all stakeholders have merged experience and information and find out the right PPE, to be provided, with adequate training and information package. PPE selection requires sound competencies about process and environmental hazards, including major accident, preventive and protective measures, maintenance activities. These pieces of knowledge previously fragmented among plant operators and contractors, have to be pooled, and used to find out the adequate PPE for a number of maintenance works. The PPE selection is per se important, but it is also a good chance to break the contractors' isolation and involve them in safety objectives. Thus by pooling experience and practical knowledge, the common understanding of safety issues has been strengthened.

Updating of adventitious fuel pin failure frequency in sodium-cooled fast reactors and probabilistic risk assessment on consequent severe accident in Monju

Experimental studies, deterministic approaches and probabilistic risk assessments (PRAs) on local fault (LF) propagation in sodium-cooled fast reactors (SFRs) have been performed in many countries because LFs have been historically considered as one of the possible causes of severe accidents. Adventitious-fuel-pin-failures (AFPFs) have been considered to be the most dominant initiators of LFs in these PRAs because of their high frequency of occurrence during reactor operation and possibility of fuel-element-failure-propagation (FEFP). A PRA on FEFP from AFPF (FEFPA) in the Japanese prototype SFR (Monju) was performed in this study based on the state-of-the-art knowledge, reflecting the most recent operation procedures under off-normal conditions. Frequency of occurrence of AFPF in SFRs which was the initiating event of the event tree in this PRA was updated using a variety of methods based on the above-mentioned latest review on experiences of this phenomenon. As a result, the frequency of occurrence of, and the core damage frequency (CDF) from, AFPF in Monju was significantly reduced to a negligible magnitude compared with those in the existing PRAs. It was, therefore concluded that the CDF of FEFPA in Monju could be comprised in that of anticipated transient without scram or protected loss of heat sink events from both the viewpoint of occurrence probability and consequences.

SAS4A analysis on hypothetical total instantaneous flow blockage in SFRs based on in-pile experiments

Local fault (LF) has been historically considered as one of the possible causes of severe accidents in sodium-cooled fast reactors (SFRs). Safety assessments on the consequences of three major LF initiators, adventitious-fuel-pin-failures, local over-powers and large flow blockages, have already been performed for the Japanese prototype fast breeder reactor (Monju) and resulted in limited damage within a fuel subassembly. Although the frequency of hypothetical total instantaneous flow blockage at the coolant inlet of a fuel subassembly (HTIB) is negligible, in-pile experiments on this event have been performed because it gives the most severe consequences among the abovementioned LF initiators. Therefore the most rapid damage propagation assumption was newly proposed in this study based on past experiments, and a safety evaluation was performed on the consequences of HTIB in Monju using the SAS4A code, additionally validated by an in-pile experiment specifically on the HTIB-related phenomena. It was shown through the evaluation that the consequences of HTIB were much less severe than that of the unprotected loss of flow (ULOF) events which represent the most severe accidents in Monju. Therefore it was concluded that all the consequences of LFs in Monju can be found among the consequences of ULOF. This evaluation method would be also applicable to enveloping safety assessments of LFs in generic SFRs.

Development of safety assessment methodology on fuel element failure propagation in SFR and its application to Monju

Probabilistic and deterministic safety assessments and experimental studies on local fault (LF) propagation in sodium-cooled fast reactors (SFRs) have been performed in many countries because LFs have been historically considered as one of the possible causes of severe accidents. Adventitious fuel pin failures have been considered to be the most dominant initiators of LFs in these probabilistic assessments because of its high frequency of occurrence during reactor operation and possibility of subsequent pin-to-pin failure propagation. Four possible mechanisms of fuel element failure propagation from adventitious fuel pin failure (FEFPA) were identified from a state-of-the-art review of open papers. All the mechanisms for FEFPA analysis including thermal, mechanical and chemical propagation are modeled into a safety assessment code which is applicable to arbitrary SFRs by developing some needed but missing methods. Furthermore, an assessment on FEFPA of Japanese prototype fast breeder reactor (Monju) was performed using this methodology. It was clarified that FEFPA was highly unlikely and limited at most within one subassembly in Monju owing to its redundant and diverse detection and shutdown systems for FEFPA even assuming the propagation. These results also suggested future possibility of run-beyond-cladding-breach operation which would enhance the economic efficiency in Monju.

RELIABILITY ANALYSIS OF MICROPROCESSOR SYSTEMS RELAY PROTECTION AND AUTOMATION FOR RAILWAY ENERGY SYSTEMS

The analysis of faults of microprocessors relay protection and automation of energy systems forrailway transport faults and opportunities to increase their reliability by duplicating the method as ahardware so are software and calculation of reliability of structures that are investigated. The technicallevel of microprocessor devices of relay protection and automation usually considered from severalpositions: technical excellence and reliability of the devices, microprocessor-based protective relaying andautomation technology level, which determines the performance of the system microprocessor relayprotection and automation algorithms embedded security and automation; functionality of microprocessorrelay protection systems and automation; possibility of integrating relaying and automation microprocessorsystems in other systems. Invalid action relaying is one of the main causes of severe accidents thatoccasionally occur in energy systems - max globally. Therefore, the reliability of relay protection largelydepends on the reliability of the entire grid. Previously developed methods to increase reliability of attitudeto the old element base and microprocessor devices of relay protection and automation with a number offeatures that can not be taken into account in the calculation of these methods. It is necessary to develop newapproaches to design microprocessor devices of relay protection and automation and methodology forassessing the performance reliability of these systems.

Comprehensive and consistent interpretation of local fault experiments and application to hypothetical local overpower accident in Monju

Experimental studies on local fault (LF) accidents in fast breeder reactors have been performed in many countries because LFs have been historically considered as one of the possible causes of severe accidents. Comprehensive and consistent interpretations of in-pile and out-of-pile experiments related to LF were arrived at in this study based on state-of-the-art review and data analysis techniques. Safety margins for a hypothetical local overpower accident, which was evaluated as a LF accident in the licensing document of the construction permit for a prototype fast breeder reactor called Monju, were also studied. Based on comprehensive interpretations of the latest experimental database, including those performed after the permission of Monju construction, it was clarified that the evaluation of the hypothetical local overpower accident in the Monju licensing was sufficiently conservative. Furthermore, it incorporated adequate safety margins in terms of failure thresholds of the fuel pin, molten fuel ejection, fuel sweep-out behavior after molten fuel ejection, and pin-to-pin failure propagation. Moreover, these comprehensive interpretations are valid and applicable to the safety evaluation of LF accidents of other fast breeder reactors with various fuel and core designs.

Evaluation of Construction Process Safety Solutions Using the TOPSIS Method

The paper discusses the problem of selecting construction process safety solutions which secure employee health and safety on construction sites. To achieve this, the causes of severe accidents on construction sites have been analyzed, factors which cause accidents at work in construction companies have been studied; a comprehensive literature review has been made, assesing all statistical data and employee health and safety improvement perspectives as well as their application in construction practice. The selection problem is stated as a mathematical multi-purpose solution making task. It expresses the management solution making problem mathematically.Investigation of severe accidents on construction sites shows that over two thirds of accidents are caused by poor work organization, lack of supervision and control as well as underestimation of professional risks. This high level of injuries is brought about not only by noncompliance with employees’ health and safety requirements, but also by factors and violations having to do with traffic, noncompliance with fire and electricity safety requirements, lack of work discipline, which is mainly displayed by usage of alcohol at work, as well as other causes. Other important factors that directly impact the number of accidents in the construction sector are the lack of training and knowledge as well as the lack of awareness of safe execution of assigned work.Studies of the dependencies between workplace accidents and their causes show that the prevailing accidents are the following: high falls, collisions with vehicles, stumbling and falling as well as falling objects. They usually result in severe and lethal outcomes.The paper emphasizes that work safety in various building construction activities can be achieved not only by collective and individual means, evaluation of professional risk, employee briefing on safety measures, but also by efficient work organization and appropriate working environment. To implement the above mentioned, the most effective solution must be found. One of the methods used to determine the priorities of safe operation in a construction company is the TOPSIS (Technique for Order Preference by Similarity to Ideal Solution) method.The effectiveness level of safety solutions for a construction process depends on numerous quantitative and qualitative indices affecting the process; their impact is evaluated in terms of their value and significance. Since the significance of quantitative and qualitative indices depends on their values, the latter should be taken into consideration. Furthermore, it is necessary to coordinate the significances of quantitative and qualitative indices in terms of their value and significance. To achieve the above-mentioned goals, the authors developed an integrated index significance determination method, in view of their quantitative and qualitative characteristics.The paper discusses the selection of objects and indicators that are under consideration. An anonymous survey was carried out with the help of questionnaires designed for the purpose. Six average-size construction companies engaged in constructing individual dwelling-houses participated in the survey. A single-storey house with an attic and no basement was selected as a study object.

Experimental strategies for the identification of substances formed in the loss of control of chemical industrial processes

The formation and release of dangerous substances as a consequence of the deviation of a process from the normal operating conditions was found to be the cause of severe accidents, the more important being that of Seveso, that took place in 1976. The present study was dedicated to the definition of specific experimental protocols for the identification of the possible products formed in the loss of control of a chemical industrial process. A set of reference experimental techniques was defined to obtain experimental data on the products formed in “out of control” conditions. The application to several case studies provided useful information on the decomposition products that may be formed in accidental scenarios. The comparison of the experimental data obtained by the application of the reference protocols with information reported in MSDS evidenced that detailed experimental information is of fundamental importance to correctly evaluate the hazard due to the unwanted formation and release of hazardous substances in “out of control” conditions. The analysis of the case studies also evidenced the severity that scenarios due to the formation and release of hazardous products in “out of control” conditions may have for some industrial processes.

The analysis of domino accidents triggered by vapor cloud explosions

Domino effect is a well-known cause of severe accidents in the chemical and process industry. Several studies pointed out that the more critical step in the quantitative assessment of domino hazards is the availability of reliable models to estimate the possibility and probability of the escalation of primary accidents. This work focused on the revision of available models for the quantitative estimation of damage probability to plant equipment caused by pressure waves generated by a primary accident. Available data on damages to process equipment caused by pressure waves were analyzed. Several specific probit functions for different elements of process equipment were obtained from the analysis of failure data. The analysis of blast wave propagation in different types of explosions allowed the estimation of the expected damage probability as a function of distance from the explosion center and of explosion strength. The results obtained were used to assess safety distance criteria and to evaluate the contribution to individual risk of domino effect due to pressure waves.

Histopathological findings in rabbits after experimental acute exposure to the Loxosceles intermedia (brown spider) venom.

Loxoscelism, the term used to describe envenomation with brown spiders, is characterized by a dermonecrotic lesion at the bite site. In the present investigation we submitted albino rabbits to an acute experimental envenomation protocol using Loxosceles intermedia (brown spider) venom, with in order to determine the pathogenesic features of the lesion induced by this spider, which is the cause of several accidents throughout the world. Rabbits received intradermal injections of the venom and were monitored over the first 4 h, and then at 12 h and 1, 2 and 5 days after envenomation. Histological specimens from 3 rabbits per time point were collected from euthanized animals and processed for histological examination by light microscopy. Major findings observed during the first 4 h were oedema, haemorrhage, degeneration of blood vessel walls, plasma exudation, thrombosis, neutrophil accumulation in and around blood vessels with an intensive diapedesis, a diffuse collection of inflammatory cells (polymorphonuclear leucocytes) in the dermis, and subcutaneous muscular oedema. Over the following hours and up to 5 days after envenomation the changes progressed to massive neutrophil infiltration (with no other leucocytes) into the dermis and even into subcutaneous muscle tissue, destruction of blood vessels, thrombosis, haemorrhage, myonecrosis, and coagulative necrosis on the 5th day.

回転翼航空機の地上共振に関する模型実験について

Self-excited vibration of the helicopters on the ground has been the cause of several accidents. It is, therefore, essential for the helicopter design that serious attention should be paid to the methods of ensuring freedom from such phenomena. In this paper, the theory of Coleman is reviewed and the results of the experimental investigations of several model rotors and small viscous dampers are presented. The models were built to represent the dynamic system of the rotor head without the freedom in the"y"direction to avoid the experimental errors. The test results showed, as expected, that the viscous dampers and the drag hinge offsets have large effect on the characteristics of ground resonance of the helicopter. The comparison between the experimental and the theoreticatl resuls, affords that Coleman's theory is useful forengineering practice.