An Introduction to the Uses and Limitations of CFD Modeling for Solving Fire Safety Problems in DOEI

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An Introduction to the Uses and Limitations of
CFD Modeling for Solving Fire Safety Problems in
DOE/Industrial Type Facilities

• Jason E. Floyd, Ph.D.
• 2003 Fire Safety Workshop _at_ PANTEX
• April 29 May 2, 2003

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Please Note

• This presentation contains several animations.
  The animations have been removed to reduce file
  size for downloading. If you would like to
  receive a copy of the presentation complete with
  animations, please contact Jason Floyd at
  410-737-8677.

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DOE Order 420.1

• Basic DOE objectives of fire protection programs
  are to minimize
• Occurrences of fires or related events
• Releases impacting health and environment both
  onsite and offsite
• Interruption of vital DOE programs
• Excessive property loss
• Damage to safety class systems or critical
  process controls

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Implementation Guide for Order 420.1

• Use of NFPA or other recognized codes
• Complete and comprehensive analysis may support
  equivalent systems
• Unique facilities, nuclear facilities, other high
  risk facilities require an FHA
• Recognized that needs of many DOE facilities are
  not adequately addressed by current codes

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DOE Need For Fire Modeling

• To determine code equivalence for fire protection
• Evaluate fire risks of unique DOE facilities
• Quantitative support of hazard analyses

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Methods of Analysis

• Hand Calculations/Handbooks
• Fast, large experience base
• Large uncertainties, limited applications
• Lumped Parameter/Zone Model
• Fast, accepted use, entire buildings
• No local values, geometry restrictions
• CFD
• Local values, arbitrary geometric complexity,
  lowest level of empiricism.
• Steep learning curve, slow

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Why CFD?
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The Ability to Give Local Information
AFFF Hose Reels
Carrier Hangar Bay Fire
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Complex Geometries
3 MW Lube Oil Fire in a Containment Building (HDR
Test 52.14)
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Fire Dynamics Simulator (FDS)

• Developed by NIST Building and Fire Research
  Laboratory
• Companion software called Smokeview for
  viewing/animating FDS output
• Large eddy simulation (LES)
• Single parameter mixture fraction
• Gray gas, finite volume radiation heat transfer
• 1D heat conduction through surfaces

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Additional FDS Capabilities

• Multi-block grids
• Ignition of remote objects
• Pool fires with calculated heat release rates
• Fire spread and growth over solid fuels
• Droplets
• Fuel spray fires
• Conventional sprinklers
• Mist sprinklers
• Fire suppression by oxygen depletion and fuel
  cooling or delivered water

Level of physical detail in submodels may not
support its use for all applications
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Mixture Fraction Surface
Virginia Tech Fire Compartment
FDS v2 Simulation
400 kW propane fire in a 50-scaled ISO-9705
Compartment
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Multiblock Grids

• Multiple computational grids
• Can have different node sizes
• Reduction of active grid cells at the expense of
  more complex boundary conditions

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ISO-9705 Corner Fire
FDS v3
Lattimer et al., 1999
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Methanol Pool Fire
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Heptane Pool, Thin Steel Wall/Floor
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Remote Ignition

• Compartment
• 4 m x 4 m x 2 m
• 2 m x1.5 m vent
• Marinte walls
• 1 m x 1 m kerosene pool fire along wall opposite
  door
• 0.5 m x 0.5 m x 0.5 m PMMA block in corner

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Cost Reduction of Experiments

• Pre-test computations for experimental design
• Given a benchmarked experiment, perform
  parametric studies in a neighborhood of the
  experiment

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Sprinkler Activation(McGrattan and Stroup, 1997)
671
Draft Curtain
Sprinklers w/10 Spacing
4x8 Roof Vent
712
4.5 MW Heptane Spray Fire
Time to Activate
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Droplet Evaporation andRadiation Attenuation
Hot Wall
Cold Wall
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Water Mist System Discharge(Hunt, Floyd, and
Cutonilli, 2003)

• 1.2 MW heptane fire
• Two LN26 Spray Systems nozzles
• PDA area of the ex-USS Shadwell

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Consequences

• Smoke spread/fallout
• Brand lofting

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High Pressure Discharge of Flammable Liquid (Oil
Well Blowout)
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Limitations

• Requires a knowledgeable user
• Grid generation
• Defining material properties
• Defining boundary conditions
• Aware of proof by pretty picture danger
• Current mixture fraction combustion model
• Does not lend itself to predicting extinguishment
• Does not properly account for vitiated fires
• Only represents a single fuel
• Difficult to quantify fire properties of solid
  materials

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Limitations

• Large inaccuracies in near-field heat feedback to
  fuel makes spread and growth predictions for
  solid fuels difficult if not impossible
• No structural failure submodels though obstacles
  can be created/removed
• Sprinklers
• Difficult to quantify spray characteristics
• No droplet breakup, condensation, or surface
  wetting submodels (assumes uniform sheet)
• Resolution vs. available time (double the nodes
  per side 16 fold increase in time)

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Potential Benefits for DOE of CFD Modeling

• Avoid under-design of fire protection
• Reduce conservatisms in risk assessments for
  unusual spaces
• Examine cost vs. benefits of passive fire
  protection features (separation distance, heat
  shields, etc.)
• Evaluate protection system design for mission
  critical or one-of-a-kind equipment and public
  safety for applications where no code guidance is
  available