Accident Process Research Articles

Evaluation of Root Cause Analysis from Occupational Health and Safety Data in a Hospital: A Retrospective Study

Introduction: Occupational accidents are increasing every year around the world. The fact that accidents will be repeated as a result of not learning the lessons is constantly forgotten. Occupational accidents should be examined on the basis of the "Root Cause" approach. Within the scope of the information obtained as a result of the analysis studies on the causes of occupational accidents, it is important for the institutions to make a plan in order to prevent the reoccurrence of the accidents. This study was carried out retrospectively to examine the root cause analysis process of occupational accidents that occurred in a state hospital and to examine how it was applied in the health facility. Methods: The population of the research consists of occupational accident records that occurred in a state hospital between January 2018 and April 2021. (N=156). In the analysis of the data; Root cause analysis forms and number-percentage distributions were used to identify all factors that could cause a particular problem. Results: Of those who had occupational accidents, 68.15% were women, 45% were nurses, 25 were cleaning staff and 3% were physicians. Fifty percent of the accidents occurred in inpatient services, 15% in emergency services, and 15% in intensive care units. Causes of accidents; needle-stick injuries (71.8%) are the most common occupational accidents. These injuries are followed by slipping and falling (14.7%). Conclusion: By establishing a safety culture that monitors occupational accidents at the institutional level, evaluates their consequences and develops precautions, the probability of occupational accidents will decrease. And the costs and compensations that will occur after the accident will decrease, and labor and service/production losses will be prevented.

Experimental study on coolability of mixed particle size debris bed under top flooding

During severe accident in reactor, a debris bed is formed after the core melt interacts with the coolant, this is the key stage to realize the melt retention in vessel and terminate the accident process. Studying the drying characteristics of such stacked particle beds can expand the safety margin of the In-Vessel Retention (IVR) strategy. In this paper, based on the debris bed's characteristics of prototype fuel coolant interaction (FCI) experiment, a one-dimensional cylindrical debris bed with irregular and multi-sized sand particles was constructed. At the uniformly stacked case, the typical characteristics were observed. Two vapor phase concentration areas appeared in the debris bed before and after drying, bubble blocking area was formed in the middle of the debris bed before drying, then a dry zone appeared at the bottom of the debris bed due to lack of liquid, the dry area extended first radially and then axially. Meanwhile, the influence of system pressure is significant, dryout heat flux (DHF) under 1.0 MPa is almost twice than normal pressure. At the sand particles layered case, it was found that DHF increased by 40%∼50% compared with uniformly stacked condition, the bubble blocked area and dry area coincided, and occurred in the middle of the debris bed. Finally, a DHF model based on Reed pressure drop model is established for one-dimensional uniform sand debris bed, and the calculated values are in good agreement with the experimental values.

Multiobjective optimization algorithm for accurate MADYMO reconstruction of vehicle-pedestrian accidents.

In vehicle-pedestrian accidents, the preimpact conditions of pedestrians and vehicles are frequently uncertain. The incident data for a crash, such as vehicle deformation, injury of the victim, distance of initial position and rest position of accident participants, are useful for verification in MAthematical DYnamic MOdels (MADYMO) simulations. The purpose of this study is to explore the use of an improved optimization algorithm combined with MADYMO multibody simulations and crash data to conduct accurate reconstructions of vehicle-pedestrian accidents. The objective function of the optimization problem was defined as the Euclidean distance between the known vehicle, human and ground contact points, and multiobjective optimization algorithms were employed to obtain the local minima of the objective function. Three common multiobjective optimization algorithms-nondominated sorting genetic algorithm-II (NSGA-II), neighbourhood cultivation genetic algorithm (NCGA), and multiobjective particle swarm optimization (MOPSO)-were compared. The effect of the number of objective functions, the choice of different objective functions and the optimal number of iterations were also considered. The final reconstructed results were compared with the process of a real accident. Based on the results of the reconstruction of a real-world accident, the present study indicated that NSGA-II had better convergence and generated more noninferior solutions and better final solutions than NCGA and MOPSO. In addition, when all vehicle-pedestrian-ground contacts were considered, the results showed a better match in terms of kinematic response. NSGA-II converged within 100 generations. This study indicated that multibody simulations coupled with optimization algorithms can be used to accurately reconstruct vehicle-pedestrian collisions.

Study on the influence of flow blockage in severe accident scenario of CAP1400 reactor

Deformed fuel rods can cause a partial blockage of the flow area in a subchannel. Such flow blockage will influence the core coolant flow and further the core heat transfer during the reflooding phase and subsequent severe accidents. Nevertheless, most of the system analysis codes simulate the accident process based on the assumed flow blockage ratio, resulting in inconsistencies between simulated results and actual conditions. This paper aims to study the influence of flow blockage in severe accident scenario of the CAP1400 reactor. First, the flow blockage model of ISAA code is improved based on the FRTMB module. Then, the ISAA-FRTMB coupling system is adopted to model and calculate the QUENCH-LOCA-0 experiment. The correctness and validity of the flow blockage model are verified by comparing the peak cladding temperature. Finally, the DVI Line-SBLOCA accident is induced to analyze the influence of flow blockage on subsequent CAP1400 reactor core heat transfer and core degradation. From the results of the DVI Line-SBLOCA accident analysis, it can be concluded that the blockage ratio is in the range of 40%–60%, and the position of severe blockage is the same as that of cladding rupture. The blockage reduces the circulation area of the core coolant, which in turn impacts the heat exchange between the core and the coolant, leading to the early failure and collapse of some core assemblies and accelerating the core degradation process.

Systematic Analysis of the Contributory Factors Related to Major Coach and Bus Accidents in China

The purpose of this study was: (1) to propose a classification system for the contributory factors behind major coach and bus accidents with mass casualties based on the human factor analysis and classification system (HFACS); and (2) to identify the main contributory factors behind accidents and the main indicators of the causal factors. Based on 56 official investigation reports of major coach and bus accidents with more than 10 fatalities, a qualitative content analysis was conducted to develop a modified classification system for the contributory factors behind these accidents, and a gray correlation analysis was conducted to identify the main causative factors and indicators by calculating the correlation degrees. The results showed that the modified classification system for the contributory factors behind major coach and bus accidents can be divided into seven levels: government regulations, the organizational influence of passenger transportation enterprises, unsafe internal operational supervision, preconditions for drivers’ unsafe acts, drivers’ unsafe acts, proximate causes other than the driver’s act, and moderating factors affecting accident severity and probability. The organizational influence of passenger transportation enterprises is the most significant factor affecting the accidents. Thus, passenger transport enterprises must systematically strengthen their responsibility and safety management to prevent accidents. Accident investigations should begin with the accident process to determine the proximate cause as well as the factors that influence the likelihood and severity of the accident.

STUDY ON THE SOCIAL RISK OF PETROLEUM EXPLORATION AND DEVELOPMENT ACCIDENTS: A CASE OF MACONDO ACCIDENT IN THE GULF OF MEXICO

The process of petroleum exploration and development is related to many factors. A large number of safety accidents occur every year around the world and have an impact on the society. Due to the particularity of Marine environment, safety accidents in the process of offshore petroleum exploration and development usually have serious impacts. Taking Macondo accident in Gulf of Mexico as an example, this paper studies the social risk of petroleum exploration and development accident. On the basis of introducing the accident background, the accident process and the accident consequence, the technical reason and the management reason of the accident are analyzed, and the social influence of the accident is further analyzed. The root cause of the incident was BP's catch-up schedule, which resulted in a lack of compliance with cementing procedures such as casing running, cement injection, cement waiting, cement bond logging, and negative pressure testing, as well as inadequate supervision. After the accident, the technical treatment effect of petroleum spill was not good, and the government blindly emphasized responsibility and took little initiative to participate in the accident treatment, which turned the social risk into a social crisis and caused terrible effects. The accident seriously affected the lives of coastal residents, caused great harm to Marine life, and damaged the Marine ecological environment of the Gulf of Mexico.

Quantitative Study on Human Error in Emergency Activities of Road Transportation Leakage Accidents of Hazardous Chemicals.

The emergency rescue process of road transportation leakage accidents involving hazardous chemicals is complex and includes various emergency activities. A quantitative study of human errors in emergency activities is conducive to seeking the focus of the emergency rescue process. To quantitatively analyze human error in emergency activities during the emergency rescue process of road transportation leakage accidents of hazardous chemicals, sequentially timed events plotting (STEP) and the cognitive reliability and error analysis method (CREAM), were used. First, STEP was used to analyze six laws, regulations and standards, as well as 54 accident cases, to derive 24 emergency activities in the emergency rescue process. Then, CREAM was used to analyze and obtain the probability of human error for each emergency activity. Two high error level emergency activities, five medium error level emergency activities, and seventeen low error level emergency activities were identified after the human error levels of the emergency activities were classified. The results show that two emergency activities, the initial handling of the accident, and cleanup of the leakage site, should be prioritized in the emergency rescue process of road transportation leakage accidents of hazardous chemicals.

Study on the influence of source term release on accident consequences in severe accidents for small pressurized water reactor

In this paper, a small PWR with no pressure vessel external cooling system (ex-vessels) is used as the research object. It is found that for the small low burnup marine reactor without ex-vessels, the more core releases at an early stage, the later core damage occurs. Considering in the case of large break loss of coolant and loss of power accident, and the ORIGEN program is coupled with the MELCOR program is used as a severe accident process simulation tool. The significant parameters have been took into account, include core melting time, core damage rate, and lower head failure time, etc. It could be found through calculation that, for a certain reactor, in case of the reactor core meltdown happened, different released amount of source term will results in a difference of core heat release in the pressure vessel. For the small reactors without ex-vessels, the amount difference of source term release can reach 20%, and the lower head failure time can be delayed by 70%.

Design of an Underground Transmission Line Condition Fault Monitoring System for Power Grids Based on Data Analysis Algorithms

With the continuous expansion of the scale, capacity, and coverage of the modern transmission network, the role of the power system in the national economy is increasingly prominent, and the disconnection of the power system will have a huge impact on society and people’s lives. Due to the long transport distance and wide coverage of transmission lines, natural conditions and human factors have caused great difficulties in line operation and maintenance. How to effectively improve the operation and maintenance of transmission lines to ensure the stability and safety of the power grid has become a common problem for the power industry and scientific researchers to discuss. In recent years, the information society has stepped into the era of big data, and big data has developed rapidly, becoming a hot area favored by academia and industry, and is widely used. Through big data analysis, potential operation rules can be discovered from a large amount of grid information, providing maintenance personnel with corresponding maintenance decision support. Using big data technology for transmission line fault analysis can effectively reduce accident processing time and avoid accident expansion. Therefore, this paper combines the underground transmission line fault of power grid with the fuzzy KNN algorithm model to apply the underground transmission line state intelligent monitoring system and conducts the study of real-time data collection and fault diagnosis analysis of the underground transmission line fault of power grid, and this paper conducts the transmission line fault analysis experiment, which fully confirms the feasibility and effectiveness of the algorithm model proposed in the paper and concludes that the data analysis model proposed in this paper. The proposed data analysis model has good innovation and practical feasibility.

Mechanisms Analysis for Fatal Accident Types Caused by Multiple Processes in the Workplace: Based on Accident Case in South Korea.

This study aimed to develop the accident mechanism of fatal accidents taking place in multiple processes at the workplace. Multiple processes were defined as the existence of multiple work types and work processes in the same workspace. Recently, various processes are frequently conducted simultaneously in one workplace with the participation of several companies, and more workers are increasingly experiencing industrial accidents while working in multiple processes. To prevent accidents in the multiple processes caused by the sameness of work period and space, the accident process was investigated by analyzing the investigation reports on serious industrial accidents in South Korea, and then the accident mechanism model was developed. By utilizing the developed model, the major safety measures to be taken by the contractor for each of the 8 types of accidents caused by the multiple processes were drawn. The roles and responsibilities of the contractor to be implemented in order to prevent accident occurrence in multiple processes were proposed through the accident mechanism of each type of fatal accident. It is expected that the accidents taking place in the multiple processes can be prevented with the drawn results.

Assessment of different internal flow blockage scenarios for LFR fuel assemblies with different configurations

Flow blockage accident is identified as one of the most serious accidents in LFR (lead-cooled fast reactor) due to the concealment of the accident process and the severity of the accident consequences. The main goal addressed in this paper is to assess the influence of different flow blockage scenarios on the thermal–hydraulic parameters of LFR single-wrapper fuel assemblies (FAs), and to identify the differences and commonalities of thermal–hydraulic response characteristics between two typical-design FAs under different flow blockage conditions. The subchannel method is adopted to implement a detailed assessment of different blockage parameters, including the axial/radial position, thickness, area and the thermal conductivity of the blockage. A case matrix is constructed based on the control variable method and covers various blockage conditions between two FAs with different configurations, which represent typical FA designs including both forced-circulation and natural-circulation LFRs. Current results show that different blockage parameters have different influences on the fluid behaviors (such as dynamic pressure drop and recirculation phenomena) and heat transfer characteristics (such as peak temperature of cladding, pellet and coolant and outlet temperature distribution). Meanwhile, different FAs show some similar phenomena and also differences in various flow blockage scenarios.

Proposed model of potential accident process at hydrogen refueling stations based on multi-level variable weight fuzzy Petri net

Hydrogen is becoming more popular as a fuel for vehicles. It is stored and dispensed at hydrogen refueling stations. Once the hydrogen in hydrogen refueling stations leaks, it easily forms a combustible cloud, and can explode by encountering a spark. It is therefore important for the safe and stable operation of hydrogen refueling stations to analyze the evolution of a leakage and explosion accident, clarify the causes and processes of the accident, and prevent the spread of risks. This paper proposes a model using multi-level variable weight fuzzy Petri net. On the basis of hierarchical consideration of the development of the accident, it adds a variable weight factor, which can quantify information in the development of the accident. According to the calculated results, the evolutionary path of risk and the most likely initial cause of the accident are deduced. Finally, taking the leakage and explosion accident of an urban hydrogen refueling station as an example, the usability and effectiveness of the model are verified.

Classification and characteristics of supercritical carbon dioxide leakage from a vessel

Accidental leakage is one of the major safety issues of carbon capture, utilization and storage (CCUS) projects. Fully understanding SCO2 leakage characteristics is very important for safety system design and leakage detection. In this paper, supercritical carbon dioxide decompression experiments were studied based on a set of 50.0 L pressurized vessel experimental apparatus. The decompression characteristics and influence of orifice sizes, initial temperature and initial pressure were analyzed. The results show that the supercritical CO2 vessel decompression undergoes two different decompression processes. This is mainly because of drastic changes in physical properties near critical point and pseudo-critical point. Supercritical region is divided into gas-like phase and liquid-like phase according to initial temperature higher or lower than pseudo critical temperature. Besides, low initial temperature and large orifice size resulted in great temperature drop in the vessel. In each decompression processes, decompression time is mainly related to leakage diameters and initial pressure. The experiments results show lower temperature will not damage material. Experiment results are of great significance for understanding process of accident and model development.

Escalator accident mechanism analysis and injury prediction approaches in heavy capacity metro rail transit stations

The semi-open character with high passenger flow in Metro Rail Transport Stations (MRTS) makes safety management of human-electromechanical interaction escalator systems more complex. Safety management should not consider only single failures, but also the complex interactions in the system. This study applies task driven behavior theory and system theory to reveal a generic framework of the MRTS escalator accident mechanism and uses Lasso-Logistic Regression (LLR) for escalator injury prediction. Escalator accidents in the Beijing MRTS are used as a case study to estimate the applicability of the methodologies. The main results affirm that the application of System-Theoretical Process Analysis (STPA) and Task Driven Accident Process Analysis (TDAPA) to the generic escalator accident mechanism reveals non-failure state task driven passenger behaviors and constraints on safety that are not addressed in previous studies. The results also confirm that LLR is able to predict escalator accidents where there is a relatively large number of variables with limited observations. Additionally, increasing the amount of data improves the prediction accuracy for all three types of injuries in the case study, suggesting the LLR model has good extrapolation ability. The results can be applied in MRTS as instruments for both escalator accident investigation and accident prevention.

Модель реактивнісної аварії на РБМК-1000

The reactor model was used to study the accident that destroyed the RBMK-1000 reactor at Unit 4 of the Chornobyl nuclear power plant on 26 April 1996. The model of reactivity accident of the RBMK-1000 reactor is based on equations of nuclear reactor kinetics, taking into account feedback in reactor reactivity. Reactivity changes as a result of both external influences – the movement of regulatory organs, changes in the reactor inlet coolant temperature, – and as a result of feedback by core parameters – changes in fuel temperature, coolant density, and 135Хе concentration. The model takes into account steam generation in the reactor core, which corresponds to the real physics of processes at the RBMK reactor, and allows obtaining simulation results that best match the recorded data and the consequences of the accident process. The study of reactivity accident on RBMK-1000 reactor is carried out for different combinations of values of control rods efficiency; reactivity coefficients by fuel temperature and coolant density; changes in the reactor inlet coolant temperature; the emergency protection time, as well as the reactor power level before closing the turbine generator stop valve. Different reactivity accident scenarios at RBMK-1000 reactor allow us to determine the most unfavorable combinations of external influences on the course of reactivity accident, namely: start time of main coolant pump rundown, time of activation of emergency protection, power level before the closing of turbine generator stop valves. In most reactivity accident scenarios, first of all, the critical values of fuel enthalpy are reached, at which the process of fuel destruction in the fuel element, destruction of the fuel assembly, and assembly channel start. Important results of studies are 1 – determination of the fact that time of activation of emergency protection after the closing of stop valves of turbine generator significantly affects the value of the maximum neutron power that is achieved during a reactivity accident; 2 – determination of the effect of reactor power before the closing of turbine generator stop valves on the course of the accident; 3 – it is not necessary to achieve supercritical on instantaneous neutrons, supercritical on delayed neutrons is enough to start fuel destruction.

Modeling the Evolution of Major Storm-Disaster-Induced Accidents in the Offshore Oil and Gas Industry.

Storm disasters are the most common cause of accidents in offshore oil and gas industries. To prevent accidents resulting from storms, it is vital to analyze accident propagation and to learn about accident mechanism from previous accidents. In this paper, a novel risk analysis framework is proposed for systematically identifying and analyzing the evolution of accident causes. First, accident causal factors are identified and coded based on grounded theory (GT). Then, decision making trial and evaluation laboratory (DEMATEL) is integrated with interpretative structural modeling (ISM) to establish accident evolution hierarchy. Finally, complex networks (CN) are developed to analyze the evolution process of accidents. Compared to reported works, the contribution is threefold: (1) the demand for expert knowledge and personnel subjective influence are reduced through the data induction of accident cases; (2) the method of establishing influence matrix and interaction matrix is improved according to the accident frequency analysis; (3) a hybrid algorithm that can calculate multiple shortest paths of accident evolution under the same node pair is proposed. This method provides a new idea for step-by-step assessment of the accident evolution process, which weakens the subjectivity of traditional methods and achieves quantitative assessment of the importance of accident evolution nodes. The proposed method is demonstrated and validated by a case study of major offshore oil and gas industry accidents caused by storm disasters. Results show that there are five key nodes and five critical paths in the process of accident evolution. Through targeted prevention and control of these nodes and paths, the average shortest path length of the accident evolution network is increased by 35.19%, and the maximum global efficiency decreases by 20.12%. This indicates that the proposed method has broad applicability and can effectively reduce operational risk, so that it can guide actual offshore oil and gas operations during storm disasters.

A Causation Analysis of Chinese Subway Construction Accidents Based on Fault Tree Analysis-Bayesian Network.

Clarifying the causes of subway construction accidents has an important impact on reducing the probability of accidents and protecting workers’ lives and public property to a greater extent. A total of 138 investigation records of subway construction accidents from 2000 to 2020 were collected in this study. Based on a systemic analysis of 29 well-known accident causation models and the formative process of the subway construction accidents, we extracted the causative factors of subway construction accidents from the collected records. Furthermore, a causation analysis index system of subway accidents was proposed based on fault tree analysis (FTA), where we considered subway construction accidents as the top event and the five dimensions, i.e., human, equipment, environment, management, and safety culture, as first-level intermediate events. Moreover, 17 causative factors were considered to be related to the severity of subway construction accidents. It is found that human factors are prone to be critical to high-risk accidents. Finally, a Bayesian network (BN) was formed to explore the causative factors of high-risk subway construction accidents. Based on the combined application of FTA and BN, this study discusses the complex influence factors and their action routes to unsafe accidents in subway construction sites, and makes efforts to correspond safety decision basis for the management of China subway construction.

Traceability and failure consequences of natural gas explosion accidents based on key investigation technology

In recent years, there have been frequent gas explosion accidents in China. On October 21, 2021, a gas explosion occurred in Northeast China, resulting in 5 deaths and 52 injuries. To further improve accident investigation theories and methods, with the help of key accident investigation technologies, this study carried out traceability, investigation, and failure analyses regarding the above-mentioned typical natural gas leakage and explosion. The investigation showed that natural gas leaked from a gas pipeline almost filled the entire accident building within 3 h and 25 min and the gas concentration was between 7 and 9 vol% before the accident. An electric spark generated by the action button of a refrigerator was the key ignition factor. The peak explosion overpressure near the ignition was 57 kPa and peak temperature reached 1620 K. The outdoor explosion venting overpressure less than 30 kPa, but the venting airflow velocity exceeded 90 m/s, with many items and fragments thrown outside, resulting in three deaths and many injuries. In addition, based on calculations of gas concentration and diffusion volume, the total amount of natural gas leakage in the accident reached 150 m3. Based on the TNT equivalent method, the TNT explosion equivalent of the accident was 80 kg. These investigation results ideally restored the entire explosion accident process and the research methods and failure analysis ideas developed here will provide scientific guidance for the investigation of such accidents and evaluation of explosion effects.

Prevention of accidents in facilities for the treatment and storage of selected agricultural products

Process safety in the storage and processing of agricultural products is an important aspect related not only to reducing the risk of damage to the human health or property, but is also strategical to national food safety. A special emphasis must therefore be placed on risk assessment of the operation of these facilities. One of the cornerstones of the risk assessment process is the use of knowledge of past accidents. As the agricultural industry is rather marginal in the field of safety engineering compared to other sectors of the economy, available publications dealing with this topic are rather an exception. The aim of this paper is to conduct research on the available information on accidents that have occurred in agricultural processing and storage facilities in the past. The purpose is to provide professionals and operators with a comprehensive source of information useful for activities related to the prevention of these accidents. The output of the work is then a previously unrealised representative database of systematically sorted information on accidents that have occurred in the process of treatment or storage of agricultural products. This information was subsequently analysed and evaluated. The created database consists of 195 records of accidents that occurred between 1989 and 2018. To create a unique representative database, mainly publicly available databases of industrial accidents or professional publications were used. The author's database contains information on accident locations, accident causes and accident prevention measures. A total of 21 persons died and 32 persons were injured during the accidents. The analysis shows that fires are the most frequent manifestation of accidents (86%) and accidents in material handling facilities are the most frequent (33%). According to the information available in the database, organisational factors were identified as the most frequent causative factors of accidents (47%). For a better understanding of the accident process, a description of selected accident scenarios was also provided in the work. A linear model was used for this purpose. Due to the strategic importance of the evaluated facilities for processing and storage of agricultural products, efforts are made to prevent accidents from recurring or to reduce their impact on the surrounding area. Therefore, an integral part of the work is the description of possible measures against the recurrence of similar accidents.

Experimental Research for CHF Sensitivity of Heat Flux Distribution under IVR Conditions

In-vessel retention (IVR) through external reactor vessel cooling (ERVC) is one of the most effective severe accident mitigation measures in the nuclear power plants. The most influential issues on the IVR strategy are in-vessel core melt evolution, the heat fluxes imposed on the lower head, and the external cooling of reactor pressurized vessel (RPV). In the molten pool research, there are mainly two different molten pool configurations: two layers and three layers. Based on the different distributions of heat flux in molten pool configurations, a new problem was raised: whether the in-vessel heat flux distribution will affect the CHF on the outer wall of RPV and further affect the effectiveness of IVR measures? A full-height external reactor vessel cooling and natural circulating facility was conducted to study the CHF sensitivity of different heat flux distributions. The experimental results show that the characteristics of natural circulation are similar and the CHF of the RPV lower head external surface is not obviously affected under the different heat flux distributions. The varying heat flux distribution during severe accident process will not threaten significantly the success of IVR strategy.