Fire Scenario Influence of Material of Boundary Condition on Results HUGHES ASSOCIATES EUROPE, srl FIRE SCIENCE & ENGINEERING Luciano Nigro Andrea Ferrari Elisabetta Filippo Hughes Associates Europe srl Jensen Hughes EU Alliance - info@hae.it
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 are described with three main aspects: 1. Characterization of the fire HRR curve, yield of soot or fire products; 2. Boundary condition of the internal or external ambient; 3. Characterization of occupant.
Developing of Fire Scenario 2 The definition of boundary condition of the domain is the way the building characteristics are an input for the model. In particular: i. Dimension/characteristic ii. Natural/mechanical ventilation iii. Thermodynamic characteristics of the enclosure iv. Detection system v. Alarm system vi. Protection system
Developing of Fire Scenario 3 The focus of the study being presented today is: Influence of physical characteristic of domain on results of analysis Namely: Influence of thermal conductivity Influence 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.
It is important to understand how the boundary conditions influence the results of the quantitative analysis. In a new building project, the type and/or the characteristics of materials that will be used to actually make the building are often not defined at the time when the performance based analysis is conducted.
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.
Real 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
The Model
Input Parameters HRR Curve Four different typical fires in a hotel atrium: Laptop 0,5 MW Christmas tree Sofa 1,0 MW 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 Curve The 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 Condition The definition of material of ceiling is the characterization of boundary condition. Floor and external walls are in adiabatic condition. Convective thermal exchange is possible through the ceiling only.
Input Parameters Boundary Condition Ceiling boundary conditions are: density 3100 kg/m 3 2. Glass specific heat 0,84 kj/kg K conductivity 0,064 W/m K thickness 4 cm 3. Concrete density 2000 kg/m 3 specific heat 0,88 kj/kg K conductivity 2 W/m K thickness 14 cm
Input Parameters Boundary Condition Two 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 m 2 )
Investigated Parameters 1/2 The first and most important parameter that was investigated with this study is the temperature. The variation of the gas temperature of the smoke layer is measured by using two different detectors. Ceiling gas temperature is measured by using detectors of temperature called thermocouples. Another detector is used to calculate the gas temperature. The name of this detector is slice.
Investigated Parameters 2/2 The second significant parameter, usually investigated when performing this kind of studies, is the visibility, correlated to the soot produced by the fire. It is possible to say that the variations in the visibility, as a consequence of the variations of the boundary conditions, are negligible, when changing the different ceiling characteristics. The visibility will not be further mentioned in the study.
Output
Output
Table of Scenario A B C D
Results Scenario A Fire 0,5 MW Changing Boundary Condition Time 500 Seconds
Results Scenario A Fire 0,5 MW Changing Boundary Condition Time 500 Seconds Fire Safety Engineering Scenarios and boundary condition
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
Results Scenario C Fire 2,0 MW Changing Boundary Condition Time 500 Seconds Fire Safety Engineering Scenarios and boundary condition
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
Conclusion The results show how the characterization of material finishing influence the gas temperature. The variation of gas temperature value is more significant when the heat release rate of the fire is greater. The adiabatic condition for the ceiling is conservative, but it is important to define the boundary conditions, in particular the materials of which shell or outer walls are constituted, not to neglect the thermal exchange with the external environment.
Conclusion It is important to define the boundary conditions not to neglect the thermal exchange with the external environment. The detailed characterization of the material has little influence. The main temperatures of the scenarios with glass ceiling are not so different when compared to the main temperature of the scenarios with concrete ceiling.
Conclusion It is very important to know if there are openings within the domain or during the evolution of the fire scenario, because the temperature of smoke layer changes dramatically when the internal domain and external environment are connected. The typical example is the breaking of the glasses
References SFPE Engineering Guide to Performance-Based Fire Protection, National Fire ProtectionAssociation, Quincy, MA (2006); B. McCaffrey, Flame Height, The SFPE Handbook of Fire Protection Engineering, 2nd ed., Society of Fire Protection Engineers and National Fire Protection Association, 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 Fire Dynamics 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 Fire Dynamics 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.