The potential for vapour cloud explosions – Lessons from the Buncefield accident

At around 06.00 on Sunday 11th December 2005, a vapour cloud explosion occurred at Buncefield Oil Storage Depot, Hemel Hempstead, Hertfordshire, UK, generating significant blast pressures. However, as a storage site, the Buncefield terminal had very little pipework congestion and at first sight would not have been considered as having much potential for a vapour cloud explosion. As a consequence, one of the actions of the Buncefield Major Incident Investigation Board (BMIIB) was to initiate a review of the possible causes of the severe explosion on the site. This review was then extended to a Joint Industry Project, Phase 1 of which has offered an explanation of the cause of the explosion. The conclusions are summarized along with reference to relevant experimental studies, illustrating how the elements of the explanation were already known. The implications of the incident for the assessment of vapour cloud explosion hazards will be discussed, both in terms of understanding worst case consequences and the use of risk based approaches.     

Prerequisites for learning from accident investigations – A cross-country comparison of national accident investigation boards

In this paper railway accident investigation reports issued by the national accident investigation boards in three Scandinavian countries during a 2-year period have been systematically studied. Content analysis of attributed causes in these reports reveals a considerable emphasis on physical processes, actor activities and equipment (the microlevel). Much less attention is paid to organisational factors (the mesolevel) and conditions related to regulators, associations and government (the macrolevel). This means that lessons will primarily be learned about aspects at the lower of these levels. Interviews show that the factors emphasised in investigation reports typically reflect the competences and experiences of the investigators, i.e. they are inclined to focus on areas of their own expertise. Since failures at the microlevel in many cases merely are symptoms of trouble at higher levels, it is argued that competence among investigators that supplements entirely technical or operational backgrounds are necessary for enabling deeper understanding of the factors leading to accidents. One possible way for achieving this is the creation of multi-modal investigation boards that provide a number of potential advantages, such as increased access to specialist competences that are shared between different sectors. Although a multi-modal approach to some degree has been adopted in all three countries, interviews reveal that these positive effects do not emerge automatically. It can therefore be concluded that multi-modal investigation boards offer a number of possible advantages, but only when these synergies are fully exploited can they provide a potential for more effective learning from accidents.     

Risk of motor vehicle accident death among 1.3 million veterans of the Iraq and Afghanistan wars

Objective: We conducted a cohort study of recent wartime veterans to determine the postservice mortality risk due to motor vehicle accidents (MVAs).

Methods: Veterans were identified from the Defense Manpower Data Center records. Deployment to te Iraq or Afghanistan war zone was determined from the Contingency Tracking System. Vital status of 317,581 deployed and 964,493 nondeployed veterans was followed from their discharge dates between 2001 to 2007 until earlier of date of death or December 31, 2009. Underlying causes of death were obtained from the National Death Index Plus.

Results: Based on 9,353 deaths (deployed, 1,650; nondeployed, 7,703), of which 779 were MVA deaths as drivers (166; 613), both cohorts had 25 to 24% lower mortality risk from all causes but had 44 to 45% higher risk of MVA deaths relative to the U.S. general population. The higher MVA mortality risk was not associated with deployment to the war zone. After controlling for age, sex, race, marital status, branch of service, and rank, the risk for deployed veterans was comparable to that of nondeployed veterans (hazard ratio = 0.91; 95% confidence interval, 0.77–1.09).

Conclusions: Veterans exhibit significantly higher risk of MVA deaths compared to the U.S. general population. However, deployment to the Iraq or Afghanistan war was not associated with the excess risk.     

Prevention of railway trespassing by automatic sound warning—A pilot study

Objective: The objective of this study was to investigate the effects of a sound warning system on the frequency of trespassing at 2 pilot test sites in Finland.

Methods: The effect of automatic prerecorded sound warning on the prevention of railway trespassing was evaluated based on observations at 2 test sites in Finland. At both sites an illegal footpath crossed the railway, and the average daily number of trespassers before implementation of the measures was about 18 at both sites.

Results: The results showed that trespassing was reduced at these sites by 18 and 44%, respectively. Because of the lack of proper control sites, it is possible that the real effects of the measure are somewhat smaller.

Conclusions: The current study concludes that automatic sound warning may be efficient and cost effective at locations where fencing is not a viable option. However, it is not likely to be a cost-effective panacea for all kinds of sites where trespassing occurs, especially in countries like Finland where trespassing is scattered along the railway network rather than concentrated to a limited number of sites.     

Systems thinking in a gas explosion accident – lessons learned from Taiwan

On July 31, 2014, at around 23:57, several huge explosions occurred that lasted for 2 h in Kaohsiung City, Taiwan. As a result of a gas leak from a ruptured underground pipeline, the catastrophic incident destroyed more than 6 km of roads, killed 32 people, injured 321 people, and damaged 3259 buildings. Pipeline explosions have been reported as a repeatedly occurring problem, indicating that (1) complex systems are difficult to manage and control, and (2) humans are unable to effectively learn from experiences of accidents. Initial analyses results reveal that root causes of this incident were a combination of a series of complex chain reactions, which eventually led to propylene leakage and explosion. This is a systematic problem, which can hardly be investigated or analyzed by traditional research approaches. Based on the investigation reports and “systems thinking” method, this study develops causal loop diagrams for the Kaohsiung gas explosion to explore the root causes of the disaster. The research results indicate that (1) this pipeline explosion incident was the result of the chain reactions and was the output of a complex system; (2) the mental model of “production first” and “experience gap” were the root causes of the disaster; and (3) to achieve a higher safety standard, continuous education to improve the mental model of “safety first and safety over production” are essential. The findings of this study may contribute toward the improvement of the standard operating procedure for disaster management and preventing similar incidents in the future.     

Is there a need for new theories,models and approaches to occupational accident prevention?

This paper discusses occupational accident modelling challenges associated with a changing working life, and asks whether ideas from models developed for high-risk, complex socio-technical systems can be transformed and adapted for use in occupational accident prevention. Are occupational accidents mainly simple component failures or is a systemic approach to the phenomenon of some interest and value?     

Road accident fatality risks for “vulnerable” versus “protected” road users in northern Ghana

Background: Road traffic injuries (RTIs) are a serious epidemic that claims more than a million lives across the globe each year. The burden of RTIs is particularly pronounced in Africa and other low- and middle-income countries. The unfavorable disparity of the burden of road trauma in the world is largely attributable to unsafe vehicles, lack of appropriate road infrastructure, and the predominance of vulnerable road users (VRUs) in developing countries. However, little research exists in northern Ghana to highlight the scale and risk of death among road users.

Objective: The objective of this research was to establish the relative risk of death among road users in northern Ghana.

Methods: Crash data from police reports between 2007 and 2011 were analyzed for the Upper Regions of Ghana. Conditional probabilities and multivariable logistic regression techniques were used to report proportions and adjusted odds ratios (AORs), respectively.

Results: Generally, crashes in northern Ghana were extremely severe; that is, 35% of all injury related collisions were fatal. The proportion of fatal casualties ranged between 21% among victims of sideswipe collisions and 41% among pedestrians and victims of rear-end collisions. Though males were 6 times more likely to die than females overall, females were more likely to die as pedestrians (90% of all female casualty deaths) and males were more likely to die as riders/drivers (78% of all male casualty deaths). Pedestrians were 3 times more likely to die (odds ratio [OR] = 3.1; 95% confidence interval [CI], 2.4 to 4.1) compared with drivers/riders. Compared with drivers, the odds of death among cyclists was about 4 times higher (AOR = 3.6; 95% CI, 2.3 to 5.6) and about 2 times higher among motorcyclists (AOR = 1.6; 95% CI, 1.2 to 2.2). Compared with casualties aged between 30 and 59 years, children under 10 years and those aged 60 years and above were independently 2 times more likely to die in traffic collisions.

Conclusion: Provision of requisite road infrastructure is vital for the safety of VRUs in northern Ghana. Cycle paths and lanes (for cyclists) as well as sidewalks (for pedestrians) in particular will separate VRUs from motorists and improve their safety. Enforcement of traffic laws particularly regarding helmet use, speeding, and alcohol use will be beneficial. Introduction of the demerit points system in the enforcement of traffic regulations may have significant deterrent effects on road users who have the penchant for violating traffic regulations. Road safety education is also required to create responsible road users.     

Safety I–II,resilience and antifragility engineering: a debate explained through an accident occurring on a mobile elevating work platform

Occupational health and safety (OHS) represents an important field of exploration for the research community: in spite of the growth of technological innovations, the increasing complexity of systems involves critical issues in terms of degradation of the safety levels. In such a situation, new safety management approaches are now mandatory in order to face the safety implications of the current technological evolutions. Along these lines, performing risk-based analysis alone seems not to be enough anymore. The evaluation of robustness, antifragility and resilience of a socio-technical system is now indispensable in order to face unforeseen events. This article will briefly introduce the topics of Safety I and Safety II, resilience engineering and antifragility engineering, explaining correlations, overlapping aspects and synergies. Secondly, the article will discuss the applications of those paradigms to a real accident, highlighting how they can challenge, stimulate and inspire research for improving OHS conditions.     

PPH (potassium polyacrylate & hectorite) composite materials – A new fire accident emergency method for thermal protection of adjacent tanks

When a chemical tank fire happens in a storage area, it is very important to protect adjacent tanks so as to decrease fire accident losses. In this paper, a new thermal protection method was put forward based on a PPH (potassium polyacrylate & hectorite) thermal insulation composite material spraying on an adjacent tank under fire. Firstly, the PPH material was prepared successfully by a polymerization reaction of potassium acrylate, hectorite, NaHSO₃ and (NH₄)₂S₂O₈. Secondly, thermal insulation performance of the PPH material was characterized by heat transfer process at high incident heat flux using cone calorimeter. The results show that thermal insulation performance of the PPH material is affected by a content change of (NH₄)₂S₂O₈, NaHSO₃ and hectorite in formulations. The content of (NH₄)₂S₂O₈ 0.14 wt%, NaHSO₃ 1.38 wt% and hectorite 1.4 wt% was an optimum formulation ratio to obtain best thermal insulation performance. Finally, possible thermal insulation mechanisms of the PPH material were presented using SEM, TG and TG-IR techniques. One of the thermal insulation mechanisms is the incident heat flux absorbed by water evaporation from the PPH material. Another is the thermal protection of the char formed from the PPH material at high incident thermal radiation, which can prevent heat and mass transfer.     

Conceptual compression discussion on a multi-linear (FTA) and systematic (FRAM) method in an offshore operation’s accident modeling

Risk assessment can be classified into two broad categories: traditional and modern. This paper is aimed at contrasting the functional resonance analysis method (FRAM) as a modern approach with the fault tree analysis (FTA) as a traditional method, regarding assessing the risks of a complex system. Applied methodology by which the risk assessment is carried out, is presented in each approach. Also, FRAM network is executed with regard to nonlinear interaction of human and organizational levels to assess the safety of technological systems. The methodology is implemented for lifting structures deep offshore. The main finding of this paper is that the combined application of FTA and FRAM during risk assessment, could provide complementary perspectives and may contribute to a more comprehensive understanding of an incident. Finally, it is shown that coupling a FRAM network with a suitable quantitative method will result in a plausible outcome for a predefined accident scenario.     

Numerical investigation and analysis of indoor gas explosion: A case study of “6·13” major gas explosion accident in Hubei Province,China

Taking the ' 6·13 ′ major gas explosion accident in Shiyan, Hubei Province, China as an example, three problems were studied in this work: (1)The determination of the volume of natural gas involved in the explosion; (2)The propagation process of shock wave inside the building and the damage evolution process of the accident-related building; (3)The overpressure and fragment injury to the person outside the building. Through the numerical simulation in ANSYS/LS-DYNA software, the volume of natural gas involved in the explosion is determined to be 10240 × 1400 × 400 cm (length × width × height) from three perspectives: the damage to the building, the distribution of overpressure inside the building, and the TNT equivalent of the explosion energy. The simulation results are in good line with the accident, which verifies the effectiveness of the scheme and the accuracy of the numerical model. Based on the reasonable filling scheme, the propagation process of shock waves inside the building, the damage evolution process of the building, and the injury ranges of overpressure and fragments outside the building are analyzed. It can be found that the propagation of shock waves in confined space is complex and variable. The explosion shock waves are first reflected and superimposed in the watercourse, resulting in pressure rise. At about 8ms, the shock waves rushed into the first-floor space of the building, and the maximum overpressure was about 0.56 MPa. At about 50 ms, the shock waves rushed into the second-floor space, and the maximum overpressure was about 0.139 MPa. The first and second-floor slabs and infilled walls were almost completely destroyed. The interior walls of the infilled walls are mainly collapsed, and the exterior walls are ejection around the building as the center. The peak displacement and peak velocity of the interior walls of each floor are about 15% of the exterior walls. The fragments which cause fragment injury mainly come from the retaining wall above the watercourse, the maximum velocity is about 89 m/s, and the maximum displacement is 8.9 m. The safety distance of fragment injury is about 8.8 m, while the safety distance of overpressure injury is about 4.6 m. The lethal distance of fragment injury is greater than that of overpressure injury. Compared with the distance between different damage levels of overpressure injury, the difference in fragment injury is small. Therefore, the safety assessment at the engineering level only needs to consider the safety distance of fragment injury. This study can provide suggestions for evaluating the damage of natural gas cloud explosions in confined spaces and is helpful for accident investigation and safety protection.     

A Contribution to the Study of the Antidust Respirators’ Real Performance

In most industrial enterprises, hazardous factors are present in quantities exceeding permissible levels. Such a situation requires using antidust respiratory protection. It has been suggested, however, that filters for respirators are not assessed properly and that lab results might not be related to real filtering efficiency in industry. This article contains test results of some commercially available filtering half-masks, including the effect of loading with real dust, high humidity, high temperature, and a combination of loading with dust and high humidity on the half-masks’ performance. The results show that the effect of these factors is considerable and that a combination of loading with silica dust and exposing to high humidity can cause a complete loss of performance.     

Why did the pilots shut down the wrong engine? Explaining errors in context using Schema Theory and the Perceptual Cycle Model

Although human error remains a dominant issue in aviation research, methods that predict human error have been criticised for not providing adequate causal explanations, rather they have focused on classification. The concept of Schemata has prevailed in the literature and has been shown to describe the contextual causes of human error. The purpose of this paper is to review the recent error literature and demonstrate that Schema Theory (as incorporated in the Perceptual Cycle framework) offers a compelling causal account of human error. Schema Theory offers a system perspective with a focus on human activity in context to explain why apparently erroneous actions occurred, even though they may have appeared to be appropriate at the time. This is exemplified in a case study of the pilots’ actions preceding the 1989 Kegworth accident. Schema Theory is presented as a promising avenue for further exploration into the context of human error in aviation.     

Learning from incidents – A method for assessing the effectiveness of the learning cycle

This paper describes a method for assessing the effectiveness in the steps of the learning cycle: the 1st loop with reporting – analysis – decision – implementation – follow-up, and the 2nd loop on an aggregated basis. For each step, the dimensions considered the most relevant for the learning process (scope, quality, timing and information distribution) and for each dimension the most relevant aspects (e.g. completeness and detail) were defined. A method for a semi-quantitative assessment of the effectiveness of the learning cycle was developed using these dimensions and aspects and scales for rating. The method will give clear indications of areas for improvement when applied. The results of the method can also be used for correlation with other safety parameters, e.g. results from safety audits and safety climate inquiries. The method is intended to be used on a sample of the broad range of incidents normally seen in process industry companies. The method was tested on a two-year incident reporting material from six companies from various types of process industries. It was found that the method and the tools worked very well in practice. The results gave interesting insights into the effectiveness of learning from the incidents.     

How does the social context fuel the proactive fire? A multilevel review and theoretical synthesis

The role of social context (e.g., leadership, team climate, and organizational support) in shaping employee proactive behavior has received considerable attention and has been investigated across multiple forms of proactive behavior. However, the research has not been well integrated. In this review, we adopt a multilevel approach to synthesize what is known about how social context factors influence employees' proactive behavior, as well as what mechanisms underpin these effects. Our analyses show that leader‐, team‐, and organization‐related social context factors mainly influence employee proactivity through shaping “reason to,” “can do,” and “energized to” states (i.e., proactive motivational states) via individual‐, team‐, and cross‐level processes. That has been most frequently investigated is the effect of the discretionary social context, particularly leadership, on proactive behavior. We also review the interaction effects between social context factors and other factors on employee proactive behavior and found inconsistent support for the motivational‐fit perspective that stimuli with the same directions enhance each other's effect. We offer a research agenda to advance theoretical insights on this important topic.     

Risk and characteristics analysis of the flow-induced vibration of the dip tube in opposed multi-burner gasifier

The vibration of dip tube in multi-burner gasifier changes the stress at the connection, causing flange seal failures and high temperature gas erosions with heavy economic losses and industrial accidents. This work aims to reveal the dip tube vibration mechanism, with special focus on obtaining the effect of operational parameters on the fatigue damage and long-term stable operation of gasifiers. A three-dimensional numerical simulation of the water-scrubbing cooling chamber was conducted to obtain the excitation source in the flow field. Then a FSI (fluid-structure interaction) transient dynamics simulation was carried out to investigate the vibration characteristics. Two major flow forms were found: a vertical annular flow near the dip tube outlet in the water-scrubbing cooling chamber; and a gas-liquid coupled flow caused by the syngas entrained the liquid. These two unstable multiphase flow forms exerted an energy excitation on the dip tube, resulting in a self-excited flutter. The dip tube vibration was similar to the first mode of a cantilever beam. The peak frequency was less affected by the initial liquid level and the syngas stream inlet velocity, which was close to its own first natural frequency. Note that, the alternating load generated by vibration may cause fatigue damage, which needs to be specifically considered in the design and manufacturing process of opposed multi-burner gasifier.     

Analysis of the experimental results of the initiation of detonation in short tubes with kerosene–oxidizer mixtures

The paper describes the experimental investigation of detonation initiation in a mixture of kerosene–oxidant in a short test tube. Various mixtures of oxygen and nitrogen were used as an oxidant, from pure oxygen to the composition of air. The goal of the study was to determine the minimum diameter of the tube and the minimum level of energy needed for the direct initiation of detonation. As a result of the measurements the pressure courses were obtained for two kinds of cases: with and without (only shock waves) of fuel injection. The results of both kinds of measurements were compared, providing information about the initiation of detonation in a fuel–oxidizer mixture. Brief analyses of the results for different initiators and different oxidizers were performed and compared with the shock wave and Chapman–Jouget velocity.     

Exploring the linkage between the home domain and absence from work: Health,motivation, or both?

The aim of this study was twofold. First, we examined depleting and enriching effects of employees' home domain (home demands and quality time spent at home) on unscheduled absence from work. Second, we tested the assumption of the medical and withdrawal models that absence duration and frequency are uniquely predicted by respectively health condition and job motivation. We used longitudinal, different‐source data from 1014 employees. The results showed that home quality time was negatively related to absence frequency and duration in the following year through a physical pathway (less physical stress symptoms and health complaints) and through a psychological pathway (less psychological stress symptoms, increased job motivation). Employees with heavy home demands reported more physical and psychological stress symptoms, more health complaints, and lower job motivation. Accordingly, they had longer and more frequent sick leaves in the consecutive year. We conclude that the home domain adds to our understanding of absence from work. In addition, the model including cross pathways between health complaints and job motivation on the one hand, and absence frequency and duration on the other, best fitted the data. Thus, a clear distinction between volitional absence (frequency) and absence due to illness (duration) seems hard to justify. Copyright © 2012 John Wiley & Sons, Ltd.