Singapore Fire Safety Engineering Guidelines 2015_1.pdf

Ii deterministic models use interrelated mathematical

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(ii) Deterministic models use interrelated mathematical expressions based on physics and chemistry to describe a compartment fire. The most common type of Deterministic model is the zone model, which solves the conservation equations in control volume(s). The other type of Deterministic model which gains popularity is the field model, which solves the fundamental equations of mass, momentum and energy in control volumes in subdivided grids. (b) Zone Models (i) Zone models are designed to predict the conditions resulting from a fire in an enclosure. These models solve the equations based on the zone assumptions within an enclosure. It provides a faster and a more accurate estimate of fire conditions than manual calculations methods. Most of the zone models can be run on personal computers. It is relatively simplicity, which permits inclusion of more phenomena in a given zone model without becoming overwhelmed by complexity. This also means that it may run far more rapidly and inexpensive. (ii) It provides estimates of the fire conditions for each of the layers as a function of time. No zone model is the best for all applications. While most of the zone model are based on the similar fundamental principles, there is a significant variation features among the different zone models. The decision to use a model is dependent upon the understanding of the assumptions and its limitations for the particular model. Most importantly, the selected model must be validated with results comparing experiment data. (iii) Application and limitations: (1) Simple geometry that can be simplified into a simple box, best applies to an enclosure which dimensions (width and length) are similar. (2) Large compartment are to be divided into multiple virtual compartments Annex C1
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(3) Radiation effects is not a primary consideration factor in the design (4) Predicting sprinkler activation time and estimating ventilation rates (5) Not well suited for comprehensive analyses involving the time-dependant interactions of multiple physical and chemical processes in developing fires (6) Primarily one-dimensional, and divides the spaces of interest into a few zones (7) Analyses of zone models assume two layers of uniform temperature and conditions; a hot upper zone and a cooler lower layer. Interaction of smoke with localised smoke logged conditions is not addressed, i.e. compartment volumes are strongly stratified (8) Different zone models may yield quite a different results (9) Not accurate in modelling long corridors, very large compartments or compartment involve radiation feedback of energy (10) Smoke movement cannot be predicted (11) Cannot generate pictorial results that describes a more realistic fire conditions (iv) Zone models are intended to be used to review the smoke transport with a wide variety of fire scenarios. Some of the limits to the inputs in the softwares are reproduced from the various references and listed below. The list of softwares shown is not exhaustive with a few commonly used software for zone model presented. It is important to understand the physics and assumptions on which the software is based in order to evaluate and interpret the results.
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