report describes the results of calculations using the NIST Fire Dynamics
Simulator (FDS) that were performed to provide insight on the thermal
conditions that may have occurred during a fire in a two-story duplex
house on December 22, 1999 in Iowa. Input to the computer model was developed
from 3 sources; investigators from the Bureau of Alcohol Tobacco and Firearms
(ATF), investigators with the National Institute for Occupational Safety
and Health (NIOSH) and from material properties taken from the FDS database.
An FDS model
scenario was developed that best represented the actual building geometry,
material thermal properties, and fire behavior based on information and
photographs from ATF. The results from this model scenario are provided
with this report.
The FDS calculations
that best represent the reported fire conditions indicate that a fire
originating on the kitchen stove spread through the house resulting in
flames that engulfed the stairwell to the second floor within approximately
9 minutes from the start of flaming ignition on the stove.
event in this fire was the onset of flashover conditions in the kitchen.
Within 60 s after the flashover occurred in the kitchen, the flames had
spread through the dining room, living room and up the stairway.
Key Words: cfd models; computer graphics; fire dynamics; fire fatalities;
fire fighters; fire investigations; fire models; flashover; ventilation
Part of the
mission of the Building and Fire Research Laboratory (BFRL) at the National
Institute of Standards and Technology (NIST) is to conduct basic and applied
fire research, including fire investigations, for the purposes of understanding
fundamental fire behavior and to reduce losses from fire.
22, 1999 a fire in a two story duplex house in Iowa claimed the lives
of three children and three firefighters. The fire occurred in the right
half of a two story duplex as shown in Figure 1. In
this figure, the entry doors to the two units are located next to each
other, under the porch roof on the left side of the photograph. The backside
of the house is shown in Figure 2. The heavily damaged
area on the 1st floor is the kitchen and the area above on the 2nd floor
is the rear bedroom. Plan views of the first and second floor are shown
in figures 3 and 4.
At the request
and under the sponsorship of the National Institute for Occupational Safety
and Health (NIOSH), NIST has examined the fire dynamics of this incident.
NIST has performed computer simulations of the fire using the newly developed,
NIST Fire Dynamics Simulator (FDS) and Smokeview, a visualization tool,
to provide insight on the fire development and thermal conditions that
may have existed in the residence during the fire. This report describes
the input and the results of the NIST FDS Version 1.0 calculations.
of the events relevant to this fire is based on information provided to
NIST by the Bureau of Alcohol, Tobacco and Firearms (ATF) and NIOSH.
On the morning
of December 22, 1999, a fire started in plastic materials on top of the
stove in the kitchen on the first floor of the residence. An adult occupant,
sleeping upstairs in the front bedroom, awoke to the cries of a child.
opened the front
bedroom door to the hall and found hot smoky conditions. The adult returned
to the front bedroom, opened a window on the front side of the house and
called for help, alerting several neighbors. It is believed that the calls
to 911 began shortly after this. The first call was received by the dispatcher's
office at approximately 8:24 AM. The adult returned to the smoky upstairs
hallway, found the crying child and exited the residence by the front bedroom
window onto the roof of the front porch. Approximately two minutes later,
8:26 AM, firefighters and police began
to arrive at
the fire scene. The smoke plume was visible as firefighters approached the
scene and there was little if any wind disturbing the plume. The adult occupant
was outside with the child and explained that there were three children
still in the house. The front door to the residence was forced open by a
police officer at approximately 8:27 AM. The officer discovered heavy smoke
conditions. He could not make entry into the house. At 8:28 AM, the first
arriving crew of firefighters prepared to enter the residence and placed
a call requesting additional firefighters. At approximately 8:31 AM, the
Fire Chief arrived at the fire scene with an additional firefighter. Three
fire fighters entered the house and brought two infants from upstairs bedrooms
to the front door. Two police vehicles were used to transport the infants
to the hospital. The fire chief was administering CPR to the second infant
and was transported to the hospital. Based on radio transmissions, the first
infant was enroute to the hospital at approximately 8:34 AM and the second
infant was enroute to the hospital at approximately 8:35 AM. According to
witness statements, the full fire involvement of the living room, leading
to a fully involved fire condition in the stairwell, occurred as the infants
were being transported to the hospital. A hose line had been advanced into
entry foyer of the house. The "dry" hose line was placed on the
floor, while the firefighter returned to the engine to charge the line.
When the hose line was "charged" (pressurized with water) it was
discovered that the hose had burned through and flames were coming out of
the doorway to the house.
8:48 AM, as a second fire crew made entry into the house and began to
attack the fire with a hose line, a firefighter was discovered on the
floor of the living room. Later the other two firefighters from the first
crew were found on the second floor. One on the landing at the top of
the stairs with a child victim and another in the doorway of the front
bedroom. All three firefighters and the one child found in the house,
and the two children taken to the hospital died from injuries caused by
fire investigation confirmed that the fire started in plastic material
on the stove. The kitchen had fire damage throughout, consistent with
a well-mixed, post-flashover fire environment, Figures 5
and 6. In addition to the kitchen area, there was
significant fire damage in the living room (Figure 8),
the stairwell, second floor hallway (Figures 9-11)
and the rear bedroom above kitchen (Figure 12). The
dining room (Figure 7), the other bedrooms and the
bathrooms had less fire damage than the other portions of the house. A
timeline of the fire events is given in Table 1.
FIRE DYNAMICS SIMULATOR (FDS)
developed a computational fluid dynamics (CFD) fire model using large
eddy simulation (LES) techniques . This model,
called the NIST Fire Dynamics Simulator (FDS), Version 1., has been demonstrated
to predict the thermal conditions resulting from a compartment fire [2,3].
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. Based on the laws of
conservation of mass, momentum, species and energy the model tracks the
generation and movement of fire gases. 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 reference
FDS can provide
valuable insight into how a fire may have developed. However the model
is only a simulation. The model output is dependent on a variety of input
values such as material properties, times lines, geometry, and ventilation
openings. Since perfect knowledge of every detail of the fire site, fuel
load or fire timeline is never known, estimations are incorporated into
the model. For example, the estimation of the energy release rate of an
initial "source fire" as a starting point for fire development
and spread throughout the structure is a necessary part of re-creating
this fire scenario. Another estimation used in this case, the plaster
ceilings and walls of the structure were modeled with the thermal properties
of gypsum board. These estimations and others used in this simulation
are further described in Section 6 of this report.
of the FDS model to accurately predict 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 . For example, if a
gas flow velocity is measured at 0.5m/s with an experimental uncertainty
of ±0.05 m/s, the FDS model gas flow velocity predictions were
also in the range between 0.45 m/s and 0.55 m/s.
scale fire tests reported in , 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
is a scientific visualization program that was developed to display the
results of a FDS model computation. Smokeview produces animations or snapshots
of FDS results .
A new feature
of Smokeview allows the viewing of FDS output in 3-dimensional animations.
An iso-surface is a three dimensional version of a contour elevation often
found on topographic maps. In this report, a beta version of Smokeview
was used in conjunction with FDS Version 1.0 to generate animated iso-surfaces
to visualize the movement and spread of the fire.
by FDS include the geometry of the structure, the computational cell size,
the location of the ignition source, the energy release of the ignition
source, thermal properties of walls, ceiling, floors and furnishings,
and the size, location, and timing of door and window openings to the
outside which critically influence fire growth and spread. The timing
of the door and window openings used in the simulation given in Table
2 are based on an approximate timeline of the fire events in Table 1.
1. Approximate Incident Timeline
call reporting fire
fighters arriving on scene
fighters on scene requesting back-up
Chief arrives on scene
infant removed from house by this time
infant enroute to hospital
infant enroute to hospital, hoseline burned
fire fighter on 1st floor
floor plans of the first and second floor of the duplex are shown in Figures
2 and 3. The two levels of the
duplex are enclosed within a 13.4 m (44.0 ft) x 6.0 m (19.7 ft) x 5.4
m (17.7 ft) tall rectangular volume. For the FDS simulation this volume
was divided into 64,800 computational cells. Each cell has dimensions
of a 0.2 m (8 in) x 0.2 m (8 in) x 0.2 m (8 in) cube. The size of the
interior walls, doorways, and windows were based on the dimensions of
the house. The size and location of the walls, doorways, and windows are
adjusted by FDS to correspond to the nearest computational cell location.
This results in walls, used in the model, that appear thicker then they
are in the actual house and stairs that are not uniform throughout.
considered three vents or openings from the structure to the outside,
the front window in the front bedroom, the front door and the kitchen
window. The lower portion of the front window in the front bedroom had
an opening approximately 0.8 m (2.6 ft) wide x 0.4 m (1.3 ft) high with
a 0.4 m (1.3 ft) sill height. This vent was open during the entire simulation.
The front doorway was 0.9 m (3.0 ft) wide x 2.2 m (7.2 ft) high. The front
door opens at 180 s of simulation time. The kitchen window was 0.84 m
(2.76 ft) wide and 1.4 m (4.6 ft) high with a 0.8 m (2.6 ft) sill height.
The windows in the house were composed of small panes with wood framing
in between each pane. With a window of this design, it typically would
not fail or break-out all at once due to a fire. To account for partial
breakage of the window and smoke leakage from
the kitchen to the outside or other parts of the structure, the window
vent opened in three sections. The upper most 0.2 m (8 in) section of
the kitchen window opened at 90 s into the simulation. This opening is
intended to account for smoke leakage out of the kitchen. The top half
of the kitchen window opened at 270 s. This time was based on the gas
temperatures being in excess of 400 °C (750 °F) near the upper
portion of the window. The vent representing the kitchen window was completely
opened at 510 s into the simulation. Again the window was opened based
on the assumption that at 400 °C (750 °F) the wooden frame would
be burning and creating excessive thermal stresses on the window glass
doorways were open with the exception of the following doors which were
closed in the fire incident and therefore were also closed in the simulation:
the door leading from the kitchen to the bathroom, the door to the closet
in the dining room, the door between the dining room and the first floor
hallway (see figure 3). On the second floor the door
from the hallway to the bathroom was closed (see figure 4).
At the time
of the fire there was no wind, therefore for the simulation it was assumed
that openings to the exterior were at ambient pressure.
2. Time of Ventilation Events for FDS Simulation
Bed Room Window
Window,Top 0.2 m (7.9 in)
ceiling material was composed of combustible wood fiber ceiling tiles,
with the exception of the dining room, which still had the original plaster
on lathe ceiling. The ceiling tiles were attached to wood furring strips,
which were attached to the bottom of an existing plaster on lathe ceiling.
The plaster ceiling assembly was modeled with the thermal properties of
walls of the first and second floor hallways, the stairwell, bedrooms
2 and 3 and the wall between bedroom 1 and bedroom 2 were covered with
wood paneling and modeled as thin pine. All other walls were covered with
floor was modeled as pine. The downstairs floor was assumed to not contribute
to the fire.
furniture items were included in the scenario; kitchen cabinets, kitchen
table, dining room table, living room sofa and two upholstered chairs.
The model inputs utilized for each material type are given below in Table
3 and the size of the furnishings are given in Table 4 [1,4].
Thermal Properties Data
In addition to wood dining furniture, a cut evergreen tree was located
in the Dining Room. The tree's contribution to the fire was estimated
by adding the heat release rate from a 2.5 m tall, 1.2 m wide Scotch Pine
with a mass of 9.5 kg . The peak heat release rate
was approximately 1.6 MW. This was the smallest tree used in the referenced
study and it appeared to be the best representation of the tree that was
in the house. As a point of reference, the maximum peak heat release rate
from a burning cut pine tree measured in the referenced study was 5.2
In the model,
the tree is represented by a rectangular box, 1.26 m by 0.8 m and 0.2
m above the floor. The box is the source of the energy emitted by the
tree, much like a gas burner. In one of the simulations, the tree was
assumed to have ignited based on the thermal conditions in the dining
room at 400 s. This did not significantly change the fire conditions in
the structure and therefore the additional heat release rate input was
eliminated from the final model simulation presented here.
Table 4. Furniture Materials and Size
m wide, 0.4 m deep, 0.6 m high
m wide, 0.6 m deep, 0.9 m high
m deep, 0.2 m thick, 1.0 m high
m deep, 0.2 m thick,0.8 m high
m wide, 0.63 m deep, 0.8 m high
m wide, 0.80 m deep, 1.20 m high
fire started in plastic material on top of the stove. This fire source
was approximated as a rectangular object representing the stove with a
specified heat release rate coming out of a opening on the top. The "stove"
can be seen in figure 15. The opening, which represents
the fire area on top of the stove, is 0.4 m wide by 0.84 m deep and 1.0
m above the floor. The heat release rate of the fire was assumed to grow
slowly, reaching a peak of approximately 400 kW in 270 s. The actual fire
may have taken longer to develop; the actual ignition time of the fire
is unknown. The simulation was started with a flaming ignition that corresponded
to the approximate time at which the adult occupant and the neighbors
became aware of the fire.
and Contents Simulation
shows a front perspective view of the right side unit of the duplex from
the Smokeview model. The outer box frame lines represent the volume modeled.
The solid base is used to indicate the inert first floor material. The
closed front door, the partially open front bedroom window and the porch
roof can be seen on the front side of the house. Figure 14
provides a side view of the model. The figure shows the front of the duplex
on the left, moving to the right is the living room and then the dining
room on the first floor. The front bedroom and middle bedroom can be seen
on the second floor. The kitchen and rear bedroom are obstructed by the
outside wall of the duplex on the far right. Significant pieces of furniture
have been modeled on the first floor. Representations of a sofa and two
chairs can be seen in the living room on the left side of the figure.
The "floating square" in the dining room represents the dining
room table and chairs. The kitchen window can be seen on the far right
side of the house. Figure 15 provides a view of the
simulated structure from the back. From this view the
stove can be seen centered in the kitchen with the kitchen cabinets on
the right side of the kitchen. The side of the house with the stairway
is shown in figure 16. From the bottom left and moving
toward the right on the first floor is a bathroom, the kitchen, a closet
under the stairs and the entry foyer. On the second floor, another bathroom,
the hall and open stairway and the front bedroom can be seen. The area
on the far right represents an area outside the front of the house. The
grid depicting the computational cell size is shown in figure 17.
Each cell has dimensions 0.2 m (8 in) x 0.2 m (8 in) x 0.2 m (8 in).
Simulation - Temperature Predictions
results in Figures 18 through 20
have had the outer walls removed to provide a clear view. The results
are shown as a "slice" or a "plane" with a color bar
that represents the corresponding numerical quantities. These figures
provide "snapshots" of the calculated fire environment conditions
that the firefighters may have been exposed to between 8:32 AM and 8:34
18 and 19 show the plane of
temperatures that align with the center of the kitchen and dining room
doorways. This plane is located 2.9 m (9.5 ft) into the duplex from the
outside wall of structure. The second temperature plane shown in the figures
is located along the centerline of the kitchen window.
18, a distinct two-layer environment can be seen
in the living and the dining room at 485 s into the simulation or approximately
8:32 AM. In the living room the upper or hot gas layer temperatures are
approximately 200 °C to 300 °C (390 °F to 570 °F). In
the dining room the hot gas temperatures are approximately 300 °C
to 450 °C (570 °F to 840 °F). In both rooms, temperatures
near the floor are near ambient. Gas temperatures in excess of 600 °C
(1110 °F) can be seen near the top of the kitchen doorway and at the
top of the kitchen window.
shows the same thermal planes, 55 s later at 540 s of the simulation.
By this time, gases in excess of 600 °C (1110 °F) had spread across
both the dining room and the living room, potentially igniting the combustible
surfaces in the top portion of these rooms. Other gases, hotter than the
ignition temperature of wood, are shown leaving the kitchen window and
spreading up the outside of the house. This rapid change is consistent
with a flashover occurring in the kitchen.
displays the plane of temperatures aligned with the center of the stairs,
0.4 m (1.3 ft) into the house from the shared interior wall. Approximately
600 s or 10 min into the simulation, gases in excess of 600 °C (1110
°F) have filled the open stairwell.
Sheet Fire Simulation
through 24 show a series of views of the simulation
that approximate the flame spread through the structure. The iso-surface
simulation provides a three dimensional approximation of the flame surface
area where fuel, heat and oxygen are present such that flames may exist.
The flames can be seen covering the top of the stove at approximately
220 s or 8:28 AM, in figure 21. Approximately 4 minutes
later, at 8:32 AM the fire has spread across the kitchen ceiling and has
vented through the kitchen window as shown in figure 22.
Figure 23 presents a side view of the house at approximately
8:33 AM. The flame front has extended through the dining room and into
the living room. The final figure in the series, figure 24,
shows the estimated flame sheet spreading up the stairway at 600 s of
simulation time or 8:34 AM. This series of figures is another demonstration
of how rapidly the fire grew and quickly the flames spread through the
house, trapping the firefighters.
FDS computer simulation predicted fire conditions and events that correlate
well with information from NIOSH and ATF.
simulation was based on a fire that started on the kitchen stove. Smoke
and hot gases from the fire began to spread through the house within seconds
after ignition occurred. However, the FDS/Smokeview simulation of the
flame front indicates that the fire itself did not spread beyond the kitchen
until approximately 8 minutes after flaming ignition.
event in this fire was the on-set of conditions consistent with flashover
in the kitchen. At this point, approximately 8:32 AM, this fire started
a transition from a single room and contents fire with smoke throughout
the structure, to a fire that involved the majority of the structure within
approximately 60 s. The hot gas layer temperatures in the living room
increased from approximately 200 °C to 300 °C (390 °F to 570
°F) to more than 600 °C (1110 °F) in less than a minute. The
hot gases and flames continued to spread rapidly from the living room
through the stairway to the second floor. This quick change in thermal
conditions and flame spread through the duplex led to the 3 firefighters
being trapped inside and succumbing to the effects of the fire environment.
Kevin B., Baum, Howard R., Rehm, Ronald G., Hamins, Anthony, Forney,
Glenn P., Fire Dynamics Simulator - Technical Reference Guide, National
Institute of Standards and Technology, Gaithersburg, MD., NISTIR 6467,
Kevin B., Hamins, Anthony, and Stroup, David, Sprinkler, Smoke &
Heat Vent, Draft Curtain Interaction - Large Scale Experiments and Model
Development, National Institute of Standards and Technology, Gaithersburg,
MD., NISTIR 6196-1, September 1998.
Kevin B., Baum, Howard R., Rehm, Ronald G., Large Eddy Simulations of
Smoke Movement, Fire Safety Journal, vol 30 (1998), p 161-178.
Kevin B., Forney, Glenn P., Fire Dynamics Simulator - User's Manual,
National Institute of Standards and Technology, Gaithersburg, MD., NISTIR
6469, January 2000.
John, M., Wood and Wood-based Products, NFPA Fire Protection Handbook,
18th ed Section 4, Chapter 3, National Fire Protection Association,
Quincy MA, 1997.
D.W., DeLauter, L., Lee, J., and Roadarmel, G., Scotch Pine Christmas
Tree Fire Tests, National Institute of Standards and Technology, Gaithersburg,
MD., Report of Test FR 4010, December 1999.
would like to thank Ms. Dawn Castillo, Mr. Richard Braddee and Mr. Thomas
Mezzanotte of the NIOSH Fire Fighter Fatality Investigation and Prevention
Program for their support of this research. The authors extend their appreciation
to Special Agent Christopher Van Vleet and Andrew Cox of the Bureau of
Alcohol, Tobacco and Firearms for their thorough documentation of the
structure involved in this fire incident. Finally we would like to thank
Dr. Kevin McGrattan for his continued development of the NIST Fire Dynamics