Fire and Smoke Modelling – The Importance of Using a Suitable Tool - Vigne
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Transcript of 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
Fire and Smoke ModellingThe Importance of Using a Suitable Tool
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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
Examples of problems/solutions
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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
Examples of problems/solutions
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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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Verification and Validation
How do we know if the model chosen is appropriate?
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Verification and Validation
Full scale fire tests in a tunnel
Validation and verification of a CFD model
Comparison between CFD and Zone models
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Verification and Validation
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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Verification and Validation
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Conclusions
Fire and Smoke ModellingThe Importance of Using a Suitable Tool
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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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Fire and Smoke ModellingThe Importance of Using a Suitable Tool
Vigne G., Borowiec P., Jnsson J.
Combustion and Fire Dynamics, Santander, 20th October 2010.
Thanks