Fire simulation in compartments

Published: 25-11-2020| Version 1 | DOI: 10.17632/d45ktjgxz8.1
Contributor:
Sourabh Chowdhury

Description

Fire modelling for assess the impact of fires and the effectiveness of fire safety measures for building designs in performance-based design. Understanding of the processes involved in fire growth is improving and, thus, the technical basis for the fire models is improving. The capabilities, documentation, and support for a given fire model can change significantly over a short period of time. In addition, computer technology itself (both software and hardware) is advancing rapidly. In the past, a large mainframe computer was required to use most of the computer fire models. Today, the fire models can be run on personal computers. Computer models are simply computer programs that implement a mathematical model simulating a process or phenomenon. Computer models have been used for some time in the design and analysis of fire protection systems. Computer fire models are computer programs that implement a mathematical model simulating a process or phenomenon. Computer models have been used for some time in the design and analysis of fire protection systems, like sprinkler or gaseous agent suppression systems. Computer fire models, commonly known as design programs, have become the industry’s standard method for designing fire water supply, automatic sprinkler systems, and gaseous agent systems. These programs perform large numbers of tedious and lengthy calculations and provide the user with accurate, cost optimized designs in a fraction of the time required by manual procedures. Perhaps the most important attribute of computer fire models is their ability to predict the relevant fire behavior within their stated limitations. Models can be classified into two broad classes: (1) physical models and (2) mathematical models. Physical models attempt to reproduce fire phenomena in a simplified physical situation. Mathematical models are sets of equations that describe the behavior of a physical system. Mathematical models can be further classified into two classes: (1) Deterministic models and (2) Probabilistic models. Deterministic models are sets of equations that describe the behavior of a physical system. The resulting mathematical model can then be used to predict the behavior of real physical systems. Probabilistic models attempt to deal with the random nature of fire behavior, whereas deterministic models presume that, given a well-defined physical situation, fire growth and behavior are entirely determined.

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Peak fire size was about 5.2 MW with a volume of room 75 m3 and 168 m3. A fire test(s) was conducted in these compartments using wooden wall (compartment 2) and plastic material (concrete wall for compartment 1) with their free burning behavior. The compartments were provided with doors of 2m x 1m size open and equipped with vents shown. Fire was ignited at a time of 60 seconds and it’s in phase of steady burning period of 700 seconds and the oxygen level dropped by a percentage of volume. The fuel was wood wall (C6H10O5) & plastic material (C9H6O2N2) for the ignition, and the heat release rate 0.25 - 0.5 MW. For a constrained fire, the heat release rate (HRR) is limited by available oxygen. This limit is applied in three places: The first is burning in the portion of the plume which is in the lower layer of the room of fire origin; the second is the portion of the plume in the upper layer, also in the room of origin; the third is in the vent flow which entrains air from a lower layer into an upper layer in an adjacent compartment. Ignition of fires were chosen based on the compartment size and the material used in it. Exponentially growing fires, with rate of heat release of 0.5 MW, were assumed for each fire scenario. In compartments, the fire was assumed to grow exponentially, with a doubling time of 60 seconds until the calculated operation of the first sprinkler head (88 seconds in compartment 1) and smoke detector (5 seconds in compartment 1). The rate of heat release (HRR) was then assumed to drop suddenly to one-half of its value at that time and then to continue to grow exponentially, but more slowly, with a doubling and more time of 180 seconds. The area of the fire source was also allowed to increase such that the local rate of heat release (HRR) per unit area did not exceed 0.5 MW/m2. ** Pyrolysis is a chemical decomposition of a material into one or more other substance due to heat alone. All solid combustible must undergo pyrolysis in order to generate gaseous fuel vapors for flaming combustion. The process of converting a solid to gaseous vapors can take many physical paths depending on the chemical composition of the fuel. Cellulosic materials, such as wood, decompose directly to gaseous vapors when heated, such as wood, decompose directly to gaseous vapors when heated, leaving behind a residue. Pyrolysis is defined as a “process of simultaneous phase and chemical species change caused by heat,” with combustion being defined as “a chemical process of oxidation that occurs at a rate fast enough to produce temperature rise and usually light, either as a glow or flame.