Introduction to Fire Modeling. Anthony R. Cole, P.E., CFPS, CFEI

Transcription

1 Introduction to Fire Modeling Anthony R. Cole, P.E., CFPS, CFEI

2 Overview Basic concepts of fire dynamics What is a model? Types of fire models Benefits of models Selecting a model Modeling applications Examples

3 Basic Concepts of Fire Dynamics The fire source Plume concept Vent flows in a room fire

4 The Fire Source Fuel types Aspects of "flammability" Phases of fire development Fire growth characterizations Fire location factors HOUSE EAST GRAND STAIR Fast Growth Rate HEAT RELEASE RATE (KW) 3,000 2,500 2,000 1,500 1,000 FIRE SIZE (Design-case with sprinklers) TIME (min)

5 Fuel Types Furnishings 3 dimensional surfaces Fixed quantity of fuel Fixed initial dimensions Evaluation based on total product Finishes 2 dimensional surfaces Quantity depends on application Evaluation normalized per unit area

6 Fuel Types Other fuel types Hydrocarbons Polar Solvents Fuel properties Quantity/depth

7 Aspects of Flammability" "Ease of ignition" Rate of fire growth Peak fire size Burning duration TOTAL HEAT FLUX (kw/m^2) TIME (MIN) 140 STANDARD DEVIATION ROOM GAS TEMP (DEG. C) GAS TEMPERATURE HEAT FLUX STANDARD DEVIATION TOTAL HEAT FLUX (kw/m^2) TIME (MIN)

8 Phases of Fire Development 1. Incipient 2. Growth 3. Fully developed 4. Decay/burnout RELEASE RATE TIME

9 Fire Growth Characterizations Exponential Q = Q exp ( t - t ) / τ o o T-Squared Q t = α ( - ) t o 2 Triangular Q = β ( t - t o )

10 Fire Location Factors Fires in the open: k if = 1 Fires along walls: k if = 2 Fires in corners: k if = 4

11 Plume Concept Types of plumes Considerations of the fire plume

12 Types of Plumes Axisymmetric plumes Morton-Taylor-Turner Zukoski McCaffrey Heskestad Line plumes Lee & Emmons Balcony spill plumes Thomas Heskestad

13 Considerations of the Fire Plume Flame height Flame/plume temperatures Air entrainment in fire plumes Gas velocities in fire plumes Continuous Flame Height Flame Height (m) kw Time Step (1/30 s)

14 Vent Flows in a Room Fire Orifice flow theory - Bernoulli s equation Hydrostatic pressure profiles in room fires P o P i H o N D P o P i

15 What is a Model? A model is a mathematical tool used to represent a real-life situation. It can be a single equation solved with a calculator or a complex program requiring a powerful computer. Q Q Q Q Q = 0.5c = = = = A A A A o o o o p [ kw] H H H H A o o o o o H o 0.5c 4 4 ( T T ) + εσ ( T T )( 0.40A ) 4 4 ( T T ) + εσ ( T T ) 4 4 ( 0.5( 1)( ) + 0.5σ ( )( 0.40)( 50) ) ( ) kw m 2 K 4 ( 600) [ m] p gu gu gu minimum for gu f o T 0.40 A Ao H T o

16 Types of Fire Models Fire Effects Models Zone Field, CFD Egress Models Heat Transfer Models Other Computer Models DETACT FPETool

17 Fire Effects Models Zone Single Room - ASET Multi-room - CFAST, HAZARD I Field/CFD FDS Smartfire Design Fires (HRR)

18 Fire Effects Models - ZONE Upper and lower zones Zones have uniform temperature Mass flow between zones by: Plume Door jet HVAC system Many zone fire models: CFAST FAST FIRST Harvard code LAVENT

19 Fire Effects Models ZONE (example)

20 Fire Effects Models FIELD/CFD Large number of cells Solves Navier-Stokes equations for each cell Detailed simulation Approximation Time consuming (machine and human) Requires high powered computer (super computer) Large output Graphics intensive

21 Fire Effects Models CFD (example)

22 Fire Effects Models CFD (example)

23 Fire Effects Models CFD (example)

24 Egress Models Pathfinder (Rolf Jensen and Associates Proprietary) Exodus

25 Egress Models (Example)

26 Heat Transfer Models Steel and Concrete Assemblies Radiation, Convection, and Conduction E119 or specified exposures SAFIR Water cooling Dynamic structural analysis

27 Other Computer Models DETACT FPETool CFAST FASTLite ALOFT ASMET ASCOS JET LAVENT

28 Benefits of Models Provides insight into fire problems Cost savings over full scale tests Repeatability

29 Selecting a Model Provides needed output Simple vs. Complex Documentation/Validation Computational Capabilities Limitations

30 Selecting a Model - Limitations Governing Assumptions Validation Data (HRR, Thermo-physical Props.) Geometry (Aspect, Surfaces) User s Abilities Effect of Sprinklers

31 Selecting a Model - Limitations Garbage In, Garbage Out Geometry (Dimensions) Material Properties Design Fires Occupant Characteristics

32 Selecting a Model Regulatory Issues Qualifications of Modeler Documentation Limitations Assumptions Data Results Uncertainty/Safety Factors

33 Selecting a Model Regulatory Issues Peer Review/Contract Review Other Resources ICC Performance Code NFPA 5000 ASTM Standards SFPE Guides NIST

34 Selecting a Model Common Errors Used Beyond Limitations Bad Input Data Optimistic Egress Times Other

35 Modeling Applications Detector/sprinkler activation time Radiant ignition of a near fuel Tenability analysis People movement

36 Detector/Sprinkler Activation Time DETACT subroutine Developed to model heat detection devices Can be used as approximation for smoke detection devices Device location Rated activation temperature RTI (response time index) Fire growth rate

37 Radiant Ignition of a Near Fuel Susceptibility of target fuel to ignition Fire exposure size Distance from source to target

38 Tenability Analysis Smoke obscuration Temperature Thermal radiation Toxicity of gases

39 People Movement Actual time = modeled time x efficiency Modeled time: fluid flow analogy Effective width Flow density relationship

40 Examples/Case Study

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46 Examples/Case Study

47 Closing Thoughts Models don t solve EVERYTHING Models only tell you, what you tell them Right model, for the right job Not as easy as TV or Movies Validate, validate, validate

48 Thanks!!