Fire and Smoke Modelling – The Importance of Using a Suitable Tool - Vigne

7/31/2019 Fire and Smoke Modelling The Importance of Using a Suitable Tool - Vigne

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Gabriele Vigne, Philip Borowiec, Jimmy Jnsson.

Arup Fire

Combustion and Fire Dynamics, Santander, 20th October 2010.

Fire and Smoke Modelling

The Importance of Using a Suitable Tool


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Overview

Introduction

Overview of the most common Modelling Tools

Examples of Good Practice

Verification and ValidationTunnel Example

Conclusions


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Introduction

Fire and Smoke ModellingThe Importance of Using a Suitable Tool


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Introduction

Fire and Smoke Modelling is becoming an important part of Fire Safety

Engineering

Simple Hand-Calcs to Advanced Computer Simulations

Which model do what

Which one is suitable for the specific design pourpose

Knowledge and understanding of limitations

A number of factors should be considered when selecting a model for a

problem

Computational resources, time limitations, required level of accuracy,

appropriateness of governing equations


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Modelling Tools



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Modelling Tools

Algebraic Models

Based on empirical formulae or based on fundamental physics

Usually tailored for specific scenarios

Zone Models

Zone models divide the space into zones in which properties

(temperature, mass etc.) are considered to be uniform.

CFD Models

They numerically solve the Navier-Stokes equations in millions of control

volumes (zones).

More useful for complex spaces with a larger range of boundaryconditions, but require more resources and understanding

Relatively new


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Algebraic Models

Examples of problems/solutions


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Algebraic Models

Evacuation through a mall of a

shopping centre

Potential fire in a shopping unit

facing the mall corridor

Objective:

Estimate when untenable conditions occur due to

radiation

Recommended width of the corridor

How can I solve this?


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Algebraic Models

The problem can be solved with the Configuration Factor

equation

Minimum distance required to achieve tenable conditions with a

maximum radiation tolerable (e.g. 2.5kW/m2 )

where:

= Stefan Boltzmann coefficient

T = Absolute Temperature

and = Angles between radius vector r and

infinitesimal areas dF1 of radiation and dF2 of a receptor

located in the origin


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Zone Models



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Zone Models

Smoke control assessment

for a small compartmentnatural ventilatated on the

roof

Objective:

Estimate the smoke layer height

Estimate the average smoke layer temperature

How can we solve the problem?


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Zone Models

The problem can be solved with a

zone model

The compartment is divided into

two uniform layersa relatively

hot layer, and a relatively cold

layer.

The interface (height) between hot

and cold layer can be calculated

The average temperature of thesmoke layer can be calculated as

well


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Zone Models

Through derivation of a set of equations using the ideal gas

law, the conservation of mass and the conservation of energy,quantities such as the pressure, layer height and temperatures

can be found given the accumulation of mass and enthalpy in

each layer


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CFD Models



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CFD Models

The validity of Algebraic and Zone Models can exceed,

particularly on larger scale projects or those whose design

pushes the limits of prescriptive based design

CFD modelling might be the only way to solve the problem


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CFD Models

Natural smoke control

assessment to guarantee safe

egress of the occupants

Large enclosure (80,000 m)

with a large double spill

plume.

Objective:

Keep the smoke layer

height above theoccupants at a certain

temperature


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CFD Models

The problem can be solved with CFD

modelling

Modelling performed with FDS

FDS was made and validated for this type

of scenario (large enclosures)


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Verification and Validation

FSB 2009


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How do we know if the model chosen is appropriate?


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Full scale fire tests in a tunnel

Validation and verification of a CFD model

Comparison between CFD and Zone models


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Zone model n.1. Space modelled as a

single compartment

Zone model n.2. Space modelled asmultiples compartments

Field model. 3 models with 3 differents

mesh resolutions


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Conclusions



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Conclusions

The large availability of tools (from the basic to the more sophisticated)available to the Fire Engineer has spawned a specific field within the Fire

Safety Engineering discipline

The potential misuse of such powerful tools is not sufficiently discussed

within the Fire Engineering community but nonetheless forms a veryimportant part of the Fire Engineering industry.

Of perhaps greater importance than the engineering tools themselves is their

appropriate use, the understanding of the limitations, the interpretation of the

results and how the results can be included in a more complex Fire

Engineering performance based analysis.


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Conclusions

This paper has attempted to highlight the importance of the Engineersunderstanding of the tools used in Fire Safety design, particularly a

knowledge of when the use of such tools is appropriate or not.


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Vigne G., Borowiec P., Jnsson J.

Combustion and Fire Dynamics, Santander, 20th October 2010.

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Fire and Smoke Modelling – The Importance of Using a Suitable Tool - Vigne