fire modelling
TRANSCRIPT
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Fire Modelling
Joakim SandstromLulea, 13th-15th of March 2014
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Introduction
• Smoke management depends strongly on geometry
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Introduction
• Smoke management depends strongly on geometry→ hard to standarise
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Introduction
• Smoke management depends strongly on geometry→ hard to standarise→ Prescriptive design often impossible
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Introduction
• Smoke management depends strongly on geometry→ hard to standarise→ Prescriptive design often impossible
• Engineering solutions needed!
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Introduction
• Smoke management depends strongly on geometry→ hard to standarise→ Prescriptive design often impossible
• Engineering solutions needed!
• This is where Fire Modelling comes into play
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Decisions to be made
• What kind of Fire Model?
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Decisions to be made
• What kind of Fire Model?• 0-D – Empirical Correlations (e.g. Heskestad’s
Plume Model)
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Decisions to be made
• What kind of Fire Model?• 0-D – Empirical Correlations (e.g. Heskestad’s
Plume Model)• 1-D – Zone Model
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Decisions to be made
• What kind of Fire Model?• 0-D – Empirical Correlations (e.g. Heskestad’s
Plume Model)• 1-D – Zone Model• 3-D – Computational Fluid Dynamics (CFD)
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Decisions to be made
• What kind of Fire Model?• 0-D – Empirical Correlations (e.g. Heskestad’s
Plume Model)• 1-D – Zone Model• 3-D – Computational Fluid Dynamics (CFD)
• What fire?
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Decisions to be made
• What kind of Fire Model?• 0-D – Empirical Correlations (e.g. Heskestad’s
Plume Model)• 1-D – Zone Model• 3-D – Computational Fluid Dynamics (CFD)
• What fire?→ Design fire based on use, geometry and fire load
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That being said....
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That being said....
The choice of Fire Model is not necessarily exclusive. Youmight need to use CFD and still use correlations.
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That being said....
The choice of Fire Model is not necessarily exclusive. Youmight need to use CFD and still use correlations.
Design fire need engineering judgement!→ There is no single solution..
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Design Fires
CIBSE Guide E
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Design Fires
• Most accepted growth model: t2-fire
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Design Fires
• Most accepted growth model: t2-fireQ = αt2
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Design Fires
• Most accepted growth model: t2-fireQ = αt2
• α depends on type of fuel
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Design Fires
• Most accepted growth model: t2-fireQ = αt2
• α depends on type of fuel→ Categorised according to use: office, storage,
dwellings etc.
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Design Fires
• Most accepted growth model: t2-fireQ = αt2
• α depends on type of fuel→ Categorised according to use: office, storage,
dwellings etc.
• Maximum Q depends on amount of fuel, or ventilationconfiguration
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Design Fires
• Most accepted growth model: t2-fireQ = αt2
• α depends on type of fuel→ Categorised according to use: office, storage,
dwellings etc.
• Maximum Q depends on amount of fuel, or ventilationconfiguration→ Engineering judgement..
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Design Fires
CIBSE Guide E
Karlsson – Enclosure Fire Dynamics
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Design Fires
CIBSE Guide E
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Design FiresThe maximum Heat Release Rate (Qmax) and fire duration haveto be estimated according to the following criteria:
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Design FiresThe maximum Heat Release Rate (Qmax) and fire duration haveto be estimated according to the following criteria:
• Ventilation condition (if flashover occurred)
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Design FiresThe maximum Heat Release Rate (Qmax) and fire duration haveto be estimated according to the following criteria:
• Ventilation condition (if flashover occurred)
• Total fuel load and Fuel density (if flashover hasn’toccurred)
![Page 28: Fire Modelling](https://reader033.vdocuments.us/reader033/viewer/2022052310/6289aa599510f312885e9f52/html5/thumbnails/28.jpg)
Design FiresThe maximum Heat Release Rate (Qmax) and fire duration haveto be estimated according to the following criteria:
• Ventilation condition (if flashover occurred)
• Total fuel load and Fuel density (if flashover hasn’toccurred)
• Engineering judgement
![Page 29: Fire Modelling](https://reader033.vdocuments.us/reader033/viewer/2022052310/6289aa599510f312885e9f52/html5/thumbnails/29.jpg)
Design FiresThe maximum Heat Release Rate (Qmax) and fire duration haveto be estimated according to the following criteria:
• Ventilation condition (if flashover occurred)
• Total fuel load and Fuel density (if flashover hasn’toccurred)
• Engineering judgement
Indications can be found in CIBSE Guide E, SFPE Handbookor NFPA.
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Some simple Calculations
2
Once we defined our Design Fire, Q(t), we can getestimations of important characteristics:
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Some simple Calculations
Once we defined our Design Fire, Q(t), we can getestimations of important characteristics:
• Air entrainment→ Volume of smoke
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Some simple Calculations
Once we defined our Design Fire, Q(t), we can getestimations of important characteristics:
• Air entrainment→ Volume of smoke
• Plume temperature
![Page 33: Fire Modelling](https://reader033.vdocuments.us/reader033/viewer/2022052310/6289aa599510f312885e9f52/html5/thumbnails/33.jpg)
Some simple Calculations
Once we defined our Design Fire, Q(t), we can getestimations of important characteristics:
• Air entrainment→ Volume of smoke
• Plume temperature
• Plume velocity
![Page 34: Fire Modelling](https://reader033.vdocuments.us/reader033/viewer/2022052310/6289aa599510f312885e9f52/html5/thumbnails/34.jpg)
Some simple Calculations
Once we defined our Design Fire, Q(t), we can getestimations of important characteristics:
• Air entrainment→ Volume of smoke
• Plume temperature
• Plume velocity
ment = E(
gρ2∞
T∞cp
)Q1/3c (z− z0)5/3 · [1 + GQ2/3
c(g1/2cpρ∞T∞)2/3(z−z0)5/3]
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Some simple Calculations
Once we defined our Design Fire, Q(t), we can getestimations of important characteristics:
• Air entrainment→ Volume of smoke
• Plume temperature
• Plume velocity
ment = E(
gρ2∞
T∞cp
)Q1/3c (z− z0)5/3 · [1 + GQ2/3
c(g1/2cpρ∞T∞)2/3(z−z0)5/3]
Tsmoke = T∞ + Qcmentcp
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Some simple Calculations
Once we defined our Design Fire, Q(t), we can getestimations of important characteristics:
• Air entrainment→ Volume of smoke
• Plume temperature
• Plume velocity
ment = E(
gρ2∞
T∞cp
)Q1/3c (z− z0)5/3 · [1 + GQ2/3
c(g1/2cpρ∞T∞)2/3(z−z0)5/3]
Tsmoke = T∞ + Qcmentcp
usmoke = 3.4 (g
ρ∞T∞cp
)1/3Q1/3c (z − z0)−1/3
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Why use Other Models?• For confined spaces, free plume correlations yield poor
results.
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Why use Other Models?• For confined spaces, free plume correlations yield poor
results.
• Heat transfer calculations from a fire to the structure.
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Why use Other Models?• For confined spaces, free plume correlations yield poor
results.
• Heat transfer calculations from a fire to the structure.
→ Requires more sophisticated models.
![Page 40: Fire Modelling](https://reader033.vdocuments.us/reader033/viewer/2022052310/6289aa599510f312885e9f52/html5/thumbnails/40.jpg)
Why use Other Models?• For confined spaces, free plume correlations yield poor
results.
• Heat transfer calculations from a fire to the structure.
→ Requires more sophisticated models.
→ If you need spatial resolution (e.g. location of exhaustoutlets, gas temperatures for heat transfer calculations),use field models (CFD).