>> 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 the fire that
resulted in the injury of seven Prince George's County firefighters.
On February 24, 2012,
a wind driven fire in a condemned single family residential structure
resulted in a series injury of an officer and a forcible entry firefighter
from truck 809 of the Prince George's County Fire Emergency Medical Department.
NIST examine the fire dynamics of this incident at the request of the department.
At 9:11 in the evening, a call was dispatched for
a residential structure fire in Riverdale Heights, Maryland.
Truck 809 was the first due truck and
arrived on scene with in seven minutes of the dispatch.
The 809 officer observed smoke moving extremely fast through the front yard and
across the street.
The truck 809 officer and forcible entry firefighter proceeded
directly from the truck to the front door of the structure.
Less than one minute after the arrival of truck 809, officer and
forcible entry firefighter both in full PPE and
SCBA have entered the structure and begin search of the first floor.
Smoke and heat conditions on the first floor worsened and
the front door slammed shut trapping the two members of truck 809.
Within 30 seconds of the door closing, the truck 809 officer cleared a portion
of the living room window on the front of the structure and exited to the outside.
Truck 809 forcible entry was unable to self-evacuate and
continued to endure the elevated thermal conditions in the living room.
Although truck 809 officer had sustained injuries and damage to his SCBA,
he alerted other firefighters that his crew member was still inside.
Fire attack had started from the basement door on the rear of the structure.
The front door was reopened and
a group of firefighters including the truck 809 officer entered the living room,
found a down firefighter and pulled him outside through the front door.
>> In February of 2012,
I had a fire on 57th avenue in the Riverdale Heights community.
It's a single family house, just like any other small,
single family home in the county.
First arriving units reported smoke and
fire showing from a basement level, about 9 PM.
It was a red flag day.
Meaning, the weather service had instituted a red flag warning for
high winds and dry conditions.
The truck and engine arrived together.
Truck crew of two for the inside crew went ahead of the engine line.
They were gonna initiate a search for what appeared to be an unoccupied home.
They made it in a front door that had a swing opposite of what you would consider.
So instead of swinging to a wall, the swing was in to the middle of a room.
Fire was in a basement below.
When they entered, the hose line had not made in the door and the energy from
the flow path that was now created coming out from the basement steps and
now out the front door that they had just opened.
That energy slam that front shut behind them.
Within a matter of two minutes,
those first two firefighters became trapped and one of them incapacitated.
The one, smaller of the two was able to bust out one window,
which was not big enough for him.
And of course, that created another flow path.
He got to a bigger window, busted that out, created a bigger flow path, but
he was able to get out.
He was unable to get the engine crew who was still on the front porch had
not made entry yet was able to get them to help him force open the front door and
pull the other young man out.
That young man was in the burn center for 45 days.
Nearly, lost his life.
>> 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 smoke view.
The inputs and details for
the FDS simulations are documented in this technical note 1870.
The fire started in the basement near the windows on the rear of the structure.
Based on on assessment of the field load on the burned area of the basement,
the estimated preheat release rate of the furnishing interior finished was
approximately nine megawatts.
However, the lack of oxygen limited the fire growth until the front door was open.
As seen in the heat release graph after the door was opened and allowed additional
oxygen to enter and mix with hot fuel gases in the basement, the fire heat
release rate increased with some of the burning occurring on the first floor.
Comparison of the simulated initial fire conditions in FDS versus the post-fire
damage of the exterior of the basement corner where the fire started.
The wind was blowing from the rear of the house to the front.
In the model, a steady wind speed of 20 miles per hour was used.
The output from the FDS simulation can be used to provide insight to the flow path
within the two level structure.
Fire gasses move from regions of higher pressure to regions of lower pressure.
Notice on the outside of the structure that the up wind side of the house or
the rear of the house is under a higher pressure than the down wind side or
the front of the house.
The inside of the house has been pressurized by the wind from the openings
on the rear side and the pressure from the fire gases.
Once the front door is open, the high pressure on the rear of the outside of
the house and the inside of the house equalize.
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 the change in gas velocity on the first floor
after the front door was opened.
Notice the distinct flow of hot gases from the doorway at the top of the basement
stairs to the front door.
An arrow shows how the hot gas is traveling at 10 to 20 miles per hour would
have impacted the front door and forced it closed behind the truck 809 crew.
This video shows the calculated change in gas temperatures as a result
of opening the front door, which increased the flow and
mixing of the fire gases within the house.
Wind can generate hazardous thermal conditions within a flow path.
Stay up wind 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.
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 the high hazard and
potentially, deadly location.
It is critical that tactics are chosen, so
firefighters are not caught in this position.
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 anterior
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 if shown that once the basement fire was
located during size up, the most effective fire attack was made from the same level.
For more information on this incident, see Prince George's County Fire and
EMS Department Safety Investigation Team Report and NIST Technical Note 1870.
These reports and other information on fire dynamics, flow paths and
wind driven fires can be found on the NIST firefighting technology website.
For updates follow NIST on Twitter.