Design: Performance: Fire Modelling

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		Introduction
		Fire Behaviour
		Norminal Fires
		Time Equivalence
		Parametric Fires
		Localised Fires
		External Window Fires
		Zone Models
		CFD

Fire Modelling

Fire model	Norminal fires	Time equivalences	Compartment fires		Zone Models		CFD / field models
			Parametric	Localised	One-zone	Two-zone
Complexity	Simple	Intermediate			Advanced
Fire Behaviour	Post-flashover fires			Pre-flashover fires	Post-flashover fires	Pre-flashover / localised fires	Complete temperature-time relationships
Temperature distribution	Uniform in whole compartment			Non-uniform along plume	Uniform	Uniform in each layer	Time and space dependent
Input parameters	Fire type No physical parameters	Fire load Ventilation conditions Thermal properties of boundary Compartment size		Fire load & size Height of ceiling	Fire load Ventilation conditions Thermal properties of boundary Compartment size Detailed input for heat & mass balance of the system		Detailed input for solving the fundamental equations of the fluid flow
Design tools	BSEN1991-1-2				COMPF2 OZone SFIRE-4	CCFM CFAST OZone	FDS SMARTFIRE SOFIE
	PD7974-1		PD7974-1
	Simple equations for hand calculations		Spreadsheet	Simple equations	Computer models

Figure 1 Options for fire modelling in compartments

Generally, the factors influencing the severity of a compartment fire can be summarised as follows:

Fire load type, density and distribution
Combustion behaviour of fire load
Compartment size and geometry
Ventilation conditions of compartment
Thermal properties of compartment boundary

The occurrence of flashover in a compartment fire imposes a transition to the fire development. Therefore, many fire models are classified under pre- or post-flashover, except for the computational fluid dynamic (CFD) models, which cover both phases.

There are a number of options available to calculate the fire severity as follows:

Standard/Nominal Fire Models – standard, external and hydrocarbon fires
Time Equivalences – relate standard fires to real fires
Parametric Fire Models – for post-flashover fires
Localised fires – for pre-flashover fires
External window fires – for fires through openings of fire compartment
Zone Models – one-zone models for pre-flashover fires – two-zone models for post-flashover fires
CFD or Field Models – for general fire and smoke modelling

The level of complexity increases from simple fire models to field models as shown in Figure 1. Basically, the first four fire models can be considered as simple models, whereas the zone and CFD models are advanced models. The input parameters for each of these models are quite different with the advanced models requiring very detailed input data and simple models requiring little input.

In the simple fire models, the gas temperature of a compartment is taken as uniform and represented by a temperature-time relationship. The smoke movement and fire spread cannot be considered. They are more suitable for modelling post-flashover fires.

The advanced fire models are normally theoretical computer models that simulate the heat and mass transfer process associated with a compartment fire. They can predict compartment gas temperatures in much more detail. The smoke movement and fire spread may be taken into account. As reflected in their names, a zone model may present the gas temperature into single or different zones, whereas a CFD model provides a space/field dependent gas temperatures distribution.

Each of the fire models will be discussed in the section.

Design
	Introduction
	Requirements
	Methodology
	Prescriptive
	Performance
	Educational Packages

Performance
	Fire Modelling
	Thermal Analyses
	Structural Analyses

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