VII Международная студенческая научная конференция Студенческий научный форум - 2015

The concept of fire safety is not static, but on the contrary are continuously updating and developing the accumulation of knowledge about the nature of the fire. Understanding under the system of fire safety of the complex of organizational and technical solutions, assumes obligation sharing requirements of fire safety, analytical methods for their study and systematic approach in the decision of problems of maintenance of fire safety. The kernel of analytical methods with a systematic approach to maintenance of fire safety is the mathematical model of a fire.

Fire models can be classified as zone models or field models. Zone models are normally made up of two zones (a hot upper layer and a cooler lower layer). Field models allow you to specify for any moment of the development of fire values of all local state parameters in all the points of space inside.

The purpose of this study is to examine some differences and amalgamations between combined effects on a structural system from multiple fires and “local” explosions. Here are some areas of similarities and differences between fire and explosion [1].

Similarities	Differences
1. Both of them have periods of ignition.	1. Non-dimensional parameters are different.
2. Both of them have a self ignition period.	2. Non-dimensional parameters characterizing self ignition are different.
3. Thermodynamics can be described by similar parameters in both cases.	3. Fire type is defined by the quantity of flammable material, size and locations of the windows in the building.
4. Hydrodynamics of both processes are described.	4. Using so-called “opening factor F” in case of fire, and similar parameter “Kv”.
6. The temperature time curves as a function of the opening factor Kv (“F” – in case of fire) had been developed.	5. Based on heat release rate the fire can be classified as slow, medium and fast
7.The total energy has a quasi-dynamic effect on structural system, depending on the period of ignition or the flash-over period in case of fire.

The problem of evaluation of critical regimes thought of as regimes separating the regions of explosive and non-explosive ways of thermo-positive chemical reactions are the main mathematical problem.

International code requirements

Analytical methods in comparison with requirements of the standards give more information and allow for more informed decision on protecting the buildings from fire. Behavior of structures under fire depends on a number of variables. These include the destruction of a material at high temperatures and preserve rigidity around a fire compartment.

Structural fire load design

Consider nonlinear singularly perturbed parabolic system (1) [2], [3].

(1)

First two equations are describing the heat and mass transfer, the second two – the Navier-Stokes equations – describe the motion of fluid substances that is substances which can flow. They are one of the most useful sets of equations because they describe the physics of a large number of phenomena of academic and economic interest.

In case of structural fire design loads these equations can be further simplified based on the following assumption.

1) Thermal properties such as conductivity, specific heat, density, and other physical parameters for all practical purposes can be assumed constant and the values shell be taken at the maximum temperature. This practice has been used for many years in theory of explosion and combustion [4], and it will allow to obtain the solution of Navier-Stokes equations separately from the energy conservation equations;

2) The pressure in the compartment is assumed to be equal to the atmospheric pressure, because the windows in the compartment are open (the grasses are broken), therefore the derivatives of pressure are zero;

3) The Navier-Stokes equations should consider the low-speed, thermally-driven flow with an emphasis on heat transport from fires. This assumption rules out the scenario involving flow speeds approaching the speed of sound, such as in case of explosion and detonation;

4) Irradiative heat transfer isincluded in the model via heat losses thought the open compartment’s windows, and it is based on the Stefan-Boltzmann law [10];

Thus, the results of approximate solution of the differential equations of Navier-Stokes equations, which allows to determine the quantity of fuel combusted in the room to achieve the temperature set point and to get the dimensionless temperature-time curve fire.

Examples

	Examples№1	Examples№2	Examples№3
Data	T* = 600°K; δ=20; KV=0.05; β=0.1; P=0.157; 0

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