This video provides an overview of an analysis
conducted by the National Institute
of Standards and Technology or NIST,
to provide insight into the dynamics of a fire
that resulted in two line of duty deaths.
On June 2, 2011 a fire in a multilevel residential structure
claimed the life of a lieutenant and firefighter paramedic
from Engine 26 of the San Francisco Fire Department.
NIST examined the fire dynamics of this incident
at the request of NIOSH,
and the San Francisco Fire Department.
At 10:45 in the morning
a call was dispatched for a reported fire
due to an electrical short.
Engine 26 arrived on scene
within three minutes of the dispatch
and reported light smoke conditions.
They made entry through the front door
with 1 3/4" hose line.
At approximately 10:54,
about six minutes after the arrival of Engine 26,
Battalion Chief 9 followed the Engine 26 hose line
up the front stairs into the front door
and then down the stairs to the first floor
or street level of the house.
Battalion Chief 9 had a face-to-face discussion
with the victims.
During this discussion,
Engine 26 confirms that the fire is below them
and Battalion Chief 9 indicates
that the attack will be made from the basement level
on the B side.
The Battalion Chief exited the building.
Engine 26 remained in position near the top of the stairway,
leading into the basement.
This was the last communication with the Engine 26 crew members
inside of the structure.
Within 11 minutes of Engine 26's arrival on the scene,
the large windows
that made up most of the side sea wall of the basement level,
began to fail due to heat from the fire.
As the windows broke,
fresh air, mixed with hot fuel-rich gases in the basement
which increased the heat release rate of the fire.
The increase in heat release rate
resulted in the rapid failure of the six window panels.
It took less than two minutes
for all of the windows to fail.
After the rear basement windows began to self-vent,
Engine 24 and Rescue 1A
tried to make entry through the pedestrian door in the garage
to attack the fire,
but they were forced back by extreme heat
and heavy black smoke.
With a pedestrian door between the garage
and the first floor hallway open,
heavy black smoke began flowing out of the open garage door
at street level on side A.
Within a minute of this change,
the side B door in the basement level was forced open,
Battalion Chief 9 reported heavy fire and smoke.
Engine 11 tried to make entry into the basement,
but they were forced back by the heat.
Battalion Chief 9 requested a second hose line.
Incident command attempted to contact Engine 26
several times via radio with no reply.
By 11:02, both Engine 11 and Engine 32
had made entry through the side B door into the basement
and initiated suppression operations.
At approximately 11:08
the lieutenant and firefighter paramedic from Engine 26
were found in the first floor hallway
between the top of the stairs from the basement level
and the door to the garage.
Both of the Engine 26 crew members died of their injuries
sustained in the fire.
NIST's Fire Dynamics Simulator or FDS
was used to provide insight
into the dynamics of this structure fire.
The results of an FDS simulation are visualized
with another NIST program called Smokeview.
The inputs and details for the FDS simulations
are documented in this technical note 1856.
The fire started in the basement near the balcony windows
on the rear of this structure.
The fire spread to a large sectional sofa
in the center of the basement living room area.
Based on an assessment of the fuel load
in the burned area of the basement,
the estimated peak Heat Release Rate
of the furnishings and interior finish
was approximately 20 MW;
however, the lack of oxygen limited the fire growth
until the rear basement windows vented.
As seen in the Heat Release Rate graph,
after the windows failed and allowed additional oxygen
to mix with hot fuel gases in the basement,
the fire rapidly increased from less than 5 MW
to more than 25 MW in less than a minute
after the first window self-vented.
The comparison of photographs from the incident
and images from Smokeview
shows the rapid fire growth initiated
by the uncontrolled ventilation of the rear basement windows.
The photographs show the fire incident time;
while the Smokeview images show the simulation time.
The comparison of a photograph from the incident
and from the simulation
shows the condition on the front side of the house
at street level
as the rear basement windows were self-venting.
Now we will use output from the simulation
to understand the flow path within the multilevel structure,
fire gases move from regions of higher pressure
to regions of lower pressure,
this video shows the pressure plain
along the center of the stairway
from the basement to the laundry room landing
between the basement and the first floor.
An estimate of the pressure increase is shown
before and after the first basement window failed.
This video shows the pressure plain
along the center of the stairway
from the basement to the laundry room landing
between the basement and the first floor.
An estimate of the pressure increase
is shown before and after the first basement window failed.
One of the hazards to firefighters
located in the exhaust portion of the flow path
is convective heat transfer from the fire gases.
Convective heat transfer depends on the velocity,
the amount of turbulence,
and the temperature of the fire gases.
This video shows a comparison
of gas velocity estimates in the stairway,
before and after the basement windows self-vented.
Another way to visualize velocity with Smokeview
is by using arrows or vectors.
In this video the vectors show both gas flow direction
and gas flow speed.
This is also representative of the amount of turbulence
or mixing within the flow path.
Notice the gas flow circulation pattern on the landing
which indicates a very turbulent or well mixed flow.
This video shows the calculated change in gas temperatures
as a result of the fire's rapid increase in Heat Release Rate
before and after the windows self-vented.
These images show the flow path
from the fire on the basement level,
2 minutes after the first basement window failed.
At this time, all of the rear basement windows are failed.
The hot gases in the basement are flowing up the stairwell
and splitting on the first floor
with some of the flow continuing up another stairwell
to the open front door
and the rest of the hot gas flow
moving out of the open pedestrian doorway
through the garage.
Notice that the open basement windows on the rear of the house
serve as bidirectional vents,
with fire gases exiting the upper portions
and air entering the lower portions.
While on the front side of the house,
the front door and the door to the garage
are unidirectional vents,
serving only as an exhaust for the fire gases.
There have been many previous fire incidents
in which changes in the flow paths
have had an adverse impact on firefighter and occupant safety.
Fires with rapidly developing or changing flow paths
are a significant hazard to firefighters.
The development of a flow path could be caused
by the failure of a component of the structure
such as a door, window,
or portion of a ceiling, wall, or floor.
Environmental conditions such as wind
can generate hazardous thermal conditions within a flow path.
Stay upwind of the fire or keep the wind at your back,
uncoordinated ventilation or uncontrolled doors
can also be the cause of increased thermal hazards
within a flow path.
In this fire incident,
the thermal degradation of vinyl-framed windows
and sliding glass doors
resulted in the self-venting of a wall of windows 19 feet wide
on the rear basement wall.
The window opening allowed hot gases to flow out of the windows
and mix with oxygen,
which enabled the fire to spread up the rear of this structure.
Oxygen in-drained into the structure
enabled additional fire growth
in the living room area of the basement;
failure of the rear windows
resulted in a rapid increase in temperature velocity
and mixing of the fire gases in the stairs
and the first floor hallway.
Conditions change from tenable to untenable within seconds.
Prediction of the failure mode
and failure time of a building component
is not a reasonable expectation
given the large number of unknowns
that firefighters face on the fire ground.
Research has been conducted by NIST and UL
with fire departments across the country
on exterior fire attack.
The studies have shown the importance of scene size up
prior to beginning interior fire operations
in order to choose tactics
that would not only be the most effective
but also increase the safety of the operations.
The experiments in single-family homes have shown that
once the basement fire was located during size up
the most effective fire attack was made from the same level.
When sizing up a structure fire
choose your tactics with potential flow paths in mind.
Recall that in a flow path,
the hot gases move from a region of higher pressure
to a region of lower pressure.
Firefighters located in the flow path downstream of the fire
can be exposed to lethal levels of heat.
Firefighters positioned in the flow path above the fire
are in a high hazard and potentially deadly location.
It is critical that tactics are chosen
so firefighters are not caught in this position.
For more information on this incident,
see NIOSH report 2012-28
San Francisco Fire Department Safety Investigation Report,
Incident 11050532, and this technical note 1856.
These reports and other information
on flow paths and fire dynamics
can be found on the NIST Firefighting Technology website.
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