NIST Fire Research: Positive Pressure Ventilation for the Fire Service

NIST Fire Research: Positive Pressure Ventilation for the Fire Service


NIST has been
conducting research on Positive Pressure Ventilation
or PPV for six years. The focus is to improve
fire fighter safety by increasing the
understanding of this ventilation tactic. NIST, with
support from USFA, DHS and fire departments
across the country, is taking engineering
principles and applying them to
fire service tactics to increase the knowledge of the street
level fire fighter. This DVD set includes
experimental results, video, and reports to improve
the understanding of PPV. In this presentation
I will explain PPV, briefly examine the
results from previous work, and focus on PPV tactics
in high-rise buildings. Our main objective is to
improve fire fighter safety by enabling a
better understanding of structural
ventilation techniques, including Positive
Pressure Ventilation (PPV) and natural venting. We do this by conducting
experiments to answer the common questions from
the fire service such as, what is the best location
to position the fan and where do you make
the exhaust opening? PPV is a technique
that is used by the fire service
to remove smoke, heat and other contaminants
from a structure in order to
perform other tasks in a more tenable atmosphere. Air from the outside is
blown into a structure to increase the
pressure inside. Air flows from a higher
pressure to a lower pressure. You control the flow
within a building. Our research began in a three
story fire training building to answer the question
what happens to conditions for fire fighters or
potential victims when you vent (either
naturally or with PPV) correctly or incorrectly? This series consisted
of 28 tests. Each test had a fuel load
of 6 pallets with hay. The position of the fire and the ventilation
location was varied. Each fuel vent
configuration was run using natural ventilation and Positive Pressure
Ventilation. Temperature, gas velocity and oxygen were measured
throughout the building. This is a comparison video
of a fire on the 2nd floor that is vented out
of an adjacent room. The video is sped up
four times real time. The views on the left
are naturally vented and the views on the
right are PPV ventilated. The inside view show that
the visibility returns much faster with
the use of PPV, but the fire size
increases more quickly. All of the data and video
views were analyzed. Average maximum ceiling
temperatures were 1100 F for naturally
ventilated fires and 1200 F for PPV
ventilated fires. To say that using PPV
makes higher temperatures is not necessarily true. Maximum temperatures
of surrounding rooms of the fire room
were almost always within 200 F of each other, independent of the
type of ventilation. PPV did not create
temperatures in adjacent rooms that would be
considered extreme as compared to naturally
ventilated fires. PPV ventilated fires
redeveloped more quickly. This was not surprising
as the fan forces fresh air to the fire. PPV also restored
visibility much faster. In most cases PPV did not
create a higher temperature between the fire
and the vent. In order to examine
the possible effects on fire fighters’ operating
in the structure, temperatures at 4 ft above
the floor were analyzed. NFPA requires that turnout gear
resist thermal degradation for five minutes
at 500 F. So 300 C or 572 F was used
as a benchmark threshold for evaluating potential
fire fighter tenability. The threshold temperature was not exceeded in
any of the scenarios, in any of the rooms
except the fire room. Temperatures were always
lower between the fan and the fire room. To determine the potential
impact of ventilation on any possible victims
in the structure, a tenability threshold of
200 F was used at 2 ft assuming a person
lying on the floor. The temperatures concluded
the turbulent mixing by the fan caused
higher temperatures at low levels beyond
the fire room. Rooms between the fan and
the fire room were cooler. In most cases the victims
located near the fire room saw temperatures above the
threshold prior to ventilation. The second set of
experiment is to compare a room fire ventilated naturally
with positive pressure. The results show
how much larger the force ventilation
can make the fire, as well as to see
the conditions that are leading
to the fire room and outside the
ventilation window. The figure show
the floor plan and the inlet door of
the corridor to the room and the ventilation window. Two similar rooms were
furnished and instrumented. The fire was started on
the bottom of the bunk beds and was allowed to grow until it became
ventilation limited. In the first experiment
the window was open and natural ventilation
was observed. In the second experiment
the window was vented, a fan was turned on
at the entrance to the corridor to
positively pressurize. Temperature, gas velocity and Heat Release Rate
measurements were made. These pictures
show a comparison of the two ventilation
techniques after ventilation. The photos on the
left show the fan forcing the flow
back to the room and out of the window, and the photos on the right
show the combustion products leaving the room out of
the window and corridor. The data show that the room
temperatures were lower for the PPV test due to
additional fresh air. The PPV fan caused a 60%
increase in burning rate during this time of initial
fire department attack, but much of it occurred
outside the room. The PPV ventilated
experiment forced the flames at least 6 ft out
of the room as compared to the 3 ft by the naturally
ventilated experiment. This could be an issue if
there are exposure concerns. The PPV forced all of
the combustion products out of the window creating better conditions
in the corridor. Results that impact fire
fighters point out that coordination of
fire fighting crews is essential to carry out
Positive Pressure Ventilation in the attack
stages of a fire. In a burning structure
any change in ventilation may lead to a rapid
change in fire. In order to increase
fire fighters safety once ventilation has taken
place and the fan was activated, the fire crew should delay
their attack for 60 seconds until the fire
has had a chance to react to the oxygen it
receives from the ventilation of the opening and the
flow from the PPV fan. Complete a 360
assessment to make sure the fan is having
the desired impact before committing crews to a rapidly changing
environment. It is important to select
a ventilation opening near the seat of
the fire to allow the increased burning to be
vented to the exterior. Conditions leading to the fire
room are greatly improved. This increases both the
speed and safety of the crews. The previous
research addressed small residential
scale structures, many questions
remained about the use of PPV tactics
in high-rise buildings. The principals
are the same, but the scale and
implementation can have a large impact on
fan effectiveness. The NFPA definition of a
high-rise is a building more than 75 ft in height from the lowest level of
fire department access. There have been many
challenging fires in high-rise buildings. Fires have been documented
in apartment buildings, hospitals, hotels, and
office high-rise buildings. The statistics from
NFPA in 2002 show 7, 300 fires in
high-rise buildings, 15 civilian deaths, 300
civilian injuries and over $26 million
in property damage. What really brought the
problem to the foreground, and it’s sad this
happens this way, but you have fire
fighter fatalities, civilian fatalities, and many
injuries on top of these. The problem being that
natural ventilation tactics in a building may
place occupants or fire fighters in the
exhaust path of hot gases and toxic combustion
products or flames. Six civilians were killed
in the stairwell of the Cook County Administration
building in Chicago in 2003. A wind-driven fire
on the tenth floor of an apartment building on
Vandalia Avenue in New York City in 1998 led to the deaths
of three fire fighters. Under normal fire fighter
operations in a high-rise, the fire department will
hook up to the standpipe, one or two floors
below the fire floor. In order to get a
hose on to the fire, the fire fighters open the
door to the fire floor. Depending on how
long it takes them to get to the seat
of the fire, the entire stacked stairwell
can fill with heat and smoke top to bottom. The fire department may
secure a second stairwell and keep that
clear of smoke by keeping the fire
floor door shut. A second stairwell will be
used to evacuate people down from the upper
floors of the high-rise. It sounds like a
good idea; however, it doesn’t usually
evolve that way. The occupants are
coming out any way they can possibly find. They are tripping
over the hose line while they are trying
to make it out, choking in smoke. Usually the
evacuation stairwell will be contaminated from smoke
leaking from the fire floor. This also causes issues
for the fire fighters operating above
the fire floor. A potential solution
is to use PPV fans to pressurize the stairwells. The increased pressure
prevents heat and smoke from entering
the stairwell, in effect increasing
occupant safety and fire fighter safety. A lot of knowledge
could be gained by looking at fixed stairwell
pressurization systems. Many newer high-rises
have fixed stairwell pressurization systems
installed in them. These systems have
been tested to work. Typically, a centrifugal
fan is mounted either at the top or the
bottom of your stair, with a single
injection point, or could be a multiple
injection point system. The key is that the
fire and hot gases won’t spread to an area
with a higher pressure. Air, and in this
case fire gases, want to flow to
a lower pressure, the path of least
resistance. If you create a pressure, you can stop the
flow fire gases and control where
that flow will go. NFPA Standard 92A;
this is a Standard for Smoke-Control
Systems Using Barriers and Pressure Differences. This is the criteria
that we will use for a lot of this research and the purposes of the
standard are listed here. The bottom line is to use
pressure differences to protect stairwells,
to protect floors, whatever you want to keep
as your area of refuge to make fire fighting
operations safer and to make
evacuation safer. The table shows the minimum
pressurization requirements from NFPA 92A. This is based on data
from fire experiments. Different pressures
are required based on the ceiling height and presence of an automatic
fire sprinkler system. The pressures are shown
in inches of water and in pascal. I will talk in pascal;
that’s a lot easier because it’s
whole numbers. For example, 0.1 of
an inch of water or 0.0037 PSI is
equal to 25 pascal; therefore, very small pressure
differences are needed to control the flow of smoke. So a real simple illustration
of what we are doing here, the fire creates
its own pressure, the hotter the
temperature, the higher the pressure
the fire creates. The NFPA standard calculates the required pressure
difference of 25 pascal, assuming the hot gas
temperature of 1700 depress F and using a safety
factor of 7.5 pascal to account for
open doors or leakage. The first set of
high-rise experiments I am going to take you
through was in Toledo, Ohio. We had a 30 story
vacant office building. The purpose of this was to
use commercially available portable fans that the fire
department has on their trucks or has the availability
to purchase and see what
kind of pressure we can create in
these high-rises. We also took a look at
larger mounted fans and we aimed to start answering
some of the questions such as, where is the best
place to put the fans, how far back from
the door do I put it, and what location do I put
it to be most effective? The instrumentation we
used to get these answers was to measure pressure and temperature on
all the odd floors, all the way up
the stairwell. We also measured
the air velocity at the ventilation doorways. You can see a velocity probe
in the photo on the left. The other photos
from left to right show our data
recording equipment, a close-up of one of our differential
pressure transducers and how it was installed
on the stair door. Experimental Variables,
first off Fan Size. You can find fans available
from all fan manufacturers ranging from 16 inches all
the way up to 46-inches. You can see a range
of fan sizes there. The larger trailer mounted
fan was 46 inches. We measure speeds on
the face of that fan over a 110 miles an hour. The local fire department came
over from Washington Township; they brought
their hovercraft. Chief of Toledo, Ohio had
mentioned that they had a warehouse fire
and in order to get the smoke out they
used the hovercraft. So if the hovercraft was
useful in the warehouse, the Chief was
curious to see if it would be effective
in high-rise operations. The Number of Fans; this can be how many
fans are on your truck or how many show
up on a box arm. We examined the pressures
created from 1 to 9 different fans at different
entrances in the building. In addition, the location
and distance from the door and fan angle were
documented to determine which conditions provided
the best pressure increases. In addition, fans were
placed inside the building to measure the effective
pressure rise in the stairwell. Here are some of the
answers for a Single Fan. The floor number is shown
on the left-hand side of the graph, from
the ground floor, all the way up to
the 30th floor and the pressure is
shown on the bottom. And because we had a
non-sprinkler building, the fan needs to create a
pressure difference of at least 25 pascal
to prevent smoke and hot gases from entering the stairwell
based on NFPA 92A. So with a single 27 inch fan at
the base of the stairwell on the ground floor, the graph shows
several things. First, this fan cannot
generate enough pressure to protect the entire stairwell; and two, in this case 4 foot and
6 foot back from the doorway, at 8 degrees gives us
the best effectiveness. What’s happening is that
if you set your fan back 4-6 feet from
that threshold, tilt it back 10 degrees, it’s not just pulling
air through the shroud; it is also through
a Venturi effect pulling air
around the shroud and then training
it around the fan, which gives you your cone
of air to seal that door up. So you don’t have to set
the fan 10 feet back. Actually, if you set
the fan 10 feet back, you are not getting nearly
the effect in this you should be from your fan. The most effective way
of pressuring the stair with the small portable fans
was to use at least two fans; one at the base
of the stair and one two floors
below the fire floor. This arrangement
provided pressures in the entire stairwell that exceeded 25 pascal and would keep any smoke
out of the stairwell. Fans inside the building
are more effective than any number of fans
at the ground level. We had nine fans at
the ground level and three of them
blowing into every door on the ground floor
of this high-rise, and we couldn’t get
close to 25 pascal. We were getting numbers in
the range of 10 pascal, which is not going
to be effective. So the number one thing is
that you want to get that fan at the base
of the stairwell, that increases
your effectiveness through your fourfold, and if you have to take
fans inside the building to do that,
that’s what you do. This always raises
a question about CO generated by the fans; I will address that
in a few slides. The second answer was a
large trailer mounted fan. In this case the recorded
pressures were over 100 pascal at the ground floor
and reached 25 pascal near the top of the stair. The fan was
located 30 feet from the doorway for this test. So what did we learn? We learned that fans
should be placed 4 to 6 feet back from the doorway and
angled back 5 to 15 degrees. That’s sort of a blanket
guidance based on 16 inch, 21 inch, and 27 inch fans. The key is to make sure
that the cone of air covers the entire
doorway opening. Fans arranged in a V-shape
are much more effective than those in series. If you put fans in a row, they block a lot of
each other’s flow, but the angle one up and angle one down
doesn’t really matter as long as you put
them in the V-shape. Portable fans at the
ground entrances or the base of the stairs alone
is not effective for high-rise; one fan by itself
can’t do it, nine fans at the base of
the building cannot do it, putting fans in the building
at the base of the stairs and one below the fire
floor was most effective. So if you can take the fan
up the elevator to two floors below the fire floor and place it set back
outside the stairwell, just like you would
at the front door. No vent is needed for
the fan in the building. The fan does not
require makeup air in order to increase the
pressure in the stairwell. It doesn’t have
to flow anywhere. It doesn’t have
to pull new air. The trailer mounted fan
was very effective and the CO produced
inside the buildings was not a major concern. We are not getting anywhere
near IDLH conditions. Giving someone a
slight headache is better than subjecting them to 1,000 of parts per
million of CO from the fire. So if I am one of you fire
guys watching this I would say, okay, show me
some air tests, that’s nice; you have got
some data, that’s nice, but how does it really
work with a fire? This took us to Chicago. We wound up in the
South Side of Chicago, in the former area of the
Robert Taylor Projects. They happened to have a
vacant 16 story building, which they were
planning to tear down. Working with the Chicago
Fire Department, this turned the building
into a fire land. We built on what
we did in Toledo. We used fans only to see what level of pressures
we could create. We burnt two furnished
rooms on three floors to develop realistic
conditions, and then we topped it of with a
wind-driven fire experiment. We instrumented
the building so that we could
measure pressure, temperature, heat flux, carbon monoxide,
and wind conditions. We also measured noise
levels to examine potential interference
with communications. If you have the fan
blowing into the stairwell and you have your command
set up on the first floor, what kind of effect is
that going to have? This is the floor
plan showing cameras. In the next few slides I
will present videos to show the effects of PPV on
the conditions on the stairwell. Each experiment we had at
least six video cameras and two thermal
imaging cameras. All these videos are included
on the enclosed DVDs. This is a photograph of the
East Side of the building. The three floors that we
conducted fire experiments on were the 3rd,
10th and 15th. These floors and the
connecting stairwell are all outlined in red. Here is a typical
floor plan, on the 10th and 15th
floors we ignited furnished living rooms
in apartment 3 and 5, on the 3rd floor we ignited a
living room in apartment 3, in apartment 4 on the
third floor a bedroom and living room
were furnished. The fire was ignited
in the bedroom and that a fan was started outside the bedroom window to
simulate a wind-driven fire. The stairwell we were
mainly interested in protecting
for fire service use is shown between
apartment 2 and 3. In some of the tests
efforts were made to protect the
elevator lobby stair for occupant
evacuation purposes. So start to finish,
here is a quick look, photograph of one of the
furnished living rooms on the top left, the photo
from outside of the building looking at the smoke coming
out of the fire apartment. Photo on the lower
left shows the flames and then post
flashover conditions. This is the video view from
the fire department stair looking at an open
door on the 15th floor, the fire floor. There are two
portable fans in use; one on the first floor and
one on the 13th floor. You are seeing the effect
of the pressure barrier. We have got a fully involved
room right next to the stair and the smoke was kept
completely out of the stairwell. Now the fans
are turned off, this is what would
normally be happening. The smoke flows
into the stairwell and up to the 16th floor, comes down to the 15th
floor and bangs down. So this is a condition
you will be working when without the fans. Then we turn the
fans right back on and open up the 16th floor
and pull the smoke out. Watch the smoke go right
back out the stairwell and right back to our
effective pressure barrier. The smoke is right there
outside the doorway, you can stick
your hand in it, but the pressure is high
enough in the stairwell, it cannot flow back
into the stairwell. This video shows the rapid
change that PPV can have on conditions in
the stairwell. The stairwell was
filled with smoke from the 3rd floor up
to the 16th floor. What you are seeing is how
quickly you can clear it out if you open the
16th floor up and have a large fan
pressurizing the stairwell. This addresses
the condition when the fire
department shows up and the stairwells are
already full of smoke. This video demonstrates
venting the stairwell to start and keeping the
stair pressurized to maintain good
working conditions. Look how much
better it gets when you have a completely
clear stairwell as opposed to not being
able to see your hand in front of your face. This is the video view from
the fire department’s stair looking at the
open doorway on the 10th floor of
the fire floor. The Chicago Fire Department
truck mounted fan was positioned at the outside
door on the ground floor. There was zero visibility so we
used thermal imaging cameras to get a view of
what was going on. Look at the amount of heat
flowing into the stairwell. Notice the temperature
reading of the ceiling from the IR camera is
about 500 degrees. It’s not measuring
the gas temperature, which is approximately 700
degrees F in the hallway. When the fan is turned on, the flow of hot gases
into the stair stops. The increased pressure in
the stair holds the heat and smoke at the doorway. This graph shows what the
temperatures in the corridor between the fire department and the stair did when
the fans got turned on. The distances in
the graph are shown measured from the ceiling. When the fan is turned on, the temperature near
the ceiling drops from 700 degrees F to below
300 degrees F within seconds. The wind-driven fire
test in apartment 304. Since 1998 there have
been a lot of questions about the fire on
Vandalia Avenue where three fire fighters
died on the 10th floor. One of the contributing
factors to that was the wind condition
that existed during that high-rise
building fire. A window failed and fire
fighters in the public corridor didn’t have time
to get to a safe area. We use the Chicago Fire
Department MVU to generate a 20 to 25 mile per hour
wind at the bedroom window. So we use this to blow
into the building instead of creating pressure to
keep smoke out of the stairwell, just to see what kind of
conditions we can get. You can see here we
furnished the living room, we furnished the bedroom,
and the fan simulating the wind was located right
outside the bedroom window. The doorway to the
hallway was open and one of the views you are
going to see right out here in the hallway looking
into the fire department. Another is looking
into the living room, and the other one is looking
at the fire in the bedroom. So here is our four
views of the experiment. The fire starts in the
bunk bed in the bedroom. Here is the window that the wind is going to
be introduced through, here is the living room, and you will start to see
smoke coming from the bedroom that’s back here. And here are the two views
looking at the apartment door from the hallway. So this is a visual view
and this is an IR view. The stuff in the way is
our instrumentation for getting temperature and
heat flux measurements. One minute into it
there is some fire developing on the bottom
bunk, up to the top bunk. Smoke is poring out
into the living room and heat is coming
out into the hallway. There is a smoke
layer in the hallway, which fire fighters
can crawl under with pretty good visibility. The fire in the room
is fully developed and approaching flashover. The smoke layer is beginning to
drop with very black smoke. Increased heat is flowing
into the hallway. At 2 minutes and 18 seconds
the fan was turned on, simulating a 20 to 25
mile an hour wind coming in through
the bedroom window. Horizontal flames are
forced down the hall through the living room
and out in the corridor. The temperatures increase
throughout the apartment and corridor very rapidly. Keep in mind that
the temperatures shown on the thermal
imaging camera display is the
temperature of the wall. Gas temperatures
in the corridor are in the order
of 1500 degrees F. This experiment gave
us some insight into what happened
at Vandalia Avenue. You can take a room
and contents fire and as soon as
that window fails and wind forces the
fire into the building, you only have a
matter of seconds to get out of the way and you oftentimes
don’t see it coming and you can’t
do it fast enough. Here is a look at temperatures
3 ft from the floor. The grading of that
temperature shows that there was less
than 10 seconds to get back to the stairwell. This is the outside view
of the same experiment. Chicago’s Mobile Ventilation
Unit is elevated up to the third floor and
blowing into the window. It’s blowing 20 to
25 miles an hour, but you can see the flame
is pulsing out of the window. What it’s doing is
actually over-pressurizing the interior space and
forcing the flames back out. After it blew opened the door
to the center stairwell, we open the door to
the south stairwell, so it’s pressurizing the
entire third floor, both stairwells, and it’s still
over-pressurized to the point where fans are able
to blew back against the 25 miles per hour wind. This research would
not be possible without the assistance
of the Fire Service. Here is a list of
those departments that had a significant
role in this research. These Fan Manufacturers have
also provided great support.

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