Richard G. Gann, Ph.D.

Senior Research Scientist

Building and Fire Research Labo

National Institute of Standards and Tec

U.S. Department of Commerce

rggann@nist.gov

Federal Building and Fire Safety Inves

of the World Trade Center Disast

Reconstruction of the Thermal an

Environment

December 2, 2003
Project Objective Project Objective

Reconstruct, with assessed uncertainty limits, thtemperature, thermal radiation, and smoke fieldCenter buildings 1, 2, and 7 for use in evaluating and fate of occupants and responders and the sperformance of the buildings
Project Approach Project Approach

• Due to lack of physical evidence, we rely almos

• Computer simulations• Experiments• Photographic evidence• Eyewitness accounts

• Since this type of reconstruction has never been 

will be re-defining the state-of-the-art in fire and modeling

• Integrated with other Projects, esp. 2 and 6• Project 5 divided into 8 tasks
Tasks

1. Visual collection and time line development [Pitt2. Characterization of combustibles [Gann] 3. Characterization of partitions [Averill]4. Characterization of structural insulation [Yang]5. Fire model (FDS) development [McGrattan]6. Experiments for model development [Mulholland7. Fire reconstruction [McGrattan]8. Reconstruction validation [Hamins]

Total: 32 people
Input Information for Experiments 

Input Information for Experiments 

Modeling [Tasks 2,3] Modeling [Tasks 2,3]

• Sources of building information

• Some tenants, Port Authority of New York an

• Building combustibles, floor geometry, partition n• Aircraft contents (from airlines, Boeing)

• Jet fuel (mass and location), cabin combustib

contents

• Interim findings

• Mass of aircraft solid combustibles was signif

the mass of the building combustibles in the i

• View through many windows was blocked by 
Performance of Ceiling Tile System

Performance of Ceiling Tile System

• Premise: Dislodging of ceiling tiles removes a ba

flames and structural members

• Purpose: Learn about the reaction of the systems 

locations away from the direct aircraft impact)

• Shake table experiments performed at University 

collaboration of Armstrong World Industries

• Tile systems very much like those in tenant a

spaces

• Varied intensity and nature of impulse pattern

• Interim finding: Impulses like those estimated fro

caused serious damage to the ceilings, enabling transport over the walls and to the joists
Performance of Ceiling Tile System

Performance of Ceiling Tile System

1.25 g single pulse 1.25 g comp
Condition of Spray Condition of Spray

-on Insulation [4

on Insulation [4

• Initial Condition

• Compiled requirements and history• Examining buildings for thickness variability

• Measurements of thermal properties• Measurements of mechanical properties
Thermal Properties of Insulation M

Thermal Properties of Insulation M

• Purpose: Obtain input data for modeling the heat 

fires to the structural members

• Materials

• Spray-on insulation (3 types) used in all 3 bui

25 

°C to 1200 

°C 

• Gypsum sheet (4 types): 25 

°C to 600 

°C 

• Measurements using adapted ASTM methods

• Thermal conductivity• Density• Heat capacity

• Samples currently at test labs
Mechanical Properties of Insulatio

Mechanical Properties of Insulatio

[4]

• Purpose: Enable estimation of the extent of dama

structural members resulting from impact of aircr

• Materials

• Spray-on insulation (2 types) used in WTC 1 

• Measurement using custom and ASTM methods

• Cohesive properties: sheer strength and tens

• Bond strength to steel substrates

• Development of simple models to predict dislodg• Work currently underway
Modeling of Thermal Transport Th

Modeling of Thermal Transport Th

Insulation [4,5] Insulation [4,5]

• Different time and dimension scales for FDS (CF

ANSYS (FE thermostructural model)

• Developed novel method for communicating resu• Performed simulations of heat transfer for varying 

thermal insulation

• Reduced thickness• Bare spots

• Determined time to weakening temperature of ste• Accuracy from comparison with data from insulat• Finding: Small areas of thin or missing insulation 

accelerated heating over much larger lengths of 
Modeling of Thermal Transport Th

Modeling of Thermal Transport Th

Insulation on a Heavy Column [5,7

Insulation on a Heavy Column [5,7

• Intac

(

∼Bl

to rato 90

• Ran

20 %lost 

• Strip

at threac

1400 K Fire; photo @ 2 h
Fire Dynamics Simulator (FDS) [5,7

Fire Dynamics Simulator (FDS) [5,7

• 3-D model• Fluid dynamics from Navier-Stokes equations• Combustion and flame spread

• Radiation-driven gasification of combustible• Combustion = stoichiometric mixture fraction

• Resolution: 0.1 m, 0.4 m• Previously validated for, e.g.,

• Tunnel fire temperatures• Sprinkler activation
Single Workstation Fire Experimen

Single Workstation Fire Experimen

• Purpose: use results to upgrade FDS• Combustible: single typical work station• Conducted under a hood with a confined ceiling• Variables

• Presence of jet fuel• 30 % coverage by inert material

• Ignition by adjacent 2 MW spray burner• Measure heat release rate (HRR), sample mass, • Film fire progress• Materials thermophysical data from Cone Calorim
Single Workstation Burn [6] Single Workstation Burn [6]

0

2000400060008000

1 104

0 500 

Full Work S

Heat Release Rate (kW/m2)
Single Workstation Results [6] Single Workstation Results [6]

• Modeling at 0.1 m resolution• Peak heat release rate (HRR) ca. 6 MW at ca. 9 • Jet fuel accelerated peak to ca. 3 min, with little c• Inert material reduced peak HRR in proportion to 

coverage

• Finding: FDS reproduced the results without ada

• HRR(t) per test• Differences among tests

• Little need to tune FDS
Multiple Workstation Experiments 

Multiple Workstation Experiments 

• Purpose: Assess the accuracy of FDS in tests of • Three workstations: two contiguous, one separat• Large compartment with one wall mostly open• Variables:

• Presence of jet fuel• ca. 70 % coverage by inert material• Location of 2 MW ignition burner (ventilation)• Condition of workstation (assembled, rubble)

• Measure HRR, mass of each workstation, [CO], t

heat flux; video

• FDS predictions completed before experiments

• Resolution reduced to 0.4 m, same as for WT

reconstruction
Multiple Workstation Burn [8] Multiple Workstation Burn [8]

23 ft

4ft 4 ft

3 ft

1 ft 

5 ft

8.5 ft 20 "

equidistant Platform to 

 8.5 PLPL

PLATFORM 3
Multiple Workstation Burn Results 

Multiple Workstation Burn Results 

• Excellent • Noise is fr

both in the experimen

• Early HRR 

due to smcombustib

• Provisiona

be used wrecreate a event
Next Steps Next Steps

• Parametric variation of building conditions

• Aircraft damage or none (WTC 1& 2)• Ventilation• Fuel load and distribution• Location and state of partitions

• Comparison of results with visual evidence and v• Identification of most likely fire patterns• Interaction with thermostructural modeling

• Potential for building collapse from fires only• Identification of most likely collapse processe
Richard G. Gann, Ph.D.

Senior Research Scientist

rggann@nist.gov

Federal Building and Fire Safety Inves

of the World Trade Center Disast

Reconstruction of the Thermal an

Environment

Thank you