Showing papers in "Journal of Loss Prevention in The Process Industries in 2000"

Removal of Volatile Organic Compounds from polluted air

Abstract: Volatile Organic Compounds (VOCs) are among the most common air pollutants emitted from chemical, petrochemical, and allied industries. VOCs are one of the main sources of photochemical reaction in the atmosphere leading to various environmental hazards; on the other hand, these VOCs have good commercial value. Growing environmental awareness has put up stringent regulations to control the VOCs emissions. In such circumstances, it becomes mandatory for each VOCs emitting industry or facility to opt for proper VOCs control measures. There are many techniques available to control VOCs emission (destruction based and recovery based) with many advantages and limitations. Therefore, deciding on a particular technique becomes a difficult task. This article illustrates various available options for VOCs control. It further details the merits, demerits and applicability of each option. The authors hope that this article will help in critically analysing the requirements and accordingly decide on the appropriate strategy to control VOCs.

Overview of dust explosibility characteristics

Abstract: This paper is an overview of and introduction to the subject of dust explosions. The purpose is to provide information on the explosibility and ignitability properties of dust clouds that can be used to improve safety in industries that generate, process, use, or transport combustible dusts. The requirements for a dust explosion are: a combustible dust, dispersed in air, a concentration above the flammable limit, the presence of a sufficiently energetic ignition source, and some confinement. An explosion of a fuel in air involves the rapid oxidation of combustible material, leading to a rapid increase in temperature and pressure. The violence of an explosion is related to the rate of energy release due to chemical reactions relative to the degree of confinement and heat losses. The combustion properties of a dust depend on its chemical and physical characteristics, especially its particle size distribution. In this paper, the explosion characteristics of combustible dusts will be compared and contrasted with those of flammable gases, using methane as an example. These characteristics include minimum explosible concentration, maximum explosion pressure, maximum rate of pressure rise, limiting oxygen concentration, ignition temperature, and amount of inert dust necessary to prevent flame propagation. The parameters considered include the effects of dust volatility, dust particle size, turbulence, initial pressure, initial temperature, and oxygen concentration. Both carbonaceous and metal dusts will be used as examples. The goal of this research is to better understand the fundamental aspects of dust explosions.

Flammability of methane, propane, and hydrogen gases

Abstract: This paper reports the results of flammability studies for methane, propane, hydrogen, and deuterium gases in air conducted by the Pittsburgh Research Laboratory. Knowledge of the explosion hazards of these gases is important to the coal mining industry and to other industries that produce or use flammable gases. The experimental research was conducted in 20 L and 120 L closed explosion chambers under both quiescent and turbulent conditions, using both electric spark and pyrotechnic ignition sources. The data reported here generally confirm the data of previous investigators, but they are more comprehensive than those reported previously. The results illustrate the complications associated with buoyancy, turbulence, selective diffusion, and ignitor strength versus chamber size. Although the lower flammable limits (LFLs) are well defined for methane (CH4) and propane (C3H8), the LFLs for hydrogen (H2) and its heavier isotope deuterium (D2) are much more dependent on the limit criterion chosen. A similar behavior is observed for the upper flammable limit of propane. The data presented include lower and upper flammable limits, maximum pressures, and maximum rates of pressure rise. The rates of pressure rise, even when normalized by the cube root of the chamber volume (V1/3), are shown to be sensitive to chamber size.

Flammability limit measurements for dusts in 20-L and 1-m3 vessels

Abstract: Two types of flammability limits have been measured for various dusts in the Fike 1-m3 (1000-L) chamber and in the Pittsburgh Research Laboratory (PRL) 20-L chamber. The first limit is the minimum explosible concentration (MEC), which was measured at several ignition energies. In addition to the three dusts studied previously (bituminous coal, anthracite coal, and gilsonite), this work continues the effort by adding three additional dusts: RoRo93, lycopodium, and iron powder. These materials were chosen to extend the testing to non-coal materials as well as to a metallic dust. The new MEC data corroborate the previous observations that very strong ignitors can overdrive the ignition in the smaller 20-L chamber. Recommendations are given in regard to appropriate ignition energies to be used in the two chambers. The study also considered the other limiting component, oxygen. Limiting oxygen concentration (LOC) testing was performed in the same 20-L and 1-m3 vessels for gilsonite, bituminous coal, RoRo93, and aluminum dusts. The objective was to establish the protocol for testing at different volumes. A limited investigation was made into overdriving in the 20-L vessel. The LOC results tended to show slightly lower results for the smaller test volume. The results indicated that overdriving could occur and that ignition energies of 2.5 kJ in the 20-L vessel would yield comparable results to those in the 1-m3 vessel using 10.0 kJ. The studies also illustrate the importance of dust concentration on LOC determinations.

Behavior of flames propagating through lycopodium dust clouds in a vertical duct

Abstract: The structure of flame propagating through lycopodium dust clouds has been investigated experimentally. Upward propagating laminar flames in a vertical duct of 1800 mm height and 150×150 mm square cross-section are observed, and the leading flame front is also visualized using by a high-speed video camera. Although the dust concentration decreases slightly along the height of duct, the leading flame edge propagates upwards at a constant velocity. The maximum upward propagating velocity is 0.50 m/s at a dust concentration of 170 g/m 3 . Behind the upward propagating flame, some downward propagating flames are also observed. Despite the employment of nearly equal sized particles and its good dispersability and flowability, the reaction zone in lycopodium particles cloud shows the double flame structure in which isolated individual burning particles (0.5–1.0 mm in diameter) and the ball-shaped flames (2–4 mm in diameter; the combustion time of 4–6 ms) surrounding several particles are included. The ball-shaped flame appears as a faint flame in which several luminous spots are distributed, and then it turns into a luminous flame before disappearance. In order to distinguish these ball-shaped flames from others with some exceptions for merged flames, they are defined as independent flames in this study. The flame thickness in a lycopodium dust flame is observed to be 20 mm, about several orders of magnitude higher than that of a premixed gaseous flame. From the microscopic visualization, it was found that the flame front propagating through lycopodium particles is discontinuous and not smooth.

Experimental mine and laboratory dust explosion research at NIOSH

Abstract: This paper describes dust explosion research conducted in an experimental mine and in a 20-L laboratory chamber at the Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH). The primary purpose of this research is to improve safety in mining, but the data are also useful to other industries that manufacture, process, or use combustible dusts. Explosion characteristics such as the minimum explosible concentration and the rock dust inerting requirements were measured for various combustible dusts from the mining industries. These dusts included bituminous coals, gilsonite, oil shales, and sulfide ores. The full-scale tests were conducted in the Lake Lynn experimental mine of NIOSH. The mine tests were initiated by a methane–air explosion at the face (closed end) that both entrained and ignited the dust. The laboratory-scale tests were conducted in the 20-L chamber using ignitors of various energies. One purpose of the laboratory and mine comparison is to determine the conditions under which the laboratory tests best simulate the full-scale tests. The results of this research showed relatively good agreement between the laboratory and the large-scale tests in determining explosion limits. Full-scale experiments in the experimental mine were also conducted to evaluate the explosion resistance characteristics of seals that are used to separate non-ventilated, inactive workings from active workings of a mine. Results of these explosion tests show significant increases in explosion overpressure due to added coal dust and indications of pressure piling.

Flammability of gas mixtures containing volatile organic compounds and hydrogen

Abstract: An experimental program was conducted to evaluate the accuracy of some current methods for predicting the flammability of gas mixtures containing hydrogen and flammable or nonflammable volatile organic compounds (VOCs) in air. The specific VOCs tested were toluene, 1,2-dichloroethane, 2-butanone, and carbon tetrachloride. The lower flammability limits (LFLs) of gas mixtures containing equal molar quantities of the components were determined in a 19.4-l laboratory flammability chamber using a strong spark ignition source and a pressure criterion for flammability. All but one of the LFL values for the individual components were in agreement with earlier literature values. However, the LFL of 1,2-dichloroethane was found to be significantly lower than the range of values reported for previous determinations in smaller chambers. Two methods for calculating the LFL of mixtures were considered. The Group Factor (atomic) Contribution Method was determined to be generally more accurate than the LeChatelier Method for estimating the LFL of the gas mixtures reported here, although the LeChatelier Method was usually more conservative. The Group Factor Method predicted higher values (nonconservative) for the LFLs of several mixtures than were experimentally measured. For the case of a mixture of hydrogen and carbon tetrachloride, the Group Method estimation of the LFL was seriously in error.

Venting of deflagrations: Hydrocarbon-air and hydrogen-air systems

Abstract: A set of 34 experiments on vented hydrocarbon–air and hydrogen–air deflagrations in unobstructed enclosures of volume up to 4000 m 3 was processed with use of the advanced lumped parameter approach. Reasonable compliance between calculated pressure–time curves and experimental pressure traces is demonstrated for different explosion conditions, including high, moderate, low and extremely low reduced overpressures in enclosures of different shape ( L max : L min up to 6:1) with different type and position of the ignition source relative to the vent, for near-stoichiometric air mixtures of acetone, methane, natural gas and propane, as well as for lean and stoichiometric hydrogen–air mixtures. New data were obtained on flame stretch for vented deflagrations. The fundamental Le Chatelier–Brown principle analog for vented deflagrations has been considered in detail and its universality has been confirmed. The importance of this principle for explosion safety engineering has been emphasized and proved by examples. A correlation for prediction of the deflagration–outflow interaction number, χ / μ , on enclosure scale, Bradley number and vent release pressure is suggested for unobstructed enclosures and a wide range of explosion conditions. Fractal theory has been employed to verify the universality of the dependence revealed of the deflagration–outflow interaction number on enclosure scale. In spite of differences between the thermodynamic and kinetic parameters of hydrocarbon–air and hydrogen–air systems, they both obey the same general regularities for vented deflagrations, including the Le Chatelier–Brown principle analog and the correlation for deflagration–outflow interaction number.

Prediction of vapour cloud explosions using the SCOPE model

Abstract: The SCOPE 3 model (Shell Code for Overpressure Prediction in gas Explosions) has been developed to predict the overpressures which could be generated by gas explosions in vented enclosures, such as offshore modules. SCOPE 3 attempts, wherever possible, to model the underlying physical processes in an explosion. This phenomenological approach gives greater confidence in predictions for full-scale events than methods based simply on correlations of experimental data.

External pressures generated by vented gas and dust explosions

Abstract: Several different data correlations have been developed for the external pressures associated with vented gas explosions and dust explosions. These correlations, which are applicable to external locations in the direct line-of-sight of the enclosure vent, are reviewed here. In addition, the application of spherically symmetric and of ellipsoidal blast wave models is explored as a possible means of calculating external pressures over a wider range of conditions than is possible with the existing data correlations. Results indicate that the spherically symmetric blast wave model can obtain a comparable accuracy (8–9 kPa standard deviation) for line-of-sight locations as the more recent data correlations. In the case of the lower blast pressures at locations perpendicular to the vent line-of-sight, the ellipsoidal blast wave provides significantly better agreement with data (to within 1 kPa standard deviation for the one set of available test data) than the spherically symmetric model.

Risk analysis of LPG transport by road and rail

Abstract: Historical data concerning more than 130 LPG rail and road transport accidents were critically examined, identifying the scenarios, following their evolution into the final accidental events, and determining their theoretical probabilities of occurrence. In principle, rail accidents are rather hazardous, the most probable scenario being a major release followed by an UVCE. However, in order to discriminate among road and rail transport, the relevant number of trips and accident rates should be taken into account. In fact, the application, concerning the transport of 5700 ton/year of LPG in Italy along one rail and two different road itineraries, showed that the risk for rail transport was more than one order of magnitude lower than that for those on the roads. The population density along the route and the accident rate, rather than the length of the route, appear the most important factors for discriminating between different itineraries.

A systematic Hazop procedure for batch processes, and its application to pipeless plants

Abstract: Increasing technological complexity together with social and legal pressures have made it necessary to develop more effective approaches to safety. This need is particularly strong in the design and operation of chemical plants. One approach, Hazard and Operability Study (Hazop), is a method of systematically identifying every conceivable process deviation, its abnormal causes and adverse hazardous consequences in a chemical plant. The technique was developed by ICI in the 1960s, and has been standardised for use in continuous manufacturing plants. Improvised attempts have been made to modify the continuous Hazop approach for use with batch processes, such as using different guide words and deviations, without the method of application being formalised. There are different issues that need to be surmounted for the methodology to be applied to batch processing plants. The standard approach, of examining a system line by line, is ideal for continuous processes but does not lend itself to the thorough examination of batch processes. A typical batch plant can be examined by dividing the process into three operational phases: charge, reaction, and discharge. A modified Hazop methodology should then be applied to the description of each phase. Although a need for this type of approach has been recognised, there is no published information to be found on an agreed format on how this should be done. This paper presents a formalised approach to applying the Hazop methodology to batch processes. A way forward in multi-product manufacturing is the emerging technology of ‘pipeless plants’. The basic idea is to move the process vessel between fixed stations for mixing, separation and other activities. This offers great flexibility for change, and allows a company to respond quickly to market demands and technological advances. Little research has been done on the safety of pipeless plants, which are essentially batch plants with mobile vessels. Therefore the batch Hazop methodology presented in this paper has been further developed in order to improve the safe design of pipeless plants.

Thermal radiation from vented dust explosions

Abstract: The fireball from a vented dust explosion presents a danger to personnel who may be within the vicinity of the event. The risk of serious injury to people caught within the fireball is great, and anyone just outside the fireball may be at risk from thermal radiation. This report describes a project in which the effects of thermal radiation from vented dust explosions was studied. The aim was to establish the areas around a fireball in which people would be at risk from thermal radiation. Six dusts were tested in a large vented vessel and external fireballs were generated under a range of conditions. The fireball geometry and the heat flux from the fireball were studied. A range of material samples were exposed to the fireball. The safe areas around the fireballs were established for each of the six dusts. Generally, the larger vent areas resulted in the larger fireballs and high heat pulse values. However, the fireball was usually too brief to ignite fabric samples unless they were very close to the fireball. The work has shown that in most cases the safe area was relatively close to the surface of the largest fireball.

Experimental research on explosibility at high initial pressures of combustible dusts

Abstract: In recent years some explosibility experiments were carried out by LOM (Spain) to look into the behaviour of the combustible dusts at hyperbaric pressures. In this way, different aspects were studied, such as the effect of initial pressure on the explosion development, the influence of the effective present turbulence or preventative existing techniques such as inertization. This paper contains a summary of the different tests performed, which covered a range of initial pressure from 1 to 15 bar. Several fuels were used within the works, and their main features are described to facilitate understanding the results.

Comparison of different methods for estimating TMRad from dynamic DSC measurements with ADT 24 values obtained from adiabatic Dewar experiments

Abstract: Recently, a method for estimating the time to maximum rate under adiabatic conditions (TMR ad ) from non-isothermal DSC measurements was presented by Keller, A., Stark, D., Fierz, H., Heinzle, E., & Hungerbuhler, K. (1997). J. Loss. Prev. Process. Ind ., 10 , 31–41. The method was tested on the basis of isoperibolic data only, because data from adiabatic experiments were not available. In this study we used results from 180 Dewar vessel experiments with an adiabatic shield and the corresponding dynamic DSC measurements provided by Aventis Research and Technologies (former Hoechst AG) to test the estimation method suggested. The data were obtained for reaction mixtures, bottom residuals, reaction residuals, and products. We found that in all cases the predicted TMR ad at a given temperature was shorter than the experimental value determined from adiabatic measurements. This result shows that the TMR ad estimation method is useful as a screening tool for the assessment of thermal risk. Furthermore, the estimation method introduced by Keller et al., is more on the safe side than other common and often applied estimation methods like the so-called 100 degree rule or the 50 degree rule. We also describe how to derive adiabatic induction times for different temperatures by using a minimum number of adiabatic experiments.

The influence of flow and turbulence on flame propagation through dust-air mixtures

Abstract: Dust explosions are time-dependent flame propagation processes. Their description with “lumped parameter models” like the K St value are of limited validity only. More evidence of the process of flame propagation may be expected from an investigation of the flame velocity being composed by the laminar and turbulent velocities and the flow velocity. In the present paper the influences of the dust concentration and the flow velocity have been investigated by experiments in tube apparatus of three different diameters showing the dominating influence of the flow velocity and the turbulent rms velocity on the flame propagation. In addition, laminar and turbulent flame propagation has been investigated by an appropriate numerical model. Furthermore flow structures and particle distributions have been computed in a real size grain silo to assess the effects of possible explosions.

Disaster management plan for chemical process industries. Case study: investigation of release of chlorine to atmosphere

Abstract: The first step in preparing a disaster management plan for any chemical process industry (CPI) is to identify and mitigate the conditions that might cause them. In practice, such a plan should start early in the design phase of the chemical facility, and continue throughout its life. The objective is to prevent emergencies by eliminating hazards wherever possible. In-spite of the advances made in knowledge and technology, failure-free design and devices have remained elusive. Even the well designed and inherently safe chemical facility must prepare to control potentially hazardous events that are caused by human or mechanical failure, or by natural forces such as floods or earthquakes. The need for effective technological disaster management programs by chemical facilities and their neighbouring communities became painfully clear in the 1980s, a decade marred by tragic events linked to the manufacture and distribution of chemical products. Unfortunately, several events during this decade, though not on a scale to match the previous one, have nevertheless cast a heavy burden and responsibility on the management. The chemical industry has vigorously responded to these problems in a wide variety of ways. The CPI took actions to improve the reliability of their operations, drew up emergency plans in consultation with the neighbourhood and the regulating authorities and practise emergency exercises regularly to alleviate public fear. Manali Industries in Chennai (Madras) is an exemplary model in India.

What is an explosion? A case history of an investigation for the insurance industry

Abstract: After a large property loss, the insured and insurers of a hydroelectric power plant in North America became embroiled in subrogation to determine if the event could be characterized as an explosion. The subject insurance policy provided coverage for explosions, but excluded mechanical breakdowns. Analysis by Exponent Failure Analysis Associates indicated that a consistent, cross-disciplinary definition for explosions can be extracted from published scientific literature, and that this incident was not an explosion because certain key requirements were missing during the accident. However, this investigation has highlighted the necessity for insurance companies and their insureds to better understand this term and thereby minimize future coverage disputes. This paper presents an analysis of this incident and describes the necessary characteristics of an explosion.

Recent development of standardization of testing methods for dust explosion in Japan

Abstract: The Dust Explosion Committee of the Association of Powder Process Industry and Engineering (APPIE) of Japan has acted to establish the standard for the member of the Association. Two testing methods have been authorized by the Association. The methods are established to evaluate sensitivity and severity for dust explosion. The ignition sensitivity is evaluated by the minimum explosive dust cloud concentration. Tapping sieve equipment and a strictly-specified Hartmann-type explosion tube have been selected as the testing apparatus. The tapping sieve equipment is applied to measure the minimum explosive concentration by forming a dust cloud supplied from a sieve on the top of the explosion chamber. The Hartmann-type tube is used to investigate roughly whether the test powder is explosive or not. A lot of explosion tests had been carried out to standardize the equipment and evaluate the sensitivity. This APPIE standard is being revised. Along with the ISO standard for explosion severity, Research Institute of Industrial Safety, the Ministry of Labour published a Guide to Test Method for Explosion Pressure and Rate of Pressure Rise for Combustible Dusts in 1994. Based on this Guide, The APPIE Committee has made the draft for the member. These standards and drafts are aimed to be the Japanese Industrial Standard (JIS). No other similar standard exists in Japan. In the present paper, technical data and explosion statistics which are the background of the APPIE standard for the ignition sensitivity are to be described.

The critical runaway condition and stability criterion in the phenol–formaldehyde reaction

Abstract: The procedure of phenol–formaldehyde polymerization is a rather important and complicated reaction in the chemical industry. This exothermic polymeric reaction releases a huge amount of heat. The high amount of energy accumulated and increasing temperature in this reaction process always lead to runaway reaction and a hazard situation owing to the high released heat and improper operation. In this investigation, we used sodium hydroxide as alkali–catalyst in the phenol–formaldehyde polymerization and estimated the reaction kinetics parameters to evaluate the thermal hazard conditions. The critical temperatures and stable criteria of the runaway reaction in this exothermic polymerization were evaluated. This technique is important and useful for safe operation in the phenol–formaldehyde polymerization process.

The application of active databases to the problems of human error in industry

Abstract: Although the general level of safety in the process industries is high a class of ‘human error’ has remained largely unaffected by engineering and regulatory advance in the industry and continues to recur. Experience is lost by industry and reports of industrial incidents are frequently inaccessible. Conventional computer database techniques are often inefficient to deal with this growing mass of data and a novel Active Database System (ADB) has been developed by Loughborough University to address this need. The ADB organises information in a novel manner using a series of loosely linked classification hierarchies, which collectively form a domain description of the chemical industrial workplace. This taxonomy has noted advantages over more traditional organisational structures. It guides both initial indexing and report retrieval. The ADB differs from other systems by being linked with other computer applications already in use by or of use to industry such as computer aided design applications or computerised Permit to Work systems. Although these systems have individual, stand-alone utility, a high degree of synergy exists making the integrated package more useful than the sum of its parts.

Ignition of methane–air mixtures by laser heated small particles

Abstract: Optical technologies have progressed rapidly in the past 15 years. One application of laser technology in underground coal mines currently under evaluation is the remote measurement of explosive methane gas. Federal regulations require that atmospheric monitoring systems used in gassy underground mines where permissible equipment is required shall be intrinsically safe. Mine Safety and Health Administration criteria for the evaluation and testing of intrinsically safe apparatus and associated apparatus contain no specific guidance for optoelectronic components such as diode lasers. The National Institute for Occupational Safety and Health is conducting a study to help provide a scientific basis for developing appropriate safety guidelines for optical equipment in underground coal mines. Results of experiments involving ignition of methane–air mixtures by collections of small heated particles of Pittsburgh seam coal and black iron oxide are reported. The inert but more strongly absorbing iron oxide targets consistently ignited methane–air mixtures at lower powers than the coal targets. Minimum observed igniting powers for laser energy delivered by 200, 400 and 800 μm core fiber optic cables and directed onto iron oxide targets in methane–air atmospheres were 0.6, 1.1, and 2.2 W, respectively. Comparisons with the results of other researchers are made. A thermal layer theoretical approach to describing the process is included as an appendix.

Modeling of maize starch explosions in a 12 m3 silo

Abstract: This paper presents a 2-dimensional numerical model of Eulerian–Lagrangian multi-phase combustion flow to predict maize starch explosions in a 12 m3 silo. The flow field after ignition, flame propagation velocity and pressure development histories etc. during the explosion, are calculated. The data of non-uniform initial conditions including dust concentration, flow velocity and turbulent RMS velocity in the silo for this model are adopted from Hauert, Vogl and Radandt (1994) [Hauert, F., Vogl, A., Radandt, S. (1994). Measurement of turbulence and dust concentration in silos and vessels. 6th international colloquium on dust explosions (pp. 71–80), Shenyang, China, August 28–September 2, 1994.]. A simple concept of dust granule taking into consideration dust dispersion efficiency is proposed and introduced. The Lagrangian method is used to trace trajectories and granules, so it is easier to consider particle size distribution. The k−e model is used to simulate the turbulence of the gas phase, and the particle's pulsation is modeled by random vector wind generated by the surrounding gas. In the combustion model, vaporization of water, volatilization of volatile, gas phase reaction and the particle's surface reaction are taken into account.

Critical dimensions of holes and slots for transmission of gas explosions

Abstract: Critical hole diameters for explosion transmission from a primary virtually closed chamber into an ambient gas cloud were determined. Most of the present experiments were conducted with a 1-l primary chamber. The motivation for the study is two-fold. First, results from this kind of experiment are of direct practical use in further improvement of design and maintenance procedures of “flame-proof” electrical equipment. However, such experiments can also contribute to improvement of the general understanding of the mechanisms of flame propagation in turbulent, premixed gases. The preliminary experimental results presented confirm that the minimum tube diameter for flame transmission depends strongly on the location of the ignition point. The generally accepted limiting values are conservative, in the sense that they can only be approached if the ignition source is located in a narrow zone in the vicinity of the entrance to the transmission hole. This must be taken into account if flame-proof equipment is to be designed on the basis of risk analysis. An observation related to mechanisms of turbulent flame propagation in premixed gases in general was also made. In the case of ignition far away from the transmission hole, i.e. for high gas velocities through the hole at the moment of flame front arrival at the hole, the re-ignition probability for a given hole diameter was in fact higher for off-stoichiometric propane concentrations than for concentrations close to stoichiometry. The average chemical reaction rate in the primary chamber had its peak in the region of stoichiometry, and hence the pressure in the primary chamber at the moment of flame front arrival at the transmission hole entrance, was also at its maximum in that concentration range. Therefore, the average turbulence intensity in the potential re-ignition zone, and hence the rate of entrainment of cold unburnt gas by the hot jet was also at its maximum. Hence, a main reason for the observed effect may be that at stoichiometry more efficient cooling by cold-gas entrainment, compared with at leaner and richer mixtures, more than compensated for the faster chemical reaction.

Analysis of results from large scale hydrocarbon gas explosions

Abstract: The recent set of large scale experiments at Spadeadam produced a considerable amount of data which consisted of sets of pressure–time histories recorded at very high sampling rates during the explosion events. In many experiments, very high over-pressures were measured, however, these high pressure peaks were of very short duration. In this paper, we examine characteristics of pressure–time data from large scale tests and present the results in three different forms, and show that the application of headline maximum over-pressure values to assess structural response is not applicable. The response characteristics of the target structure must be included in the definition of maximum over-pressure for structural assessment. While work is still ongoing at BP Amoco, preliminary results are presented in this paper. Our initial finding would indicate that (a) depending on the structure of interest, very different conclusions could be drawn concerning the relative severity of various explosion events and the benefits of mitigation measures, and (b) it is potentially dangerous to arbitrarily strengthen structures to withstand these high peak over-pressures.

Comparison of blast curves from vapor cloud explosions

Abstract: Several sets of blast curves are frequently used in the prediction of blast effects from vapor cloud explosions. However, they have not been validated by experiments since systematic experimental data have only become available in recent years. The aim of this paper is to present a comparison between the calculated blast curves and available experimental data. Also presented is a comparison between several blast curves. The comparison showed that for detonations and subsonic flames, the blast curves produced by one-dimensional numerical calculations are generally in agreement with experimental data. However, there is great difference between the measured and calculated overpressures for supersonic deflagrations. The experimental overpressures fall well below the calculated values and decay much faster. The discrepancy is more pronounced for less reactive mixtures. It can be concluded from the comparison that the prediction using one-dimensional numerical calculations is conservative and may be overly conservative for supersonic deflagrations.

Suppression of dust explosions by means of different explosive charges

Abstract: The research was aimed at the development and testing of a super fast explosion suppression system using different explosive charges. The experiments were carried out on a prototype device (steel container) of 2 l capacity, closed by means of a membrane. Below the membrane, there was an exhaust connector pipe, at the end of which was a dispersing head. About 1 kg of extinguishing material was located inside the container. The membrane was ruptured by the explosion of a miniature cumulative charge placed on the membrane surface inside the container. In some experiments the explosive charge was located both on the membrane surface and in the upper part of the container—over the extinguishing material. Pentryt, pyrotechnic charge and powder charge were used as the explosive material. In the first case, the container was filled up (above the extinguishing material surface) with nitrogen under pressure in the range of 30–50 bar. In two other cases, there was no overpressure inside the container. The pyrotechnic charge and powder charge were used as gas generators in order to produce the overpressure only after triggering the system by the signal from the protected volume. Standard electric igniters were applied to initiate the explosive material. The main reason for using the explosive materials for membrane perforation was their high combustion velocity, that enabled opening of the membrane within several microseconds. The dust explosion suppression occurred as a result of the activity of extinguishing material blown out of the container by means of compressed gases. The suppressing powders were used as the extinguishing material. The results of the research into optimization of the shape and miniaturization of the explosive charge mass are presented. Also, the process of shaping of the exhaust stream of the extinguishing material was recorded. Finally, the dust explosion suppression process in a 1.25 m 3 chamber, using the developed super fast extinguishing system was studied.

Predicting the maximum gas deflagration pressure over the entire flammable range

Abstract: This paper describes a semi-empirical method to predict the maximum pressure for fuel/air deflagrations over the entire flammable range The method is based on availability, which is a thermodynamic concept representing the maximum mechanical energy extractable from a given mass of material In total eight fuel/air systems were considered — the deviation between the predicted and experimental maximum pressure is from −20 psia to +15 psia This is a significant improvement over ideal gas or equilibrium prediction methods

Propagation of smouldering in dust deposits caused by glowing nests or embedded hot bodies

Abstract: Smouldering fires in storage equipment are often caused by glowing nests or embedded hot bodies. Due to large temperature gradients near the glowing nest in a deposit of bulk material the detection of a smouldering fire is difficult and the smouldering fire may remain unnoticed until the reaction front breaks through the surface of the deposit. The present paper reports experimental investigations on thermal conditions, which may cause or promote an ongoing smouldering process, e.g. critical initial temperatures of embedded hot bodies or critical initial sizes of glowing nests. Propagation velocities of smouldering fires were dependent on the sample size, the oxygen content within the sample and on the caloric properties of three combustible dusts.

Smoldering combustion of dust layer on hot surface

Abstract: The critical temperature as well as the critical flux for ignition of a dust layer of cornflour and a mixture of wheatflour and cornflour (80% wheatflour+20% cornflour) on a hot plate have been determined. The moulded sample was cylindrical in shape and of different heights and diameters. The particle size of dusts ranged between 63 μm to 150 μm. The temperature–time histories for self-heating without ignition and with ignition are offered, showing the critical boundaries between them. Also the times to ignition for each dust, showing the effect of sample size on their values, are determined. Certain experimental correlations which relate to times to ignition, as well as the critical temperature for ignition and thermal and geometrical dimensions of sample are presented.