Density, velocity and flow relationships for closely packed crowds

Work undertaken to quantify the relationships between crowd velocities, flow rates and densities for uni-directional motion is reviewed. Most of the available data has been generated for underground stations in the UK; similar work for commuter stations in Japan is introduced and developed. Maximum observed flow rates from this work are compared with those suggested in the ‘Green Guide’ for the evacuation of sports grounds. The ‘Green Guide’ figures are higher than the maximum values obtained from the work reviewed.     

Bifocal/varifocal spectacles, lighting and missed-step accidents

Good lighting and the correct use of spectacles generally improve vision and presumably reduce the risk of accidents. However, bifocal and varifocal spectacles can increase the risk of misjudging distances when negotiating underfoot hazards. In some circumstances, the portion of the lens used for close work may inadvertently be used where accurate judgement of distance is necessary. This paper reports results from two studies of patient interviews using the Merseyside Accident Information Model; the first a study of accidents which occurred during paid employment (1504 cases) and the second of 1326 accidents mainly in domestic and leisure activities. Underfoot accidents were identified by the first unforeseen event perceived by the patient. The relationship between underfoot events and the type of spectacles worn by the patient at the time of accident was analysed. In both studies there was a significant association between accidents where the first event was ‘missed edge of’ (step) and wearing bifocal/varifocal spectacles. Corporal movements reported in both studies indicated that ‘stepping down’ when wearing bifocal/varifocal spectacles, increased the risk of ‘missed edge’ accidents. In the work environment corporal movements associated with manual handling of loads also increased the risk of ‘missed edge’ accidents when wearing bifocal/varifocal spectacles.     

Working in small enterprises – Is there a special risk?

Ownership structure is an important factor. For independent enterprises, the ergonomic, physical and chemical work environment is more hazardous in small enterprises than in large ones. For enterprises that are part of a larger organization, the work environment tends to be more hazardous in large enterprises when controlling for the same factors. For the psychosocial factors, the trend is different – better in small than in large enterprises independent of ownership. In all enterprises, both public and private, the quality of health and safety management systems and workplace assessment is remarkably higher in large than in small enterprises.These differences in work environment for small and large enterprises have been studied in the ‘Danish Work Environment Cohort Study’ and ‘Surveillance of health and safety activities in enterprises’. These datasets are linked together to a reliable database with data on work environment and enterprises including size, ownership structure, and health and safety management.     

Vent Sizing Criteria for Partial Volume Deflagration

The accidental spill of volatile solvents or the release of flammable gases within equipment and buildings is likely to form fuel concentration gradients unless efficient mixing is provided. As a consequence, even small amounts of fuel can form flammable clouds, and partial volume deflagrations may occur. Nevertheless, few indications are given in international guidelines for vent sizing and only over-conservative well-mixed stoichiometric assumptions are used. In this paper, we propose a predictive methodology for the evaluation of the dynamics of partial volume deflagration, aiming at defining useful correlations for the design of vent devices, starting from the fundamental equation for the rate of pressure rise and flame propagation in closed vessel. We define a ‘stratified gas deflagration index’ K_G(m), where m is the filling ratio, and use it with the most common design equations for vent sizing. The approach has been validated by means of a CFD code for the simulation of stratified laminar methane–air explosion by varying both filling ratio and volume.     

Rain-out investigation: Initial droplet size measurement

Droplet size distribution inside water flashing jets and corresponding rain-out fraction were measured. Mass distribution showed that a few droplets are ‘large’ (d>150 μm) and count for more than 85% of the liquid mass in the jet because of their large individual mass. This could be due to incomplete thermal fragmentation. It could explain the rain-out falling near the orifice or pipe exit.     

Application of a predictive safety model in a combustion testing environment

A predictive safety model for accident prevention and system failure, called Continuous Hazard Tracking and Failure Prediction Methodology, is applied at the Marshall Space Flight Center's promoted combustion test chamber. It combines the underlying principles of work sampling, control charts, and multivariate analysis. The sampling is performed to observe the occurrence of conditions which may be becoming hazardous in a given system. These building blocks of hazards, which we have called dendritics, could result in an accident, system malfunction, or unacceptable risk conditions. The data collected is plotted to generate the appropriate control chart, which depends on the characteristics of the given system and the protection desired. Based on the pattern of the control chart, a system ‘under control’ is not disturbed whereas a system ‘out of control’ is investigated for potential conditions becoming hazardous. Then appropriate steps are taken to eliminate or control these conditions in order to maintain a desired safety status of the system. The continuously running characteristic of this model allows for the verification that the corrective measures taken to ameliorate the ‘out of control’ conditions were satisfactory or whether more proactive action is required. The results provided by the predictive model were validated with historical safety data.     

Some experiences in hazard identification and risk shortlisting

‘Rapid ranking’ has been used for many years as a method of determining the priority which should be given to formal investigation of the wide range of hazards and risks present on major process industry sites. Such methods tend to evolve to meet the needs of specific applications. Some historical and recent applications are outlined, and the nature of the developments which they led to are discussed. Particular topics discussed include: development of the method such that it is usable by operating managers rather than specialists; use to raise risk consciousness; adaptation for use as an aid to hazard identification; use to define both which risks should be studied and which risks, even if low, should be incorporated in routine monitoring and periodic auditing programmes; use as a basis for comparison of the relative risks presented by a variety of different industrial installations; use for a range of different types of risk; and extension beyond ranking to include ‘shortlisting’ i.e. deciding which risks to include in a study programme and which to leave out. Philosophical difficulties with the approach are discussed, including the danger of omitting from detailed study a risk which is erroneously shown as low, and the uncertainty of the absolute level of the ranked risks. Approaches to minimizing these problems are discussed.     

Exploring the risk information gap. Research into information supply and information demand of different parties concerned

The Dutch National Institute for Public Health and the Environment (RIVM), a governmental research institute, provides information on environmental and health risks. The primary contractors’ information demands are served well. But the risk information available from the RIVM does not always correspond to the desires and requirements of other parties concerned. It became apparent that – to a certain extent – an information gap exists, arising from a difference between the institute’s information supply and the information demand of the different parties concerned.This explorative study focuses on the information demand and supply with regard to three different risks: flooding by rivers, air pollution and food related risks.For each risk, the information supply was determined by listing the available risk information in RIVM reports. In a second step, the information demand of the five different parties, as well as different channels of communication, were examined. The parties’ perceptions and requirements concerning risk information were identified in interviews and focus group discussions.The public, which in general appeared to be quite unfamiliar with the institute and its information sources, preferred risk information tailored to its personal circumstances. Policy makers mainly appreciated personal contacts in order to keep up to date on risk topics, whereas NGOs and fellow researchers judged the institute’s website and reports to be more relevant. Press releases appeared to add little to satisfying the information demand of the media.     

Bhopal gas tragedy: scientific challenges and lessons for future

Some of the challenges of BGT were answered by two multi-disciplinary projects of the ICMR on Pathology and Toxicology and Pathophysiology. Unlike other chemical disasters, the aerosol inhaled by the Bhopal victims contained a mixture of MIC and its trimers and dimers, as well as aqueous and thermal decomposition products, including HCN. A coordinated GC–MS study of the blood and autopsy tissues and chemicals in the Tank residue confirmed their role.

Autopsy studies revealed the pathological changes in the acute, sub-acute and chronic phases progressive changes of pulmonary edema and bronchiolitis, followed by chronic pulmonary fibrosis. Cerebral edema resulted in ‘acute histotoxic anoxia’. Intensive experimental studies with the help of newer tools of molecular biology might throw more light on the underlying mechanisms and newer therapeutic approaches.

The initial finding of cherry-red discoloration of lungs led to a suspicion of cyanide toxicity. Eventually, elevated blood and tissue cyanide levels confirmed the prompt therapeutic response to NaTS and accompanying increase of urinary NaSCN excretion. However, periodic clinical recurrences and relapses pointing towards ‘chronic cyanide toxicity’ remained enigmatic.

Specific changes the 2–3 DPG levels and Blood Gases were explained on the basis of N-carbamoylation of end-terminal valine residues of Hb. Soon, several other end-terminal -amino groups of tissue proteins were also found to be N-carbamoylated. Had the attempts at demonstrate S-carbamoylation of glutathione and other SH radicals of tissue enzymes like rhodanese succeeded, perhaps the underlying mechanism of chronic cyanide toxicity due to MIC might have been resolved.

Based on the practical lessons learnt in Bhopal, an attempt will be made to present the salient pathological and toxicological findings, followed by a brief outline of the principles of planned laboratory management for alleviation of human suffering from future chemical disasters.     

On the implementation of an International Curriculum on Hydrogen Safety Engineering into higher education

This paper describes the implementation of an International Curriculum on Hydrogen Safety Engineering into higher education. The curriculum is being developed as part of the educational and training activities of the European Network of Excellence Safety of Hydrogen as an Energy Carrier (HySafe) and has been implemented into a 1-year Postgraduate Certificate Course in Hydrogen Safety Engineering by the University of Ulster. The course is taught in the distance learning mode and comprises of two 30 CATS-point modules, namely, ‘Principles of Hydrogen Safety’ and ‘Applied Hydrogen Safety’. The first delivery of this course began in January 2007 and the second delivery will commence in September 2007.     

Don't wait for accidents — possibilities to assess risk in traffic by applying the ‘Wiener Fahrprobe’

In Vienna during more than 10 years of research work a special traffic behaviour observation method has been developed, evaluated and applied by Risser et al. in the frame of many different traffic safety projects. Car drivers are accompanied by two observers who register not only errors in behaviour of drivers but also their communication and interaction with other road users. Malfunction of communication and interaction are judged as main sources for problems for danger in traffic. For example, if they lead to a bad traffic climate fealings of discomfort, anger and frustration will prevent cooperative actions of road users. Being able to recognize such negative or dangerous interaction patterns in time it seems to be easier to protect road users — most often the ‘unprotected’ ones — from getting involved in accidents. This contribution gives an impression about theory and practice of the observation method and shows results of different studies, where the method called ‘Wiener Fahrprobe’ has been applied. Furthermore it will show how the method and its results can be used in the frame of the European traffic (safety) research projects ‘PROMETHEUS’ and ‘DRIVE’. Till now no accident data exist in respect to new RTI systems. Therefore it seems to be important to have a sophisticated social-psychological method for testing the behaviour and interaction of road users in connection with these systems. This is a necessary prediction for deciding whether the systems are socially compatible or not.     

CFD modelling of hydrogen release, dispersion and combustion for automotive scenarios

The paper describes the analysis of the potential effects of releases from compressed gaseous hydrogen systems on commercial vehicles in urban and tunnel environments using computational fluid dynamics (CFD). Comparative releases from compressed natural gas systems are also included in the analysis.

This study is restricted to typical non-articulated single deck city buses. Hydrogen releases are considered from storage systems with nominal working pressures of 20, 35 and 70 MPa, and a comparative natural gas release (20 MPa). The cases investigated are based on the assumptions that either fire causes a release via a thermally activated pressure relief device(s) (PRD) and that the released gas vents without immediately igniting, or that a PRD fails. Various release strategies were taken into account. For each configuration some worst-case scenarios are considered.

By far the most critical case investigated in the urban environment, is a rapid release of the entire hydrogen or natural gas storage system such as the simultaneous opening of all PRDs. If ignition occurs, the effects could be expected to be similar to the 1983 Stockholm hydrogen accident [Venetsanos, A. G., Huld, T., Adams, P., & Bartzis, J. G. (2003). Source, dispersion and combustion modelling of an accidental release of hydrogen in an urban environment. Journal of Hazardous Materials, A105, 1–25]. In the cases where the hydrogen release is restricted, for example, by venting through a single PRD, the effects are relatively minor and localised close to the area of the flammable cloud. With increasing hydrogen storage pressure, the maximum energy available in a flammable cloud after a release increases, as do the predicted overpressures resulting from combustion. Even in the relatively confined environment considered, the effects on the combustion regime are closer to what would be expected in a more open environment, i.e. a slow deflagration should be expected.

Among the cases studied the most severe one was a rapid release of the entire hydrogen (40 kg) or natural gas (168 kg) storage system within the confines of a tunnel. In this case there was minimal difference between a release from a 20 MPa natural gas system or a 20 MPa hydrogen system, however, a similar release from a 35 MPa hydrogen system was significantly more severe and particularly in terms of predicted overpressures. The present study has also highlighted that the ignition point significantly affects the combustion regime in confined environments. The results have indicated that critical cases in tunnels may tend towards a fast deflagration, or where there are turbulence generating features, e.g. multiple obstacles, there is the possibility that the combustion regime could progress to a detonation.

When comparing the urban and tunnel environments, a similar release of hydrogen is significantly more severe in a tunnel, and the energy available in the flammable cloud is greater and remains for a longer period in tunnels. When comparing hydrogen and natural gas releases, for the cases and environments investigated and within the limits of the assumptions, it appears that hydrogen requires different mitigation measures in order that the potential effects are similar to those of natural gas in case of an accident. With respect to a PRD opening strategy, hydrogen storage systems should be designed to avoid simultaneous opening of all PRD, and that for the consequences of the released energy to be mitigated, either the number of PRDs opening should be limited or their vents to atmosphere should be restricted (the latter point would require validation by a comprehensive risk assessment).     

A criterion for developing credible accident scenarios for risk assessment

Maximum credible accident analysis is one of the most widely used concepts in risk assessment of chemical process industries. Central to this concept is the aspect of ‘credibility’ of envisaged accident scenarios. However, thus far the term credibility is mostly treated qualitatively, based on the subjective judgement of the concerned analysts. This causes wide variation in the results of the studies conducted on the same industrial unit by different analysts.

This paper presents an attempt to develop a criterion using which credible accident scenarios may be identified from among a large number of possibilities. The credible scenarios thus identified may then be processed for detailed consequence analysis. This would help in reducing the cost of the analysis and prevent undue emphasis on less credible scenarios at the expense of more credible ones.     

A quantitative risk assessment tool for the external safety of industrial plants with a dust explosion hazard

A quantitative risk assessment (QRA) tool has been developed by TNO for the external safety of industrial plants with a dust explosion hazard. As a first step an industrial plant is divided into groups of modules, defined by their size, shape, and constructional properties. Then the relevant explosion scenarios are determined, together with their frequency of occurrence. These include scenarios in which one module participates, as well as domino scenarios. The frequency is partly based on casuistry.

A typical burning velocity is determined depending on the ignition type, the dust properties and the local conditions for flame acceleration. The resulting pressure development is predicted with the ‘thin flame model’. Module failure occurs when the explosion load exceeds thresholds, which are derived from single degree of freedom (SDOF) calculations for various types of modules. A model has been developed to predict the process of pressure venting after module failure and the related motion of launched module parts.

The blast effects of the primary explosion are based on results from calculations with BLAST3D. The blast and flame effects of the secondary external explosion due to venting are calculated using existing models. The throw of fragments and debris is quantified with a recently developed model. This model is based on trajectory calculations and gives the impact densities, velocities, and angles as output. Furthermore the outflow of bulk material is taken into account. The consequences for external objects and human beings are calculated using existing models. Finally the risk contours and the Societal risk (FN curve) are calculated, which can be compared to regulations.     

Risk assessment of antagonistic hazards

This paper considers the risk to major hazard plant from terrorists deliberately causing catastrophic industrial accidents. The United States of America Department of Justice [Assessment of the increased risk of terrorist or other criminal activity associated with posting off-site consequence analysis information on the internet, 2000] reports that “breaching a containment vessel of an industrial facility with an explosive or otherwise causing a chemical release may appear relatively simple to…a terrorist”. They concluded that the risk of such action is “real and credible”.

Analysis of terrorism is often hampered by its being described as ‘irrational’; one corollary would be that it is unpredictable. However, terrorism may usefully be treated as a rational behaviour and in doing so it becomes possible to assess the risks it causes.

We analyse the vulnerability of major hazard plant to terrorist attack and identify nine factors (access, security, visibility, opacity, secondary hazard, robustness, law enforcement response, victim profile, and political value) that might be used as a starting point for more formal risk assessment and management.     

加油站新旧输油管线碰头焊接方法探讨

《汽车加油加气站设计与施工规范》(GB50156-2002)中提到加油站输油管道宜采用无缝钢管、连接方式采用焊接是输油管道敷设的基本要求,其优点是焊缝少、比较严密可靠、施工速度快、省材省工、便于防腐、不容易出现渗漏隐患。但加油站在改造输油管线时,新旧管线碰头焊接过程中产生的火花易点燃管线中的油气引发火灾及爆炸。因此,如何在新旧输油管线碰头焊接时安全施工就成为了需要我们探讨的问题。本文结合丹东太平湾加油站输油管线改造的实际情况,简要的阐述了加油站含油气管线碰头焊接的几种方法。     

Home based workers at risk: Outworkers and occupational health and safety

Outwork is work done for payment at, about or from home. Outworkers generally work under conditions which are less favourable that those of their counterparts doing similar work ‘on site’. There are significant occupational health and safety issues associated with outwork. Terms and conditions of work (e.g. rate of pay, hours of work, degree of worker control over the work process, legislative coverage etc.) will significantly influence health and safety outcomes for outworkers. The paper addresses these more general issues as well as detailing specific workplace hazards and injuries, and other health impacts arising from the work.     

Toward an integrative approach of the industrial risk management process in France

Management in the field of environmental protection and risk prevention has evolved to the increasing participation of all stakeholders in the decision-making process. It certainly results from the development of the Information society and the global increase of knowledge of the population, combined with the concerns of the populations related to a sustainable development of our civilisation. Our ‘risk society’, following the big industrial disasters (Flixborough,Tchernobyl, Bhopal, Challenger, and more recently Toulouse), has also developed a cautious attitude towards the role of the expertise when it comes to assessing risks, along with a question of the ability of science to give definite answers.

This has lead in particular to the adoption of the Aarhus convention in 1998 and the evolution of several regulations in the developed countries. For example, in France the new law no. 2003–699 of 30 July 2003 about the ‘prevention of the technological and natural risks and to the compensation for the damages’ has introduced an important innovation into the process of technological risks prevention.

This law has enabled the involvement of the stakeholders in the decision-making process related to risk prevention and has urged the development of specific tools to deal with the complexity of risk management issues, in particular for those related to land-use planning.

As technical support to decision-makers in risk management from both public and private sectors, INERIS has played an important role for the evolution of the French risk management system.

This paper describes an analysis on the difficulty to control major accident hazards in an evolving context where the industrial systems becomes more and more complex and where the expectations of the civil society has increased. Then, the authors describe how an integrated vision for industrial risk management has emerged in France and is being implemented in a new law adopted after the Toulouse disaster.