Fire ScenarioInfluence of Material of Boundary Condition on

Results

Luciano Nigro – Andrea Ferrari – Elisabetta FilippoHughes Associates Europe srl – Jensen Hughes EU Alliance - info@hae.it

HUGHES ASSOCIATES EUROPE, srl FIRE SCIENCE & ENGINEERING

Performance-Based Design Process

SFPE Engineering Guide to Performance-Based Fire Protection defines the main steps of design process:1. Defining project scope: identifying goals.2. Developing fire scenarios: with determinist and statistic

analysis 3. Developing trial designs: quantifying design fire curves,

evaluating trial designs.

Developing of Fire Scenario

Events description represents the fire scenario. The events aredescribed with three main aspects:

1. Characterization of the fire – HRR curve, yield of soot or fireproducts;

2. Boundary condition of the internal or external ambient;3. Characterization of occupant.

Developing of Fire Scenario 2The definition of boundary condition of the domain is the way thebuilding characteristics are an input for the model.

• In particular:i. Dimension/characteristicii. Natural/mechanical ventilationiii. Thermodynamic characteristics of the enclosureiv. Detection systemv. Alarm systemvi. Protection system

Developing of Fire Scenario 3

The focus of the study being presented today is:

Influence of physical characteristic of domain on results ofanalysisNamely:Influence of thermal conductivityInfluence of density and transmittance

Why the Boundary Conditions Are a Problem

Main steps for characterization of fire in a fire model are:• Chemical composition of

material;• Heat release rate curve;• Yield of soot or fire

products;• Area of fire.

In a new building project, the type and/or thecharacteristics of materials that will be used toactually “make” the building are often not defined atthe time when the performance based analysis isconducted.

It is important to understandhow the boundary conditionsinfluence the results of thequantitative analysis.

Object of the Study

• To measure the effect of different boundary conditions on the results that can be achieved by the model when applied to a simple case study

• Elisabetta will show the case study and the results that were obtained.

The ModelReal geometry of hotel atrium• Rectangular plane 13,2 x

18,8 m• Prismatic roof: maximum

high 6,4m• Open door 1,2 x 2,2 m

The Model

Input Parameters – HRR CurveFour different typical fires in a hotel atrium:

• 0,5 MW • Laptop • Christmas tree

• 1,0 MW • Sofa• Metal office storage units clear aisle

• 2,0 MW • 12 chairs in 2 stacks • Kiosk

• 9,0 MW • Flashover

Input Parameters – HRR Curve

• 0,5 MW • Laptop • Christmas tree

[Rif: Morgan J. Hurley, The SFPE Handbook of Fire Protection Engineering, Fifth Edition, 2015]

Input Parameters – HRR Curve• 1,0 MW

• Sofa • Metal office storage units clear aisle

[Rif: Morgan J. Hurley, The SFPE Handbook of Fire Protection Engineering, Fifth Edition, 2015]

T. Stainhaus, W. Jahn, Laboratory Experiments and their applicability,– The Dalmarnock Fire tests: Experiments and Modelling – University of Edinburgh 2007

Input Parameters – HRR Curve

• 2,0 MW • 12 chairs in 2 stacks • Kiosk

[Rif: Morgan J. Hurley, The SFPE Handbook of Fire Protection Engineering, Fifth Edition, 2015]

Input Parameters – HRR Curve

• 9,0 MW • Flashover

[Rif: Morgan J. Hurley, The SFPE Handbook of Fire Protection Engineering, Fifth Edition, 2015]

Input Parameters – HRR CurveThe analysis is on steady state condition. The HRR curve is constant over a period of simulation

[Rif: Morgan J. Hurley, The SFPE Handbook of Fire Protection Engineering, Fifth Edition, 2015]

Input Parameters – Boundary ConditionThe definition of material of ceiling is the characterization ofboundary condition.Floor and external walls are in adiabatic condition.

Convective thermal exchange ispossible through the ceiling only.

Input Parameters – Boundary ConditionCeiling boundary conditions are:

2. Glass

• density 3100 kg/m3

• specific heat 0,84 kJ/kg°K• conductivity 0,064 W/m°K• thickness 4 cm

3. Concrete

• density 2000 kg/m3

• specific heat 0,88 kJ/kg°K• conductivity 2 W/m°K• thickness 14 cm

Input Parameters – Boundary ConditionTwo basic cases are considered in order to have a comparison with conditions that are generally accepted for the boundary conditions:

Case 1:• adiabatic boundary condition:• Ideal condition, not real. All materials of the boundary are adiabatic.

The whole heat is kept inside the domain because there is no heat transfer with the external ambient.

Input Parameters – Boundary Condition

Second case:• adiabatic boundary condition with opening on ceiling:• All materials of boundary are adiabatic but there are openings

on the ceiling, which may be: the permanent openings, occasionally open windows, natural smoke and heat exhaust ventilators, or even a glass window that has crashed after a few minutes because of the high temperature.

Basic Case 1 – Adiabatic Boundary Condition

Adiabatic external walls: no heat transfer internal/external ambient.

Basic Case 2 – Adiabatic Boundary Condition with Opening on Ceiling

Openings

2% of total area (4,4 m2)

The first and most important parameter that was investigated with thisstudy is the temperature.

The variation of the gas temperature of the smoke layer is measured byusing two different detectors. Ceiling gas temperature is measured byusing detectors of temperature called thermocouples.Another detector is used to calculate the gas temperature. The name ofthis detector is slice.

Investigated Parameters 1/2

The second significant parameter, usually investigated when performingthis kind of studies, is the visibility, correlated to the soot produced by thefire.

It is possible to say that the variations in the visibility, as a consequenceof the variations of the boundary conditions, are negligible, whenchanging the different ceiling characteristics.

The visibility will not be further mentioned in the study.

Investigated Parameters 2/2

Output

Output

Table of Scenario A – B – C – D

Results Scenario A – Fire 0,5 MW – Changing Boundary Condition – Time 500 Seconds

Fire Safety Engineering Scenarios and boundary condition

Results Scenario A – Fire 0,5 MW – Changing Boundary Condition – Time 500 Seconds

Results Scenario B – Fire 1,0 MW – Changing Boundary Condition – Time 500 Seconds

Results Scenario B – Fire 1,0 MW – Changing Boundary Condition – Time 500 Seconds

Results Scenario C – Fire 2,0 MW – Changing Boundary Condition – Time 500 Seconds

Fire Safety Engineering Scenarios and boundary condition

Results Scenario C – Fire 2,0 MW – Changing Boundary Condition – Time 500 Seconds

Results Scenario D – Fire 9,0 MW – Changing Boundary Condition – Time 500 Seconds

Results Scenario D – Fire 9,0 MW – Changing Boundary Condition – Time 500 Seconds

Table of Scenario Concrete

Results Scenario Concrete – Fire 2,0 MW – Changing Boundary Condition – Time 500 Seconds

Results Scenario Concrete – Fire 2,0 MW – Changing Boundary Condition – Time 500 Seconds

• The results show how the characterization of material finishing influence thegas temperature.

• The variation of gas temperature value is more significant when the heatrelease rate of the fire is greater.

• The adiabatic condition for the ceiling is conservative, but it is important todefine the boundary conditions, in particular the materials of which shell orouter walls are constituted, not to neglect the thermal exchange with theexternal environment.

Conclusion

• It is important to define the boundary conditions not to neglect thethermal exchange with the external environment.

• The detailed characterization of the material has little influence. Themain temperatures of the scenarios with glass ceiling are not sodifferent when compared to the main temperature of the scenarios withconcrete ceiling.

Conclusion

• It is very important to know if there are openings within the domain orduring the evolution of the fire scenario, because the temperature ofsmoke layer changes dramatically when the internal domain andexternal environment are connected.

• The typical example is the breaking of the glasses

Conclusion

• SFPE Engineering Guide to Performance-Based Fire Protection, National Fire Protection Association, Quincy, MA (2006);

• B. McCaffrey, “Flame Height,” The SFPE Handbook of Fire Protection Engineering, 2nd ed., Society of Fire Protection Engineers and National Fire ProtectionAssociation, Quincy, MA, pp. 2-1–28 (1995);

• P.H. Thomas, “The Size of Flames from Natural Fires,” Ninth Symposium on Combustion, Combustion Institute, Pittsburgh, PA, pp. 844–859 (1963);

• Morgan J. Hurley, The SFPE Handbook of Fire Protection Engineering, Fifth Edition, 2015;

• McGrattan K., Klein B., Hostikka S., Floyd J., NIST Special Publication 1019-5, Fire Dynamics Simulator (Version 6) User’s Guide, NIST, Nov. 2013;

• McGrattan K., Hostikka S., Floyd J., NIST Special Publication 1018-5, Fire Dynamics Simulator (Version 5) Technical Reference Guide, Volume 1: Mathematical Model,NIST, Oct. 2008;

• Kevin McGrattan, Simo Hostikka, Randall McDermott, Jason Floyd, Craig Weinschenk, Kristopher Overholt. NIST Special Publication 1018-2 Sixth Edition FireDynamics Simulator Technical Reference Guide Volume 2: Verification, November 2015;

• Kevin McGrattan, Simo Hostikka, Randall McDermott, Jason Floyd, Craig Weinschenk, Kristopher Overholt. NIST Special Publication 1018-2 Sixth Edition FireDynamics Simulator Technical Reference Guide Volume 2: Validation, November 2015;

• Antonio La Malfa, Prevenzione incendi Approccio ingegneristico alla sicurezza antincendio 5a Edizione, Settembre 2007;

• Kai Kang, Assessment of a model development for window glass breakage due to fire exposure in a filed model, Fire Safety Journal, October 2008;

• U. Wickstrom, D. Duthinh, K. McGrattan, Adiabatic surface temperature for calculating heat transfer to fire exposed structures;

• EUROCODE 1 – Actions on structures - Part 1-1: General actions - Densities, self-weight, imposed loads for buildings, 2004 – Incorporating corrigendum March 2013.

References