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- Andersson, Petra
(författare)
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Evaluation and Mitigation of Industrial Fire Hazards
- 1997
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A tool suitable for conducting industrial fire and explosion hazard analysis is presented, together with an identification of weak links in the hazard evaluation chain. For some of the weak links additional research has been carried out. The tool, "FREIA", evaluates the consequences for humans and components due to fires and accidental releases indoors and outdoors using established engineering methods. Investigations have been carried out to find possible methods to simulate detector activation. The temperature, velocity, soot, CO2, CO and oxygen concentration were determined in the plume above a fire. Close agreement was found between the different compound fields. A CFD simulation of the same plume closely matched the experiments. However, there are large uncertainties involved when transforming light attenuation measurements into soot volume fraction. Simulations of tests according to the EN54 detector standard were also carried out. The agreement differed for different fuels. In addition, there is a problem with comparing light attenuation measurement performed at different wavelengths. All the results obtained indicate that it is possible to model smoke detector activation by treating the soot as an inert gas, or by assuming the soot concentration closely corresponds to one of the other compound fields. Heat detector activation is not as complicated to simulate. The phasing out of halons often demands new solutions in order to maintain the given protection level. More recently water mist has been mentioned as a possible replacement for halons. Experiments together with theoretical considerations have shown that no presently available water mist system fulfils the requirements of a total flooding system. A narrow window exists, however, in which a water mist can function as a total flooding system. Several halon-like agents have been developed. These, however, produce more thermal decomposition products than halons, the amount produced was found to be proportional to the amount of fuel burnt in the presence of the agent. In addition, experiments have shown that they can actually increase the fire instead of extinguishing it, if not properly designed. Estimating human burns is difficult; a test dummy for such measurements is presented.
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| 2. |
- Frantzich, Håkan
(författare)
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Uncertainty and Risk Analysis in Fire Safety Engineering
- 1998
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Two Quantitative Risk Analysis (QRA) methods are presented which can be used to quantify the risk to occupants in, for example, a building in which a fire has broken out. The extended QRA considers the inherent uncertainty in the variables explicitly. The standard QRA does not consider the uncertainties in the variables and must be complemented by a sensitivity analysis or an uncertainty analysis. Both methods provide risk measures, such as individual risk and FN curves. In the extended QRA these are presented in terms of statistical distributions. The standard QRA is more simple to perform and has been used extensively in many engineering fields. Both QRA methods have been applied to an example, structured with the event tree technique, to determine the risk to patients on a hospital ward. In addition to the two risk analysis methods, separate uncertainty analysis methods are also presented. Both stochastic uncertainty and knowledge uncertainty are considered in the analysis, separately and combined. The importance of the variables is also investigated. As both QRA methods are rather complex to use, a more simple method using design values in deterministic equations would be preferable for fire safety design purposes. A method of deriving these design values, based on quantified risk, is presented and complemented with an example which provides design values for a class of buildings. When these design values are known, so-called partial coefficients can be derived.
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| 3. |
- Ingason, Haukur
(författare)
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Experimental and Theoretical Study of Rack Storage Fires
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- A theoretical and experimental study of rack storage fires and responsiveness of sprinklers is presented. Free-burn tests with non-combustible and combustible material were carried out in reduced scale with verification in large scale. Formulas for in-rack flame height, excess gas temperature, gas velocity and heat flux to storage walls are provided. The formulas include overall heat release rate, vertical flue width, height above the floor, height of virtual origin and sootiness of fuel. They can be used to predict activation times of in-rack sprinklers and it is possible to directly incorporate them into engineering models designed to predict fire growth in storage geometries.The storage arrangement is important for the initial flame spread and fire growth rate. The reduced scale study shows that the initial fire growth rate decreases with increasing vertical gaps (flues) and that the vertical and lateral flame spread rate increase when the lateral flue height increases. The fire growth rate of rack storages is usually described by a power law dependence on time to the third power. The large scale test shows, however, that the initial fire growth rate is better described by an exponential function.The present work provides measurements of the heat flux distribution at the surface of four square steel towers representing an idealisation of a rack storage at reduced scale. Three gaseous fuels, carbon monoxide (CO), propane (C3H8), and propylene (C3H6) were supplied from a circular gas burner at the floor. The fuels were chosen to cover a wide range of sooting tendencies leading to distinctly different flame heat fluxes. The differences are surprisingly large. For the same overall fire heat release rate the peak heat flux from C3H8 flames is twice that from CO flames, whereas the peak heat flux from C3H6 is 2.8 times greater than from CO flames. The heat fluxes were measured by thermocouples spot-welded onto the backside of the exposed steel tower sheets. The measuring technique was found to be simple, accurate and rugged in addition to being inexpensive.
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| 4. |
- Yan, Zhenghua
(författare)
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Numerical Modeling of Turbulent Combustion and Flame Spread
- 1999
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Theoretical models have been developed to address several important aspects of numerical modeling of turbulent combustion and flame spread. The developed models include a pyrolysis model for charring and non-charring solid materials, a fast narrow band radiation property evaluation model (FASTNB) and a turbulence model for buoyant flow and flame. In the pyrolysis model, a completely new algorithm has been proposed, where a moving dual mesh concept was developed and implemented. With this new concept, it provides proper spatial resolution for both temperature and density and automatically considers the regression of the surface of the non-charring solid material during its pyrolysis. It is simple, very efficient and applicable to both charring and non-charring materials. FASTNB speeds up significantly the evaluation of narrow band spectral radiation properties and thus provides a potential of applying narrow band model in numerical simulations of practical turbulent combustion. The turbulence model was developed to improve the consideration of buoyancy effect on turbulence and turbulent transport. It was found to be simple, promising and numerically stable. It has been tested against both plane and axisymmetric thermal plumes and an axisymmetric buoyant diffusion flame. When compared with the widely used standard buoyancy-modified model, it gives significant improvement on numerical results. These developed models have been fully incorporated into CFD (Computational Fluid Dynamics) code and coupled with other CFD sub-models, including the DT (Discrete Transfer) radiation model, EDC (Eddy Dissipation Concept) combustion model, flamelet combustion model, various soot models and transpired wall function. Comprehensive numerical simulations have been carried out to study soot formation and oxidation in turbulent buoyant diffusion flames, flame heat transfer and flame spread in fires. The gas temperature and velocity, soot volume fraction, wall surface temperature, char depth, radiation and convection heat fluxes, and heat release rate were calculated and compared with experimental measurements. In addition, to provide comprehensive data for comparison, experiments on room corner fire growth were undertaken, where the gas temperature, solid fuel surface temperature, radiative heat flux, char depth and heat release rate were all measured.
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| 9. |
- Plos, Mario, 1963, et al.
(författare)
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Nonlinear FE Analyses of RC Bridge Frame Corners, Based on Fracture Mechanics
- 1998
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Ingår i: Journal of Bridge Engineering. - 1084-0702. ; 3:4, s. 204-209
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Tidskriftsartikel (refereegranskat)abstract
- Reinforced concrete frame corners were analyzed using the nonlinear finite-element method and fracture mechanics. The objective of the study was to determine whether the reinforcement detailing in frame bridges could be simplified, with preserved structural safety, by splicing the reinforcement within the frame corner. A constitutive model for concrete, based on nonlinear fracture mechanics and plasticity, was used. An interface model was used to account for slip between the reinforcement and surrounding concrete. Analysis of previously tested frame specimens, with both spliced and unspliced corner reinforcement, was used to study the overall behavior of the frames; more detailed analysis of only the frame corner regions was used to study the influence of the reinforcement splices. The analyses were found to reflect the mechanical behavior of the specimens, and are in good agreement with the test results. The analysis results support, together with the test results, the idea that it would be feasible to splice all reinforcement in a portal frame bridge within the corner regions.
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