Evaluation of the Ability of Fire 

Dynamic Simulator to Simulate 

 Positive Pressure Ventilation 

in the Laboratory and 

Practical Scenarios

Stephen Kerber

NISTIR 7315

 

NISTIR 7315

Evaluation of the Ability of Fire 

Dynamic Simulator to Simulate 

 Positive Pressure Ventilation 

in the Laboratory and 

Practical Scenarios

Stephen Kerber

Building and Fire Research Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8661

April 2006

U.S. Department of Commerce

Carlos M. Gutierrez, Secretary

Technology Administration

Michelle O'Neill, Acting Under Secretary of

Commerce for Technology

National Institute of Standards and Technology

William A. Jeffrey, Director

Department of Homeland Security 

Michael Chertoff, Secretary

Federal Emergency Management 

Agency 

R. David Paulison, Under Secretary of 

Emergency Preparedness and Response 

U.S. Fire Administration 

Charlie Dickinson, Deputy Administrator
Evaluation of the Ability of Fire Dynamics Simulator to Simulate 

Positive Pressure Ventilation in the Laboratory and Practical Scenarios 

Stephen Kerber 

Abstract 

Positive Pressure Ventilation (PPV) is a tactic that is used on fire grounds worldwide 

everyday, both to improve tenability after the extinguishment of a fire and/or to improve 

firefighting conditions during fire attack. PPV has proven that it can be a useful tool on 

the fire ground, but if used improperly it can also kill or injure fire fighters and civilians. 

Data from three full-scale experiments are compared with simulations completed with the 

computational fluid dynamic model Fire dynamics simulator (FDS). The full-scale 

experiments characterize a PPV fan in an open atmosphere, in a simple room geometry 

and in a room fire. 

All experiments qualify and quantify the comparison of the experimental results with the 

FDS results. A concluding scenario is modeled utilizing the calibration of the full-scale 

experiments to examine the effects of PPV on a fire in a two-story, colonial style house. 

Disclaimer 

Certain trade names and company products are mentioned in the text or identified in an 

illustration in order to specify adequately the experimental procedure and equipment 

used. In no case does such identification imply recommendation or endorsement by the 

National Institute of Standards and Technology, nor does it imply that the products are 

necessarily the best available for the purpose. 
ii 

Acknowledgements 

The author would like to thank staff members of the Building and Fire Research 

Laboratory at NIST: William D. Walton, Daniel Madrzykowski, Kevin McGrattan, 

and Glenn Forney for their technical assistance and Robert Vettori, David Stroup, 

William Twilley, Roy McLane, Andrew Milliken, Jessica Naff, Laurean DeLauter, 

Ed Hnetkovsky, Jack Lee, Robert Anleitner, Jay McElroy and Alexander 

Maranghides for the support they provided during this set of experiments. In 

addition, the author expresses gratitude to the United States Fire Administration, part 

of the Department of Homeland Security, Robert McCarthy, Meredith, Lawler and 

William Troup for their support of this important research program. 

A special thank you to Dr. James Milke for guiding me through this process, and to 

Dr. Frederick Mowrer and Dr. Arnaud Trouve for participating as part of the advisory 

committee. 
iii 

Table of Contents 

Acknowledgements ..................................................................................................... ii

Table of Contents .......................................................................................................iii

List of Tables ............................................................................................................... v

List of Figures............................................................................................................. vi

Chapter 1: Introduction ............................................................................................. 1

1.1 Positive Pressure Ventilation ........................................................................ 1 

1.2 Fire Dynamics Simulator .............................................................................. 2 

1.3 Smokeview.................................................................................................... 3 

Chapter 2: Mapping the PPV Velocity Flow Field .................................................. 4

2.1 Experimental Description ............................................................................. 4 

2.1.1 Experimental Facility............................................................................ 4 

2.1.2 Experiment Components....................................................................... 4 

2.1.3 Experiment Procedure........................................................................... 7 

2.1.4 Flow Visualization Experiment ............................................................ 8 

2.2 Computer Simulation.................................................................................... 9 

2.2.1 Domain.................................................................................................. 9 

2.2.2 Geometry and Vents ............................................................................. 9 

2.2.3 Output Files......................................................................................... 10 

2.3 Results......................................................................................................... 11 

Chapter 3: Simple Room Experiment..................................................................... 16

3.1 Experimental Description ........................................................................... 16 

3.1.1 Experimental Facility.......................................................................... 16 

3.1.2 Experiment Components..................................................................... 16 

3.1.3 Experiment Layout.............................................................................. 17 

3.1.4 Experiment Procedure......................................................................... 18 

3.1.5 Flow Visualization Experiment .......................................................... 19 

3.2 Computer Simulation.................................................................................. 20 

3.2.1 Domain................................................................................................ 20 

3.2.2 Geometry and Vents ........................................................................... 22 

3.2.3 Output Files......................................................................................... 22 

3.3 Results......................................................................................................... 22 

3.4 Mapping and Simple Room Summary........................................................ 26 

Chapter 4: Room Fire Experiments........................................................................ 30

4.1 Experimental Description ........................................................................... 30 

4.1.1 Instrumentation ................................................................................... 33 

4.1.2 Fuel Load ............................................................................................ 37 

4.1.3 Procedure ............................................................................................ 44 

4.2 Experimental Results .................................................................................. 46 

4.2.1 Heat Release Rate ............................................................................... 50 

4.2.2 Room Gas Temperature ...................................................................... 53 

4.2.3 Doorway Gas Temperature................................................................. 55 

4.2.4 Window Gas Temperature .................................................................. 57 
iv 

4.2.5 Corridor Gas Temperature .................................................................. 59 

4.2.6 Room Differential Pressure................................................................. 61 

4.2.7 Window Gas Velocity......................................................................... 63 

4.2.8 Doorway Gas Velocity........................................................................ 65 

4.3 Computer Simulation.................................................................................. 67 

4.3.1 Domain................................................................................................ 67 

4.3.2 Geometry............................................................................................. 70 

4.3.3 Materials ............................................................................................. 70 

4.3.4 Vents and Ignition Source................................................................... 71 

4.3.5 Output Files......................................................................................... 72 

4.4 Simulation Results ...................................................................................... 72 

4.4.1 Naturally Ventilated Simulation ......................................................... 72 

4.4.2 Positive Pressure Ventilated Simulation............................................. 85 

4.5 Discussion................................................................................................... 96 

4.6 Room Fire Summary................................................................................... 98 

Chapter 5: Colonial House Practical Scenario.................................................... 100

5.1 Scenario Overview.................................................................................... 100 

5.2 Computer Simulations .............................................................................. 100 

5.2.1 Domain.............................................................................................. 100 

5.2.2 Geometry........................................................................................... 103 

5.2.3 Vents ................................................................................................. 107 

5.2.4 Materials ........................................................................................... 108 

5.2.5 Fire Source........................................................................................ 110 

5.2.6 Output Files....................................................................................... 110 

5.3 Results....................................................................................................... 111 

5.3.1 Fire Growth and Smoke Spread........................................................ 111 

5.3.2 Heat Release Rate ............................................................................. 114 

5.3.3 Temperature ...................................................................................... 115 

5.3.4 Oxygen.............................................................................................. 119 

5.3.5 Velocity............................................................................................. 123 

5.4 Colonial House Summary......................................................................... 128 

Chapter 6: Uncertainty.......................................................................................... 130

6.1 Experimental............................................................................................. 130 

6.2 Fire Dynamics Simulator .......................................................................... 133 

Chapter 7: Conclusion........................................................................................... 134

References................................................................................................................ 136
v 

List of Tables 

Table 1. Comparison of Experimental and FDS Velocity Mapping Results............. 11 

Table 2. Comparison of Experimental and FDS Simple Room Results.................... 23 

Table 3. Summary of FDS Characteristics Needed to Model the Fan Flow.............. 26 

Table 4. Summary of Multi-block Characteristics Needed to Model Simple Room 

Flow .................................................................................................................... 26 

Table 5. Fire Load Weights ....................................................................................... 38 

Table 6. Experimental Procedure............................................................................... 44 

Table 7. Observations ................................................................................................ 47 

Table 8. Room Fire FDS Input Material Properties................................................... 71 

Table 9. Colonial FDS Input Material Properties .................................................... 109 

Table 10. Mapping and Simple Room Experimental Uncertainty............................ 131 

Table 11. Room Fire Experimental Uncertainty...................................................... 132 
vi 

List of Figures 

Figure 1-1. Two Common PPV Fans........................................................................... 2 

Figure 1-2. PPV Cone of Air [4].................................................................................. 2 

Figure 2-1. The Flow Characterization Grid................................................................ 5 

Figure 2-2. Flow Visualization Threads ...................................................................... 5 

Figure 2-3. Front and Back of PPV Fan ...................................................................... 6 

Figure 2-4. Anemometer.............................................................................................. 6 

Figure 2-5. Anemometer in Indexer on Track ............................................................. 6 

Figure 2-6. Velocity Mapping Experimental Layout................................................... 7 

Figure 2-7. Velocity Mapping Measurement Points.................................................... 8 

Figure 2-8. Smoke Generator Flowing ........................................................................ 8 

Figure 2-9. Layout for Supplemental Experiment ....................................................... 8 

Figure 2-10. Visualization of PPV Flow...................................................................... 9 

Figure 2-11. Fan and Smoke Generator....................................................................... 9 

Figure 2-12. FDS PPV Fan Visualized in Smokeview.............................................. 10 

Figure 2-13. FDS Layout Visualized with Smokeview............................................. 11 

Figure 2-14. Fine Grid Cell Visualization ................................................................. 11 

Figure 2-15. Smokeview Visualization of FDS PPV Flow Pattern........................... 12 

Figure 2-16. Experimental Velocities 1.8 m (6 ft) From the Fan .............................. 13 

Figure 2-17. FDS Velocities 1.8 m (6 ft) From the Fan ............................................ 13 

Figure 2-18. Experimental Velocities 2.4 m (8 ft) From the Fan .............................. 14 

Figure 2-19. FDS Velocities 2.4 m (8 ft) From the Fan ............................................ 14 

Figure 2-20. Experimental Velocities 3.1 m (10 ft) From the Fan ............................ 15 

Figure 2-21. FDS Velocities 3.1 m (10 ft) From the Fan .......................................... 15 

Figure 3-1. Floor Plan of Simple Room .................................................................... 17 

Figure 3-2. Simple Room Experimental Layout........................................................ 17 

Figure 3-3. Experimental Layout Looking at Room Inlet and Outlet........................ 17 

Figure 3-4. Inlet and Outlet From a Different Perspective ........................................ 18 

Figure 3-5. Doorway (Inlet) Measurements Points.................................................... 19 

Figure 3-6. Window (Outlet) Measurement Points.................................................... 19 

Figure 3-7. Visualization of Supplemental Experiment as Soon as Room is 

Pressurized .......................................................................................................... 20 

Figure 3-8. Visualization of Supplemental Experiment Once Constant Flow is 

Achieved ............................................................................................................. 20 

Figure 3-9. FDS Layout for Simple Room Experiment............................................. 21 

Figure 3-10. Grid Cell Visualization, Multi-blocking ............................................... 21 

Figure 3-11. FDS Layout Looking at Room Inlet and Outlet.................................... 22 

Figure 3-12. FDS Layout with Fan Operating........................................................... 23 

Figure 3-13. Experimental Velocity Measurements in the Doorway (Inlet) ............. 24 

Figure 3-14. FDS Velocities in the Doorway (Inlet) ................................................. 24 

Figure 3-15. Experimental Measurements in the Window (Outlet) .......................... 25 

Figure 3-16. FDS Velocities in the Window (Outlet)................................................ 25 

Figure 3-17. Smokeview Visualization of FDS PPV Flow Pattern........................... 27 

Figure 3-18. Experimental Visualization of the PPV Flow Pattern........................... 27 
vii 

Figure 3-19. FDS Visualization of Supplemental Experiment as Soon as Room 

is Pressurized ...................................................................................................... 28 

Figure 3-20. Visualization of Supplemental Experiment as Soon as Room is 

Pressurized .......................................................................................................... 28 

Figure 3-21. FDS Visualization of Supplemental Experiment Once Constant 

Flow is Achieved ................................................................................................ 29 

Figure 3-22. Visualization of Supplemental Experiment Once Constant Flow is 

Achieved ............................................................................................................. 29 

Figure 4-1. Experimental Floor Plan ......................................................................... 31 

Figure 4-2. External View of Window in Closed Position ........................................ 32 

Figure 4-3. External View of Open Corridor Doorway............................................. 32 

Figure 4-4. Furniture Floor Plan ................................................................................ 33 

Figure 4-5. Instrumentation Floor Plan (TC: thermocouples, BDP: bidirectional 

probes)................................................................................................................. 35 

Figure 4-6. Doorway and Window Probe and Thermocouple Combination............ 36 

Figure 4-7. View of Doorway From Inside the Room into Corridor and Window 

with Instrumentation ........................................................................................... 36 

Figure 4-8. Bidirectional Probe and Thermocouple Combination............................. 37 

Figure 4-9. Water Cooled Camera............................................................................. 37 

Figure 4-10 - Book Case............................................................................................. 39 

Figure 4-11 - Book Case Dimensions......................................................................... 39 

Figure 4-12 - Desk and Monitor ................................................................................. 40 

Figure 4-13 - Desk Dimensions .................................................................................. 40 

Figure 4-14 - Monitor ................................................................................................. 41 

Figure 4-15 - Monitor Dimensions ............................................................................. 41 

Figure 4-16 - Chair...................................................................................................... 42 

Figure 4-17 - Chair Dimensions ................................................................................. 42 

Figure 4-18 – Bunk Bed.............................................................................................. 43 

Figure 4-19 – Bunk Bed Dimensions ......................................................................... 43 

Figure 4-20. Ignition Setup........................................................................................ 45 

Figure 4-21. Electrically Activated Matchbook Locations........................................ 45 

Figure 4-22. Exterior View of Doorway to Corridor After the Start of Forced 

Ventilation (470 s) .............................................................................................. 48 

Figure 4-23. Exterior View of Window After the Start of Forced Ventilation 

(380 s) ................................................................................................................. 48 

Figure 4-24. Doorway During Natural Ventilation Experiment (645 s).................... 49 

Figure 4-25. Window During Natural Ventilation Experiment (470 s)..................... 49 

Figure 4-26. Heat Release Rate ................................................................................. 51 

Figure 4-27. Heat Release Rate Detail For 200 s Following Peak Output ................ 52 

Figure 4-28. Total Heat Released .............................................................................. 52 

Figure 4-29. PPV Room Temperatures, Distances Measured From Ceiling............. 54 

Figure 4-30. Natural Ventilation Room Temperatures.............................................. 55 

Figure 4-31. PPV Doorway Temperatures................................................................. 56 

Figure 4-32. Natural Ventilation Doorway Temperatures......................................... 57 

Figure 4-33. PPV Window Temperatures.................................................................. 58 

Figure 4-34. Natural Ventilation Window Temperatures.......................................... 59 
viii 

Figure 4-35. PPV Corridor Temperatures.................................................................. 60 

Figure 4-36. Natural Ventilation Corridor Temperatures.......................................... 61 

Figure 4-37. PPV Room Differential Pressure .......................................................... 62 

Figure 4-38. Natural Ventilation Room Differential Pressure................................... 63 

Figure 4-39. PPV Window Velocities ....................................................................... 64 

Figure 4-40. Natural Ventilation Window Velocities................................................ 65 

Figure 4-41. PPV Room Doorway Velocities............................................................ 66 

Figure 4-42. Natural Ventilation Room Doorway Velocities.................................... 67 

Figure 4-43. FDS Naturally Ventilated Domain........................................................ 68 

Figure 4-44. FDS PPV Ventilated Domain................................................................ 69 

Figure 4-45. Grid Cell Visualization ......................................................................... 69 

Figure 4-46. Rectangular Geometries........................................................................ 70 

Figure 4-47. Location of Ignition Source .................................................................. 72 

Figure 4-48. Bunkbed View at Time of Ignition (0 s) ............................................... 73 

Figure 4-49. Doorway and Window View at Time of Ignition (0 s) ......................... 73 

Figure 4-50. Fire Starting on Corner of Mattress (90 s) ............................................ 74 

Figure 4-51. Flames Involving Bunkbed (230 s)....................................................... 74 

Figure 4-52. Onset of Flashover (275 s) .................................................................... 75 

Figure 4-53. Visibility Lost in Bunk Bed View (300 s) ............................................ 75 

Figure 4-54. Combustion Products Flow From Corridor Doorway (330 s) .............. 76 

Figure 4-55. Flames Extend From Corridor Doorway Once Window is Opened 

(360 s) ................................................................................................................. 76 

Figure 4-56. Flames From Window (360 s)............................................................... 77 

Figure 4-57. Flames Continue From Window (430 s)............................................... 77 

Figure 4-58. Fire in Decay Stage (540 s)................................................................... 78 

Figure 4-59. Room Continues to Burn (720 s) .......................................................... 78 

Figure 4-60. FDS and Experimental Naturally Ventilated Heat Release Rate.......... 79 

Figure 4-61. FDS and Experimental Naturally Ventilated Total Heat Released....... 80 

Figure 4-62. FDS Naturally Ventilated Room Temperatures.................................... 81 

Figure 4-63. FDS Naturally Ventilated Room Doorway Temperatures.................... 82 

Figure 4-64. FDS Naturally Ventilated Corridor Doorway Temperatures................ 83 

Figure 4-65. FDS Naturally Ventilated Window Velocities...................................... 84 

Figure 4-66. FDS Naturally Ventilated Room Doorway Velocities.......................... 85 

Figure 4-67. External Door View With Fan Prior to Ignition (0 s) ........................... 86 

Figure 4-68. Bunkbed View as Flames Involve Corner of Mattress (60 s) ............... 86 

Figure 4-69. Doorway and Window View as Flames Spread to Top Mattress 

(170 s) ................................................................................................................. 86 

Figure 4-70. Flames Involving Bunk Bed (240 s) ..................................................... 87 

Figure 4-71. Visibility Lost in Bunk Bed View (300 s) ............................................ 87 

Figure 4-72. Thick Smoke Flows From Corridor Doorway (300 s).......................... 88 

Figure 4-73. Doorway and Window View, From Inside the Room, Obstructed 

by Flames (360 s)................................................................................................ 88 

Figure 4-74. Doorway View 10 s After Fan is Turned On (360 s)............................ 88 

Figure 4-75. Flames From Window (360 s)............................................................... 89 

Figure 4-76. Flames Continue From Window (400 s).............................................. 89 

Figure 4-77. Combustion Products Forced into Room by Fan (410 s)...................... 90 
ix 

Figure 4-78. Fire in Decay Stage (445 s)................................................................... 90 

Figure 4-79. Fan Forcing Flow Through Room (500 s) ............................................ 90 

Figure 4-80. FDS and Experimental Positive Pressure Ventilated Heat Release 

Rate ..................................................................................................................... 92 

Figure 4-81. FDS Heat Release Rate Comparison of natural and PPV ventilation... 92 

Figure 4-82. FDS PPV Ventilated Room Temperatures............................................ 93 

Figure 4-83. FDS PPV Ventilated Room Doorway Temperatures............................ 94 

Figure 4-84. FDS PPV Ventilated Corridor Doorway Temperatures........................ 95 

Figure 4-85. FDS PPV Ventilated Window Velocities ............................................. 95 

Figure 4-86. FDS PPV Ventilated Room Doorway Velocities.................................. 96 

Figure 5-1. Colonial House and Grid Locations...................................................... 101 

Figure 5-2. Display of Grid Cell Size ...................................................................... 102 

Figure 5-3. Colonial House and PPV Fan Placement.............................................. 102 

Figure 5-4. Floor Plan of First Floor........................................................................ 103 

Figure 5-5. Furniture Locations on First Floor ........................................................ 104 

Figure 5-6. Smokeview Display of First Floor ........................................................ 104 

Figure 5-7. Floor Plan of Second Floor ................................................................... 105 

Figure 5-8. Furniture Locations on Second Floor.................................................... 105 

Figure 5-9. Smokeview Display of Second Floor.................................................... 106 

Figure 5-10. Basement Floor Plan ........................................................................... 106 

Figure 5-11. Smokeview Display of Basement ....................................................... 107 

Figure 5-12. Front and Rear View of House............................................................ 108 

Figure 5-13. Location of Room Vents with Roof Removed.................................... 108 

Figure 5-14. View of Interior from Inside the Front Door ...................................... 109 

Figure 5-15. Fire Source in Bedroom ...................................................................... 110 

Figure 5-16. Growth of Fire Prior to Ventilation, 60 s to 240 s .............................. 112 

Figure 5-17. Comparison of Simulations at 250 s (Natural left, PPV right) ........... 113 

Figure 5-18. Comparison of Simulations at 360 s (Natural left, PPV right) ........... 113 

Figure 5-19. Comparison of Simulations at 360 s (Natural left, PPV right) ........... 113 

Figure 5-20. Comparison of Simulations at 600 s ................................................... 114 

Figure 5-21. Colonial House Heat Release Rate Comparison................................. 115 

Figure 5-22. Comparison of Second Floor Temperatures 100 s to 300 s, 

Naturally Ventilated (Left) and PPV Ventilated (Right) .................................. 117 

Figure 5-23. Comparison of Second Floor Temperatures 400 s to 600 s, 

Naturally Ventilated (Left) and PPV Ventilated (Right) .................................. 118 

Figure 5-24. Comparison of First Floor Temperatures 200 s to 600 s, 

Naturally Ventilated (Left) and PPV Ventilated (Right) .................................. 119 

Figure 5-25. Comparison of Second Floor Oxygen Volume Fractions 100 s to 

300 s, Naturally Ventilated (Left) and PPV Ventilated (Right)........................ 121 

Figure 5-26. Comparison of Second Floor Oxygen Volume Fractions 300 s to 

600 s, Naturally Ventilated (Left) and PPV Ventilated (Right)........................ 122 

Figure 5-27. Comparison of First Floor Oxygen Volume Fractions 200 s to 

600 s, Naturally Ventilated (Left) and PPV Ventilated (Right)........................ 123 

Figure 5-28. Vertical Velocity Slice Through Center of Fan .................................. 124 

Figure 5-29. Velocity Slice Through Center of Vent Window During PPV 

Ventilation Scenario at 320 s ............................................................................ 125 
x 

Figure 5-30. Velocity Slice Through Center of Vent Window During Natural 

Ventilation Scenario at 320 s ............................................................................ 125 

Figure 5-31. Horizontal Velocity Slice Through Second Floor During PPV 

Ventilation Scenario at 320 s ............................................................................ 126 

Figure 5-32. Horizontal Velocity Slice Through Second Floor During Natural 

Ventilation Scenario at 320 s ............................................................................ 126 

Figure 5-33. Horizontal Velocity Slice Through First Floor During PPV 

Ventilation Scenario at 320 s ............................................................................ 127 

Figure 5-34. Horizontal Velocity Slice Through First Floor During Natural 

Ventilation Scenario at 320 s ............................................................................ 127 
1 

1 Chapter 1: Introduction 

Positive Pressure Ventilation (PPV) is a common tactic used by fire departments to 

ventilate a structure after a fire has been extinguished. Typically this allowed fire 

fighters to complete salvage and overhaul operations in a less hazardous environment. 

PPV is also used during a fire attack. The fan is started in coordination with a 

ventilation opening during the initial phase of the fire attack. This tactic was 

designed to increase visibility and force heat away from the attack team as they locate 

and extinguish the fire. PPV has been implemented with some success, but also with 

some difficulty. It has not been carefully characterized in terms of gas temperatures, 

gas velocities and mass burning rates. The uncertainties associated with PPV have 

given rise to several issues: When should PPV be used, and just as important, when 

should it not be used? What is the best location for the fan and where should the 

exhaust or vent opening be made? Does PPV provide oxygen to the fire and allow for 

quicker fire growth? What is the consequence if fire fighters or building occupants 

are between the fire and the exhaust opening? Are there certain types of construction 

when PPV should not be used? 

As early as 1989, fire department training publications questioned whether PPV fans 

would intensify a fire by introducing additional oxygen. Carlson [1] responded to this 

question, stating that it was a possibility, but there was no evidence or research to 

substantiate his answer. As part of their “Roundtable” discussion in 1999, Fire 

Engineering polled fire chiefs from around the country to determine the extent to 

which their departments used PPV. Many of the polled departments used PPV, but 

some did not use it offensively with the explanation that intensifying the fire was a 

concern and this phenomenon was not well understood [2]. 

In 2001, Yates conducted an investigation and survey of the usage of PPV in the Tyne 

and Wear Metropolitan Fire Brigade in the United Kingdom, Salt Lake City, Utah 

Fire Department in the United States, and Aachen Fire Department in Germany [3]. 

The survey suggested a few reasons for the lack of implementation of PPV. Two of 

these reasons were the potential for increased damage to structures and insufficient 

research data and evidence available to support its benefits. This is further evidence 

that PPV lacks the firm scientific foundation necessary for salvage, overhaul, and fire 

suppression operations. 

1.1 Positive Pressure Ventilation 

PPV is a ventilation technique used by the fire service to remove smoke, heat and 

other combustion products from a structure. This allows the fire service to perform 

other tasks in a more tenable environment. PPV fans are commonly powered with an 

electric or gasoline engine and range in diameter from 0.30 m to 0.91 m 

(12 in to 36 in) (Figure 1-1). Typically, a PPV fan is placed about 1.8 m to 3.0 m 

(6 ft to 10 ft) outside the doorway of the structure. It is positioned so that the “cone 
2 

of air” produced by the fan extends beyond the boundaries of the opening (Figure 1-

2). With the doorway within the cone of air, pressure inside the structure increases. 

An exhaust opening in the structure, such as an opening in the roof or an open 

window, allows the air to escape due to the difference between the inside and outside 

air pressure. The smoke, heat and other combustion products are pushed out of the 

structure and replaced with ambient air [4]. 

Figure 1-2. PPV Cone of Air [4] 

1.2 Fire Dynamics Simulator 

The National Institute of Standards and Technology’s Fire Dynamics Simulator 

(FDS) is a computational fluid dynamics (CFD) model of fire-driven fluid flow. It 

numerically solves a form of the Navier-Stokes equations appropriate for low-speed, 

thermally driven flow with an emphasis on smoke and heat transport from fires [5]. 

Version 1 was publicly released in February 2000. The predictions performed here 

were made with the public pre-release version 4 of the model [6]. Version 4 includes 

Figure 1-1. Two Common PPV Fans 
3 

several new features such as multi-blocking which were critical in performing the 

room fire simulations. 

A CFD model requires that the room or building of interest be divided into small 

three-dimensional rectangular control volumes or computational cells. The CFD 

model computes the density, velocity, temperature, pressure and species 

concentration of the gas in each cell as the model steps through time. Based on the 

laws of conservation of mass, momentum, species and energy, the model tracks the 

generation and movement of fire gases. Radiative heat transfer is included in the 

model via the solution of the radiation transport equation for a non-scattering gray 

gas. All solid surfaces are assigned thermal boundary conditions, in addition to 

information about the burning behavior of the material. Heat and mass transfer to and 

from solid surfaces is usually handled with empirical correlations. FDS utilizes 

material properties of the furnishings, walls, floors, and ceilings to compute fire 

growth and spread. A complete description of the FDS model is given in references 

[5, 6]. 

Inputs required by FDS include the geometry of the structure and furnishings, the 

computational cell size, the location of the ignition source, the energy release rate of 

the ignition source, thermal properties of walls, ceilings, floors, furnishings, and the 

size, location, and timing of door and window openings to the outside. Each of these 

inputs can significantly influence fire growth and spread. 

1.3 Smokeview 

Smokeview is a scientific visualization program that was developed to display the 

results of an FDS model computation [7]. Smokeview allows the viewing of FDS 

results in three-dimensional snapshots or animations. Smokeview can display 

contours of temperature, velocity and gas concentration in planar slices. It can also 

display properties with iso-surfaces that are three-dimensional versions of a constant 

value of the property. Iso-surfaces are most commonly used to provide a threedimensional approximation of the flame surface where fuel and oxygen mix and burn. 
4 

2 Chapter 2: Mapping the PPV Velocity Flow Field 

This research effort used a series of full-scale experiments to examine how PPV may 

impact structural ventilation. These same experiments were simulated with FDS to 

provide more insight into the impact of ventilation on fire behavior. The computer 

simulations were compared with the full-scale test results. This enabled the 

validation of the computer simulation and as necessary, identified areas that need 

improvement. Ultimately, PPV computer simulations could be used to improve fire 

fighter safety by enabling improved understanding of structural ventilation 

techniques. 

PPV fans are engineered to maximize airflow while allowing the fan to remain light 

and durable for fire service use. Simply, a blade or impeller pulls air through a 

shroud creating the airflow. This blade or impeller is driven by an electric or gasoline 

engine all of which are mounted in a frame. The velocity field that is created is 

complex due to the speed at which the blade or impeller rotates to achieve a conical 

flow. These mapping experiments examine FDS’s ability to accurately characterize 

this complex flow. 

2.1 Experimental Description 

The initial series of experiments served to determine the flow field created by PPV 

fans. In order to implement a PPV fan in FDS it was necessary to characterize the fan 

in terms of FDS input parameters such as obstruction and vent locations and 

orientations. This basic environment was an open atmosphere with the fan located on 

a stand that had negligible effects on the flow, essentially placing the fan in open 

space. This placement minimized the impact from obstructions such as walls and 

doorways on the flow field. 

2.1.1 Experimental Facility 

These experiments were conducted at NIST’s Building and Fire Research Laboratory 

Large Fire Facility. Each experiment was located in an area inside the facility so that 

the airflow created by the PPV fan was not affected by external factors such as wind 

or weather. The facility has the interior dimensions, 36.6 m (120 ft) long, 

18.3 m (60 ft) wide and 7.6 m (25 ft) high. 

2.1.2 Experiment Components 

Grid 

A grid frame, 2.44 m x 2.44 m (8 ft x 8 ft), was constructed with 51 mm x 102 mm 

(2 in x 4 in) wood members to form a square. The corners were reinforced with 
5 

plywood triangles. Cotton strings approximately 1.6 mm (0.0625 in) in diameter 

were placed on the frame both vertically and horizontally to form a grid. The center 

was highlighted by using orange string, while white strings were placed every 0.1m 

(4 in) for the first 0.31m (12 in) then every 0.15 m (6 in) towards the edge of the 

frame in both directions. The frame was notched to keep the strings in place (Figure 

2-1). Once the strings were all in place, 0.2 m (8 in) long threads were added to each 

point on the grid. These threads made it possible to view the direction of airflow 

(Figure 2-2). Finally, black felt was added to the frame, parallel to the threads in 

order to give a contrasting background to the threads and aid in photographic 

documentation. 

 

Fan 

The fan used was an 18-inch, variable speed, electric, positive pressure ventilator. 

The fan had a depth of 0.48 m (18.75 in), width of 0.62 m (24.5 in) and height of 

0.62 m (24.5 in). It had a maximum speed of 2200 rpm, a horsepower rating of 

746 W (1 hp) and a flow rating of 6.64 m3

/s (14,060 ft3/min). The fan was mounted 

on a stand to set the fan at the proper height of 1.28 m (50.5 in), measured from the 

center of the fan to the ground (Figure 2-3). The grid was positioned so that the 

center of the fan impeller was aligned with the centerline of the grid. 

Figure 2-1. The Flow 

Characterization Grid Figure 2-2. Flow Visualization 

Threads 
6 

Anemometer 

The digital anemometer used was a 25.4 mm (1 in) diameter vane-type probe 

(Figure 2-4). It is microprocessor-based with a range of 0.3 m/s (1.0 ft/s) to 35.0 m/s 

(115 ft/s) with an accuracy of 0.5% of the readings [8]. 

In order to position the anemometer at various locations an anemometer indexer was 

fabricated. The indexer allowed the anemometer to be placed at any point on the grid 

by moving it horizontally and vertically. The indexer also permitted the anemometer 

to rotate around both the x and y-axis. This rotation allowed the measurement of 

velocities that were not parallel to the ground and perpendicular to the fan. The 

indexer moved horizontally across the grid on wheels that were grooved to ride an 

angle iron track. This track was positioned on the ground parallel with the grid 

(Figure 2-5). 

Figure 2-5. Anemometer in Indexer on Track 

Figure 2-3. Front and Back of PPV Fan 

Figure 2-4. Anemometer 
7 

2.1.3 Experiment Procedure 

The grid and track were placed perpendicular to the flow. The fan was positioned so 

that the flow was centered on the grid 1.28 m (4.2 ft) above the floor. The 

anemometer indexer was moved along the track and the height of the anemometer 

adjusted to correspond with the measurement position on the grid (Figure 2-6). The 

vane of the anemometer was maintained perpendicular to the flow. The fan was 

started and run for two minutes at the maximum speed of 2200 rpm. The anemometer 

output was recorded every two seconds for four minutes using 16 second averaging. 

This process was repeated for the selected points on the grid shown in Figure 2-7. 

 Figure 2-6. Velocity Mapping Experimental Layout 
8 

Figure 2-7. Velocity Mapping Measurement Points 

2.1.4 Flow Visualization Experiment 

In order to visualize and qualify the flow from the fan, a supplemental test was 

performed. A smoke generator was placed 0.3 m (1 ft) to the rear of the fan 

(Figure 2-11). The fan was turned on to a speed of 2200 rpm and allowed to reach 

steady state operating conditions. The smoke generator was then turned on to 

maximum output and pictures were taken against a black background with heights 

labeled in 0.3 m (1 ft) intervals and widths labeled in 0.6 m (2 ft) intervals. See 

Figures 2-8 through 2-11. 

Figure 2-9. Layout for Supplemental Experiment 

 

Figure 2-8. Smoke Generator Flowing 
9 

Figure 2-11. Fan and Smoke Generator 

2.2 Computer Simulation 

Inputs required by FDS in order to model PPV fans included the following: domain 

size, computational cell size, vent velocity, vent geometry, fan geometry, slice 

location and velocity measurement points. Many of the inputs that were used for 

preliminary FDS runs are explained in the following sections. 

2.2.1 Domain 

Many issues need to be considered when modeling a PPV fan using FDS. The most 

important is the computational cell size. It was found that the cells needed to be no 

larger than 16.4 cm3

 (1 in3). For cells greater than 18.0 cm3 (1.1 in3) the flow from 

the fan did not form a cone. The cell size in the computation in Figures 2-12 through 

2-14 are 16.4 cm3

 (1 in3). 

The next consideration was the domain size. At least 1 m (3.3 ft) to the rear of the 

fan was needed in order for it to create a cone of air. If the fan were located at or 

within 1 m (3.3 ft) of the boundary, whether the boundary was open or closed, the fan 

flow was not predicted accurately. 

2.2.2 Geometry and Vents 

The obstructions and vents that make up the fan itself needed to be prescribed 

correctly. FDS only allows rectangular obstructions and vents to be created. This 

leads to an issue due to the cylindrical nature of the fan shroud. In order to get the 

proper flow pattern the shroud must be prescribed as a series of obstructions oriented 

in a circle such as Figure 2-12. The degree of roundness depends of the accuracy that 

is desired. The shroud in Figure 2-12 yielded results within 15% of the experimental 

but the shroud can be created more cylindrical if desired. 

Figure 2-10. Visualization of PPV Flow 
10 

The velocity planes or vents were prescribed as the interior dimensions of the shroud. 

Vents were also located on the front of the shroud, opposite the motor and handle. 

This allowed air to be pulled through the shroud creating a more realistic flow 

pattern. If the vents are placed to the rear or middle of the shroud the flow pattern 

would appear linear and unrealistic. The velocity into the vents was also prescribed 

equal to the maximum speed of the experimental PPV fan, 17.89 m/s (40 mi/h). This 

input was based on the maximum speed of the experimental PPV fan from the 

previous section. The prescribed velocity corresponded to a pressure drop in the 

calculation which created the conical flow pattern. Altering this input allowed the 

user to characterize the fan operating at different speeds. 

The final items to be described were the obstructions in the center of the fan, 

simulating the center of the blade connected to the shaft, and the motor and handle to 

the rear of the shroud. Adding these obstructions created a more realistic flow 

pattern. They affected the air moving through the shroud in the FDS simulation 

similarly as they did in the experiment. Pulling air past the motor affected the flow 

pattern significantly so it had to be included in the model. 

2.2.3 Output Files 

Slice files and prediction points were prescribed. The slice files were placed at the 

center of the fan in both the horizontal and vertical directions to visualize the flow 

pattern. Velocity measurement points were placed in the model in conjunction with 

the measurement points used experimentally, in order to make a comparison of the 

two at a distance of 1.83 m, 2.44 m, and 3.05 m (6 ft, 8 ft and 10 ft) from the PPV 

fan. 

Figure 2-12. FDS PPV Fan Visualized in Smokeview 

Vents 

Handle 

Blade Center 

Fan Shroud 

Motor 
11 

Figure 2-14. Fine Grid Cell Visualization 

 

2.3 Results 

Velocity measurements were taken at the locations depicted in Figure 2-7. These 

measurements were recorded with the fan at 1.83 m, 2.44 m, and 3.05 m (6 ft, 8 ft and 

10 ft) from the anemometer, corresponding to typical distances of a PPV fan from a 

structure. The magnitudes of the velocities are shown in Figures 2-16, 2-18 and 2-20. 

The average velocities of the three distances were 2.42 m/s, 2.72 m/s and 3.35 m/s 

(7.9 ft/s, 8.9 ft/s and 11.0 ft/s), respectively. Many simulations were performed 

examining the possibilities of creating a PPV fan that closely portrays the actual fan 

that was used for experimentation. The final fan geometry, Figure 2-15, yielded 

velocity measurements that are graphed in Figures 2-17, 2-19 and 2-21. The average 

velocities of the three distances were 2.65 m/s, 3.19 m/s and 3.25 m/s (8.7 ft/s, 

10.5 ft/s and 10.7 ft/s) respectively. Average velocities were compared due to the 

fluctuations in flow across the measurement plane of interest. Velocities were 

averaged over the duration of the simulation and across the plane of interest. This 

comparison gave an average difference of slightly less than 10 % (Table 1). The 

quality of the flow was compared in Figures 2-17 and 2-18. 

Table 1. Comparison of Experimental and FDS Velocity Mapping Results 

 Average Velocities, m/s (ft/s) 

Distance from fan 1.8 m (6 ft.) 2.4 m (8 ft.) 3.1 m (10 ft.) 

Experimental 2.42 (7.9) 2.72 (8.9) 3.35 (11.0) 

Fire dynamics 

simulator 

2.65 (8.7) 3.19 (10.5) 3.25 (10.7) 

Relative Difference (%) 

(Exp-FDS)/Exp x 100 

8.7 14.7 -3.1 

Note: Experimental velocity total expanded uncertainty is ± 14%, See Table 10. 

Figure 2-13. FDS Layout Visualized with 

Smokeview 
12 

Figure 2-15. Smokeview Visualization of FDS PPV Flow Pattern 
13 

Figure 2-16. Experimental Velocities 1.8 m (6 ft) From the Fan 

Figure 2-17. FDS Velocities 1.8 m (6 ft) From the Fan 
14 

Figure 2-18. Experimental Velocities 2.4 m (8 ft) From the Fan 

Figure 2-19. FDS Velocities 2.4 m (8 ft) From the Fan 
15 

Figure 2-20. Experimental Velocities 3.1 m (10 ft) From the Fan 

Figure 2-21. FDS Velocities 3.1 m (10 ft) From the Fan 
16 

3 Chapter 3: Simple Room Experiment 

3.1 Experimental Description 

A series of experiments were conducted to determine the impact that basic room 

geometries have on the flow of PPV fans. The experimental results were compared to 

FDS simulations to see if FDS predicted the airflow accurately. 

3.1.1 Experimental Facility 

These experiments were also conducted at NIST’s Building and Fire Research 

Laboratory Large Fire Facility. The experiments were located in an area within the 

facility so that the airflow created by the PPV fan was not affected by external factors 

to the experiments. The facility had the following interior dimensions: 36.6 m 

(120 ft) long, 18.3 m (60 ft) wide and 7.6 m (25 ft) high. 

3.1.2 Experiment Components 

Fan and Anemometer 

The same fan and anemometer used in the chapter 2 experiments were used in this 

series of experiments. A complete description of the fan and the anemometer can be 

found in section 2.1.2 of this report. 

Room 

The floor plan for the room is shown in Figure 3-1. The room was on a 0.2 m (8 in) 

high base with plywood decking and had a ceiling that was 2.6 m (8 ft - 8 in) high, 

measured from the top of the base. The window on the left hand side of the room was 

located 0.45 m (18 in) off the floor and was 1.4 m (54 in) tall. The door centered in 

the front wall was 2.0 m (80 in) tall. All of the walls were finished with gypsum 

board. There was a 1.8 m (6 ft) overhang that extended over the front of the room 

(Figures 3-2, 3-3 and 3-4). 
17 

Figure 3-1. Floor Plan of Simple Room 

3.1.3 Experiment Layout 

The fan was positioned in the center of the doorway and allowed to run at the 

maximum speed, 2200 rpm. The cone of air coming from the fan covered the 

doorway when the fan was 3.05 m (10 ft) from the doorway so that was the location 

selected for the tests. The doorway and window were marked with anemometer 

measurement locations. These locations are shown in Figures 3-5 and 3-6. 

Figure 3-3. Experimental Layout Looking at 

Room Inlet and Outlet 

Figure 3-2. Simple Room Experimental 

Layout 
18 

Figure 3-4. Inlet and Outlet From a Different Perspective 

3.1.4 Experiment Procedure 

The fan was turned on and allowed to run for two minutes at the maximum speed 

setting, 2200 rpm. While the fan was running, the door was rechecked to make sure 

there was a cone of airflow around the door, and the window was checked to make 

sure there was a constant flow prior to measurement. Once the fan had been running 

for two minutes the data recording was started. Four minutes of readings were taken 

using sixteen second averaging with no rotation of the anemometer. Readings were 

recorded every two seconds and the output was an average of the previous eight 

readings. Air velocity readings were taken at specific points at the door and window 

as seen in Figures 3-5 and 3-6. 
19 

Figure 3-5. Doorway (Inlet) Measurements Points 

Figure 3-6. Window (Outlet) Measurement Points 

3.1.5 Flow Visualization Experiment 

In order to visualize and qualify the flow through the room a supplemental 

experiment was performed. A smoke generator was placed in the room and turned on 

to produce enough artificial smoke to fill the room. Cameras were set up and the fan 

was turned on to the maximum speed of 2200 rpm. Pictures were taken of the 

artificial smoke flowing from the room (figures 3-7 and 3-8). 
20 

Figure 3-8. Visualization of Supplemental 

Experiment Once Constant Flow is Achieved 

 

3.2 Computer Simulation 

The inputs required by FDS in order to model the PPV fan for this experiment were 

the same as those in chapter 2. The difference was the addition of the room. The 

room required additional inputs such as the properties of the ceiling, walls and 

openings. 

3.2.1 Domain 

The main issue that arises with the use of both the fan and the room was 

computational cell size. As stated in chapter 2 the simulated fan required a 

computation cell size of 16.4 cm3 (1 in3). If the domain containing the fan and room 

were completely 16.4 cm3 (1 in3) cells then there would be in excess of 15 million 

cells. Past experience with FDS suggests that if the number of cells exceeds one 

million, the computer computational time becomes excessive. In the case of 

15 million cells one simulation would require over a month to complete on a Linux 

workstation. 

In order to reduce the number of cells and still maintain sufficient accuracy of the 

calculation, FDS utilizes a multi-blocking feature. Multi-blocking allowed 

computational time to be saved by applying relatively fine grids in areas of interest 

and coarse grids elsewhere [6]. In this case, a fine grid was used for the domain 

surrounding the fan and a coarser grid was used for the room. There were many 

considerations that needed to be taken into account when using multi-blocking, 

especially for these cases with a large quantity of air movement. First, the finer grid 

containing the fan had to be specified first in the input file. This allowed FDS to give 

precedence to this domain and decreased calculation times. Second, the grids needed 

to overlap by at least 1.0 m. This helps accelerate calculations because information 

was transferred from grid to grid via external boundaries. When the grids overlapped 

they shared the same information, which also helped to speed up calculations. Third, 

Figure 3-7. Visualization of Supplemental 

Experiment as Soon as Room is Pressurized 
21 

neither of the domain boundaries could be within one meter of the face of the fan. 

This allowed for airflow in and out of the fan. Placing the end of a domain too close 

to the fan face caused inaccurate simulation of the air entrainment. Next, the fan grid 

could not be completely imbedded within the room grid. When this was done 

information is not transferred between the grids and there would be no results for the 

fan. Finally, the cell size for the room domain could not be larger than 0.1 m (4 in) 

on a side. This allowed for a small step between the grids sizes and sufficient 

amounts of data to be shared. 

Another issue that needs to be addressed was the positioning of the PPV fan. From 

the Smokeview visualization, it appeared that the fan was floating in mid air. The 

reason for this was the inability of FDS to portray angled geometry. Typically the 

fire service places the fan away from the door and adjusts the angle of the fan to 

achieve a cone surrounding the opening [9]. In order to reduce the complexity of the 

simulation the fan was modeled at the mid-height of the doorway. The fluid 

dynamics of the two situations are assumed to be similar. 

Figure 3-9. FDS Layout for Simple Room Experiment 

Figure 3-10. Grid Cell Visualization, Multi-blocking 

Fine grid 

for fan 

Coarse grid 

for room 
22 

Figure 3-11. FDS Layout Looking at Room Inlet and Outlet 

3.2.2 Geometry and Vents 

The PPV fan used for these runs was the same fan created in Chapter 2. See section 

2.2.3 for details on fan geometry and vent considerations. Chapter 3 involved the 

addition of a room with dimensions of that in Figures 3-1 through 3-5. This room 

was prescribed in FDS as a series of blocks with characteristics of gypsum board. 

The dimensions and openings were the same as those in the experimental setup. All 

of the room boundaries, including the walls and ceiling were contained within the 

domain. 

3.2.3 Output Files 

Vertical velocity slices were positioned through the center of the doorway and 

window. Velocity measurement points were also prescribed at the same locations as 

in the experimental layout. These output files were compared with the experimental 

measurements (Section 3.3). 

3.3 Results 

Velocity measurements were taken at the locations in the door shown in Figure 3-5, 

and in the window in Figure 3-6. These measurements were recorded with the fan 

3.0 m (10 ft) from the front door of the room, just as in the chapter 2 experiments. 

Having the fan 3.0 m (10 ft) from the door provides a cone of air around the front 

door per International Fire Service Training Association recommendations [9]. The 

magnitudes of the velocities into the door are shown in Figure 3-13. The magnitudes 

of the outlet velocities at the window are in Figure 3-15. The average inlet velocity at 

the door was 2.2 m/s (7.2 ft/s). The average outlet velocity at the window was 
23 

2.6 m/s (8.5 ft/s). The model was used to examine the use of the PPV fan from 

chapter 2 in the same configuration as in the experiment. FDS yielded an inlet 

velocity averaged over the door area of 4.1 m/s (13.5 ft/s) and an outlet velocity of 

3.0 m/s (9.8 ft/s) averaged over the window area (Figures 3-14 and 3-16). These 

comparisons provided a difference of 84 % at the door and a difference of 16.5 % at 

the window (Table 2). The air movement at the window was the result of the 

pressure change in the room, interaction of the geometry of the room and the airflow. 

The door point predictions were dependent upon the local turbulence that FDS creates 

from the fan simulation shown in Figure 3-12. Experimentally this turbulence was 

very complex and difficult to measure. Qualitatively, the flow was compared in 

Figures 3-19 to 3-22. 

Table 2. Comparison of Experimental and FDS Simple Room Results 

 Average Velocities, m/s (ft/s) 

 Door Window 

Experimental 2.2 (7.2) 2.6 (8.5) 

Fire dynamics simulator 4.1 (13.5) 3.0 (9.8) 

Relative Difference (%) 

(Exp-FDS)/Exp x 100 

84.0 16.5 

Note: Experimental velocity total expanded uncertainty is ± 14%, See Table 10. 

Figure 3-12. FDS Layout with Fan Operating
24 

Figure 3-13. Experimental Velocity Measurements in the Doorway (Inlet) 

Figure 3-14. FDS Velocities in the Doorway (Inlet) 
25 

Figure 3-15. Experimental Measurements in the Window (Outlet) 

Figure 3-16. FDS Velocities in the Window (Outlet) 
26 

3.4 Mapping and Simple Room Summary 

A comparison of the computational fluid dynamic model Fire dynamics simulator 

(FDS) was made with data from two different sets of data collected from full-scale 

experiments. The full-scale experiments characterized a Positive Pressure Ventilation 

(PPV) fan in an open atmosphere, and with a simple room geometry. Both 

experimental data sets provided insight into the gas velocities, as well as providing 

the opportunity to validate the predictions of the Fire dynamics simulator. 

The measurements for the fan in an open atmosphere compared favorably with the 

FDS predictions. With the correct geometry, vent placement and boundary location 

FDS predicted velocities that were within 10 % of the experimental results (Table 3). 

FDS’s visualization of the flow pattern also correlated well with the experimental 

visualization. 

The measurements for the fan and a single room also compared favorably with the 

FDS predictions for the flow out the window. The flow that was created out of the 

window in FDS was within 20 % of that measured experimentally. FDS’s 

visualization of the flow out of the window using Multi-blocking also correlated well 

with that captured experimentally (Table 4). 

The results from these two experiments indicated that FDS was able to portray the 

general room flow created by PPV fans. Future experiments need to be conducted to 

examine the flow in multi-floor structures and structures with a more complex 

geometry. Further, the impact of the fan on other factors in the fire environment such 

as temperature, burning rate, and gas concentrations has not been examined here. 

Table 3. Summary of FDS Characteristics Needed to Model the Fan Flow 

1 Computational cell size of less than or equal to 1 cubic inch 

2 At least 1 meter of domain to the rear of the fan 

3 Shroud must be cylindrical 

4 Vents must be located on the front face of the shroud 

5 A velocity must be prescribed for the vents (17.88 m/s for this fan) 

6 A block must be added to the center of the shroud to simulate the blade center 

(effects air movement) 

7 A motor must be added to the rear of the fan (effects air movement) 

Table 4. Summary of Multi-block Characteristics Needed to Model Simple Room Flow 

1 Specify the fan grid (finer) first in the data file 

2 Overlap the grids by at least 1 meter 

3 Neither of the domain boundaries should be within 1 meter of the fan 

4 Do not embed one grid completely within the other 

5 Computational cell size for the non-fan grid should not be greater than 102 mm 

(4 in) on a side. 
27 

Figure 3-17. Smokeview Visualization of FDS PPV Flow Pattern, see Figure 2-15 for velocities 

Figure 3-18. Experimental Visualization of the PPV Flow Pattern 
28 

Figure 3-19. FDS Visualization of Supplemental Experiment as Soon as Room is Pressurized, see 

Figure 3-12 for velocity magnitudes 

Figure 3-20. Visualization of Supplemental Experiment as Soon as Room is Pressurized 
29 

Figure 3-21. FDS Visualization of Supplemental Experiment Once Constant Flow is Achieved, 

see Figure 3-12 for velocity magnitudes 

Figure 3-22. Visualization of Supplemental Experiment Once Constant Flow is Achieved 
30 

4 Chapter 4: Room Fire Experiments 

4.1 Experimental Description 

A pair of full-scale experiments was performed at NIST’s Building and Fire Research 

Laboratory Large Fire Facility. The facility has interior dimensions, 36.6 m (120.0 ft) 

long, 18.3 m (60.0 ft) wide and 7.6 m (25.0 ft) high. A room was constructed within 

the facility under a 6 m x 6 m (20 ft x 20 ft) hood which was instrumented to allow 

for oxygen depletion calorimetry to measure the heat release rate produced by the fire 

in the room. The room had interior dimensions of 3.66 m x 4.27 m (12 ft x 14 ft) and 

a ceiling height of 2.44 m (8 ft) (Figure 4-1). A window was located in the center of 

one of the 4.27 m walls (Figure 4-2) and a doorway was located on the center of one 

of the 3.66 m walls. The doorway opened to a 1.22 m wide x 2.29 m long (4.0 ft x 

7.5 ft) corridor (Figure 4-3). Another doorway was located at the end of the corridor 

that was the same size as the doorway to the room. Both doorways were 2.06 m 

(6.75 ft) tall and 0.91 m (3 ft) wide. The window was 1.2 m (3.9 ft) tall and 0.89 m 

(2.9 ft) wide and 0.81 m (2.7 ft) from the floor to the sill (Figure 4-1). A 6.1 m (20 ft) 

wall was constructed between the corridor doorway and room window to the exterior 

of the room in order to isolate the effects of the fan and not allow recirculation of 

smoke from the window back through the doorway. All of the walls and the ceiling 

were framed with 0.050 m x 0.100 m (2.0 in x 4.0 in) pine studs and sheathed with 

two layers of 0.0095 m (0.38 in) gypsum board. The room was furnished with a bunk 

bed, stuffed chair, book case and desk (Figure 4-4). The floor was covered with 

carpet and a computer monitor was placed on the desk. 

Two experiments were conducted with nearly identical fuel loads, examining the 

effect of the PPV fan on the room fire. The first experiment utilized the same fan 

used in previous experiments to forcibly ventilate the room just after the window was 

opened. The second experiment was similar to the first experiment except that it was 

naturally ventilated. The fan used was identical to that used in the previously 

described experiments. It was a 0.75 m (18 in) in diameter and had a depth of 0.48 m, 

(18.75 in), width of 0.62 m (24.5 in) and height of 0.62 m (24.5 in). It had a 

maximum speed of 2200 rpm, a power rating of 746 W (1 hp) and a volumetric flow 

rating of 6.64 m3

/s (14,060 ft3/min) [10]. The fan was positioned 2.44 m (8 ft) from 

the open doorway to the corridor at an angle of approximately 15 degrees from 

horizontal to create the cone of air around the doorway. 
31 

Figure 4-1. Experimental Floor Plan 

4.27 m

3.66 m

1.68 m

1.37 m 1.37 m

1.68 m

1.22 m

0.15 m

0.15 m

2.29 m

2.03 m to Top of Doorway

CEILING HEIGHT = 2.44 m

2.03 m to Top of Doorway

2.03 m to Top

0.81 m to Sill

Separation Wall
32 

Figure 4-2. External View of Window in Closed Position 

Figure 4-3. External View of Open Corridor Doorway 
33 

4.27 m

3.66 m

0.16 m

0.22 m

0.3 m

Bunk Bed

Chair

Desk

Book Case

0.39 m

Figure 4-4. Furniture Floor Plan 

4.1.1 Instrumentation 

Temperature measurements were made with 0.5 mm (0.02 in) nominal diameter type 

K bare bead thermocouples. A vertical thermocouple array was located in the center 

of the fire room with measurement locations of 0.025 m, 0.30 m, 0.61 m, 0.91 m, 

1.22 m, 1.52 m, 1.83 m and 2.13 m (1 in, 1 ft, 2 ft, 3 ft, 4 ft, 5 ft, 6 ft and 7 ft) below 

the ceiling. The corridor doorway also had a vertical array with measurement 

locations of 0.025 m, 0.30 m, 0.61 m, 0.91 m, 1.22 m, 1.52 m, 1.83 m (1 in, 1 ft, 2 ft, 

3 ft, 4 ft, 5 ft and 6 ft) below the top of the doorway opening. Three thermocouples 

were located in the room doorway, 0.30 m (1 ft) from the top of the doorway, 0.30 m 

(1 ft) from the bottom of the doorway and the midpoint of the doorway at 1.02 m 

(Figure 4-5). Six additional thermocouples were placed in the ventilation window. 
34 

Three were located 0.30 m (1 ft) in from each side of the window at heights of 

0.15 m, 0.61 m and 1.07 m (0.5 ft, 2 ft and 3.5 ft) from the bottom of the window 

(Figures 4-6 and 4-7). 

Gas velocity measurements were recorded in the window and in the fire room 

doorway using bi-directional probes (Figure 4-8). The doorway had measurement 

locations of 0.30 m (1 ft) from the top of the doorway, 0.30 m (1 ft) from the bottom 

of the doorway and the midpoint of the doorway. The ventilation window had six bidirectional probes in the same locations as the thermocouple locations shown in 

Figure 4-6. Probes were connected to Setra Systems Model 264 differential pressure 

transducers. Since both in and outflow was expected, each transducer had the 

capacity to monitor positive and negative pressure differentials. Bi-directional high 

pressure ranges up to 62 Pa (0.01 psi) were utilized because of the flow that was 

expected in the two openings. A set of pressure transducers was also positioned in 

the rear corner of the room adjacent to the bookcase to examine the differential 

pressure created at 0.30 m, 1.22 m, 2.13 m (1 ft, 4 ft and 7 ft) from the floor [11]. 

Video recordings were made of each experiment. Two cameras were positioned on 

the exterior of the room. One had the view of the ventilation window and the other 

the open doorway to the corridor. Two water cooled cameras were positioned inside 

the room (Figure 4-9). One camera was placed just above the floor near the bunk beds 

viewing the gas flow between the window and doorway. The second interior camera 

was positioned near the floor viewing the ignition location and flame spread across 

the bunk beds. 

The combustion products were captured by a 6 m x 6 m (20 ft x 20 ft) hood which 

was instrumented for oxygen consumption calorimetry. Oxygen depletion, 

temperature and pressure readings were continuously monitored in order to calculate 

the total heat release rate of the fire room [12]. 
35 

4.27 m

3.66 m

1.83 m

2.13 m

0.46 m

0.3 m

TC/BDP

TC/BDP

TC/BDP

TC

TC

0.46 m

1.42 m

CAMERA

1.12 m

CAMERA

0.3 m

Figure 4-5. Instrumentation Floor Plan (TC: thermocouples, BDP: bidirectional probes) 
36 

0.91 m

1.02 m

0.3 m

0.46 m

0.15 m

0.61 m

1.22 m

0.3 m

0.89 m

0.3 m

2.03 m

0.15 m

0.3 m

Figure 4-6. Doorway and Window Probe and Thermocouple Combination 

 Figure 4-7. View of Doorway From Inside the Room into Corridor and Window with Instrumentation 

TC/BDP
37 

Figure 4-9. Water Cooled Camera 

 

4.1.2 Fuel Load 

The fuel load was selected to represent a typical child’s bedroom. It was also 

intended to create a fuel rich atmosphere to make burning dependent on the available 

oxygen. Both experiments had similar furniture and a total fuel mass that was 

250.6 kg and 251.6 kg for experiment 1 and 2, respectively (Table 5). The book case 

was made of 0.013 m (0.5 in) thick compressed particle board covered with a plastic 

laminate top (Figures 4-10 and 4-11). The desk was also made of compressed 

particle board with a laminate top, but was 0.038 m (1.5 in) thick (Figures 4-12 and 

4-13). The 0.38 m (15 in) nominal size computer monitor on the desk had a plastic 

shell and a glass face (Figures 4-14 and 4-15). The chair located in the corner had a 

wood frame, polyurethane cushions and cotton cover (Figures 4-16 and 4-17). 

Finally, the bunk beds were framed out with 0.050 m x 0.100 m (2 in x 4 in) nominal 

pine lumber (Figures 4-18 and 4-19). All of the mattresses were placed on box 

springs and were covered with cotton bedding consisting of fitted sheets, blankets, 

comforters, pillows and pillow cases. The mattresses consisted of a polyester cover, 

twin inner springs, and polyurethane foam. The carpet was polypropylene based and 

covered the floor wall to wall, but did not extend into the corridor. There was no 

padding under the carpet, but a 0.01 m (0.375 in) thick sheet of gypsum board was 

placed under the carpet. 

Figure 4-8. Bidirectional Probe and 

Thermocouple Combination 
38 

Table 5. Fire Load Weights 

Item 

 

 

Mass (PPV Experiment) 

(kg) 

 

Mass (Natural Experiment)

(kg) 

 

Bunk Bed Frame 19.15 20.13 

Top Mattress 14.60 17.14 

Top Box Spring 12.63 13.06 

Bottom Mattress 14.98 14.44 

Bottom Box Spring 14.21 12.94 

Pillows 0.57 0.56 

 0.58 0.56 

Pillow Cases 0.11 0.10 

 0.11 0.10 

Fitted Sheets 0.40 0.34 

 0.39 0.37 

Blankets 1.15 1.19 

 1.18 1.22 

Comforters 1.54 1.55 

 1.59 1.56 

Chair 27.13 27.80 

Book Case 27.08 26.17 

Desk 55.48 55.48 

Computer Monitor 17.09 17.90 

Carpet 40.66 39.00 

 

Total Weight 250.63 251.61 

Note: Experimental mass measurement total expanded uncertainty is ± 12%, See 

Table 11. 
39 

Figure 4-10 - Book Case 

1.82 m

0.91 m

0.91 m

0.31 m

Figure 4-11 - Book Case Dimensions 
40 

Figure 4-12 - Desk and Monitor 

0.36 m

0.74 m

0.03 m

1.04 m

1.04 m

0.64 m

0.6 m

0.03 m

Figure 4-13 - Desk Dimensions 
41 

Figure 4-14 - Monitor 

0.41 m

0.37 m

0.41 m

0.33 m

0.25 m

0.03 m

0.19 m

Figure 4-15 - Monitor Dimensions 
42 

Figure 4-16 - Chair 

0.94 m

0.57 m

0.61 m

0.18 m

0.58 m 0.1 m

0.28 m

0.14 m

0.15 m

0.86 m

0.18 m

Figure 4-17 - Chair Dimensions 
43 

Figure 4-18 – Bunk Bed 

1.89 m

2.06 m

0.31 m

1.07 m 0.99 m

1.73 m

1.32 m

0.71 m

0.2 m

0.2 m

0.09 m 0.04 m

Figure 4-19 – Bunk Bed Dimensions 
44 

4.1.3 Procedure 

The fire was ignited using two electrically activated matches located in the mattress 

of the lower bunk, in the corner nearest the center of the room (Figure 4-20). The 

electric matches consisted of a match book with the cover placed behind the matches, 

exposing the match heads. Nickel-Chromium wire was spiraled through the match 

heads and taped to the bottom corners of the match book. A copper wire was 

connected to each end of the nickel-chromium wire with alligator clips and run to the 

exterior of the room where they were connected to an igniter box. The igniter box 

sent current through the wire, heating the wire and, in turn, igniting the matches. One 

of the match books was cut into the mattress and the second was placed under the 

bedding, directly on top of the mattress to ensure a strong ignition (Figure 4-21). 

At the time of ignition, the window was closed and the fire’s only source of oxygen 

beyond the room was through the open room doorway which connected to the 

corridor via a doorway. The fire was allowed to grow until flashover conditions were 

reached and the fire became oxygen limited. This was determined by the internal 

video. Once the fire was oxygen limited for a short period of time, the window was 

opened from the outside of the room to ventilate the fire. Both of the experiments 

were ventilated 345 s after ignition. In the PPV experiment, the window was opened 

and 5 s later the fan was turned on to full speed until 1380 s after ignition, when the 

fan was turned off to assess the structure and begin extinguishment. In the naturally 

ventilated experiment, the window and doorway provided ventilation until the fuel in 

the room burned to completion. Table 6 provides the timeline of events. 

Table 6. Experimental Procedure 

Time (s) Natural Ventilation Positive Pressure Ventilation 

0 Ignition Ignition 

345 Window Open Window Open 

350 - PPV Fan On 

* Fire burned until all fuel was exhausted 
45 

Figure 4-20. Ignition Setup 

Figure 4-21. Electrically Activated Matchbook Locations 
46 

4.2 Experimental Results 

Cameras at four locations allowed for the visualization of most of the fire growth and 

the combustion gas flow out of the furnished room. Both experiments experienced 

very similar fire growth up until the time that the window was opened. In the PPV 

ventilated experiment, flashover occurred at 275 s and near zero visibility at 278 s. In 

the natural ventilation experiment, flashover occurred at approximately 285 s and 

near zero visibility at 298 s. While the growth was very similar in both experiments, 

visibility returned more rapidly in the PPV experiment. The view from the water 

cooled camera focused on the corner of the room with the bunk beds. The camera 

showed visibility began to return 181 s after the ventilation in the PPV experiment 

and 395 s after the ventilation of the naturally ventilated case. Clear visibility inside 

the room returned to the PPV ventilated experiment 120 s prior to that of the naturally 

ventilated experiment. 

In both experiments, black smoke was observed in the corridor prior to 300 s and 

flames were not observed in the corridor doorway until the window was ventilated. 

Within 10 s of opening the window, flames extended out of the corridor doorway. 

Once the fan was activated, it required 130 s to reverse completely the flow back into 

the room. The PPV fan forced all of the smoke and flames out of the corridor and 

back into the room by 516 s after ignition. At that point, little or no smoke was seen 

coming out of the room doorway. Flames were observed in the corridor of the 

naturally ventilated experiment until 1200 s (Figures 4-22 and 4-24). 

The exterior view of the window showed that it took less than 5 s for flames to come 

out of the window after ventilation in both experiments. The flames in the PPV 

ventilated experiment extended approximately 1.83 m (6 ft) from the window. This 

length was referenced by the known width of the gypsum board sheets in the 

background. The flames from the naturally ventilated experiment extended 

approximately 0.91 m (3 ft) from the outside edge of the window (Figures 4-23 and 

4-25). Detailed observations of both experiments are tabulated in Table 7. 
47 

Table 7. Observations 

PPV 

Ventilated 

Experiment 

Time (s) 

Natural 

Ventilation 

Experiment 

Time (s) 

Observation 

0 0 Ignition 

86 120 Flames touch top bunk box spring 

105 120 Black smoke out of corridor 

156 180 Flames extend to top bunk 

190 220 Top bunk fully involved in flames 

190 225 Smoke layer drops to bottom of window 

210 240 Bunk bed fully involved in flames 

275 285 Flashover 

278 298 Zero visibility 

270 300 Smoke down to 0.30 m (1 ft) above corridor floor 

345 345 Window Open 

350 350 Flames out of window 

420 460 Flames on corridor floor 

- 650 Reduction in smoke out of corridor, increase in flames 

480 - Little - no smoke out of corridor 

526 740 Limited visibility returned 

645 765 Room clear, everything burning 

- 900 Flames out of room but not out of corridor 

NA 960 Flames no longer extend out of window 

1200 - Bunk bed falls against thermocouple tree 

1230 1230 Burnout 

1380 - Fan is turned off 

Note: Times were estimated from the video camera views 
48 

Figure 4-22. Exterior View of Doorway to Corridor After the Start of Forced Ventilation (470 s) 

Figure 4-23. Exterior View of Window After the Start of Forced Ventilation (380 s) 
49 

Figure 4-24. Doorway During Natural Ventilation Experiment (645 s) 

Figure 4-25. Window During Natural Ventilation Experiment (470 s) 
50 

4.2.1 Heat Release Rate 

The peak measured heat release rate was 14 MW for the PPV ventilated fire and 

approximately12 MW for the naturally ventilated fire. Peak heat release rates of both 

fires occurred approximately 40 s after window ventilation with a spike to their 

respective maximum. The peak of the PPV experiment occurred 5 s after that of the 

natural experiment. This corresponded to the 5 s period before the PPV fan was 

started. Comparing the heat release rate between the time of peak and the time where 

the two curves intersect showed that the PPV created a greater burning rate by 

approximately 60 % for about 200 s after the fire reached its maximum output. After 

the heat release rate spiked, the PPV output remained 4 MW above that of the 

naturally ventilated experiment for 70 s. At the end of those 70 s, the rates converged 

until 590 s when the naturally ventilated fire had the higher heat release rate. The 

naturally ventilated fire remained roughly 1 MW above the output of the PPV 

ventilated fire until the end of the experiment (Figures 4-26 and 4-27). The integral 

of the heat release rate curve in Figure 4-28 provided the total heat released over the 

duration of both experiments. The PPV ventilated experiment released 3.7x106

 kJ 

and the naturally ventilated experiment released 3.4x106 kJ. The fan caused heat to 

be released quicker in the PPV experiment, but ultimately both experiments released 

approximately the same amount of heat. 

For fires burning in the open under the laboratory hood, the chemical power measured 

by the oxygen depletion calorimeter was equal to the heat release rate from the fire as 

a function of time. However, for a fire within a room, the effluent from the enclosure 

was a mixed average of the upper layer gases, and does not represent the 

instantaneous heat release rate of the fire. Prior to ventilation there was a delay in 

the heat release rate measured due to the room configuration and the time needed for 

combustion products to travel out of corridor doorway. After the window was opened 

a majority of the burning took place on the exterior of the room which shortened the 

time between the release of heat by the fire and when it was detected by the oxygen 

depletion calorimeter. 
51 

0

5000

10000

15000

0 500 1000 1500 2000

PPV

Natural

Heat Release Rate, kW

Time, s

Figure 4-26. Heat Release Rate 
52 

0

5000

10000

15000

400 440 480 520 560 600

PPV

Natural

Heat Release Rate, kW

Time, s

Figure 4-27. Heat Release Rate Detail For 200 s Following Peak Output 

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

4000000

0 500 1000 1500 2000

PPV

Natural

Total Heat Released, kJ

Time, s

Figure 4-28. Total Heat Released 
53 

4.2.2 Room Gas Temperature 

The gas temperatures measured in the room were similar for both experiments prior 

to ventilation as each fire grew to an initial peak of approximately 800  ̊C (1470  ̊F) 

(Figure 4-29). Flashover occurred approximately 270 s after ignition and both fires 

became ventilation limited. Once the fires were ventilation limited, the upper layer 

temperatures decreased to 700  ̊C (1290  ̊F). When ventilation was started in the 

experiment with a PPV fan, the upper layer temperature increased temporarily to 

800  ̊C (1470  ̊F), quickly dropped to 550  ̊C (1020  ̊F) and then rapidly increased to 

the maximum temperature of approximately 980  ̊C (1800  ̊F). The maximum 

temperature was maintained for a short period of time and then the temperatures in 

the room steadily decreased to 400  ̊C (750  ̊F) at a rate of 0.8  ̊C /s. At 1200 s into 

the experiment a piece of the burning bunk bed fell onto the thermocouple leads and 

caused the room gas temperatures shown in Figure 4-29 to be invalid after this point. 

The naturally ventilated fire produced a much smoother time evolution of room 

temperatures. After ventilation, the temperatures rapidly increased to the maximum 

temperature of 1050  ̊C (1890  ̊F). The temperatures remained approximately 

1000  ̊C (1830  ̊F) for approximately 300 s. Once the temperatures began to decrease 

the values did so steadily to 500  ̊C (932  ̊F) at a rate of 0.8  ̊C /s. At 1430 s there was 

a rapid decrease in temperature to 100  ̊C (210  ̊F) as the fuel in the room was 

consumed (Figure 4-30). 
54 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 m (6 ft)

2.13 m (7 ft)

Gas Temperature, °C

Time, s

Window Open

Figure 4-29. PPV Room Temperatures, Distances Measured From Ceiling. Note: A piece of the 

bunk bed fell on the thermocouple tree at 1200 s, therefore temperatures cannot be compared to 

the natural ventilation experiment after that point. 
55 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 m (6 ft)

2.13 m (7 ft)

Gas Temperature, °C

Time, s

Window Open

Figure 4-30. Natural Ventilation Room Temperatures 

4.2.3 Doorway Gas Temperature 

The temperatures recorded in the upper portion of the doorway to the room were 

comparable to those within the room. For both experiments the temperatures at the 

top and middle of the doorway were approximately 600  ̊C (1110  ̊F) while the lower 

portion of the doorway remained less than 100  ̊C (212  ̊F) prior to window 

ventilation. This was consistent with the fire drawing ambient air into the room 

through the lower section of the doorway. 

After positive pressure ventilation was initiated, the gas temperatures increased 

quickly to the peak temperatures of 1000  ̊C (1830  ̊F) at the top, 800  ̊C (1470  ̊F) in 

the center and 550  ̊C (1020  ̊F) at the bottom of the doorway. Once the fan forced 

the air into the room, the doorway temperatures began to decline and continued to 

decrease until the end of the experiment (Figure 4-31). A small increase in 
56 

temperature occurred at approximately 1380 s which was consistent with the turning 

off of the fan. The increase was further evidence of the cooling effects of the fan. 

The doorway temperatures for the naturally ventilated experiment were higher than 

those of the PPV experiment for a longer time period. It took approximately 

300 s for the maximum temperatures to be reached at the top of the doorway. Both 

the top and center of the doorway reached a maximum of 1000  ̊C (1830  ̊F). The 

bottom of the doorway briefly peaked at 700  ̊C (1290  ̊F) before dropping to 200  ̊C 

(390  ̊F) as the fire continued to burn. Temperatures slowly declined to 100  ̊C 

(212  ̊F) over the 700 s after the peak (Figure 4-32). 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

Top

Middle

Bottom

Gas Temperature, °C

Time, s

Window Open

Figure 4-31. PPV Doorway Temperatures 
57 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

Top

Middle

Bottom

Gas Temperature, °C

Time, s

Window Open

Figure 4-32. Natural Ventilation Doorway Temperatures 

4.2.4 Window Gas Temperature 

The gas temperatures monitored at the window were significantly different depending 

on the method of ventilation. The PPV experiment created more uniform gas 

temperatures in the window due to the unidirectional flow out of the window. Flames 

and hot gases were observed coming out of the entire cross sectional area of the 

window. A bidirectional flow pattern existed in the naturally ventilated fire 

experiment. Flames were seen in the entire window for a short period of time and 

then air entered the lower third of the window for the remainder of the experiment. 

The gas temperatures in the PPV experiment were relatively uniform top to bottom 

between 900  ̊C (1650  ̊F) and 1100  ̊C (2010  ̊F) while the naturally ventilated 

experiment had temperatures of 1000  ̊C (1832  ̊F) at the top and 600  ̊C (1110  ̊F) at 

the bottom of the window. The PPV experiment required 200 s to reach these 

temperatures while the naturally ventilated experiment took approximately 400 s 

(Figures 4-33 and 4-34). 
58 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

Top Left

Middle Left

Bottom Left

Top Right

Middle Right

Bottom Right

Gas Temperature, °C

Time, s

Window Open

Figure 4-33. PPV Window Temperatures 
59 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

Top Left

Middle Left

Bottom Left

Top Right

Middle Right

Bottom Right

Gas Temperature, °C

Time, s

Window Open

Figure 4-34. Natural Ventilation Window Temperatures 

4.2.5 Corridor Gas Temperature 

The corridor doorway gas temperatures also showed a significant difference between 

the two ventilation tactics. Approximately 120 s after the fan was started; the fan 

reversed the natural tendency for the air to be drawn back into the room. This created 

a unidirectional flow. After ventilation started in the PPV experiment, the gas 

temperature reached nearly 700  ̊C (1290  ̊F) at the very top of the doorway. Once 

the fan was turned on, the upper doorway temperatures never increased above 200  ̊C 

(390  ̊F). The bottom half of the doorway remained slightly above ambient 

temperatures of 25  ̊C (77  ̊F). 

The naturally ventilated gas temperatures were different due to the flow of 

combustion gases and flames that ventilated out of the corridor doorway. Gas 

temperatures in the upper third of the doorway were between 600  ̊C (1110  ̊F) and 

900  ̊C (1650  ̊F) after ventilation (window opened). The mid doorway temperature 
60 

rose as high as 400  ̊C (750  ̊F) while the temperature at the bottom remained 

approximately 100  ̊C (212  ̊F). The temperature trends in the corridor were very 

similar to those of the room doorway (Figures 4-35 and 4-36). 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 m (6 ft)

2.13 m (7 ft)

Gas Temperature, °C

Time, s

Window Open

Figure 4-35. PPV Corridor Temperatures 
61 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 m (6 ft)

Gas Temperature, °C

Time, s

Window Open

Figure 4-36. Natural Ventilation Corridor Temperatures 

4.2.6 Room Differential Pressure 

Differential pressure readings were monitored to track the static pressure in the room 

created by the fire and the impact of the PPV fan on this pressure. The interior 

pressure readings were referenced to the pressure at the same elevation on the outside 

of the room. The negative time values represent times prior to ignition. Before 

ignition in the PPV experiment, the fan created uniform pressures at all three 

elevations of 21 Pa (0.003 PSI). After ignition, the fire created pressures of 34 Pa 

(0.005 PSI) at the top probe, 14 Pa (0.002 PSI) at the middle probe and -14 Pa 

(-0.002 PSI) at the lower probe. Once the window was opened and the fan was turned 

on, these differential pressures became 62 Pa (0.009 PSI), 41 Pa (0.006 PSI) and 

21 Pa (0.003 PSI) respectively. These pressures held constant for a period of time 

when the fire was at peak and then declined steadily. The naturally ventilated fire 

created differential pressures of 28 Pa (0.004 PSI) at the top probe, 7 Pa (0.001 PSI) 

at the middle probe and -14 Pa (-0.002 PSI) at the bottom probe. These differential 

pressures declined slightly until the fire diminished (Figures 4-37 and 4-39). 
62 

-40

-20

0

20

40

60

80

-2400 -1600 -800 0 800 1600 2400

Top

Middle

Bottom

Pressure, Pa

Time, s

Window Open

Figure 4-37. PPV Room Differential Pressure 
63 

-40

-20

0

20

40

60

80

-2400 -1600 -800 0 800 1600 2400

Top

Middle

Bottom

Pressure, Pa

Time, s

Window Open

Figure 4-38. Natural Ventilation Room Differential Pressure 

4.2.7 Window Gas Velocity 

Before the PPV ventilated experiment, an ambient flow experiment (without a fire) of 

the fan through the room was conducted. The experiment produced an average 

velocity of 5 m/s (16 ft/s) out of the window. For the PPV experiment, velocities on 

the order of 5 m/s (16 ft/s) to 20 m/s (66 ft/s) were measured. The highest velocity 

occurred just after the window was opened and the fan was turned on. With the fire 

growing, the velocity increased to 20 m/s (66 ft/s) and slowly decreased to the fan 

velocity of 5 m/s (16 ft/s) as the fire decreased. The naturally ventilated experiment 

had a bidirectional flow through the window with the highest velocities of 12 m/s 

(39 ft/s) at the top of the window. The gas velocity in the middle of the window was 

about 7 m/s (23 ft/s) out of the room while the bottom of the window had a flow into 

the room of 2 m/s (7 ft/s). It took longer for the maximum velocities to be reached 

than in the PPV experiment but this was also directly proportional to the growth of 

the fire (Figures 4-39 and 4-40). In the three minutes following the window being 
64 

opened, the average gas velocity produced by the PPV experiment was 14 m/s 

(46 ft/s) while in the naturally ventilated experiment, the average gas velocity was 

5.5 m/s (18 ft/s). 

-10

-5

0

5

10

15

20

25

-2400 -1600 -800 0 800 1600 2400

Top Left

Middle Left

Bottom Left

Top Right

Middle Right

Bottom Right

Gas Velocity, m/s

Time, s

Window Open

Figure 4-39. PPV Window Velocities 
65 

-10

-5

0

5

10

15

20

25

-2400 -1600 -800 0 800 1600 2400

Top Left

Middle Left

Bottom Left

Top Right

Middle Right

Bottom Right

Gas Velocity, m/s

Time, s

Window Open

Figure 4-40. Natural Ventilation Window Velocities 

4.2.8 Doorway Gas Velocity 

The gas velocities into the room through the doorway were lower than those out 

through the window. The PPV fan alone created average flow velocities of 3 m/s 

(10 ft/s) to 4 m/s (13 ft/s) as shown in Figure 4-41 for times of -2000 s to -1200 s. 

The negative time values represent times prior to ignition. Prior to ventilation, there 

was a 4 m/s (13 ft/s) to 6 m/s (20 ft/s) flow out of the top two-thirds of the doorway 

and a flow into the room in the bottom one-third of the doorway of 2 m/s (7 ft/s). 

After the fan was activated, the air flowed into the room via the bottom two-thirds of 

the doorway and the flow in the upper third of the doorway fluctuated between in and 

out of the room. Eventually, the fan was able to completely move air into the room 

over the entire doorway cross section. The naturally ventilated experiment began in 

the same manner as the PPV experiment with bidirectional flow through the doorway. 

Once ventilation was started, the gas velocities held rather steady until the fire began 

to decrease with the velocities decreasing as well. 
66 

The flows into the room may be underestimated due to the orientation of the bidirectional probes. The probes were faced into the room and perpendicular to the 

corridor which may not have measured the full magnitude of the velocity into the 

room but were accurate for the flows out of the room (Figures 4-41 and 4-42). The 

flow out of the room had to pass in the direction of the centerline of the probes 

yielding a more accurate differential pressure as opposed to the flow into the room 

that may have passed the bi-directional probe at an angle to the centerline of the 

probe causing lower differential pressure readings, which correspond to under 

estimation of the gas velocities. 

-10

-5

0

5

10

-2400 -1600 -800 0 800 1600 2400

Top

Middle

Bottom

Gas Velocity, m/s

Time, s

Window Open

Figure 4-41. PPV Room Doorway Velocities 
67 

-10

-5

0

5

10

-2400 -1600 -800 0 800 1600 2400

Top

Middle

Bottom

Gas Velocity, m/s

Time, s

Window Open

Figure 4-42. Natural Ventilation Room Doorway Velocities 

4.3 Computer Simulation 

The two experiments documented above were simulated using FDS in an attempt to 

visualize and accurately quantify the effects of a PPV fan on a post flashover room 

fire. The outputs of both simulations were then compared to the experimental data 

collected. Although very complex, FDS was able to replicate the global effects of the 

PPV fan on the room fire. 

4.3.1 Domain 

The domain used for the room fire calculation measured 6.0 m (19.7 ft) x 6.2 m 

(20.3 ft) x 3.0 m (9.8 ft) and was comprised of approximately 380,000 grid cells that 

measured 0.067 m (2.62 in) on a side (Figure 4-43). The domain was larger than the 

room in all directions to allow for more accurate pressure differences that would be 

created by the PPV fan. For the simulation with the PPV fan, the domain 
68 

characteristics described in chapter 1 were utilized. The grid for the fan and the grid 

for the room were multi-blocked together for a total of just over 1.6 million grid cells 

(Figure 4-44). 

The grid cell size was selected in order to resolve accurately the furniture in the room 

and to minimize the difference in grid cell size between the room grid and the fan 

grid. Numerous variables existed such as fire growth rate and time to flashover that 

needed to correspond with the experiment without the fan. Therefore, numerous 

partial simulations were run in order to accurately replicate the variables that took 

place in the first 345 s. The grid cell size that was selected allowed this fire 

development time to be simulated in approximately 40 hours. The final simulation 

was allowed to run for 1500 s until the fire was only smoldering as compared to the 

experimental data. This run required 15 days of computational time to complete on 

3.2 GHz processors. Preliminary runs were completed with grid cell sizes that varied 

from half to twice the size of the 0.067 m (2.62 in) on a side (Figure 4-45). The runs 

with larger grid cells developed much slower as compared to the experiment and the 

smaller grid took too long to complete so grid cell independency can not be claimed 

for this analysis. The final simulation with the fan was allowed to run for 33 days and 

produced 588 s of simulation prior to an unexpected power outage. The simulation 

time was into the decay stage of the fire so it was of sufficient duration to use for 

comparison to the first portion of the actual PPV experiment. 

Figure 4-43. FDS Naturally Ventilated Domain 
69 

Figure 4-44. FDS PPV Ventilated Domain 

Figure 4-45. Grid Cell Visualization 
70 

4.3.2 Geometry 

The simulation geometry was input into the model using the dimensions from the 

experimental floor plan. All of the geometry was prescribed using rectangular 

obstructions that were forced to conform to the rectilinear grid described in the 

previous domain description. For this reason the walls and furniture items were not 

the exact dimensions or in the exact location as they were in the experiment. These 

slight variations typically had little impact on the calculation and were analyzed to 

determine the impact of grid cell dependency. Obstructions were also not able to be 

entered diagonally. For example the computer monitor appeared sideways in the 

calculation but contained a similar amount of fuel. The front of the desk also 

appeared stepped for this same reason (Figure 4-46). Subtle differences also existed 

as the round edges of the chair cushions or mattresses were not able to be exactly 

captured. 

Figure 4-46. Rectangular Geometries 

4.3.3 Materials 

Each obstruction in the domain was given a set of physical and thermal properties that 

were used in the calculation. Each wall, ceiling, floor and piece of furniture was 

defined with properties such as thermal diffusivity, heat of vaporization, density and 

thickness. These values are shown in Table 8. All of the walls and the ceiling of the 

room were gypsum board and the floors were covered in carpet, as in the 

experiments. The primary fuels in the room were upholstery and oak. The chair and 

mattresses were prescribed as upholstery and the bookcase and desk were both oak. 

All of the material properties were derived from standard reference literature, not 

from measurements of the items themselves [25, 26]. 
71 

Table 8. Room Fire FDS Input Material Properties 

Material Ignition 

Temperature 

(

o

C) 

Thickness 

(m) 

Heat Release Rate 

Per Unit Area 

(kW/m2) 

Heat of 

Vaporization 

(kJ/kg) 

Upholstery 280 n/a n/a 1700 

Oak 340 0.02 n/a 4000 

Plastic 370 n/a 500 n/a 

Carpet 280 n/a n/a 3000 

Gypsum Board 400 0.013 100 n/a 

4.3.4 Vents and Ignition Source 

All of the external domain boundaries were prescribed as open with the exception of 

the floor outside the room. This floor was treated as an inert, cold solid boundary. 

Another small vent measuring 0.067 m (0.2 ft) by 0.13 m (0.4 ft) used for ignition 

was located at the corner of the bottom mattress (Figure 4-47). The vent had a 

constant heat release rate of 25.0 kW. This vent produced heat for the duration of the 

simulation. The location of the vent corresponded with the location of the electric 

match in the experiments. 

Initially the only openings within the domain were the door to the corridor and the 

door to the room. The doorways both measured 0.9 m (3.0 ft) wide and 2.0 m (6.6 ft) 

high. At 345 s the room window was opened as it was in the experiments. The 

domain extended outside the door and window to allow for the combustion products 

to flow out of the room. When the fan was added for the PPV simulation the 

boundaries to its domain were also open and the vents for the fan were located as 

described in chapter 1. 
72 

Figure 4-47. Location of Ignition Source 

4.3.5 Output Files 

Output files were prescribed to best replicate the measurements taken during the 

experiments. Vertical and horizontal temperature and velocity slices were placed 

through the center of the room, corridor, each doorway and the window. Velocity 

and temperature measurement points were also prescribed at the same locations as in 

the experiment layout using FDS’s thermocouple input. Heat release rate was 

continually recorded in the domain as well as the flame isosurface locations. A three 

dimensional smoke was also used for comparisons of smoke movement and visibility. 

4.4 Simulation Results 

4.4.1 Naturally Ventilated Simulation 

The results of the naturally ventilated simulation were compared with the video 

record of the experiment and the measurements of gas temperature, gas velocity and 

heat release rate. Visual comparisons of the experiment and simulation are shown in 

Figures 4-48 through 4-59. Quantitative comparisons between the experimental data 

and the model predictions are given in Figures 4-60 through 4-66. 

4.4.1.1 Visual Comparisons 

Figures 4-48 through 4-59 are composed of pairs of images. The still frames captured 

from experimental video tape appear on the left. The frames were not all taken from 

the same camera view. The camera view is included in the figure caption because 
73 

some of the views are obstructed by smoke and or flames. The images on the right 

were rendered in Smokeview. Both images represent the same time after ignition. 

The images shown are at times 0, 90, 230, 275, 300, 330, 360, 430, 540 and 

720 s after ignition. 

 

Figures 4-48 and 4-49 show the two interior camera views just before ignition. 

Figure 4-48 shows the gypsum board walls and ceiling, carpeted floor, bunk bed 

covered with linens on the right, and the desk and computer monitor on the left. The 

thermocouple tree in the center can also be seen. The image from the simulation, on 

the right, the comparable finishes and fuel items can be seen. The yellow cubes 

represent the locations of the thermocouples. 

Figure 4-49 shows the opposite corner of the room comprised of the wall with the 

room door and the wall with the window. The chair was located in the corner with 

some of the bunk bed and desk visible on the edges of the image. The room 

thermocouple tree was also located in this view. The image from the simulation 

demonstrates the same items. The white stripes that appear in the experimental video 

images are the locations of the gypsum board joints that have been spackled. 

 

Figure 4-48. Bunkbed View at Time of Ignition (0 s) 

 

Figure 4-49. Doorway and Window View at Time of Ignition (0 s) 
74 

Figure 4-50 compares the fire development at 90 s after ignition. A flame was 

located on the corner of the bottom mattress. In the case of FDS, the yellow block 

was the simulated ignition source. The area that appeared to be involved with flames 

was based on the stoichiometric mixture fraction, where there was the ideal mixture 

of fuel and oxygen for a robust flame to exist. The heat release rate per unit volume 

represented by the simulated flames was 428.6 kW/m3

. The simulation was not able 

to account for the drop down of flaming material that takes place in the experiment. 

The experimental video frame to the left in Figure 4-51 shows fire development 

230 s after ignition. The flames have spread across the bottom mattress and have 

involved the top box spring and mattress. The amount of drop down material had 

increased due to the burning, melting and falling of the bedding materials and foam 

mattress. A smoke layer had developed and had begun to descend. To the right the 

FDS simulation was behaving similarly with slightly less flaming materials. The 

smoke in the simulation appeared to compare well qualitatively with the experimental 

video frame. 

 

Figure 4-50. Fire Starting on Corner of Mattress (90 s) 

 

Figure 4-51. Flames Involving Bunkbed (230 s) 
75 

At 275 s after ignition the room has gone to flashover as can be seen in Figure 4-52. 

In the experiment, the flames were burning the carpet and the bunk bed to the left. 

The smoke had thickened and the layer lowered to the floor as the fire transitioned to 

an oxygen deficient state. The FDS simulation on the right has also gone to flashover 

and showed similar flaming and smoke yield as the experimental video frame. 

Figure 4-53 has images captured at 300 s after ignition. In both the experiment and 

the FDS simulation, visibility had decreased to almost zero due to smoke filling. The 

experimental video was completely black while some of the chair was seen in the left 

portion of the FDS simulation frame. Even though the door to the room is open to the 

corridor the camera view suggested that there was little if any fresh air being drawn 

into the room. 

 Figure 4-52. Onset of Flashover (275 s) 

 

Figure 4-53. Visibility Lost in Bunk Bed View (300 s) 
76 

While visibility was lost in the room, the external door view in Figure 4-54, at 

330 s, showed thick black smoke pouring from the top two thirds of the corridor 

doorway. There did not appear to be flames coming from the corridor door in the 

experiment but the FDS simulation was representing flames in this region. This could 

be due to the difficulty that FDS had when simulating oxygen limited scenarios. By 

representing the flames in that region FDS predicted that there was enough fuel and 

oxygen to have combustion but the temperature may not have been high enough to 

actually have combustion. 

The images in Figure 4-55 show the corridor doorway view after the window was 

opened. Flames began to extend out of the corridor doorway and the amount of 

smoke decreased as the fire transitions to a fuel limited stage with the additional 

oxygen provided by the open window. The flames were also seen over the separation 

wall coming from the open window. The FDS simulation also showed flames coming 

from both openings and a decrease in smoke production. 

 

Figure 4-54. Combustion Products Flow From Corridor Doorway (330 s) 

 

Figure 4-55. Flames Extend From Corridor Doorway Once Window is Opened (360 s) 
77 

Figure 4-56 has images taken from the window side of the separation wall at 

360 s after ignition. This was 15 s after the window was opened. Both images 

showed flames filling the entire cross section of the window and extending above the 

height of the room. (The square piece of plywood that can be seen outside the 

window was used in support of another project and was far enough away from the 

window to have no effect on the fire flows.) 

The same window view is shown in Figure 4-57. Seventy seconds after the previous 

Figure, there were still flames coming from the entire cross section of the window in 

both the experimental video frame and the FDS simulation. 

 

Figure 4-56. Flames From Window (360 s) 

 

Figure 4-57. Flames Continue From Window (430 s) 
78 

The fire began to decay in both the experiment and the simulation as shown in Figure 

4-58. The experiment had thick black smoke and some flames coming from the 

doorway. Flames were also seen coming from the window in the experiment video 

frame in Figure 4-59. The FDS simulation under predicted both the amount of smoke 

and flames present in both figures. The smoke was thinner and the flames pulled into 

the room from the corridor. Flames were still coming from the window in the FDS 

simulation but not at the same magnitude and intensity of that in the experiment. The 

FDS simulation appeared to run out of fuel before the actual experiment. 

4.4.1.2 Numerical Comparisons 

In this section, values of heat release rate, gas temperatures and gas velocities 

generated by the naturally ventilated FDS simulation are compared to measurements 

from the full-scale experiments described in Section 4.2. 

Figure 4-60 compares the measured heat release rate from the experiment and the 

heat release rate predicted by FDS. The experimental peak was 12 MW shortly after 

the window was opened and the FDS value was approximately 11 MW. The FDS 

peak occurred within 30 s of the experimental peak. The FDS heat release rate 

increased more quickly than the experimental values but this can be expected because 

the fire is in an enclosure. In FDS the heat release rate was measured immediately 

 

Figure 4-58. Fire in Decay Stage (540 s) 

 

Figure 4-59. Room Continues to Burn (720 s) 
79 

throughout the domain while the actual experiment did not record any measurable 

heat release rate until the combustion products left the room and traveled through the 

calorimetry hood. Both cases showed a large increase once the window was opened 

and a quick decline from the maximum values once post flashover conditions 

occurred. The FDS simulation held its peak value for a longer duration than the 

actual experiment and declined at a faster rate but both cases seemed to burn for a 

similar duration according to the total amount of heat released (Figure 4-61). 

0

5000

10000

15000

0 500 1000 1500 2000

Exp. Natural

FDS Natural

Heat Release Rate, kW

Time, s

Figure 4-60. FDS and Experimental Naturally Ventilated Heat Release Rate 
80 

0

500000

1000000

1500000

2000000

2500000

3000000

3500000

0 500 1000 1500

Exp. Natural

FDS Natural

Total Heat Released, kJ

Time, s

Figure 4-61. FDS and Experimental Naturally Ventilated Total Heat Released 

Gas temperatures, both measured and predicted, increased rapidly both before and 

after ventilation (Figure 4-30 on page 55). In both the experiment and the FDS 

simulation, gas temperatures rose to approximately 800  ̊C (1470  ̊F) prior to 

ventilation and began to decrease as the room became oxygen limited. Immediately 

after the window was opened, the room temperatures increased to a peak of 1000  ̊C 

(1830  ̊F) in the experiment and 1100  ̊C (2000  ̊F) in the FDS simulation. There was 

a difference after ventilation in the lower level temperatures. The experiment 

produced more uniform temperatures throughout the room, while the FDS simulation 

yielded much lower temperatures lower in the room. Part of this discrepancy can be 

attributed to the strong radiative heating of the lower thermocouples by the hot upper 

layer in the experiments which is not included in FDS since the model predicts the 

gas temperature and not the thermocouple temperature. Previous work done at NIST 

has demonstrated that lower layer thermocouple readings can be as much as 225  ̊C 

(440  ̊F) below the actual gas temperature [13,14]. This can account for a portion of 

the difference between lower layer temperatures in figure 4-30 and 4-62, but not all, 

suggesting that FDS is not capturing all of the details of the flow in the experiment. 

After the simulation reached its peak temperature and transitioned to a free burn stage 

the temperature at the ceiling (0.025 m (0.08 ft)) was slightly over-predicted, the 

temperatures at 0.3 m (1 ft) and 0.61 m (2 ft) from the ceiling matched very well with 

the experimental room temperatures. At 0.91 m (3 ft) below the ceiling FDS slightly 
81 

under-predicted the experimental temperature. The three lowest temperature 

measurements were under-predicted by 400  ̊C (750  ̊F). 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 m (6 ft)

2.13 m (7 ft)

Gas Temperature, o

C

Time, s

Window Open

Figure 4-62. FDS Naturally Ventilated Room Temperatures 

Figure 4-63 displays the FDS simulation fire room door temperatures. In both the 

simulation and the experiment, the top and middle measurement points increased to 

approximately 800  ̊C (1470  ̊F) prior to ventilation. After ventilation the 

experimental fire room door temperatures peaked at 1000  ̊C (1830  ̊F) (Figure 4-32 

on page 57) while the simulation predicted temperature peaks at 1100  ̊C (2000  ̊F). 

Similar to the lower level room temperatures, the simulation middle temperature in 

the doorway was significantly lower than in the experiment. The bottom 

measurement point in both the experiment and the simulation remained low with a 

peak at the time of ventilation. The FDS simulation also under-predicted this 

temperature as compared to the experiment. 
82 

0

200

400

600

800

1000

1200

0 500 1000 1500 2000

Top

Middle

Bottom

Gas Temperature, o

C

Time, s

Window open

Figure 4-63. FDS Naturally Ventilated Room Doorway Temperatures 

Experimental gas temperatures in the upper third of the corridor doorway were 

between 600  ̊C (1110  ̊F) and 900  ̊C (1650  ̊F) after ventilation (window opened) 

(Figure 4-35 on page 60). Simulation gas temperatures at the top of the doorway 

were higher, peaking at 1300  ̊C (2370  ̊F) (Figure 4-64). After the peak the top three 

temperature measurements in both cases progressed similarly. The experimental middoorway temperature rose as high as 400  ̊C (750  ̊F) while the bottom remained 

approximately 100  ̊C (212  ̊F). The simulation predicted temperatures at the low 

level were under-predicted just as they were in the room doorway and in the center of 

the room. The temperature trends in the corridor were very similar to those of the 

room doorway. 
83 

0

200

400

600

800

1000

1200

1400

0 500 1000 1500 2000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 M (6 ft)

Gas Temperature, o

C

Time, s

Window Open

Figure 4-64. FDS Naturally Ventilated Corridor Doorway Temperatures 

The naturally ventilated experiment had a bidirectional flow through the window with 

the highest velocities of 12 m/s (39 ft/s) at the top of the window (Figure 4-40 on 

page 65). The simulation window velocity peaked at 10 m/s (33 ft/s) at the top of the 

window (Figure 4-65). Velocities at the top of the window decreased linearly to 

5 m/s (16 ft/s) at 1000 s in both the experiment and the simulation. The experimental 

gas velocity in the middle of the window was about 7 m/s (23 ft/s) out of the room 

while the bottom of the window had flow into the room of 2 m/s (7 ft/s). The lower 

window velocities in the simulation were lower in magnitude but were in the same 

direction. The simulation’s mid-window velocities were approximately 

5 m/s (16 ft/s) and the lower window velocities were approximately 1 m/s (3 ft/s) out 

into the window. In both the experiment and the simulation there was a brief time 

just after the window was opened where the lower window flow is out of the room. 

Shortly after this, the flow switched into the room as the fire drew air into the room. 
84 

-2

0

2

4

6

8

10

12

0 500 1000 1500 2000

Top Left

Middle Left

Bottom Left

Top Right

Middle Right

Bottom Right

Gas Velocity, m/s

Time, s

Window Open

Figure 4-65. FDS Naturally Ventilated Window Velocities 

Experimental and simulation fire room doorway velocities are shown in Figures 4-42 

(on page 67) and 4-66. Both cases had flow out of the top of the doorway and flow 

into the bottom two-thirds of the doorway. The experimental flow out of the top of 

the door fluctuated between 3 m/s (10 ft/s) and 4 m/s (13 ft/s) and the simulation flow 

ranged between 2 m/s (7 ft/s) and 3 m/s (10 ft/s). Flows into the room in the lower 

portions of the door were between 3 m/s (10 ft/s) and 6 m/s (20 ft/s) in both the 

experiment and the simulation. 
85 

-6

-4

-2

0

2

4

6

0 500 1000 1500 2000

Top

Middle

Bottom

Gas Velocity, m/s

Time, s

Window Open

Figure 4-66. FDS Naturally Ventilated Room Doorway Velocities 

4.4.2 Positive Pressure Ventilated Simulation 

The results of the positive pressure ventilated simulation are compared with the video 

record of the experiment and the measurements of gas temperature, gas velocity and 

heat release rate. Visual comparisons of the experiment and simulation are shown in 

Figures 4-67 through 4-79. Quantitative comparisons between the experimental data 

and the model predictions are given in Figures 4-80 through 4-86. 

4.4.2.1 Visual Comparisons 

Figures 4-67 through 4-79 are composed of pairs of images. The still frames captured 

from experimental video tape appear on the left. The frames were not all taken from 

the same camera view. The camera view is included in the figure caption because 

some of the views are obstructed by smoke and or flames. The images on the right 

were rendered in Smokeview. Both images represent the same time after ignition. 

The images shown are at times 0, 60, 170, 240, 300, 360, 400, 410, 445 and 

500 s after ignition. 
86 

Figure 4-67 shows the external corridor doorway view prior to ignition. This was the 

only view that differs from the natural ventilation test due to the addition of the PPV 

fan. The difference can also be seen in the placement of the fan as explained in 

chapter one. The fan in the experiment was angled upward to cover the doorway. 

The fan in FDS was translated upward to cover the doorway as described in chapter 3. 

Figures 4-68 and 4-69 show two camera views during the growth stage of the fire. 

The bunk bed view shows the fire beginning and spreading on the corner of the 

 

Figure 4-67. External Door View With Fan Prior to Ignition (0 s) 

 

Figure 4-68. Bunkbed View as Flames Involve Corner of Mattress (60 s) 

 

Figure 4-69. Doorway and Window View as Flames Spread to Top Mattress (170 s) 
87 

mattress. The doorway and window view show the fire as it began to extend to the 

top bunk at 170 s. Some drop down of burning materials can be seen in the 

experimental frame of Figure 4-69; this was not captured in FDS and therefore 

increased the uncertainty of the simulation. The fire growth in this experiment was 

very comparable to the growth in the naturally ventilated experiment. 

 

Figure 4-70 compares the fire development at 240 s after ignition. In both frames the 

fire is involving both mattresses that make up the bunk bed. The experimental 

growth was slightly ahead of that of the simulation. One reason for this could be the 

melted materials that have pooled below the bottom mattress in the experiment 

allowing for the bottom of the lower mattress to become involved in flames. The 

smoke was also denser in the experimental frame for the same reason. 

Figure 4-71 has images captured 300 s after ignition. In both the experiment and the 

FDS simulation visibility had decreased greatly due to smoke filling and the bunk bed 

can no longer be seen. The naturally ventilated experiment lost visibility at 

approximately the same time. 

 

Figure 4-70. Flames Involving Bunk Bed (240 s) 

 

Figure 4-71. Visibility Lost in Bunk Bed View (300 s) 
88 

At the same time that visibility was lost in the room, Figure 4-72 shows the thick 

black smoke flowing from the corridor doorway. The smoke in the experiment 

appeared to be thicker than that of the simulation but both had smoke in the same 

regions of the doorways. Unlike the naturally ventilated simulation the positive 

pressure ventilated simulation did not over-predict the flame isosurface location. 

 

Figure 4-72. Thick Smoke Flows From Corridor Doorway (300 s) 

 

Figure 4-73. Doorway and Window View, From Inside the Room, Obstructed by Flames (360 s) 

 

Figure 4-74. Doorway View 10 s After Fan is Turned On (360 s) 
89 

Figures 4-73, 4-74 and 4-75 were all captured at 360 s after ignition and 10 s after the 

fan was turned on. The internal view showed that the room was fully involved in 

flames. The experimental frame had some condensation on the lens which 

evaporated quickly. The external corridor doorway view displayed the ignition of the 

combustion products leaving the doorway both in the experiment and the simulation. 

The simulation under-predicted the amount of flames coming from the doorway. The 

final view at 360 s was an external view of the window. A large amount of flames 

were coming from the window in both scenarios. The flames filled the entire cross 

section of the window just as they did in the naturally ventilated scenario but due to 

the increased velocity added by the fan the flames extended outward away from the 

room more than in the naturally ventilated experiment. 

Figure 4-76 has images taken of the window 55 s after the window was opened. Both 

images show flames filling the entire cross section of the window and exiting the 

window with force. Both images also have approximately the same amount of smoke 

being produced as the free burning from the window continues. 

 

Figure 4-75. Flames From Window (360 s) 

 

Figure 4-76. Flames Continue From Window (400 s) 
90 

At 410 s the fan had nearly turned the flow of combustion products back into the 

room from the corridor doorway as shown in Figure 4-77. In both the experiment and 

simulation there was some smoke still coming from the top of the doorway but all 

burning was forced back into the room as can be seen from the glow in both images. 

This was evidence of the fans ability to reverse strong fire flows and FDS’s ability to 

predict the phenomena. 

 

Figure 4-77. Combustion Products Forced into Room by Fan (410 s) 

 

Figure 4-78. Fire in Decay Stage (445 s) 

 

Figure 4-79. Fan Forcing Flow Through Room (500 s) 
91 

Figures 4-78 and 4-79 show the fire in its decay stage. The experiment experienced 

its peak heat release rate although it continued to have burning outside of the room. 

The simulation frame showed significantly less combustion occurring outside the 

room. This was further evidence that it was difficult in FDS to create furniture that 

contained the same amount of fuel as actually exist. There was still burning in the 

room in the simulation but not of the magnitude of the experiment. This underprediction of flames in the simulation was consistent with the under-prediction of 

temperatures in the room that was seen in the naturally ventilated scenario. 

4.4.2.2 Numerical Comparisons 

In this section, values of heat release rate, gas temperatures and gas velocities 

generated by the positive pressure ventilated FDS simulation will be compared to 

measurements from the full-scale experiments described in section 4.2. 

Figure 4-80 compares the measured heat release rate leaving the experimental room 

to the heat release rate from the fire within the room as predicted by FDS. The 

experimental heat release rate peaked at 14 MW while the simulation heat release rate 

peaked at 16 MW. The difference in peak time corresponded to the time for the 

combustion products to leave the corridor doorway and window and reach the oxygen 

consumption calorimetry instrumentation in the exhaust hood. Both curves increased 

at a similar slope to the maximum output. This demonstrated that the sudden opening 

of the window was handled accurately by FDS. As with the naturally ventilated 

simulation the heat release rate curve in the simulation declined more rapidly than in 

the experiment. This was also due to the large uncertainty associated with the 

modeling of the rooms furnishings. 

Figure 4-81 is a comparison of the naturally ventilated and positive pressure 

ventilated FDS simulations to isolate the fan’s impact on the heat release rate. The 

naturally ventilated simulation peaked at 11 MW and the positive pressure ventilated 

simulation peaked at 16 MW, an increase of 45 %. This compared with the 

experimental increase of 60 % for the 200 s following ventilation. FDS also had 

convergence of the heat release rates of the two simulations as the fire burned down. 

This was based on the 100 s from 488 s to 588 s, when the PPV simulation 

terminated. 
92 

0

5000

10000

15000

20000

0 500 1000 1500 2000

Exp. PPV

PPV FDS

Heat Release Rate, kW

Time, s

Figure 4-80. FDS and Experimental Positive Pressure Ventilated Heat Release Rate 

0

5000

10000

15000

20000

0 500 1000 1500

PPV FDS

Natural FDS

Heat Release Rate, kW

Time, s

Figure 4-81. FDS Heat Release Rate Comparison of natural and PPV ventilation 

The room gas temperatures in the FDS simulation, illustrated in Figure 4-82, 

increased similarly to those of the experiment in Figure 4-29 (on page 54). At 300 s 

both peaked at approximately 800  ̊C (1470  ̊F) at the ceiling prior to ventilation as 
93 

the fire became oxygen limited. Once the window was opened the temperature in the 

simulation peaked 40 % ( ̊C) higher than that of the experiment. At 500 s both the 

simulation and the experiment were 1000  ̊C (1830  ̊F) at the ceiling and decreasing at 

a similar rate. By the end of the simulation the ceiling temperatures decreased to 

800  ̊C (1470  ̊F) in both cases. The lower level gas temperatures were lower than the 

experimental temperatures, partially due to radiation effects on the thermocouples as 

mentioned previously. 

0

500

1000

1500

0 200 400 600 800 1000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 m (6 ft)

2.13 m (7 ft)

Gas Temperature, o

C

Time, s

Window Open

Figure 4-82. FDS PPV Ventilated Room Temperatures 

Figure 4-83 presents the gas temperatures predicted in the fire room doorway. The 

simulation prediction points correspond to the measurements shown in Figure 4-31 

(on page 69). The temperatures at all three points corresponded well between both 

cases. Top temperatures fluctuated between 600  ̊C (1110  ̊F) and 800  ̊C (1470  ̊F) 

prior to ventilation, peak at 1000  ̊C (1830  ̊F) to 1250  ̊C (2280  ̊F) after ventilation 

and decline to 600  ̊C (1110  ̊F) at the end of the simulation. Contrary to the previous 

lower level temperatures that were under-predicted, the temperatures in the lower half 

of the door in this simulation matched well with the experiment. This could be due to 

the decrease in radiation effects as increased amounts of ambient air was forced past 

the bare-bead thermocouples in the experiment. 
94 

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000

Top

Middle

Bottom

Gas Temperature, o

C

Time, s

Window Open

Figure 4-83. FDS PPV Ventilated Room Doorway Temperatures 

Figure 4-84 shows the simulated corridor doorway temperatures that are compared to 

the experimental values in Figure 4-35 (on page 73). The temperatures in the top 

third of the doorway became greatly over-predicted as the window was opened and 

the temperatures peaked. For approximately 50 s after ventilation the simulated 

temperatures were double those in the experiment. This corresponds to the slightly 

longer time the fan in the simulation required to turn the flow around and out the 

window than occurred in the experiment. The lower level temperatures remained low 

in both cases as ambient air was being pulled directly in from the outside. 

Figure 4-85 displays the gas velocities exiting the room out of the window. There 

was no bidirectional flow as the fan is turned on 5 s after the window was opened. 

These velocities are compared to the experimental velocities in Figure 4-39 (on page 

64). Simulated velocities ranged from 6 m/s (20 ft/s) to 12 m/s (39 ft/s) at the time of 

ventilation as compared to experimental values of 10 m/s (33 ft/s) to 19 m/s (62 ft/s). 

In both cases the velocities decreased at a similar rate following the peak as the fire 

decreased in magnitude. The addition of the fan in the simulation caused a 3 m/s 

(10 ft/s) to 5 m/s (16 ft/s) increase in maximum velocity which was the same as the 

increase seen in the experiment. 
95 

0

200

400

600

800

1000

1200

1400

0 200 400 600 800 1000

0.025 m (1 in)

0.30 m (1 ft)

0.61 m (2 ft)

0.91 m (3 ft)

1.22 m (4 ft)

1.52 m (5 ft)

1.83 m (6 ft)

Gas Temperature, o

C

Time, s

Window Open

Figure 4-84. FDS PPV Ventilated Corridor Doorway Temperatures 

0

2

4

6

8

10

12

0 200 400 600 800 1000

Top Left

Middle Left

Bottom Left

Top Right

Middle Right

Bottom Right

Gas Velocity, m/s

Time, s

Window Open

Figure 4-85. FDS PPV Ventilated Window Velocities 

Figure 4-86 displays the gas velocities entering and exiting the room through the 

room’s doorway. There was bidirectional flow as the fan was not able to completely 

reverse the fire flow at the plane of the doorway. These velocities are compared to 

the experimental velocities in Figure 4-41 (on page 66). Simulated velocities ranged 
96 

from -6 m/s (-20 ft/s) to 5 m/s (16 ft/s) at the time just after ventilation as compared to 

experimental values of -6 m/s (-20 ft/s) to 6 m/s (20 ft/s). In both cases the flow was 

out of the room at the top and into the room at the middle and bottom of the doorway. 

The addition of the fan in the simulation caused a 2 m/s (7 ft/s) to 4 m/s (13 ft/s) 

increase in maximum velocity which was the same as the increase seen in the 

experiment. This correlation was favorable for FDS’s ability to capture the bulk 

effect of the PPV fan as the air is forced into the room. 

-10

-5

0

5

10

0 200 400 600 800 1000

Top

Middle

Bottom

Gas Velocity, m/s

Time, s

Window Open

Figure 4-86. FDS PPV Ventilated Room Doorway Velocities 

4.5 Discussion 

Previous work has investigated the impact of positive pressure ventilation on gas 

temperature, window gas velocity, and mass burning rate by examining different fuel 

packages and different room/structural configurations. Stott studied typical home 

furnishings in a single story structure. Svensson utilized flammable liquid fires in 

three rooms of a larger structure. Ezekoye employed a polyurethane foam fuel in a 4 

room residential structure. Different capacity PPV fans were utilized by each study. 

Instrumentation typically included upper and lower layer gas temperatures and one 

experimental series included pressure transducers for monitoring gas velocities. 

Stott [15] conducted a series of experiments in Preston, U.K. utilizing furnished 

rooms. These experiments were instrumented with thermocouples but also relied 

upon subjective feedback from the participants that suppressed the fire or watched 

from outside. These experiments showed that there was a minor temperature increase 
97 

after the use of the fan, approximately 10  ̊C (18  ̊F). The experiments also 

demonstrated that there was no flame extension to the corridor, the temperature 

decreased and the visibility improved after the initiation of PPV. The report also 

stated that the fire growth rate was not greatly increased by the fan. The increase in 

burning rate as PPV was initiated is consistent with this study for a single furnished 

room. 

Svensson [16] of the Swedish Rescue Services Agency also conducted an 

experimental study of ventilation during fire fighting operations. His experimental 

setup utilized three rooms on the first floor of a fire training facility. A 0.5 m (1.6 ft) 

diameter heptane pool fire was utilized which generated a heat release rate of 

0.37 MW. This was a significantly smaller fire (in terms of heat release rate) than the 

fully furnished rooms in these experiments which released heat at a rate of 11 MW to 

14 MW. The smaller heat release rate heptane pool fire generated much lower 

temperatures, 300  ̊C (570  ̊F), than was monitored in the current study, 800  ̊C 

(1470  ̊F). Svensson did report an increase of 40 % in the burning rate after PPV was 

initiated. This is comparable to the 60 % increase that was produced in the furnished 

room in this study. The furnished room had a greater fuel surface area which would 

have been consistent with the difference in the burning rate. Svensson also reported 

significantly lower pressure differentials. The larger room size may account for some 

of this difference but the main reason is likely the smaller fan output. The fan used in 

Svensson’s experiments was rated at approximately one third that of the one used in 

these experiments. This difference in fan size is also consistent with the smaller 

flows that were recorded in Svensson’s experiments. 

Another set of experiments was conducted in the United States by Ezekoye, et al[17] 

of the University of Texas at Austin. These experiments examined positive pressure 

attack for heat transport in a house fire. The fuel source chosen for those experiments 

was 9 kg (19.8 lb) of polyurethane foam, oriented on a rack, capable of generating a 

peak heat release rate per unit area of 1.2 MW/m2

. This fuel package produced 

temperatures of 760  ̊C (1400  ̊F) at the ceiling and 200  ̊C (390  ̊F) at the lower 

levels but did not appear to cause post flashover conditions that were present in the 

furnished room fire experiments. The fan flow rate was similar to the one used in the 

furnished room. The mixing which caused higher temperatures in the lower layer are 

seen in both sets of experiments. Those experiments only reported temperatures so 

pressure differential, burn rate and gas flow velocity could not be compared. 

There has been very little documented computational fluid dynamics modeling of 

positive pressure ventilation. The only other documented FDS modeling is briefly 

explained in the University of Texas report [17]. In these simulations the fan was 

prescribed as a single vent at the face of the door. These simulations did not examine 

the effects of the fan on the fire and only looked at the temperatures in a victim room. 

The authors reported that the FDS simulations created similar trends but there was no 

figures displaying the correlations. 
98 

Another CFD model, SOFIE, was used by Gojkovic and Bengtsson [18] in Sweden to 

examine the possibility of backdraft conditions. A three room setup was used to 

examine the possible effects of PPV both correctly and incorrectly on an underventilated fire. The fan was prescribed as an inflow boundary in the front door. The 

authors stated, “an inflow boundary does not simulate the characteristics of the fan 

very well.” The authors also concluded that the PPV causes increased mixing and 

increased chance of backdraft but for a short duration. 

4.6 Room Fire Summary 

Compared to natural ventilation, positive pressure ventilation caused lower fire room 

temperatures, increased window gas flows and higher pressure differentials for this 

set of furnished room burns. After the peak heat release rate was reached in both 

experiments, the temperatures with PPV remained 200  ̊C (360  ̊F) to 400  ̊C (720  ̊F) 

below the temperatures with natural ventilation for 800 s. The doorway temperatures 

with PPV peaked 200 s before, but quickly dropped to 200  ̊C (390  ̊F) to 500  ̊C 

(930  ̊F) below the naturally ventilated temperatures for 900 s following the peak in 

the PPV experiment. The window gas temperatures generated during the PPV 

experiment peaked 200 seconds before gas temperatures at the same location in the 

naturally ventilated experiment. In the naturally ventilated experiment, gas 

temperatures in the top two thirds of the window were higher than the PPV 

experiment, but gas temperatures in the bottom third were lower due to the inflow of 

air. Once the fan was running, the PPV corridor temperatures were as much as 

500  ̊C (930  ̊F) less than comparable temperatures in the naturally ventilated 

experiment. 

The PPV fan alone generated gas velocities of 5 m/s (16 ft/s) in the window while the 

naturally ventilated fire generated velocities of nearly 12 m/s (39 ft/s). In the 

experiment with the PPV fan, window gas velocities of nearly 20 m/s (66 ft/s) were 

generated, approximately equal to the additive velocities from the fan and the 

naturally ventilated fire. The fan quickly forced a unidirectional flow out of the 

window but took a period of time to completely reverse the flow out of the doorway 

and create a flow into the room. The fan was able to create a more tenable 

atmosphere as soon as it was turned on by reversing the natural flow out of the 

corridor, where the fire fighters would be approaching the fire for extinguishment. 

The heat release rate of the fire was increased by the fan for the 200 s following the 

peak heat release rate. This was critical because this is the time period during which 

the fire department would typically be advancing to extinguish the fire. The peak 

heat release rate for the two experiments occurred at approximately the same time and 

the rate with the PPV fan was 2 MW higher. The PPV fan caused a 60 % increase in 

burning rate during this time of initial fire department attack. This reinforces the 

importance of selecting a ventilation location close to the seat of the fire that allows 

for all of the combustion products to be ventilated to the exterior of the structure. The 

PPV ventilated experiment forced the flames at least 1.83 m (6 ft) out of the room as 

compared to the 0.91 m (3 ft) by the naturally ventilated experiment. Flame 
99 

extension out of the building openings may also pose a potential ignition hazard to 

materials nearby. 

While the use of PPV in this particular configuration caused an increase in the room’s 

fire burning rate, it lowered the temperatures in the room, forced all of the 

combustion products to flow out of the room without affecting the corridor and 

improved the visibility leading up to and in the room itself. In this experimental 

configuration, a fire fighting team would likely have been able to attack the PPV 

ventilated fire more easily than the naturally ventilated fire. 

This limited data set indicates that coordination of fire fighting crews is essential to 

carry out positive pressure ventilation in the attack stages of a fire. In this 

experiment, ideal coordination was simulated as the window was ventilated in the 

correct location and the fan was initiated seconds later. Once the fan was turned on, it 

took approximately 60 s to 90 s for the fire to reach its peak burning rate and for the 

flow to be forced away from the entrance. After this transition, the fire remained at a 

steady burning rate until the fuel was consumed. This would indicate that for the 

conditions in this experiment fire fighters should delay 60 s to 120 s after ventilation 

and fan start before advancing towards the fire. This would allow the flows to 

stabilize, temperatures to decrease and visibility to improve. The burning rate of the 

fire could become steady at the rate determined by the modified air flow and would 

be less likely to change rapidly as the fire fighters approach. The time to reach this 

new steady condition could vary with building layout, fire size, fuel load and fan 

capacity. 

The visual and numerical comparisons demonstrate that the fire behavior of a room 

fire both with and without positive pressure ventilation can be modeled by FDS and 

visualized with Smokeview. Some differences exist in the geometry and material 

properties, but the fire dynamics and the net impact of the positive pressure 

ventilation fan can be captured with an acceptable degree of accuracy. 

The heat release rate, gas temperature and gas velocity comparisons show reasonable 

agreement between the experiments and the model in terms of both trends and range. 

Significant differences were displayed in the gas temperatures, partially due to 

radiative effects. Future simulations could utilize the FDS prescription 

“THERMOCOUPLE” identification of measurement points instead of “temperature” 

to better compare the simulation results to experimental results by incorporating the 

radiative effects in the model as well. The two experiments simulated using FDS, 

reproduced the effects of a positive pressure ventilation fan on a post flashover room 

fire, and support the use of the model fan on larger scale scenarios that may not be 

able to be supported by full scale experimental data. 
100 

5 Chapter 5: Colonial House Practical Scenario 

5.1 Scenario Overview 

In order to expand the understanding of the effects of positive pressure ventilation, it 

would be very informative to perform experiments in various types of full-scale 

structures. These structures are very difficult to obtain and very expensive to 

instrument. Using the lab scale tests documented above as a calibration for the FDS, 

it is possible to visualize the effects of positive pressure ventilation applications in 

full-scale scenarios. 

A colonial house was chosen due to the potential for many fire fighting scenarios. 

The house had two floors and a basement. The first floor was made up of a study, 

living room, dining room, kitchen, bathroom, laundry room, sun room, family room 

and garage. The second floor had four bedrooms and two bathrooms. The basement 

had an open floor plan and was unfinished. 

Two scenarios were examined with a fire in the rear bedroom of the second floor. 

The fire started next to the bed to simulate a fire that originated in a trashcan. The 

doors to all of the rooms on the floor were open and the fire grew without 

intervention for the first 240 s. At 240 s in both scenarios the front door was removed 

(opened) to simulate the fire department’s arrival at the front door. Five seconds 

after the front door opened, the window to the fire room was removed to simulate the 

fire department venting the fire room. One simulation allowed the fire to behave 

without fire department intervention, and in the second scenario a PPV fan located at 

the front door was activated at 250 s. The purpose of the two scenarios was to 

analyze the impact of the addition of the PPV fan on the fire conditions. 

The simulations were run for 800 s and provided insight into the potential fire 

development and spread as well as the potential impact of the positive pressure 

ventilation implementation. Issues that were addressed include the fans’ effect on fire 

growth, smoke spread, temperatures, oxygen concentrations and velocities in the 

pathway to the fire room potentially occupied by fire fighters and tenability criteria of 

adjacent rooms to the fire room that could be occupied by victims of the fire. 

5.2 Computer Simulations 

5.2.1 Domain 

The computational domain used for this analysis measured 16.4 m (53.8 ft) wide x 

13.9 m (45.6 ft) deep x 10.0 m (32.8 ft) tall. The computational domain was divided 

into 3 grids (Figure 5-1). The grid containing the basement (grid 1) measured 16.4 m 

(53.8 ft) wide x 13.9 m (45.6 ft) deep x 2.5 m (8.2 ft) tall. The grid containing the 

first floor (grid 2) measured 16.4 m (53.8 ft) wide x 13.9 m (45.6 ft) deep x 3.125 m 
101 

(10.3 ft) tall. The grid containing the second floor (grid 3) measured 16.4 m (53.8 ft) 

wide x 13.9 m (45.6 ft) deep x 4.4 m (14.4 ft) tall. All three grids were composed of 

0.15 m (6 in) cubic grid cells. The domain contained a total of 636,000 grid cells 

(Figure 5-2). 

The use of 3 grids or “multiple meshes” allowed the simulations to be parallel 

processed. The three meshes were processed on three separate CPU’s which greatly 

reduced computational time. Each mesh contained the same size grid cells which 

allowed for optimum sharing of data from mesh to mesh. The governing equations 

were solved with a time step based on the fire plume spread rate in the particular 

meshes. Due to the fact that each mesh could have different time steps, this saved 

CPU time by updating the meshes only when necessary. When the fan was added for 

the PPV simulation, the boundaries to its domain were also open and the vents for the 

fan were located as described in chapter 1 (Figure 5-3). 

Figure 5-1. Colonial House and Grid Locations 
102 

Figure 5-2. Display of Grid Cell Size 

Figure 5-3. Colonial House and PPV Fan Placement 
103 

5.2.2 Geometry 

The floor plans of the house are shown in Figures 5-4 through 5-11. The size and 

location of the walls, doorways, windows and furniture were based on the floor plans. 

All of these obstructions were adjusted by FDS to correspond to the nearest 

computational cell location. This resulted in objects, used in the model, that appear 

thicker then they would be in reality. 

Sun Room

4.67 m x 2.83 m

Family Room

6.98 m x 3.87 m

Garage

6.65 m x 6.30 m

Laundry

1.66 m x 2.55 m

Living Room

3.54 m x 4.83 m

Dining Room

3.87 m x 3.54 m

Kitchen

5.49 m x 3.26 m

Study

2.96 m x 3.05 m

Dn

Up

Bath

1.02 m

 x

1.97 m

Figure 5-4. Floor Plan of First Floor 
104 

Figure 5-5. Furniture Locations on First Floor 

Figure 5-6. Smokeview Display of First Floor 
105 

Master Bedroom

3.68 m x 4.83 m

Closet

3.04 m x 1.63 m

Bedroom 3

3.04 m x 3.35 m

Master Bath

3.96 m x 2.74 m

Bath

2.51 m x 1.74 m

Bedroom 2

3.54 m x 3.35 m

Bedroom 1

3.54 m x 3.38 m

Dn

Foyer

2.26 m

 x 5.44 m

Figure 5-7. Floor Plan of Second Floor 

Figure 5-8. Furniture Locations on Second Floor 
106 

Figure 5-9. Smokeview Display of Second Floor 

Basement

9.72 m x 8.81 m

Up

Figure 5-10. Basement Floor Plan 
107 

Figure 5-11. Smokeview Display of Basement 

5.2.3 Vents 

This simulation considered seven vents or openings from the structure to the outside, 

the front door, the window of the fire room, and five small openings to the roof area. 

The front door was 0.76 m (2.5 ft) wide x 2.0 m (6.7 ft) high. This vent was opened 

at 240 s in both scenarios. The window of the fire room measured 1.1 m (3.5 ft) wide 

x 1.25 m (4.1 ft) high with a 0.8 m (2.6 ft) sill height (Figure 5-12). This vent was 

opened at 245 s in both scenarios. The small openings in the second floor were 

placed in all four bedrooms and in the master bathroom to simulate air vents and 

leaks to the roof area. The front and rear edges of the roof area were open to the 

exterior of the house to simulate the eaves and leaks from the roof. The small 

openings to the roof measured 0.3 m (1.0 ft) long x 0.15 m (0.5 ft) wide 

(Figure 5-13). The openings along the edges of the roof were 0.3 m (1.0 ft) wide. 

The openings in the ceiling and the roof edges were also open over the entire duration 

of the simulation. 
108 

Figure 5-13. Location of Room Vents with Roof Removed 

5.2.4 Materials 

Each obstruction in the domain was given a set of physical and thermal properties that 

were used in the calculation. Each wall, ceiling, floor and piece of furniture is 

defined with properties such as ignition temperature, heat of vaporization, density and 

thickness (see Table 9). All of the walls and the ceiling of the house were gypsum 

board and the floor was covered in carpet. The primary fuels in the house were 

upholstery and oak. Figure 5-14 displays a view from inside the front door. Many 

materials can be identified, the brown steps were oak, the white walls were gypsum 

board, the light blue floor was carpet, the orange floor was also carpet (aesthetic 

purposes only) and the light blue couch was upholstery. All of the material properties 

were derived from the FDS database [6]. 

Figure 5-12. Front and Rear View of House 

Fire 

Room 
109 

Table 9. Colonial FDS Input Material Properties 

Material Ignition 

Temperature 

(

o

C) 

Thickness 

(m) 

Heat Release Rate 

Per Unit Area 

(kW/m2) 

Heat of 

Vaporization 

(kJ/kg) 

Upholstery 280 1700 

Oak 340 0.02 4000 

Plastic 370 500 

Carpet 280 3000 

Gypsum Board 400 0.013 100 

Sheet Metal N/A 0.0013 N/A N/A 

Pine 390 0.02 2500 

Concrete N/A 0.2 N/A N/A 

Glass N/A 0.005 N/A N/A 

Thin Oak 340 0.005 4000 

Floor Tile 280 3000 

Grass N/A 1.0 N/A N/A 

Figure 5-14. View of Interior from Inside the Front Door 
110 

5.2.5 Fire Source 

A vent measuring 0.15 m x 0.15 m (0.5 ft x 0.5 ft) was used for ignition and was 

located between the bed and the night stand in the rear bedroom on the second floor. 

The vent had a defined heat release rate per unit area of 2150 kW/m2

 to simulate a 

50 kW trashcan fire. The vent was placed on top of a 0.15 m (0.5 ft) cube to 

simulate a small trashcan. This vent produced fuel for the duration of the simulation 

(Figure 5-15). 

Figure 5-15. Fire Source in Bedroom 

5.2.6 Output Files 

Output files were prescribed to best analyze the fan’s effect on fire intensity in and 

around the fire room. In addition, smoke movement, temperatures, oxygen 

concentrations, and velocities in the pathway from the front door to the fire room 

which potentially would be occupied by fire fighters were analyzed. Tenability 

criteria of adjacent rooms to the fire room that could be occupied by victims of the 

fire were evaluated as well. Vertical and horizontal temperature, oxygen and velocity 

slices were placed through the center of each room and many of the openings. Heat 

release rate was continually recorded in the domain as well as the flame isosurface 

locations. Three dimensional smoke was also used for analysis of smoke movement 

and visibility. Comparisons of these output files between the two scenarios are 

located in Section 5.3. 
111 

5.3 Results 

5.3.1 Fire Growth and Smoke Spread 

Images were rendered from the naturally ventilated and positive pressure ventilated 

FDS simulations to characterize the effects of the positive pressure ventilation tactic 

on fire growth and smoke spread. Iso-surfaces of the heat release rate per unit 

volume and three-dimensional smoke density parameters are displayed in Figures 

5-16 through 5-20. 

Figure 5-16 shows the fire growth and smoke spread prior to ventilation. These 

images from 60 s to 240 s were identical for both ventilation scenarios up to 240 s. 

At 60 s the fire was growing between the night stand and the bed. Smoke was 

beginning to layer at approximately 1.2 m (4 ft) from the floor. The flames began to 

attach to the bed at 120 s and the smoke layer thickened. At 180 s the flames were 

spreading across the bed and the flames appeared to reach the ceiling. The smoke 

continued to thicken and the layer descended to 0.9 m (3 ft) from the floor. By 240 s 

the smoke layer had reached the floor and visibility was significantly decreased in the 

bedroom of origin. The view was moved to just inside the front door at 240 s. This 

frame shows the smoke almost reaching the floor in the hallway at the top of the stairs 

to the second floor. Another view from the exterior at 240 s displays smoke coming 

from the eaves of the roof on the front side of the house. 

Figures 5-17 through 5-20 show comparisons of the two ventilation techniques; 

natural ventilation on the left and positive pressure ventilation on the right. 

Figure 5-17 is the comparison five s after ventilation of the rear of the house. Both 

frames have smoke coming from the window and eaves of the roof. At this point 

there was not much of a difference between the two. Figure 5-18 shows the front of 

the house at 360 s. The naturally ventilated frame had smoke flowing from the eaves 

across the whole front of the house. The PPV ventilated frame had increased flow out 

of the eaves due to the increased flow from the fan. Figure 5-19 is a view of the rear 

of the house at the same time as the previous Figure. At this time there were flames 

coming out of the entire cross section of the ventilation window. Both frames had 

about the same amount of flames with the PPV frame having the flames further out of 

the frame as opposed to the flames in the naturally ventilated flame that go straight 

upward. This is another sign of the increased flow created by the PPV fan. The final 

comparison in Figure 5-20 shows the fire in the decay stage at 600 s. Flames were no 

longer projecting from the windows in either frame but the amount of smoke being 

forced out the window was greater in the PPV simulation. 
112 

 60 s 120 s 

 180 s 240 s 

 240 s 240 s 

Figure 5-16. Growth of Fire Prior to Ventilation, 60 s to 240 s 
113 

 

Figure 5-17. Comparison of Simulations at 250 s (Natural left, PPV right) 

 

Figure 5-18. Comparison of Simulations at 360 s (Natural left, PPV right) 

 

Figure 5-19. Comparison of Simulations at 360 s (Natural left, PPV right) 
114 

5.3.2 Heat Release Rate 

The heat release rate for the duration of both simulations is plotted in Figure 5-21. As 

expected the two curves are identical for the first 250 s prior to ventilation. After 

ventilation the naturally ventilated simulation peaks approximately 25 s prior to that 

of the PPV simulation. The reason for this may be due to the proximity of the vent 

window to the seat of the fire. The naturally ventilated fire was able to pull fresh air 

from the window while the forced flow of the PPV fan caused the flow to be out of 

the window and the source of fresh air came from the flow in through the front door 

of the house. This was seen in the room fire experiment but at a lower magnitude due 

to the lack of a long distance between the fire room and the fan. 

The heat release rate in both simulations peaked at approximately the same value of 

7.3 MW. This is not consistent with the room fire scenario but could also be due to 

the increased distance between the fire room and the PPV fan. The curves were 

consistent with the experiments after the peak was achieved. The positive pressure 

ventilated scenario maintained an elevated heat release rate of approximately 3 MW 

higher for the 70 s following the peak output. This is consistent with the room fire 

comparison which also demonstrated a comparable heat release rate differential for a 

similar period of time. After this 70 s of increased burning, the two curves 

converged, similar to the experimental results. The sudden drop in the natural 

ventilation scenario was due to a transition to a ventilation limited state in the fire 

room. The forced ventilation of the fan caused more air to reach the fire and 

minimize the sudden drop in heat release rate. 

 

Figure 5-20. Comparison of Simulations at 600 s 
115 

0

1000

2000

3000

4000

5000

6000

7000

8000

0 100 200 300 400 500 600 700 800

Natural Ventilation

Positive Pressure Ventilation

Heat Release Rate, kW

Time, s

Figure 5-21. Colonial House Heat Release Rate Comparison 

5.3.3 Temperature 

Temperature slices were examined to assess the tenability conditions that existed for 

the duration of the fire. Horizontal slices were taken at 1.2 m (4 ft) above the floor 

with the geometry above the slice rendered transparent to examine the temperature 

distribution throughout the floor of the house. Threshold temperatures were chosen 

for victims and firefighters. 

Research by Montgomery [19] in 1975 indicated that in humid air rapid skin burns 

would occur at 100  ̊C (212  ̊F), and 150  ̊C (300  ̊F) was the exposure temperature at 

which escape was not likely. In 1947, Moritz [19] experimented on large animals and 

found that 100  ̊C (212  ̊F) represented the threshold for local burning and hyperemia 

(general burning). For this analysis, a temperature value of 100  ̊C (212  ̊F) was 

considered the temperature at which victims could be incapacitated. 

Fire fighters operating in structures were also susceptible to injury from temperature 

exposures. Fire fighter protective clothing standards such as NFPA 1971 refer to 

exposures of 260  ̊C (500  ̊F) for five minutes [20]. This same temperature was the 

minimum temperature to which the thread that holds the garments together must 

endure. Other data exists that a firefighter can survive flashover conditions of 816  ̊C 
116 

(1500  ̊F) for up to 15 s [27]. For this analysis, a temperature value of 300  ̊C 

(572  ̊F) was considered the temperature at which firefighter’s turnout gear will begin 

to degrade and it is no longer safe for the fire fighter to remain in the atmosphere. 

Figures 5-22 and 5-23 show the second floor temperatures 1.2 m (4 ft) above the floor 

in 100 s intervals for 600 s. At 100 s the fire is still in the growth stage and the 

temperatures in both scenarios remained below 100  ̊C (212  ̊F). The temperatures 

increased to approximately 130  ̊C (266  ̊F) at 200 s in both scenarios which was 

consistent with the fact that ventilation had not taken place. At 200 s it can be 

estimated that victims in the fire room would be incapacitated but fire fighters could 

still operate safely. All other rooms on the second floor remained thermally tenable 

by both victims and fire fighters. 

By 300 s the window and front door had been opened for 60 s and the fan had been 

flowing for 50 s. In both scenarios the fire room temperatures had reached those 

consistent with flashover and firefighters could no longer operate in the fire room. 

The PPV ventilated fire room had lower temperatures than the naturally ventilated 

scenario. At this time, a difference in temperature was obvious in the rooms left of 

the stairwell and the stairwell itself. The flow created by the PPV fan had kept the 

temperatures near ambient while the naturally ventilated temperatures were reaching 

or had reached the tenability limit for victims. 

The fire had reached its maximum output by 400 s and had heated a good portion of 

the second floor. The fire room temperature of the PPV ventilated scenario was 

higher than that of the naturally ventilated scenario but the rest of the second floor 

was cooler in the PPV scenario. In the naturally ventilated scenario the tenability 

criteria for victims was reached in all of the second floor rooms, but the master 

bathroom in the remote corner from the fire. Temperatures reached as high as 200  ̊C 

(392  ̊F) in the stairwell which was not above the fire fighter temperature threshold 

but it was in the path they would take to attack the fire, thus making advancement 

more difficult. In the PPV ventilated scenario, the rooms to the left of the stairwell 

exceeded the victim incapacitation temperature but the right half of the floor and the 

stairwell remained thermally tenable for both victims and fire fighters. 

The fire continued through its decay stages in the 500 s and 600 s comparisons. The 

naturally ventilated scenario remained thermally untenable in most of the second 

floor while the only room that remained untenable for victims in the PPV scenario is 

the fire room. Through the duration of the fire the addition of the PPV fan increased 

the amount of tenable area for victims and lowered temperatures in the attack path of 

the fire fighters. 

Figure 5-24 displays comparisons of first floor temperatures 1.2 m (4 ft) from the 

floor in two hundred second intervals for 600 s. The first floor remained at ambient 

temperatures for the duration of the simulation for both ventilation scenarios. 
117 

 

 

 

Figure 5-22. Comparison of Second Floor Temperatures 100 s to 300 s, Naturally Ventilated 

(Left) and PPV Ventilated (Right) 
118 

 

 

 

Figure 5-23. Comparison of Second Floor Temperatures 400 s to 600 s, Naturally Ventilated 

(Left) and PPV Ventilated (Right) 
119 

5.3.4 Oxygen 

Oxygen volume fraction concentrations were also examined in the simulations to 

assess the tenability conditions that existed in the house during the evolution of the 

fire. This horizontal slice was located at the same elevation as the temperature slice, 

1.2 m (4 ft) above the floor. This analysis utilized a volume fraction of 12 % as the 

oxygen tenability threshold for victims [21]. It was assumed that fire fighters utilized 

 

 

 

Figure 5-24. Comparison of First Floor Temperatures 200 s to 600 s, Naturally Ventilated (Left) 

and PPV Ventilated (Right) 
120 

self contained breathing apparatus. Therefore in this analysis, no oxygen tenability 

threshold was considered for fire fighters. 

Figures 5-25 and 5-26 show the second floor oxygen volume fractions 1.2 m (4 ft) 

above the floor in 100 s intervals for 600 s. For the first 200 s the entire second floor 

was tenable for both ventilation scenarios. After ventilation at 300 s the fire was 

much larger and consuming more oxygen even though the window and front door 

were open. In the naturally ventilated scenario the left hand side of the second floor 

and the stairwell were approaching untenable conditions while the PPV ventilated 

scenario remained tenable everywhere but the fire room. 

By 400 s the entire second floor in the naturally ventilated scenario was untenable 

with the front left bedroom as low as 5 % oxygen. This same room along with the 

fire room in the PPV ventilated scenario reached un-tenability, but the rest of the 

floor remained tenable. The front left bedroom oxygen concentration dropped so low 

because it is adjacent to the fire room and all its oxygen is consumed by the fire but 

there was no supply because the window was closed and the fire room drew all the 

oxygen from the front door. 

The final two comparisons show the fire in the decay stage as the oxygen levels rise. 

The PPV ventilated scenario returned tenability to the second floor much more 

rapidly than the naturally ventilated scenario. This was expected as the fan was 

forcing fresh air into the house. This increased oxygen increases the survivability of 

victims and allowed fire fighters to perform overhaul procedures sooner. 

Figure 5-27 displays comparisons of first floor oxygen volume fractions 1.2 m (4 ft) 

from the floor in 200 s intervals for 600 s. The first floor remained at ambient oxygen 

levels for the duration of the simulation for both ventilation scenarios. 
121 

 

 

 

Figure 5-25. Comparison of Second Floor Oxygen Volume Fractions 100 s to 300 s, Naturally 

Ventilated (Left) and PPV Ventilated (Right) 
122 

 

 

 

Figure 5-26. Comparison of Second Floor Oxygen Volume Fractions 300 s to 600 s, Naturally 

Ventilated (Left) and PPV Ventilated (Right) 
123 

5.3.5 Velocity 

Figures 5-28 through 5-34 are velocity slice files taken at 320 s, 80 s after the window 

and front door were opened. Figure 5-28 is located vertically through the center of 

the fan. This slice shows the cone of air described in chapter 1 and how it covers the 

entire height of the door. The velocity range was consistent with that achieved in 

chapter 2 (Figure 2-15). 

 

 

 

Figure 5-27. Comparison of First Floor Oxygen Volume Fractions 200 s to 600 s, Naturally 

Ventilated (Left) and PPV Ventilated (Right) 
124 

Figure 5-29 and Figure 5-30 compare the velocities out of the fire room window. 

From this comparison it can be seen that the velocity was increased by the addition of 

the PPV fan. The fan increased the flow from approximately 4 m/s (13 ft/s) to 8 m/s 

(26 ft/s) which was consistent with the effect of the fan seen in chapter 4. Comparing 

figures 4-39 and 4-40 show how the experimental gas velocities were roughly 

doubled with the addition of the fan. 

Figures 5-31 through 5-34 compare the velocities on the first and second floors 1.2 m 

(4 ft) above the floor at 320 s. The addition of the fan only slightly increased these 

mid-level velocities through the fire room; however, what is not shown is the 

direction of flow. Much of the flow in the naturally ventilated scenario was out of the 

door and into the hallway while the PPV ventilated flow was forced back into the fire 

room. On the first floor the difference was obvious with the addition of the PPV fan. 

It can also be observed that some of the flow created by the PPV fan circulated back 

to the front door. This could be due to the increased pressure and could be affected 

by the size of the exhaust vent. 

Figure 5-28. Vertical Velocity Slice Through Center of Fan 
125 

Figure 5-29. Velocity Slice Through Center of Vent Window During PPV Ventilation Scenario 

at 320 s 

Figure 5-30. Velocity Slice Through Center of Vent Window During Natural Ventilation 

Scenario at 320 s 
126 

Figure 5-31. Horizontal Velocity Slice Through Second Floor During PPV Ventilation Scenario 

at 320 s 

Figure 5-32. Horizontal Velocity Slice Through Second Floor During Natural Ventilation 

Scenario at 320 s 
127 

Figure 5-33. Horizontal Velocity Slice Through First Floor During PPV Ventilation Scenario at 

320 s 

Figure 5-34. Horizontal Velocity Slice Through First Floor During Natural Ventilation Scenario 

at 320 s 
128 

5.4 Colonial House Summary 

Two simulations were run for 800 s to examine the effects of a positive pressure 

ventilation fan on fire spread, smoke movement, temperature, oxygen concentration 

and velocities in a colonial house. These parameters were compared to smaller scale 

experimental data and published tenability criteria. There wais no direct experimental 

data that can be used for comparison; however the trends from the room fire 

experiments were a good guideline to understanding the accuracy of the simulations. 

Prior to ventilation, fire growth and smoke spread were identical for both simulations. 

After ventilation the smoke movement out of the eaves and the flames from the fire 

room window were intensified by the positive pressure ventilation fan. Both of these 

observations were consistent with the room fire experiments in chapter 4. 

The heat release rate from both simulations peaked at the same maximum value. This 

is not consistent with the room fire experiments but could be due to the longer path 

between the fan and the fire. After this peak heat release rate the PPV fan caused an 

increased heat release rate for approximately 70 s which is consistent with the room 

fire experiments. After this 70 s of increased burning the two curves converged just 

as was seen in the experiments. 

In the PPV scenario gas temperatures were lower in all of the rooms on the second 

floor with the exception of the fire room than the temperatures in the naturally 

ventilated scenario. By 400 s most of the second floor was thermally untenable for 

victims in the naturally ventilated scenario while only one additional room next to the 

fire room reached the tenability limit in the positive pressure ventilated scenario. The 

addition of the PPV fan also lowered temperatures in the path to the fire room that 

would be used by fire fighters to attack the fire. The only room thermally untenable 

for fire fighters was the fire room. Temperatures on the first floor remained ambient 

for the duration of both simulations. 

Oxygen levels followed similar trends as the temperature. As the temperature 

increased the oxygen levels typically decreased, as would be expected. Oxygen 

tenability limits were exceeded on the entire second floor during the naturally 

ventilated scenario by 400 s and was maintained until 600 s. Limits were only 

reached in the fire room and adjacent front bedroom during the PPV ventilated 

scenario. At 600 s the increased flow created by the PPV fan created tenable oxygen 

limits on the entire second floor. Oxygen levels remained ambient on the first floor 

for the duration of both simulations. 

Velocity slices showed that the fan itself created flow at the doorway that was of the 

proper magnitude and direction to create the cone of air necessary for positive 

pressure ventilation. These values were also consistent with laboratory experiments 

in Chapter 2. Much of the flow in the naturally ventilated scenario is out of the fire 

room door and into the second floor hallway while the PPV ventilated flow forced the 

fire gases back into the fire room. On the first floor the difference was obvious with 
129 

the addition of the PPV fan. It was also observed that some of the flow created by the 

PPV fan circulated back to the front door. This could be due to the increased pressure 

and could be affected by the size of the exhaust vent. 

The results of this comparison show that the PPV fan created tenable conditions in the 

house that would not normally be there under natural ventilation tactics. This is only 

one ideal scenario with well coordinated ventilation tactics assumed. These 

simulations follow the fire dynamics seen in laboratory experiments and provide 

confidence that the positive pressure ventilation tactic can be analyzed without the 

need for countless full-scale field tests. If full-scale opportunities arise in the future 

they could be beneficial as there is no true replacement for such data. Countless 

ventilation scenarios can be performed on this colonial style house at the expense of 

computational time, examining variables such as ventilating other rooms, ventilating 

at different times and starting the fire in other rooms. As computers continue to 

advance in speed and capability this cost will decrease allowing for a more timely 

result of the impact of the PPV fan. Simulating more scenarios would allow for a 

better understanding of the tactic, better training and potentially could assist in 

equipment design. 
130 

6 Chapter 6: Uncertainty 

6.1 Experimental 

There are different components of uncertainty in the length measurements, gas 

temperatures, mass of fuel packages, gas velocity and heat release rate data reported 

here. Uncertainties are grouped into two categories according to the method used to 

estimate them. Type A uncertainties are those which are evaluated by statistical 

methods, and Type B are those which are evaluated by other means [22]. Type B 

analysis of systematic uncertainties involves estimating the upper (+ a) and lower 

(- a) limits for the quantity in question such that the probability that the value would 

be in the interval (± a) is essentially 100 %. After estimating uncertainties by either 

Type A or B analysis, the uncertainties are combined in quadrature to yield the 

combined standard uncertainty. Multiplying the combined standard uncertainty by a 

coverage factor of two results in the expanded uncertainty which corresponds to a 

95 % confidence interval (2σ). 

Components of uncertainty are tabulated in Table 10 (chapter 2 and 3 experiments) 

and Table 11 (chapter 4 experiments). Some of these components, such as the zero 

and calibration elements, are derived from instrument specifications. Other 

components, such as radiative cooling/heating, include past experience with 

thermocouples in high temperature fuel rich environments. 

Each length measurement was taken carefully but due to some construction issues 

such as the size and straightness of the lumber, the slots for the strings on the grid 

having thickness, and the symmetry of the rather large room the total expanded 

uncertainty was estimated to be 6 %. The flow measurements were taken in the 

complex flow of the positive pressure ventilation fan, which created a total expanded 

uncertainty of 14 % primarily due to the repeatability and the randomness of the 

measurements. 

The uncertainty in the upper layer gas temperature measurements includes radiative 

cooling in each of the experimental series, but also includes radiative heating for 

thermocouples located in the lower layer of the full-scale experiments. Pitts et al. 

[13] quantified the errors of bare bead thermocouples as ranging from 7 % in the hot 

upper gas layer to as much as 75 % in the lower layer. The potential for large errors 

in the lower layer are a function of the effective temperature of the surroundings. In 

cases where the effective temperature of the surroundings is high, the error can be 

more significant. In cases, similar to a developing fire in a compartment, the 

temperature measurement errors in the lower layer are smaller as the fire develops 

through flashover, since the effective temperature of the floor and walls are relatively 

cool. Post-flashover, the potential for measurement error increases as the temperature 

of the surroundings increase. Small diameter thermocouples were used to limit the 

impact of radiative heating and cooling. This resulted in an estimate of ±15 % total 

expanded uncertainty in temperature measurements. 
131 

Differential pressure reading uncertainty components are derived from pressure 

transducer instrument specifications. The transducers were factory calibrated and the 

zero and span of each was checked in the laboratory prior to the experiments. The 

readings from the pressure transducers were used to generate gas velocities. 

Load cells were utilized to measure fuel package mass. The load cell was calibrated 

with a standard mass prior to recording the mass of each fuel item. After obtaining 

mass data on each of the fuel components, items were selected at random to be 

reweighed in order to estimate repeatability. 

Total expanded uncertainties associated with oxygen calorimetry techniques are 

discussed in greater detail by Bryant et al. [12]. This uncertainty was estimated to be 

11 % and included components derived from gas concentrations, temperature and gas 

flows. This estimation is based on the calorimetry system alone and does not account 

for the uncertainty that exists due to the experimental configuration. There is a delay 

time for the combustion gases to reach the hood and calorimetry instrumentation. 

The heat released within the fire room has an additional uncertainty associated with it. 

This uncertainty varies during the experiment. After the window was opened the 

uncertainty was minimized due to the majority of the burning occurring outside of the 

room. 

Table 10. Mapping and Simple Room Experimental Uncertainty 

 Component 

Standard 

Uncertainty 

Combined Standard 

 Uncertainty 

Total Expanded 

 Uncertainty 

Length Measurements 

 Grid Size 

 String Location 

 Fan Stand Height 

 Anemometer Location 

 Fan Location 

 Room Dimensions 

 Repeatability 

 Random 

± 1 % 

± 0.5 % 

± 0.5 % 

± 1 % 

± 1 % 

± 1 % 

± 2 % 

± 2 % 

 3 % 6 % 

Flow Measurements 

 Calibration 

 Repeatability 

 Random 

± 0.5 % 

± 5 % 

± 5 % 

 7 % 14 % 

Note: Random and repeatability evaluated as Type A, other components as Type B 
132 

Table 11. Room Fire Experimental Uncertainty 

Component 

Standard 

Uncertainty 

Combined 

Standard 

Uncertainty 

Total 

Expanded 

Uncertainty 

Gas Temperature 

 Calibration[23] 

 Radiative Cooling 

 Radiative Heating 

 Repeatability 1

 Random 1

± 1 % 

- 5 % to + 0 % 

- 0 % to + 5 % 

± 5 % 

± 3 % 

- 8 % to + 8 % - 15 % to + 15 % 

Differential Pressure 

 Calibration[11] 

 Accuracy[11] 

 Repeatability 1

 Random 1

± 2 % 

± 1 % 

± 5 % 

± 5 % 

- 8 % to + 8 % - 15 % to + 15 % 

Mass of Fuel Package 

 Zero 

 Calibration 

 Repeatability1

 Random1

± 0.02 % 

± 1 % 

± 5 % 

± 3 % 

± 6 % ± 12 % 

Length Measurements 

 Instrumentation 

 Locations 

 Furniture 

Dimensions 

 Fan Location 

 Room Dimensions 

 Repeatability1

 Random1

± 1 % 

± 1 % 

± 1 % 

± 1 % 

± 2 % 

± 2 % 

± 3 % ± 6 % 

Notes: 1. Random and repeatability evaluated as Type A, other components as Type B. 
133 

6.2 Fire Dynamics Simulator 

FDS can provide valuable insight into how a fire may develop or how the combustion 

gases will move throughout a structure. However the model is only a simulation. 

The model output is dependent on a variety of input and default values such as 

computational cell size, material properties, geometry, and vents. 

The ability of the FDS model to predict accurately the temperature and velocity of 

fire gases has been previously evaluated by conducting experiments, both lab-scale 

and full-scale, and measuring quantities of interest. For relatively simple fire driven 

flows, such as buoyant plumes and flows through doorways, FDS predictions are 

within the experimental uncertainty of the values measured in the experiments [21]. 

For example, if a gas flow velocity is measured at 0.5 m/s (2 ft/s) with an 

experimental uncertainty of ± 0.05 m/s (± 0.2 ft/s), the FDS model gas flow velocity 

predictions were also within the range between 0.45 m/s (1.5 ft/s) and 0.55 m/s 

(1.8 ft/s). 

In large-scale fire tests reported in [24], FDS temperature predictions were found to 

be within 15% of the measured temperatures and the FDS heat release rates were 

predicted to within 20% of the measured values. Therefore the results are presented 

as ranges to address these uncertainties. 

These experiments indicate that using the correct set of inputs, FDS is able to model 

the flows of positive pressure ventilation fans within a useful level of uncertainty. 
134 

7 Chapter 7: Conclusion 

Data from three sets of full-scale experiments were compared with simulations 

completed with the computational fluid dynamic model Fire dynamics simulator 

(FDS). The full-scale experiments characterized a Positive Pressure Ventilation 

(PPV) fan in an open atmosphere, in a simple room geometry and during a room fire. 

Experimental results were visually and numerically compared to FDS results. The 

comparison showed reasonable agreement. A concluding scenario was modeled 

utilizing the calibration of the full-scale experiments to examine the effects of PPV on 

a fire in a two-story colonial-style house. 

Numerous geometries were experimented within FDS to obtain a fan that provided 

both numerical and visual comparisons that were accurate. The positive pressure 

ventilation fan mapped in the open atmosphere yielded an average velocity difference 

between the experiment and the simulation of less than 10 %. Visually the 

experimental flow obtained by using the smoke generator compared well to the FDS 

simulation. Special attention must be given to the grid cell size, grid location and fan 

design to accurately model the fan flow. 

The simple room geometry experiments added a change in flow direction and a 

pressure gradient to challenge the computer model. Experimental and simulation 

comparisons gave a velocity difference of 16.5 % at the window. The air movement 

at the window is the result of the pressure change in the room, interaction of the 

geometry of the room and the airflow. Qualitatively the flow visualized using the 

smoke generator matched the simulation very well. 

The room fire experiments incorporated the interaction between the fan flow and a 

fire. The naturally ventilated and the positive pressure ventilated comparisons 

showed the fan created higher fire room temperatures, increased window gas flows 

and higher pressure differentials. The experiments also showed that the PPV fan 

created a 60 % increase in burning rate during the potential time of fire department 

attack. The limited set of data also provided insight to fire fighting tactics including 

the necessity of coordination of fire fighting crews to carry out positive pressure 

ventilation in the attack stages of a fire and the recommendation to delay 

advancement towards the fire until conditions created by the fan stabilized 60 s to 

120 s after ventilation. 

Computationally, visual and numerical comparisons demonstrate that the fire 

behavior of a room fire both with and without positive pressure ventilation can be 

modeled by FDS and visualized with Smokeview. Differences exist in the geometry 

and material properties but the fire dynamics and the net impact of the positive 

pressure ventilation fan can be captured with a reasonable degree of accuracy. 

In order to expand the understanding of the effects of positive pressure ventilation it 

would be very informative to perform experiments in various types of full-scale 

structures. These buildings of opportunity are very difficult to obtain and very 

expensive to instrument. Using the lab scale tests documented above as a calibration 
135 

for the Fire dynamics simulator it was possible to visualize the effects of positive 

pressure ventilation fan on a colonial style house with a fire on the second floor. 

The results of this comparison show that the PPV fan created tenable conditions in the 

house that would not normally be there under natural ventilation tactics. This is only 

one ideal scenario with well coordinated ventilation tactics assumed. These 

simulations follow the fire dynamics seen in laboratory experiments and provide 

confidence that the positive pressure ventilation tactic can be analyzed with reduced 

need for full-scale field tests. If full-scale opportunities arise in the future they would 

be beneficial as there is no true replacement for such data. A wide range of 

ventilation scenarios can be performed on this colonial style house at the expense of 

computational time. As computers continue to advance in speed and capability this 

cost will decrease allowing for a more timely result of the impact of the PPV fan. 

The ability to model the effects of PPV given the proper input parameters in FDS 

provides a technique to add to the current deficient but fast growing understanding of 

positive pressure ventilation. Future research should incorporate FDS to answer 

specific fire department concerns with the use of PPV so that this tool can be utilized 

safely and effectively. 
136 

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