Showing papers in "Journal of Loss Prevention in The Process Industries in 1999"

Major accidents in process industries and an analysis of causes and consequences

Abstract: This paper briefly recapitulates some of the major accidents in chemical process industries which occurred during 1926–1997. These case studies have been analysed with a view to understand the damage potential of various types of accidents, and the common causes or errors which have led to disasters. An analysis of different types of accidental events such as fire, explosion and toxic release has also been done to assess the damage potential of such events. It is revealed that vapour cloud explosion (VCE) poses the greatest risk of damage. The study highlights the need for risk assessment in chemical process industries.

The importance of near miss reporting to further improve safety performance

Abstract: Dealing with accidents implies that such events have in common the potential to affect people and the environment in a significant way. Therefore, all parties involved in industrial risk management processes, i.e. industry, regulatory authorities, public as well as scientific and technical institutions, are well aware of the importance of considering and analysing such type of events for the purposes of accident prevention. Also, the methods of Quantitative Risk Assessment (QRA) have large experience in numerically expressing the various degrees of risk related to accidents. On the other hand, the topic of including `near misses' (i.e. any event which could have escalated to an accident) in safety management systems with the aim to prevent major accidents and the occurrence of similar events in the future is relatively new. Although its importance has more and more been recognised in the last few years, it is not yet a commonly accepted fact that near miss reporting and investigation of near misses should be an integral part of a safety management system in industrial facilities. In the European Council's new `Seveso II Directive' 96/82/EC, there is—in addition to the mandatory requirements of major accident reporting—an explicit recommendation to report near misses to the Commission's Major Accident Reporting System (MARS) on a voluntary basis. In this paper, examples of current experience in the chemical industry with the collection and analysis of data on near misses are presented and discussed with regard to industry-wide conclusions. In addition to this more qualitative discussion, quantitative arguments are put forward regarding the impact of near misses on risk estimates derived from QRA.

On the use of probabilistic and deterministic methods in risk analysis

Abstract: Risks to human beings arise from an inherent characteristic to make plans and try to make them happen, while external forces resist and tend to move our endeavours away from the plan. Any such “endeavour” is a complex ensemble of a bewildering variety of interacting elements which together form something “whole”, usually called a “system” (e.g. a chemical process plant, a nuclear power plant, the stock market, air traffic control). A system has a certain state in the present and subsequent states in the future. There are deterministic and probabilistic systems and corresponding approaches to analyse them, that is to make their current states apparent and predict their future behaviour. In this paper, it is shown in which ways both analyses appear in risk analysis and it is hypothesised that both approaches are modelling the same process, though probabilistic analysis may reveal more information since it explicitly incorporates uncertainty in the form of numbers (and “there is safety in numbers”). The overall objective of this paper is to make clear what the differences between the two approaches really are. Their respective main strengths and weaknesses are discussed. A more refined objective is to discuss the specific role of probabilities in risk analysis. Examples of both approaches are given from applications in the nuclear power and chemical process industries, and some of the main problems encountered thereby are identified. Further, the challenge to system analysis posed by “chaos theory” is discussed. Due to its non-linear dynamic character, the future behaviour of a “chaotic system” is difficult to predict over a long period of time because it depends on arbitrarily small and thus not observable variations in the current state. Such behaviour might have serious consequences for human operators involved in the control of such systems. The paper concludes that, although both approaches to risk analysis can provide adequate safety levels to systems if applied in a correct and non-biased way, probabilistic methods seem to be more cost-effective and the results easier to communicate to decision- and policy-makers.

Major Hazard Pipelines: A Comparative Study of Onshore Transmission Accidents.

Abstract: Failures of pipelines conveying dangerous substances can pose major risks. Identification of pipeline hazards associated with the different pipeline system functions is essential for risk analysis and historical data are of great importance. Incident data are analysed, following a review of official sources, by failure mechanism, size and function of the systems in two types of transmission networks around the world, i.e. natural gas and hazardous liquids. The development of the networks and the reporting criteria used by the official sources for the collection of incidents in the last twenty five years have shown remarkable differences. The performance of both gas and liquid transmission lines in Europe, the US and the former Soviet Union in terms of failures has shown a progressive improvement but the extent of consequences following gas releases and oil spillages have not shown any change in the last fifteen years. External interference is not always the predominant cause of failures in all systems depending also on pipe size. Failures with casualties in gas transmission have not shown any decrease over the last decade and there is a clear indication that many are connected with the parts and functions other than the main body of the pipeline. A comparison between European and US gas frequency data, derived under common constraints, shows that valuable information can be lost when criteria for incidents collection are only limited to the body of the pipeline.

Modeling of vented hydrogen-air deflagrations and correlations for vent sizing

Abstract: Modeling of hydrogen-air deflagrations on the base of advanced lumped parameter theory and comparison with experiments in closed and vented large scale vessels have been carried out. Burning velocity and overall thermokinetic index for hydrogen-air mixtures with hydrogen concentrations of 20.0–41.7% by volume and at elevated temperature 373.15 K were determined. The slight decrease of overall thermokinetic index with equivalence ratio in enriched by hydrogen mixtures has been revealed, that is inverse to observed for hydrocarbon-air systems. It has been determined that flame stretch during vented deflagration constitutes about 1.5–2.2 for investigated conditions. The Le Chatelier-Brown principle analog, revealed previously for vented hydrocarbon-air deflagrations, has been verified for hydrogen-air systems. It has been shown that suggested correlation for the deflagration-outflow-interaction number, χ/μ, in dependence on vessel scale and Bradley number is right for both hydrocarbon- and hydrogen-air mixtures. It has been concluded that gained data on vented hydrogen-air deflagrations obey the same general physical regularities that were revealed previously for hydrocarbon-air systems.

New detailed numerical procedures for calculating risk measures in hazardous materials transportation

Abstract: Historical evidence has shown that accidents due to hazardous material releases during transportation can lead to consequences as heavy as those created by releases occurring at fixed plants and therefore quantified risk analysis has to be performed for transportation networks too. The calculation of risk measures, like individual and societal risk, due to transportation networks has considerable complexity and needs a great computational effort. For this application two new detailed procedures, named T rans I n and T rans S oc , for the evaluation of individual and societal risk, have been introduced, which can take into account, at the same time, different transportation modes, hazardous materials, meteorological conditions and seasonal situations, a non uniform wind probability density distribution and an accurate description of the indoor and outdoor population both on-route and off-route. In this paper, firstly, the arrangement of the input data is explained, and then the fundamentals of the methodology are described, often focusing attention on mathematical ways to perform operations saving accuracy without increasing calculation time.

Assessment of risks posed by chemical industries—application of a new computer automated tool maxcred-III

Abstract: The paper describes the application of a new computer automated tool, developed by us, in the risk analysis of a typical chemical industry engaged in the manufacture of linear alkyl benzene. Using the tool—a comprehensive software package maxcred-III (MAXimum CREDible accident analysis)—nine different scenarios, one for each storage unit, have been studied. It is observed that the accident scenario for chlorine (instantaneous release followed by dispersion) leads to the largest area-under-lethal-impact, while the accident scenario for propylene (CVCE followed by fireball) forecasts the most intense damage per unit area. The accidents involving propylene, benzene, and fuel oil have a high possibility of causing domino/secondary accidents as their destructive impacts (shock waves, heat load) would envelope other storage and process units. Besides demonstrating the utilizability of maxcred-III, this study also focuses attention on the need to bestow greater effort towards risk assessment/crisis management. The authors hope that the study will highlight the severity of the risk posed by the industry and thus generate safety consciousness among plant managers. The study may also help in developing accident-prevention strategies and the installation of damage control devices.

Safety management systems under Seveso II : Implementation and assessment

Abstract: The `Seveso II Directive' (96/82/EC) requires certain establishments holding hazardous substances to implement a Safety Management System (SMS). The first part of the paper discusses the origin of this requirement, the guidance drawn up to help companies fulfil it, and the results of preliminary testing of this guidance. One important element in implementing and inspecting SMS is the identification of SMS weaknesses, the safety culture that effects SMS and finally the evaluation of safety performance. The second part of this paper examines some principles underlying industrial practice in evaluating SMS. Audit-related activities, involving proactive performance indicators for monitoring compliance with standards, are used nowadays to identify weaknesses of the SMS. Preventive actions to control risks and policy updating within the company through strategic plans are found to be sensitive to the number and type of SMS elements taken into account as indicators. The value of quantifying performance using simple rating systems in audits may be limited to the single installation. The guidelines and evaluation methods could thus produce useful results only when safety aspects and system elements are identified and evaluated separately for each installation; the value of quantification is limited to the individual elements after considering their functional relation with the rest of the elements in the SMS environment and the local safety culture into which they are developed.

Numerical simulation of gas explosions in linked vessels

Abstract: The ability of the CFD code AutoReaGas to simulate a gas explosion in two linked vessels was investigated. These explosions present an anomalous destructive power because both peak pressures and rates of pressure rise are much higher than those generated in single vessel explosions. A fair agreement was observed between the computed results and experimental data taken from literature. Moreover, the computed values of the turbulence intensity at varying diameters of the connecting pipe demonstrate that turbulence induced in both vessels represent a major factor affecting the explosion violence.

Analysis and control of major accidents from the intermediate temporary storage of dangerous substances in marshalling yards and port areas

Abstract: This paper deals with the major accident hazards associated with the intermediate temporary storage of dangerous substances in transportation-related activities. In particular, the hazards related to the presence of dangerous substances in port areas and marshalling yards are identified and analysed. Furthermore, a number of past accidents in transport interfaces have been collated from various sources and have been statistically analysed. Finally, the framework for major accident control in these activities is reviewed and discussed.

Optimal Feed Profile for a Second-order Reaction in a Semi-batch Reactor under Safety Constraints - Experimental Study

Abstract: Maximising the yield of the second order reaction (2-butanol+propionic anhydride) by manipulating the inlet flow rate is considered for an isothermal semi-batch process. First a procedure for the determination of the kinetic parameters using coupled spectroscopic and calorimetric methods is presented. Then an optimisation of the reaction system is performed numerically and verified experimentally. Constraints on the amount of heat produced and on the temperature attainable in the case of cooling failure are imposed for safety consideration.

Failure of a horizontal pressure vessel containing a high temperature liquid: the velocity of end-cap and rocket missiles

Abstract: Many process plant installations include cylindrical vessels which contain high temperature liquids with the remaining space above occupied by vapour or a vapour/gas mixture. If such a pressure vessel were to be ruptured, missiles (i.e. fragments) may be generated and equipment in the vicinity put at risk. There is a particular threat from large missiles. Theoretical models have been developed to describe the peak velocity achieved by end-caps and `rocket' missiles generated by the circumferential failure of a vessel. The end-cap missile model assumes that the action of the escaping vapour/liquid on the end-cap is analogous to a missile driven by a gas jet from a constant pressure source. The `rocket' missile velocities are derived via a simple approximation to the impulse applied to the internal face of the closed end of the `rocket'. Experiments have confirmed the validity of these approaches and upper limit values to end-cap and `rocket' velocities have been defined.

Prediction of thermal hazards of chemical reactions

Abstract: A large number of products of the chemical industry are produced using potentially hazardous reactions. The experimental investigation of the hazards of all reactions involved in production processes would be very expensive. The primary reactions—desired reactions which are part of the process—and the secondary reactions—undesired successive or side reactions—should both be considered. In this paper the methods of prediction of thermodynamic and kinetic properties of reactions are discussed. Thermodynamic data are of eminent practical importance because low heats of reaction may indicate that no further experimental investigations are necessary. For primary reactions, e.g. polymerization, diazotization and hydrogenation reactions, reaction enthalpies have been obtained by experimental methods. Typical data can be found in the public literature for the different reaction classes. When compared with theoretical thermodynamic data estimated by the chetah computer program, the agreement is satisfactory. chetah implements Benson's second-order group contribution technique ( Benson, 1976 ). For secondary reactions, especially exothermic decomposition reactions, typical heats of reaction—mostly measured by DSC—have been associated with functional groups. Decompositions and other undesired exothermic reactions that proceed from the same functional group, e.g. a nitro group, have about the same heat of reaction. For the estimation using the chetah program, decomposition reactions have to be assumed which are typical for the functional group. The reaction yielding the maximum exothermic reaction energy was selected. The comparison of experimental heats of reaction with estimated data shows satisfactory agreement. In principle it is also possible to predict kinetic data of secondary reactions, but sufficient experimental data are missing.

Steady-state critical two-phase flashing flow with possible multiple choking phenomenon: Part 1: Physical modelling and numerical procedure

Abstract: In this paper, the modelling of pure fluid steady-state adiabatic flashing flow through a pipe involving an abrupt enlargement is presented. The thermal non-equilibrium two-phase flow model DEM has been adjusted for subcooled inlet conditions close to saturation and/or for inlet two-phase mixture state. The multichoking flow phenomenon occurs when two basic criteria are simultaneously fulfilled. A general procedure taking into account this possible occurrence is developed on the basis of two iterative algorithms. The first algorithm is applied to the mass flow rate upstream from the enlargement and the second algorithm is based on the length of the pipe downstream from the enlargement. The proposed methodology involves the improved physical one-dimensional two-phase flow model DEM and the global non-equilibrium model through the abrupt enlargement. (C) 1999 Elsevier Science Ltd. All rights reserved.

Trends in accidents, disasters and risk sources in Europe

Abstract: Most of the adverse impacts on man and/or the environment result from routine human activities such as the process industry, electricity generation and use, transport and agriculture (hazards, i.e. sources of risk). Apart from such essentially technological hazards, possibly resulting in “accidents”, human health and the environment can also be affected by natural hazards, possibly resulting in “disasters”, such as earthquakes or floods. This paper examines current trends in the risk sources and occurrences of four classes of such types of undesired events, entailing largely involuntary risk (e.g. neither car-driving nor smoking): • major accidents at fixed installations in the process industry, • incidents/accidents at nuclear installations, • marine transport and offshore installation accidents, • disasters caused by natural hazards and their potential exacerbation by human activities. It aims to provide an integrated overview of such events in Europe ( ≡ 15 EU Member States, 4 EFTA, 13 PHARE, 7 TACIS and 5 other South and South Eastern European countries ) during the last decade, estimating and interpreting trends in the number of risk sources and accidental events. For each type of event, specific “accident” definitions are given, illustrating the differences in the perception of the respective risk.

Trends in major industrial accidents in Germany

Abstract: Lessons learnt from accidents are essential sources for updating state-of-the-art requirements in process safety. To improve this input in the Federal Republic of Germany in a systematic way, a central body for collecting and evaluating major accident and near miss events (ZEMA) was established in 1993. ZEMA is part of the Federal Environmental Agency (Umweltbundesamt, UBA). All events which are to be notified due to the German regulation on major accidents (Hazardous Incident Ordinance) are centrally collected, evaluated and documented by ZEMA. The bureau is also responsible for the dissemination of the lessons learnt to all stakeholders. This work is done in co-operation with the German Hazardous Incident Commission (Storfallkommission) and other national and international bodies. At the time being over 200 events from 1980–1997 are registered. For each event a separate data-sheet is published in annual reports, first started in 1993. In this paper, a summary evaluation on the events from 1993 to 1996 is presented and some basic lessons learnt are shown. The results from root cause analysis underline the importance of maintenance, detailed knowledge of chemical properties, human factor issues and the role of safety organisation, especially connected with sub-contractors. Keeping in mind that collecting information from major accidents is only a small amount compared with that from all the events which might be interesting to learn from, the recent plans for collecting minor accidents in Germany are reported.

Technical note on the contribution of sociotechnical factors to accidents notified to MARS

Abstract: Not least due to the new `Seveso II Directive', Safety Management Systems (SMS) have become a hot topic in the `safety business'. To reveal in a structured way how organisations manage safety at their plants, classification schemes can be applied to identify plant-specific precautions on different hierarchical levels, e.g. from `top level' equipment reliability to `bottom level' safety climate. In this paper, such a model is used to classify the accidents reported to the European Commission's Major Accident Reporting System (MARS) according to the levels on which failures resulting in actual accidents did occur, and to cross-compare the levels of causation with the overall `severity' of the accidents. It is analytically shown that ∼66% of the accidents are caused by latent SMS failures, and that especially those accidents which are caused by failures in the `deepest layers of latency' have significantly higher `severities' than accidents caused by more `immediate' failures. In other words, it is quite likely that the deeper the underlying causes of an accident, the more `severe' its consequences. Implementing SMS is thus worth the effort.

EU initiative on the control of major accident hazards arising from pipelines

Abstract: The European Council and the Parliament recognised that pipeline accidents had occurred in Europe and worldwide, which clearly indicated the `major accident hazard' potential of pipelines. The present paper presents an overview of the Community Policy on the control of major accident hazards arising from pipelines, summarises the Commission review/assessment of existing legislation on pipelines within the Member States and outlines the principles on which a possible EU initiative should be based. The review has shown that many Member States do not have comprehensive `major accident hazard' legislation in place for pipelines and therefore an EU initiative would complete existing industrial risk management legislation, based on the `precautionary principle'.

Modelling and control of the dispersion of hazardous heavy gases

Abstract: Dispersion of several common `heavy' gases (ethylene, propylene, ammonia, and chlorine) has been modelled on the basis of modifications in plume path theory. The model takes into account, among other things, the variations in temperature, density, and specific heat during the movement of the heavy gas plume. The effects of wind speed, density of the gas, and venting speed on the plume dispersion have been simulated. Based on the simulations a set of empirical equations has been developed. The equations have been validated by theoretical as well as experimental studies. Studies have also been carried out to simulate the effect of venting speed (manipulated by injecting hot air with the released gas) on the plume dispersion. The study reveals that the effect of venting speed on dispersion is very pronounced and can be used to reduce the risk posed by the accidental luxurious release of toxic/flammable gases. For example an increase of 20% in venting speed of chlorine (54.1 m/s) can reduce the distance up to which toxic concentration would occur by about 1100 meters.

Trends in chemical hazards in Japan

Abstract: In the past, the chemical industry in Japan has been the cause of a number of major industrial accidents Subsequent to each accident, specific lessons have been learned These lessons learned have been implemented in terms of safety education of the employees and/or safety measures of the equipment and facilities resulting in a rapid decrease of corresponding accident frequencies In this paper, we summarized both recent and past major accidents caused by chemical substances in fixed installations in Japan Case studies show that runaway reactions are among the main causes of major accident occurrences in the chemical process industry in Japan A recent fatal poisoning accident caused by H2S gas generated during maintenance work again highlights the necessity of adequate safety management in a chemical factory Therefore, even if hazard evaluation of chemical substances and chemical processes is necessary to prevent runaway reactions, human error is also an important factor contributing to reaction hazards [Wakakura, M (1997) Human factor in chemical accidents, J Safety Eng High Press Gas Safety Inst Japan, 34, 846]

HAZDIG: a new software package for assessing the risks of accidental release of toxic chemicals

Abstract: HAZDIG (HAZardous DIspersion of Gases) is a user-friendly PC- based software for generating scenarios for the emissions and gaseous dispersion of hazardous chemicals. It can simulate accidental as well as normal release but has been specifically developed as a tool for studying accidental release of hazardous chemicals and the consequences. HAZDIG is made-up of five main modules—data, release scenario generation, dispersion, characteristics estimation, and graphics. HAZDIG incorporates the latest models for estimating atmospheric stability and dispersion. The data needed to run the models is easy to obtain and feed—properties of chemicals, operating conditions, ambient temperature, and a few commonly available meteorological parameters. A database containing various proportionality constants and complex empirical data has been built into the system. The graphics module enhances the user friendliness of the software, and enables presentation of the results in an easy-to-understand and visually appealing manner. The output of the software is formatted so that it can be directly used for reporting the results without the need of editing.

Dust explosion protection in linked vessels: guidance for containment and venting

Abstract: Much industrial dust-handling plant consists of vessels connected by pipelines. If a dust explosion propagates through such a system, the overall explosion event can be more violent than if a single vessel only is involved, due to a combination of increased turbulence, pressure piling and a jet flame ignition source in the second vessel. This paper gives guidance, based on an extensive experimental programme reported previously, on two aspects of the protection of interconnected vessels: containment and venting.

Trends in major industrial accidents in Korea

Abstract: From the 1960s onwards, Korean industries were encouraged by the government to nurture heavy and chemical industry and to modernize the economics and industrial structures In particular, the development of the chemical industry became the turning point in industrial development, and played a major role in the construction of a new industrialized country It is expected that the chemical industry will be developed all the more due to process automation, the synthesis of new chemicals and the advancement of new process technology The process systems in the chemical industry also became more complex and larger and the inventory of hazardous chemicals that are produced or consumed is increasing continuously Therefore, the hazards from potential accidents such as the probabilities of fire, explosion and the release of toxic chemicals are expected to increase In Korea, 93 major industrial accidents were reported to have occurred from 1988 to 1997 Transportation accidents are not included in this figure In this paper, the analysis of these accidents focuses on the following descriptors: • Year of occurrence, • Industrial activity, • Type of major accident, • Equipment concerned, • Operating circumstances

Towards an alternative criterion for the shipping safety of activated carbons

Abstract: A new criterion for shipping safety of activated carbons is developed which requires microcalorimetric measurements for its implementation. It is examined by making microcalorimetric measurements on a variety of commercial activated carbons. Results are compared with those for the same carbons according to the critical ignition temperature approach.

Major industrial accidents regulation in the European Union

Abstract: This paper describes the background and contents of European Union legislation in the area of prevention of major accidents in fixed industrial installations, especially the famous `Seveso Directive'. The legal basis, aims and obligations of both the old `Seveso I Directive' (82/501/EEC) and the new `Seveso II Directive' (96/82/EC) are explained in detail with regard to their prescriptions on accident prevention.

Fire and explosion hazards during filling/emptying of tanks

Abstract: Loading and unloading operations produce 8% of all accidents which occur in process plants and in the transportation of hazardous materials. A survey of 738 accidents was performed, allowing the identification of the accident type distribution and of their cause. Some considerations on flammable mixtures are also presented, and the procedures to avoid these mixtures occurring when filling or emptying a tank are briefly discussed.

International co-operation in hazardous materials accident prevention

Abstract: Accident prevention relies on a proper understanding of relevant hazards so that appropriate controls can be put in place to safeguard those who are potentially endangered. Setting deaths from war, natural events and domestic accidents to one side, industrial chemicals in their manufacture, transport, storage and use arguably contribute significantly to society's accident toll. National and international regimes have been developed over the years to characterise the properties of these hazardous materials so that risks to society and workforces handling such `dangerous goods' are reduced. Sometimes it has taken a disaster to show that a hazard formerly unrecognised did in fact exist; sometimes the closer scrutiny of test methods has shown that a dangerous property may have gone unrecognised; sometimes misuse of materials precipitated controls. However, in all the deliberations surrounding hazardous materials characterisation, accident investigation and prevention, and development of controls, suitable exchange of information and viewpoints between experts is necessary to promote development and adoption of international conventions. These international protocols are normally agreed by policy makers who have technical advisers to support their negotiations. These technical advisers need to meet in an appropriate forum to develop an understanding of all the relevant factors and to test ideas; often such group discussions pave the way to agreements being reached at formal policy negotiations, to solutions being provided for certain disasters, to better methods of testing. The International Group of Experts on the Explosion Risks of Unstable Substances (OECD-IGUS) created by the OECD is one such group. It first met in 1962. Set up initially to harmonise test methods used by countries to identify and quantify the explosive properties of unstable materials, it has continued over the years to offer scientists who are advisers to their governments (and others) a forum to exchange data and information primarily in support of the development of classifications regimes to protect society from the hazards of unstable substances and remove barriers to international trade but also in understanding and quantifying the resulting effects—such as explosion—from accidents involving these and other `dangerous goods'. This paper describes some of the accidents which show the need for international controls for `dangerous goods' and some of the contributions made by OECD-IGUS (often referred to as `IGUS') to their developments.

The velocity of end-cap and rocket missiles generated by failure of a gas pressurised vessel containing particulate material

Abstract: Many industrial installations include pressure vessels which contain high pressure gas and particulate material. Given the rupture of such a vessel, it is established that provided the particulate acceleration is not greater than the acceleration of a detached end-cap, the end-cap velocity will be similar to that generated by rupture of a gas filled vessel with the same available gas expansion energy. In contrast, if the particulates accelerate to overtake the end-cap, the momentum transfer resulting from the bombardment of the end-cap by the particulates generates a higher end-cap velocity. The latter can be similar to that generated when the rupturing vessel contains only high pressure gas and a consequent greater gas expansion energy than available when the vessel contains both high pressure gas and particulates. The velocity of a `rocket' missile resulting from failure of a gas-pressurised vessel containing particulate material is greater than that generated by failure of a similar vessel containing only high pressure gas.

An experimental study of viscous flows in contractions

Abstract: The need to improve the methods used when designing emergency, pressure-relief systems on polymerisation reactors, has made the flow of highly viscous fluids in pipeline fittings highly topical. This paper investigates the flow processes involved in single-phase, viscous flows in nozzles and orifice plates. These fittings were chosen because they would give an insight into the behaviour of highly viscous flows in other geometries, such as the flow upstream of the seat in a pressure relief valve. Experimental data are presented for a pipe, two conical nozzles and a sharp-edged orifice plate for laminar flows in the Reynolds number range 50–400 and for turbulent flows. The volume flow rate—pressure drop characteristics are presented for both nozzles and the orifice plate. The discharge momentum flow rate for the pipe, a nozzle and the orifice plate are also given. Analysis of the data shows that nozzles and orifice plates that are geometrically similar have a similar resistance to flow. It is also shown that the contraction coefficient for an orifice plate tends to unity at low Reynolds numbers.

Modelling the response of masonry structures to gas explosions

Abstract: In practice no system is infallible no matter how stringent the safety standards and procedures are concerning the release and use of gas in the process industries. Structural damage arising from an internal explosion often has serious repercussions. It is, therefore, imperative for engineers to be able to predict the extent of the damage that may occur, and to develop means to mitigate such effects. An accurate prediction of the structural behaviour requires an accurate formulation of the material's failure criteria. Experimental studies have shown that the response of masonry structures to gas explosions is non-linear. The cracking of masonry in tension and crushing of the material in compression are the major contributory sources of non-linearity. This paper presents a method of predicting the non-linear response based on the formulation of a numerical model to describe the material's failure criteria. The model has been validated using full-scale explosion test data provided by the Building Research Establishment in the UK. Although some minor discrepancies have been observed, overall the simulated values correlated very favourably with the actual test data. The probable causes of discrepancies are also discussed at the end of this paper.