Study on Values Taking of Ignition Probabilities in Hazardous Chemical Leakage Accidents
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Abstract:
In order to calculate accident probabilities of fire and explosion after dangerous chemicals leaking and improve the quantification level of risk assessment,the value taking for ignition probabilities was researched based on the domestic and foreign literatures.Firstly,the value taking for ignition probabilities was discussed from calculation models and direct reference value,and some advice for taking value under different situation was proposed.Then through an example,a verification and comparative analysis was made between the application of calculation models for ignition probabilities and the application of direct reference value.The results show that the calculation models for ignition probabilities have bigger computational uncertainty and limited applicability while direct reference value from a series of statistical events is scientific.Actual value taking more depends on empirical data or existing data,and considers the actual situation(such as safety conditions,etc.) so as to make the value more scientific.Keywords:
Value (mathematics)
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Roughly half of the scenarios identified in Process Risk Analysis are fires and explosions of gases, vapors or combustible dusts. These involve ignition sources including electrical equipment, hot surfaces, friction, incandescent substances, gas compression, ionizing radiation, static electricity etc. To judge whether the risk of a given scenario is acceptable or not, it is necessary to estimate the Severity of the consequences of an unwanted event for man and the environment, and the Probability of occurrence of the scenario.This paper presents the semi-quantitative method used within Solvay to estimate the frequency of all types of ignition sources in such scenarios and to judge whether the risk level is acceptable or not.
Incandescent light bulb
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The paper is inclined to present a simulated model for predicting the probability of chain-fire accidents caused by the explosion in chemical industry parks based on the analysis of the fire and explosion liability of the oil tanks over there.Careful study of the Domino Effect of the accidents helps us to confirm that the main physical effects of the chain accidents taking place in such parks are the explosion of incontrollable vapor clouds and the pool fires.To make the problem clearer,we have drawn the curves of the shock-waves in relation with the accident distance and the heat radiation with the distance by using MATLAB technology.At the same time,we have also worked out the probability curve of the overpressure with the damage, and that of the heat radiation with the damage.The fitting of the two groups of curves has enabled us to establish the connection between the objective hazardous sources affected and the original hazardous sources themselves,which may in turn promote the building-up of the connection between the hazardous material sources with the original hazardous sources,that is,the probability matrixes,on the basis of which we have worked out the accident probabilities of the hazardous oil tanks in a given affected field of the fire and the explosion.In so doing,it is possible for us to deduce the likely chain effects and the probability of the accidents in advance,which enabled us to prepare essential preventive methods.The example analysis shows that the probability of the chain accidents can be affected by the physical and chemical properties of the hazardous material sources in the field,the geographical location and the solidness of the container of the material. Corresponding relationship of the accident probabilities has been established with the MATLAB.Differences of the correspondent relationship or the accident order may in turn lead to the difference of the probabilities of the chain accidents.The above considerations may help us to take the most effective measures at the minimum cost as well as prevent some potentially dangerous chain reactions so as to reduce human casualty and material losses.
Domino Effect
Overpressure
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Gas explosion
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For most fuels transported by pipeline, whether or not ignition of an accidental release occurs is a critical factor in determining the extent of the resulting hazard. The probability of ignition is therefore a key input when undertaking pipeline risk assessments and the value chosen is a direct multiplier of the risk calculated. Typically, the ignition probability assigned is based on an analysis of historical data. However, the pipeline industry has a good safety record and major incidents are rare, sometimes resulting in widely differing values being used due to the scarcity of reliable data. For high pressure natural gas transmission pipelines, it is observed that ruptures of large diameter underground pipelines operating at high pressures can result in ignited releases even in remote areas with no obvious ignition sources present. Conversely, failures of small diameter pipelines operating at lower pressures rarely result in ignited releases, suggesting that ignition sources generated as a result of the failure event itself may be significant in causing ignition of high pressure natural gas releases from underground pipelines. The results of analysis previously reported at IPC2002 indicated a trend for the ignition probability to increase with pd2, with p the pipeline operating pressure (bar) and d the pipeline diameter (m). The relationship forms the basis of the default ignition probabilities recommended for use in the PIPESAFE package developed for risk assessment of gas transmission pipelines. Since the previous study was carried out, the number of pipeline rupture incidents in the dataset used has increased by about 20%, and following a recent review, the statistical analysis has been extended and refined. This paper reports the results of recent analysis of the most comprehensive incident dataset available to Advantica for natural gas transmission pipelines, presenting the correlation derived from a simple statistical analysis together with consideration of possible physical explanations for the trends observed based on an ongoing programme of research into the causes of ignition.
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A study was made of the feasibility of putting hazardous area classification (HAC) on
a more quantitative basis.
A review of current HAC practice showed that the widespread policy of setting fixed
zone distances around sources of hazard was subjective and sometimes led to inconsistencies
between different codes of practice when applied to the same situation. Fatality and injury
statistics were used to show that there is a significant risk to workers from the ignition of
flammable atmospheres. which should be reduced.
Data were researched and compiled to fit into a proposed framework for the quantification
of HAC. These included information concerning leak source inventory: source leak frequency:
and source leak size distribution. Mathematical models were collected which could be used to
describe the emission and dispersion of flammable releases. Example calculations were performed
for typical leak scenarios to illustrate the variation in hazard distances.
Estimates were made of the ignition and explosion probabilities of flammable leaks. which
depended princi pally on emission size.
To compensate for uncertainties in the researched data. a fire and explosion model was
devised to estimate the ignition frequency on a typical process plant. The model was applied
to a standard plant which was formulated from researched data. By iteratively checking the
estimated ignition frequencies against historical data it was concluded that reasonable agreement
was achieved with some adjustment of the input data.
The special problems of HAC of indoor plants were also addressed.
It was concluded that the results of this study provided a basic framework for the
quantification of HAC. although the quality of currently available data necessary for
quantification is generally poor. The acquisition of better quality leak and ignition data should
provide a platform from which the current work may progress. Further work should include
the further refinement of the basic fire and explosion model to account for ignitions which
HAC cannot protect against such as autoignitions. It was also noted that the behaviour of indoor
releases requires clarification. together with the concept of a minimum flammable inventory
below which there is negligible risk of ignition.
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Risk management of loss of containment at facilities processing or storing liquid flammable fluids is crucial in order to ensure safe operations. To control the risk, an extensive set of safety functions are in general implemented in design, for example systems that minimize the occurrence for initiating events (e.g., spontaneous leak of flammable material due to fatigue) and measures that reduce explosion loads arising in case of delayed ignition of the dispersed fluid mixed with air. Effective ventilation of the released fluid that potentially generates an explosive atmosphere (gas and/or droplets generated from the liquid phase) is one of the crucial barrier elements to mitigate the explosion hazard. Hence, the gas explosion hazard in enclosed modules with poor ventilation is of particular concern as a flammable mixture may accumulate even for small release rates. This may result in both high likelihood of ignition and considerable explosion loads in case of ignition due to the big amount of chemical energy taking part in the combustion process relative to the size of the enclosure. Computational fluid dynamics (CFD) methods are increasingly being used to characterize the consequences of leaks of flammable fluid in complex geometries, both modeling of the initial gas dispersion process and the resulting explosion and fire loads following from the combustion process in case of ignition. This paper presents an advanced methodology based on the CFD tool OpenFOAM for detailed assessment of the transient gas dispersion process and the associated likelihood of ignition for leaks of flammable fluid inside enclosures. The objective is to understand how to optimize the design of safety functions that affect the fire and explosion risk picture. This custom made tool, denoted cloudIgnitionFoam, accounts for the transient gas leak behavior based on real-time gas detection, subsequent initiation of emergency shutdown (ESD) and blow down systems and computes ignition probability based on the transient history of the dispersed gas cloud. The consistent methodology based on the CFD technology available in OpenFOAM and its ability to present the results in detail leverages the risk-based decision process. Measures that can be assessed quantitatively includes number and types of gas detectors and their optimal positioning, ignition source isolation, gas detection system voting philosophy, capacity of depressurization system and structural integrity of explosion barriers.
Flammable liquid
Transient (computer programming)
Minimum ignition energy
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It is a key step of quantitative risk analysis (QRA) to estimate ignition probability of flammable materials after leakage accidents. This paper reviews the available literature and expert opinion on how to evaluate and determine ignition probability value, and it was detailedly discussed on the main influencing factors of ignition probability, including flammable material properties, mass flow rate of flammable materials spillage, ignition resources and ignition controls. Moreover, the operational and practical ignition probability value could be estimated from the all way of classifications of flammable material, mass flow rate, ignition resources, hazardous areas and ignition prevention and control measure. Furthermore, the more practical ignition probability model was put forward that the ignition probability was the maximum value of the probability decided by material properties (PMP), mass flow rate(PQ) and ignition resources(PIS) with the factor of preventing and controlling ignition (KIC). Finally, the further research was proposed to assign some feasible weigh factors of the ignition probability for flammable materials after leakage accidents.
Flammable liquid
Spillage
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