DOCUMENT Analysis of Changing Residential Fire Dynamics and

DOCUMENT Analysis of Changing Residential Fire Dynamics and
Analysis of Changing
Residential Fire Dynamics and
Its Implications on Firefighter
Operational Timeframes
Analysis of Changing Residential Fire Dynamics
Analysis of Changing Residential Fire Dynamics and
Its Implications on Firefighter Operational Timeframes
Stephen Kerber
There has been a steady change in the residential fire environment over the past several
decades. These changes include larger homes, different home geometries, increased
synthetic fuel loads, and changing construction materials. Several experiments were
conducted to compare the impact of changing fuel loads in residential houses. These
experiments show living room fires have flashover times of less than 5 min when they
used to be on the order of 30 min. Other experiments demonstrate the failure time of
wall linings, windows and interior doors have decreased over time which also impact
fire growth and firefighter tactics. Each of these changes alone may not be significant
but the all-encompassing effect of these components on residential fire behavior has
changed the incidents that the fire service is responding to. This analysis examines
this change in fire dynamics and the impact on firefighter response times and
operational timeframes.
Introduction
There is a continued tragic loss of
firefighters’ and civilian lives, as
shown by fire statistics [1, 2]. One
significant contributing factor is the
lack of understanding of fire behavior in
residential structures resulting from the
changes that have taken place in several
components of residential fire dynamics.
The changing dynamics of residential fires
as a result of the changes in home size,
geometry, contents, and construction
materials over the past 50 years add
complexity to the fire behavior (Figure 1).
NFPA estimates [3] that from 2003 to
2006, US fire departments responded to
an average of 378,600 residential fires
annually. These fires caused an estimated
page 2
annual average of 2,850 civilian deaths
and 13,090 civilian injuries. More than
70% of the reported home fires and 84%
of the fatal home fire injuries occurred
in one- or two- family dwellings, with
the remainder in apartments or similar
properties. For the 2001–2004 period,
there were an estimated annual average
38,500 firefighter fire ground injuries
in the US [4]. The rate for traumatic
firefighter deaths when occurring
outside structures or from cardiac arrest
has declined, while at the same time,
firefighter deaths’ occurring inside
structures has continued to climb over the
past 30 years [5]. Additionally, on average
firefighters in the United States receive
less than 1% of their training on the
subject of fire behavior [6]. The changes
Analysis of Changing Residential Fire Dynamics
Figure 1: Modern fire formula
in the residential fire environment
contents and construction materials have
to the responding fire service resources
training are significant factors that are
more years. Each of these factors will be
the average home size has increased 56%,
firefighter traumatic deaths and injuries.
safety of occupants and the responding
combined with the lack of fire behavior
contributing to the continued climb in
As homes become more energy
efficient and fuel loads increase fires will
become ventilation limited making the
introduction of air during a house fire
extremely important. If ventilation is
increased, either through tactical action
of firefighters or unplanned ventilation
resulting from effects of the fire (e.g.,
failure of a window) or human action
(e.g., door opened by a neighbor) heat
changed significantly over the past 50 or
examined in detail as they pertain to the
fire service.
Home Size
Many contemporary homes are larger
than older homes built before 1980.
Based on United States Census data [7]
homes have increased in average area
from approximately 144 m2 in 1973 to over
232.3 m2 in 2008. Twenty-six percent of
homes constructed in 2008 were larger
than 278.7 m2 (Figure 2). In addition to
release will increase, potentially resulting
increased area more homes are being
induced fire conditions are sometimes
homes were two-story and that has
for firefighters to react and respond.
percentage of single story homes has
Background
time period (Figure 3).
in flashover conditions. These ventilation
built with two stories. In 1973 23% of
unexpectedly swift providing little time
increased to 56% by 2008. The
While the physics of fire development
has not changed over time, the fire
environment or more specifically the
single family home has evolved. Several
factors including home size, geometry,
page 3
decreased from 67% to 44% in the same
The larger the home is the more air
available to sustain and grow a fire in that
home. Additionally, the larger the home
the greater the potential to have a larger
fire, and the greater the potential hazard
if the proper tactics aren’t utilized. While
the fire service resources available to
respond have not increased proportionally
in many areas of the United States. This
is emphasized in suburban areas where
larger homes are being built but fewer
fire service resources are available [8].
The increase in the number of homes with
a second story means a potential for more
volume above the fire which allows the
smoke layer to remain above the fire and
allows a longer time for the fire to grow. It
also means more above ground areas for
the fire service to access for civilian rescue
and egress, potentially increasing the
chance of injury.
Home Geometry
Newer homes tend to incorporate
features such as taller ceilings, open
floor plans, two-story foyers and great
rooms [9]. All of these features remove
compartmentation, add volume and
can contribute to rapid smoke and fire
spread. Commercial building codes
require fire and smoke separations to
Analysis of Changing Residential Fire Dynamics
Figure 2: Average area of new single-family homes from 1973 to 2008 [7]
Figure 3: Percentage of number of stories of single family homes [7]
limit the impact of the fire on occupants,
content of the air decreases. Newer
to much of the home. In the living spaces
compartmentation in single family
taller than the traditional 2.4 m, upwards
archways creating large open spaces
there are minimal codes requiring
homes [10].
A trend in new homes is to incorporate
taller ceilings and two-story spaces or
great rooms [11]. Much like the impact of
having a two-story home, taller ceilings
create a longer smoke filling time that
homes are being constructed with ceilings
of 4.3 m to 6.1 m [9]. It is also common for
great rooms and open foyers to directly
connect the living spaces to the sleeping
spaces allowing for smoke generated in
the living spaces to rapidly trap potential
sleeping occupants.
allow for more oxygen to be available
Another trend in homes is to remove
surrounded by smoke filled, oxygen
home [12]. As these walls are removed the
to the fire for it to grow before being
deficient air. The heat release rate of a fire
slows down significantly once the oxygen
page 4
walls to open up the floor plan of the
compartmentation is lessened allowing
for easier smoke and fire communication
doors are often replaced with open
where there were traditionally
individual rooms.
Combining of rooms and taller ceiling
heights creates large volume spaces
which when involved in a fire require
more water and resources to extinguish.
These fires are more difficult to contain
because of the lack of compartmentation.
Water from a hose stream becomes
increasingly more effective when steam
conversion assists in extinguishment,
Analysis of Changing Residential Fire Dynamics
without compartmentation this effect
is reduced. The simple tactic of closing a
door to confine a fire is no longer possible
in newer home geometries.
calorimetry was utilized to measure the
heat release rate of furniture. A study led
by Babrauskas [16] compared different
constructions of upholstered chairs. The
cotton padded chair covered in cotton
Home Contents
The challenge of rapid fire spread is
exacerbated by the use of building
contents that have changed significantly
in recent years, contributing to the
decrease in time to untenable (life
threatening) conditions. Changes include:
(a) the increased use of more
flammable synthetic materials
such as plastics and textiles
(b) the increased quantity of
fabric produced a peak heat release rate
of 370 kW at 910 s after ignition. The
foam padded chair covered in polyolefin
fabric produced a peak heat release of
1,990 kW at 260 s after ignition. Both
chairs had a very similar total heat
released 425 MJ for the natural chair
and 419 MJ for the synthetic chair.
Home Construction Materials
Another change that has taken
place over the last several decades
combustible materials
(c) the use of goods with unknown
composition and uncertain
is the continual introduction of new
construction materials into homes [17].
The construction industry is continually
flammability behavior
introducing new engineered products
Over time home contents have
transitioned from being compromised
of natural materials to dominated by
synthetic materials [13, 14]. Synthetic
materials such as polyurethane foam
have replaced cotton as the padding
found in upholstered furniture. Today
more than 95 million kilograms of flexible
polyurethane foam are produced in the
US, enough to make 140 million sofas
[15]. This difference was examined in the
early 1980s when oxygen consumption
that provide better structural stability,
allow for faster construction time and
are more cost effective. Additionally,
the market for green or environmentally
sustainable building materials
experienced a growth rate of 23%
through 2006 and is expected to continue
growing at a rate of 17% through 2011
according to Green Building Materials in
the US [18]. The increased market demand
for environmentally sustainable products
is driving engineered lumber products to
CONSTRUCTION MATERIAL
Plaster and lath
Structural components
Old growth lumber
Windows
Single glazed (Wood framed)
Interior doors
Solid core
page 5
potentially result in even further concern
for fire safety in building construction
today and in the future. Environmentally
sustainable products take into account
resource efficiency, indoor air quality,
energy efficiency, water conservation and
affordability [19]. Life and fire safety are
not part of the material selection criteria,
while using less material and being more
affordable are.
Many home construction materials have
changed significantly for numerous
reasons such as lack of supply, ease of
manufacturing, cost, improved structural
or energy efficiency performance, and
many other reasons [20]. Home wall
linings, structural components, windows
and doors are some of the construction
materials that have evolved. Table 1 shows
some iterations of the evolution.
Evolutions in building materials create
changes in the fire environment. How all
of these changes compound to impact
fire behavior and firefighting tactics is not
well understood.
Experimental Series
Experiments were conducted to
examine the changes in contents and
construction materials. Six room fire
experiments examined the difference
between modern and legacy living room
LEGACY ---> MODERN
Wall linings
Table 1: Construction material evolutions
further reduce material mass that could
Gypsum board
New growth number
Wood trusses
Engineered I-joists
Double glazed (Vinyl Framed)
Hollow core
Composite hollow core
Analysis of Changing Residential Fire Dynamics
Experimental Description — The
placed in the rooms. In the second set
experiments were conducted in three
of rooms the modern room had a fuel
pairs of living room fires (Table 2). The
loading of 19.0 kg/m2 while the legacy
purpose was to develop comparative data
room had a fuel loading of 22.9 kg/m2.
on modern and legacy furnishings. The
The difference was due to the legacy
first four rooms measured 3.7 m by 3.7 m,
sofa and chair weighing 47% and 31%
with a 2.4 m ceiling and had a 2.4 m wide
more than the modern furniture. In the
by 2.1 m tall opening on the front wall.
third set of rooms, both the modern
The last two rooms measured 4.0 m by
room and legacy room had a fuel loading
5.5 m, with an 2.4 m ceiling and had a 3.0
of approximately 11.2 kg/m2. A similar
found in a mid-twentieth century house.
m wide by 2.1 m tall opening on the front
amount of fuel was in both sets of room
The modern rooms utilized synthetic
wall. All sets of rooms contained similar
experiments however the third set of
contents that were readily available
types and amounts of like furnishings.
rooms was 8.4 m2 larger. Each experiment
new at various retail outlets, and the
Weight measurements were not taken
was ignited using a candle placed onto
legacy rooms utilized contents that were
for the first set of experiments. However,
the sofa. An array of 0.8 mm gage Inconel
purchased used from a number of second
in the second and third set of rooms, all
thermocouples was located in each room
hand outlets.
furnishings were weighed before being
with measurement locations of every
furnishings. Furnace experiments were
conducted to quantify changes in wall
linings, structural components, windows
and interior doors.
Comparison of Modern and Legacy Room
Furnishings Experiments
Six fire experiments were conducted to
examine the changes in fire development
in a room with modern contents versus a
room with contents that may have been
EXPERIMENT
DESCRIPTION
ROOM
DIMENSIONS (M)
FRONT OPENING
DIMENSIONS (M)
FUEL LOADING
(KG/M2)
1
Modern
3.7 x 3.7 x 2.4
2.4 x 2.1
NA
2
Legacy
3.7 x 3.7 x 2.4
2.4 x 2.1
NA
3
Modern
3.7 x 3.7 x 2.4
2.4 x 2.1
19.0
4
Legacy
3.7 x 3.7 x 2.4
2.4 x 2.1
22.9
5
Modern
4.0 x 5.5 x 2.4
3.0 x 2.1
11.2
6
Legacy
4.0 x 5.5 x 2.4
3.0 x 2.1
11.2
Table 2: Experimental overview
Figure 4: Experiment 1 setup
page 6
Figure 5: Experiment 1 furniture layout
Analysis of Changing Residential Fire Dynamics
Figure 6: Experiment 2 setup
Figure 7: Experiment 2 furniture layout
Figure 8: Experiment 3 setup
Figure 9: Experiment 3 furniture layout
0.3 m from floor to ceiling. Temperatures
were sampled and recorded every 1 s.
The first set of rooms was 3.7 m by 3.7 m
The modern room (Experiment 1) was
lined with a layer of 12.7 mm painted
gypsum board and the floor was covered
with carpet and padding (Figure 4).
The furnishings included a polyester
microfiber covered polyurethane foam
filled sectional sofa, engineered wood
coffee table, end table, television stand
and book case. The sofa had a polyester
lower shelf. The coffee table had six color
unfinished hardwood flooring (Figure
synthetic plant on it. The television stand
covered, cotton batting filled sectional
panel television. The book case had two
tables, and television stand. The sofa
two glass vases on it. The right rear corner
side. Both end tables had a lamp with
magazines, a television remote and a
had a color magazine and a 37 inch flat
sofa, solid wood coffee table, two end
small plastic bins, two picture frames and
had a cotton throw placed on its right
of the room had a plastic toy bin, a plastic
polyester shade on top of them. The
toy tub and four stuffed toys. The rear
wall had polyester curtains hanging from
a metal rod and the side walls had wood
framed pictures hung on them (Figure 5).
throw placed on its right side. The end
The legacy room (Experiment 2) was lined
on top of it and a wicker basket on its
board and the floor was covered with
table had a lamp with polyester shade
page 7
6). The furnishings included a cotton
with a layer of 12.7 mm painted cement
one on the left side of the sofa had two
paperback books on it. A wicker basket
was located on the floor in front of the
right side of the sofa at the floor level.
The coffee table had three hard-covered
books, a television remote and a synthetic
plant on it. The television stand had a
27 inch tube television. The right front
Analysis of Changing Residential Fire Dynamics
Figure 10: Experiment 4 setup
Figure 11: Experiment 4 furniture layout
Figure 12: Experiment 5 setup
Figure 13: Experiment 5 furniture layout
corner of the room had a wood toy bin,
and multiple wood toys. The rear wall had
cotton curtains hanging from a metal
rod and the side walls had wood framed
pictures hung on them (Figure 7).
The second set of rooms was also
3.7m by 3.7 m with a 2.4 m ceiling and
a 2.4 m wide by 2.1 m tall opening on
the front wall. Both rooms contained
identical furnishings with the exception
of the sofa and the chair. The first room
(Experiment 3) had a polyurethane foam
filled sofa and chair with microfiber fabric
covering (Figures 8, 10). The second room
(Experiment 4) had a cotton padded,
page 8
innerspring sofa and chair with cotton
television. The book case had two baskets
were similar to those used in the first
the room had a plastic toy bin, a plastic
in polyester carpet over polyurethane
wall had polyester curtains hanging from
engineered wood coffee table, two end
wood framed picture hung on it.
cover fabric (Figures 9, 11). The contents
and a picture frame on it. The left side of
modern room. The floors were covered
toy tub and four stuffed toys. The rear
foam padding. The contents included an
a metal rod and the left side walls had a
tables, television stand and book case.
The third set of rooms was larger and
The sofa had a polyester throw placed on
its left side. The left end table had a lamp
with polyester shade on top of it and the
right end table had a television remote,
candle and vase filled with synthetic rose
pedals. The coffee table had four color
magazines and a synthetic plant on it. The
television stand had a 37 inch flat panel
measured 4.0 m by 5.5 m. The modern
room (Experiment 5) was lined with a
layer of 12.7 mm painted gypsum board
and the floor was covered with nylon
carpet and polyurethane padding (Figure
12). The furnishings included a polyester
microfiber covered polyurethane
foam filled sofa, two matching chairs,
Analysis of Changing Residential Fire Dynamics
Figure 14: Experiment 6 setup
Figure 15: Experiment 6 furniture layout
Figure 16: Experiment 1 and 2 room temperatures
Figure 17: Experiment 3 and 4 room temperatures
engineered wood coffee table, end table,
walls had wood framed pictures hung
had a polyester throw placed on its left
The legacy room (Experiment 6) was
television stand and book case. The sofa
side and two polyfill pillows, one on
each side. The end table had a lamp with
polyester shade on top of it. The coffee
table had three color magazines, a wicker
basket and a synthetic plant on it. The
television stand had two picture frames
and a 32 inch flat panel television. The
book case had a plastic basket on it. The
right rear corner of the room had a plastic
toy bin, a plastic toy tub and four stuffed
toys. The rear wall had polyester curtains
hanging from a metal rod and the side
page 9
on them (Figure 13).
lined with a layer of 12.7 mm painted
gypsum board and the floor was covered
glass vases. The television stand had a 13
in tube television with a plant on top of
it. The right rear corner of the room had a
wood/wicker toy bin, and multiple wood
toys. The rear wall had cotton curtains
with finished hardwood flooring (Figure
hanging from a metal rod and the side
covered, cotton batting filled sofa, two
them (Figure 15).
14). The furnishings included a cotton
walls had wood framed pictures hung on
matching chairs, solid wood coffee table,
Results — The fire in Experiment 1 grew
two end tables, and television stand. The
sofa had a cotton throw placed on its left
side. Both end tables had a lamp with
glass shade on top of them and a wicker
basket. The coffee table had a wicker
basket filled with five books and two
slowly for the first minute as the candle
flame extended to the polyester throw
blanket and sofa cushion. At 2 min the
fire had spread to the back cushion of the
sofa and a black smoke layer developed
in the top two to three feet of the room.
Analysis of Changing Residential Fire Dynamics
Figure 18: Experiment 3 and 4 heat release rate comparison
Figure 19: Experiment 5 and 6 room temperatures
At 3 min approximately one half of the
fire spread to the television stand at 4 min
an oxygen consumption calorimeter.
had begun to burn and the hot gas layer
radiant energy from the gas layer at 4 min
at approximately 7.5 MW at 450 s after
third of the room opening. The modern
top of the front opening at 4 min and 20
and 40 s (Figure 16). Time to lashover was
s. Room temperature was measured with
approximately the same amount
inside the opening of the room as a result
the opening and 1.5 m from the left wall
experiments. Experiment 3 released 3.2
Experiment 5 was ignited and the fire
sofa was involved in the fire, the carpet
and the left arm of the sofa ignited from
Figure 18 shows Experiment 3 peaked
ignition, while Experiment 4 peaked at
was thickening and flowed out of the top
and 16 s. Flames began to come out of the
room transitioned to flashover in 3 min
s and flashover occurred at 4 min and 45
ignition. Both experiments released
indicated by ignition of the flooring just
a thermocouple array placed 0.9 m inside
of energy over the duration of the
of the heat flux from the flames coming
(Figure 17). Flashover was observed at
MJ and Experiment 4 released 3.5 MJ.
out of the top of the opening.
285 s after ignition.
The fire in Experiment 2 also grew slowly
Experiment 4 was also ignited on the
spread to the sofa cushion and pillow by
spread to the cotton throw blanket and
after ignition the fire was still in the
approximately one-third of the top of the
the arm of the sofa and extended to
the fire involved 2/3 of the right arm of
min the top of the entire sofa was on fire
the fire had spread to approximately
of the right seat cushion. At 20 min the
the sofa. The modern room transitioned
min the fire continued to spread across
cushions, and the flames were burning
gas layer in the room. The legacy room
0.3 m above the back of the sofa. The
s after ignition (Figure 16).
involved in the fire 30 min after ignition.
approximately 6 MW at 2,200 s after
in the first minute as the candle flame
right hand corner of the sofa. At 5 min
the 1 min mark. By 2 min the fire involved
sofa cushion. At 5 min the fire involved
corner where it was ignited. By 10 min
sofa and spread to the lamp shade. At 3
the curtains behind the sofa. At 10 min
the sofa and back cushion and only 1⁄4
and the carpet began to burn adjacent to
one-third of the sofa. From 10 min to 20
fire spread to the second back and seat
to flashover in 3 min and 20 s (Figure 19).
the sofa and began to develop a hot
behind the seat cushion and extending
transitioned to flashover at 29 min and 30
end table and television stand became
Experiment 3 was ignited on the right
hand corner of the sofa where the arm,
seat and back joined. The fire involved the
right 1/3 of the sofa at 3 min and 45 s. The
page 10
The room transitioned to flashover at 34
min and 15 s after ignition (Figure 17).
Heat release rate was also measured
during Experiments 3 and 4 utilizing
Experiment 6 was also ignited on the left
side and it spread to the throw blanket
and sofa cushion by 1 min. By 5 min the
fire involved the left side of the sofa and
spread to the curtains burning the left
panel away. At 10 min the entire surface
of the sofa was burning and by 15 min
the fire involved the entire sofa including
the underside. The flames reached the
Analysis of Changing Residential Fire Dynamics
ceiling but did not extend to the adjacent
In many other experiments conducted
According to the National Association
never transitioned to flashover so it was
line walls for room fire experiments like
home floor systems are being built with
furnishings. The fire burned down and
extinguished at 30 min after ignition
(Figure 19).
at UL that utilize gypsum wallboard to
those described in Section 4 it is observed
that the gypsum wallboard fails at the
seams. As drywall compound is heated
New Construction Materials
Wall Linings — UL conducted a series of
floor furnace experiments to examine
modern and legacy construction practices
[21]. Two of the experiments compared
a dimensional lumber floor system with
different protective linings. The first was
lined with 12.7 mm unrated gypsum board
that is used in most homes. The second
was lined with a plaster and lath lining.
Both assemblies were identical with the
exception of the lining and had the same
loading and bearing conditions
The gypsum board protected assembly
it dries and falls out exposing a gap for
heat to enter the wall space and ignite
the paper on the back of the wallboard
and the wood studs used to construct
the walls. Gypsum wallboard also shrinks
when heated to allow gaps around the
edges of the wallboard. Plaster and lath
does not have the seams that wallboard
has and therefore does not allow for
heat penetration as early in the fire. This
change in lining material allows for easier
transition from content fire to structure
fire as the fire has a path into void spaces.
of Home Builders, 46% of single family
engineered I joists, 15% with wood trusses
and 39% with lumber joists. Adequate
fire performance provides a necessary
level of safety for building occupants
and emergency responders responsible
for mitigating fire incidents. Previous
research by various organizations,
including UL, NIST [23, 24], NFPA [25] and
National Research Council Canada [26],
provided evidence of the greater risk
in structural failure of engineered floor
systems in fire events.
In 2008, UL conducted a series of
experiments on a standard floor furnace
[21], exposing unprotected wood
floor systems to the standard time
exceeded the deflection criteria of L/240
Structural Components — Engineered
temperature curve (Table 3). Loading
the plaster and lath protected assembly
and structural benefits to building
of the floor to simulate the load from
and 45 s. The gypsum board protective
performance needs to be addressed as
30 s while the plaster and lath was
the amount of lightweight construction
at 35 min and 30 s after ignition and
floor products provide financial
exceeded the same criteria at 75 min
construction; however, adequate fire
membrane was breached at 23 min and
well. Statistics from 2005 [22] highlight
breached at approximately 74 min.
materials that are on the market.
STRUCTURAL ELEMENT
TYPE
CEILING
consisted of 195.3 kg/m2 along two edges
furniture and two 136 kg mannequins
that simulated firefighters in the
center of the floor. Two unprotected
floor systems compared a modern /
lightweight floor system compromised
ALLOWABLE DEFLECTION
L/240 (MIN:SEC)
FIRE FIGHTER BREACH
(MIN:SEC)
2 x 10 joist floor
Legacy
None
3:30
18:35
Wood I joist floor
Modern
None
3:15
6:00
2 x 10 joist floor
Legacy
Lath and plaster
75:45
79
2 x 10 joist floor
Legacy
Gypsum wallboard
35:30
44:40
Wood I joist floor
Modern
Gypsum wallboard
3:30
26:43
Metal gusset truss floor
Modern
Gypsum wallboard
20:45
29
Finger joint truss floor
Modern
Gypsum wallboard
24:00
26:30
Table 3: UL study experiment description and collapse times [21]
page 11
Analysis of Changing Residential Fire Dynamics
Figure 20: Window experimental setup.
Figure 21: Windows after the experiment (middle window was modern)
of 0.3 m deep engineered wood I joists
incident commanders, company officers
floor system. The engineered I joist floor
hazards present during a given incident,
to a legacy/dimensional lumber 2 by 10
collapsed in 6 min while the dimensional
and fire fighters in evaluating the fire
and allow a more informed risk–benefit
lumber collapsed in 18 min and 35 s. In
analysis when assessing life safety risks
tested with a protective layer of 12.7 mm
Windows — With increased fuel loads
the same study two truss floors were
gypsum wallboard, one test had metal
gusset plated trusses and the other had.
finger jointed trusses. They both failed
to building occupants and fire fighters.
in houses the amount of air available
to allow a fire to grow has become
the limiting factor and therefore very
fire event prior to fire service arrival
(Figure 20).
Different window construction
parameters assessed include:
1. Wood frame and vinyl frame
construction
2.Single and multi-pane designs
3.Single and multi-glazed designs
important. How long it takes for a
Modern windows are defined as
been extensively examined. Most of
purchased new and that are typically
This study clearly highlights the inferior
commercial windows or windows
year 2000. The legacy windows used in
structural components under fire
object of this series of experiments [28]
and are meant to be representative of
assemblies have the potential to collapse
six different window assemblies, by
built between the years 1950 and 1970
conditions. When it comes to lightweight
with the furnace temperatures controlled
There were a number of different
safety. There is less wood to burn
curve presented in the Standard, ‘‘Fire
collapse. The results of tests comparing
8th Edition dated July 2, 2009 [29].
in less than 30 min as compared to the
residential window to fail has not
windows that are able to be easily
the previous research has dealt with
found in houses constructed after the
structural performance of lightweight
impacted by wildland fires [27]. The
these experiments were purchased used
conditions. Engineered wood floor
was to evaluate the reaction to fire of
windows that would be found on houses
very quickly under well ventilated fire
means of fire endurance experiments
(Table 4).
construction there is no margin of
in accordance with the time–temperature
and therefore potentially less time to
Tests of Window Assemblies,’’ UL 9,
the fire performance of conventional
Fire performance experiments were
passage for air to enter the structure,
the understanding of the hazards of
selfventilation performance of windows,
breaking out of the glass as opposed to
dimensional lumber test with the same
protection of 12.7 mm gypsum wallboard,
which failed in approximately 45 min.
and modern construction will improve
lightweight construction and assist
page 12
conducted to identify and quantify the
comparing legacy to modern, in a
window failure mechanisms and
degrees of failure observed during the
experiments. In order to have an impact
on the fire growth there has to be a
therefore the failure of interest was the
the cracking of the glass. Failure is defined
Analysis of Changing Residential Fire Dynamics
DESIGNATION
TYPE
TYPE
SIZE (MM)
WIDTH(M) X HEIGHT(M) / GLASS THICKNESS
A
Wooden frame, two pane, single glazed, storm
Legacy
0.8 x 1.2 / 2.4
B
Vinyl clad wood frame, two pane, double glazed
Modern
0.8 x 1.4 / 2.2
C
Wood/metal frame/nine pane over one pane, single glazed
Legacy
0.7 x 1.5 / 2.9
D
Premium plastic frame, two pane, double glazed
Modern
0.7 x 1.4 / 2.2
E
Plastic frame, two pane, double glazed
Modern
0.7 x 1.4 / 2.2
F
Premium wooden frame, two pane, double glazed
Modern
0.7 x 1.4 / 2.3
Table 4: Window experiment sample descriptions
WINDOW [MM:SS(SEC)]
EXPERIMENT
A(L)
B(M)
C(L)
D(M)
E(M)
F(M)
1
6:34 (394)
4:24 (264)
11:49 (709)
3:58 (238)
5:16 (316)
3:39 (219)
2
10:06 (606)
4:38 (278)
14:30 (870)
3:39 (219)
4:26 (266)
5:49 (349)
3
12:11 (731)
3:56 (236)
16:00 (960)
5:05 (305)
5:55 (355)
4:02 (242)
AVERAGE
9:37 (577)
4:19 (259)
14:06 (846)
4:14 (254)
5:12 (312)
4:30 (270)
Table 5: Window failure times
as a passage through the window of 25%
It is proposed that this occurred for
Interior Doors — Much like structural
cases this was the failure of the top or
had thicker glazing than the modern
been changed from a solid slab of wood
or more of the total glass area. In most
bottom pane(s) of the window but in
some cases the top window sash moved
downward, opening the window 25%
or more. The two legacy windows with
single glazing failed later than the four
modern windows with double glazing
(Figure 21). The two legacy windows failed
at 577 s and 846 s respectively while the
modern windows failed at 259 s, 254 s, 312
s, and 270 s respectively (Table 5).
These experiments demonstrated a
significant difference in legacy and
modern windows exposed to fire
conditions. In this series of experiments
the legacy single glazed windows
outperformed the modern double glazed
windows in terms of longer failure times.
page 13
two reasons. First the legacy windows
windows. The legacy windows had glass
thicknesses of 2.4 mm and 2.8 mm,
while the modern window thicknesses
were 2.2 mm. Second, the method the
glass was fixed into the frame differed
greatly between the two eras. The
legacy window glass was held in place
with putty like substance and there was
room in the frame for expansion of the
glass. The modern glass was fixed very
tightly into the frame with an air tight
gasket and metal band, to provide better
components, doors have
to an engineered approach where doors
are made hollow to use less material.
To examine the impact of this change
on fire resiliency three different interior
door designs were exposed to the panel
furnace following the temperature curve
specified in ‘‘Positive Pressure Fire Tests
of Door Assemblies,’’ UL 10C, 2nd Edition
dated January 26, 2009 [30].
Different door construction parameters
assessed include:
thermal insulation. This configuration
1. Hollow and solid core construction;
therefore stressed the glass as it heated
2.Different wood types (Figure 22)
did not allow for much expansion and
and expanded.
and
Analysis of Changing Residential Fire Dynamics
Figure 22: Door samples prior to testing.
Figure 23: Door samples after the test
DOOR
EXPERIMENT
1
HOLLOW OAK
5:12 (312)
HOLLOW COMPOSITE
5:15 (315)
SOLID 6-PANEL
5:02 (302)
Table 6: Door failure times
Figure 24: Fire service timeline
There was only one door failure
thickness. The thicker portions of the door
of the door. The hollow core doors had the
times are shown in Table 6. Failure
experiment (Figure 23). This experiment
of the solid core door and therefore the
interior doors during a well-ventilated
Without the panels cut into the solid core
min. For the doors evaluated in this
longer as indicated by the amount of
experiment conducted and the failure
was defined to have occurred when
the unexposed surface of the door
sustained burning. All of the doors failed
at approximately 300 s (Table 6). There
was very little difference between the
two hollow core doors (1 and 2). The
fire ignited the unexposed side and
quickly consumed what was left of
remained intact at the termination of the
same overall wood thickness as the panels
shows the fire containment ability of
fire breached them at very similar times.
compartment fire is approximately 5
door it would have lasted substantially
experiment it can also be concluded
wood remaining in the post test analysis
impact on failure time.
Impact on Firefighting
that the type of wood had no noticeable
the door. The solid core door (3) had a
The doors evaluated in this experiment
was different. Door 3 burned through
no noticeable impact on failure time. The
of the door.
Operational Timeframes
similar failure time but the mechanism
demonstrated that the type of wood had
The most significant impact of the
at the panels because of their reduced
failure time was dictated by the thickness
firefighting tactics is the dramatic shift of
page 14
changing residential fire environment on
Analysis of Changing Residential Fire Dynamics
YEAR
INCIDENT COUNT
AVERAGE RESPONSE TIME
2006
42,584
6.2
2007
49,664
6.5
2008
50,775
6.6
2009
49,386
6.4
Table 7: Average fire department response times
Note: Fires in homes >$10,000 in value with >$1 in loss
Figure 25: Fire service timeline example
Figure 26: Modern versus legacy fire timelines
the safe operational timeline for the fire
The time t4 is the time it takes for the
Some international comparisons of fire
the fire service begins with their arrival
fire. Following NFPA 1710, the goal for
In 2006, the average response time to
service. The operational timeframe for
on scene and ends when the fire is placed
firefighters to drive to the scene of the
department response times are available.
fire emergency response is to arrive
dwelling fires in England was 6.5 min [34].
under control (Figure 24). To compare the
at the scene within 4min after the 911
important to examine the time prior to
Following NFPA 1720 [33], the goal for fire
modern and legacy fire environment it is
call is made. That is, t2 +t3 +t4 <6min.
fire department arrival.
emergency response is to arrive at the
The time t1, depends upon a number of
factors such as when the fire is detected
after initiation, and the time to call for
fire service assistance. This time can
vary greatly depending on the source
of ignition, item ignited, presence of
occupants, presence of fire protection
devices and many other factors.
The time t2, is the time for the 911
operator to call the appropriate fire
station to respond. The US national
standard NFPA 1221 [31] define the
maximum value for t2 as 60 s.
The time t3 is the time it takes for the
firefighters to get onto the fire apparatus
and respond. As per NFPA 1710 [32] this
equals 60 s to begin the response.
page 15
A report comparing residential fire safety
in several countries states, ‘‘Response
time goals in Sweden and Norway are
more lenient than in the United States.
scene within 9 min in an urban area
(~384 people/km2), 10 min in a suburban
area (192 people/km2 to 384 people/km ),
2
14 min in a rural area (~192 people/ km2)
and directly related to driving distance
for remote areas greater than 8 miles
from the closest fire station. Therefore
t2 + t3 + t4 < 11 min to 16 min.
The Scandinavian nations require the
first responding unit to arrive in 10 min,
versus a goal of 6 min in the typical
United States city. Scandinavia generally
gives more weight to prevention and
early extinguishment by homeowners,
less to rapid response’’ [35]. A report
written by a German Fire Officer in 2004
Analyzing the National Fire Incident
examined response times in Europe by
a very consistent average fire department
them questions about their acceptable
detached homes (Occupancy Code 419
internet search. Many countries such as
shows an average response time (t2 + t3 +
and Sweden had acceptable urban
to 2009.
times to suburban or rural areas of
Reporting System (NFIRS) database yields
contacting country officials and asking
response time to one and two family
response times and conducting an
in NFIRS) in the United States. Table 7
Denmark, France, Greece, Ireland, Norway
t4) of approximately 6.4 min from 2006
response times of 10 min and response
15 min to 30 min [36].
Analysis of Changing Residential Fire Dynamics
EXPERIMENTS
MODERN
LEGACY
1,2
3:40
29:30
3,4
4:45
34:15
5,6
3:20
Not Achieved
Table 8 Comparison of flashover times
Conservatively assuming the fire is
noticed quickly and the fire department
is called quickly t1 could be 2 min. Using
the average response time for the US fire
service, the operational timeframe would
begin at 10 min (Figure 25).
To compare modern and legacy fires as
they pertain to the operation timeframe,
times to flashover can be added to the
respective times to collapse. Times to
flashover were taken from the room fire
experiments in Section 4. The modern
room flashed over in 3:30 to 4:45 and
the legacy room flashed over in 29:30
to 34:15. The unprotected modern
floor system (Engineered Wood I joist)
collapsed in 6:00 (Table 3), and adding
a layer of gypsum board increased the
collapse time to 26:43. The unprotected
legacy floor system (Dimensional Lumber
2 by 10) collapsed in 18:35, and adding
a layer of plaster and lath increased the
and the greater the potential hazard to
the responding fire service resources.
Combining of rooms and taller ceiling
more water and resources to extinguish.
slower than the fast burning synthetic
This also means shorter escape times
flashover show that the a flaming fire in
be compromised earlier due to lack
significantly less time for occupants to
which when involved in a fire require
in the legacy room released energy
These fires are more difficult to contain.
furnished modern room. The times to
for occupants as the egress routes may
a room with modern furnishings leaves
of compartmentation.
escape the fire. It also demonstrates to
Comparing the experiments, times to
flashover are very similar between the
three modern experiments and the three
legacy experiments (Table 8). All of the
modern rooms transitioned to flashover
in less than 5 min while the fastest legacy
room to achieve flashover did so at in over
29 min. In these three sets of experiments
legacy furnished rooms took at least
700% longer to reach flashover.
Discussion
front opening a similar fuel load was
8.4 m2 larger and had a 1.3 m2 larger
able to flash the room over in the
residential fire environment over the past
same time. The 4.0 m by 5.5 m legacy
larger homes, more open floor plans and
flashover because it did not have enough
volumes, increased synthetic fuel loads
and new construction materials. The
larger the home is the more air available
to sustain and grow a fire in that home.
Additionally, the larger the home the
greater the potential to have a larger fire,
page 16
demonstrated very different fire behavior.
It was very clear that the natural materials
Even though the third modern room was
several decades. These changes include
The modern rooms and the legacy rooms
heights creates large volume spaces
collapse time to 79:00 (Figure 26).
There has been a steady change in the
heated to their ignition temperatures.
experiment did not transition to
fuel burning at the same time to create
significant heat in the upper gas layer to
ignite items that were not adjacent to
the sofa. The chairs on the left side of the
room and the television and bookcase
of the right side of the room were never
the fire service that in most cases the fire
has either transitioned to flashover prior
to their arrival or became ventilation
limited and is waiting for a ventilation
opening to increase in burning rate. This
difference has a substantial impact on
occupant and firefighter safety. This
change leads to faster fire propagation,
shorter time to flashover, rapid changes in
fire dynamics, and shorter escape times.
Four examples of new construction
materials were examined; wall linings,
structural components, windows and
interior doors. The change in wall linings
now allows for more content fires to
become structure fires by penetrating
the wall lining and involving the void
spaces. This change allows for faster
fire propagation and shorter times
to collapse. The changes in structural
components have removed the mass
of the components which allows them
to collapse significantly earlier. In these
experiments an engineered I joist floor
Analysis of Changing Residential Fire Dynamics
Figure 27: Fire service arrival times versus fire development
system collapsed in less than 1/3 the
environment while arriving at 8 min to a
is important that firefighters study this
system collapsed. Modern windows
stage and less volatile.
on their safety and tactics. The first
time that the dimensional lumber floor
and interior doors fail faster than their
legacy counterparts. The windows failed
in half the time and the doors failed in
approximately 5 min. If a fire in a closed
room is able to get air to burn from a
failed window, then it can burn through a
door and extend to the rest of the house.
This can lead to faster fire propagation,
rapid changes in fire dynamics and
shorter escape times for occupants as
well as firefighters.
legacy fire, it would still be in the growth
Looking beyond fire development and to
collapse further hazards are highlighted.
In the modern fire environment, after
arriving at 8 min, collapse is possible as
soon as 1:30 later. Firefighters may not be
in the house yet or may be just entering
to search for occupants. The legacy fire
collapse hazard begins 40 min after
arrival of firefighters. This allows for a
significant amount of fire operations to
take place all while reading the safety
Using the conservative value of 10 min
of the structure. Figure 27 shows the
and comparing it to the modern and
types of fire departments and the
that the modern fire environment poses
that they arrive in both the modern and
the operational timeframe begins after
The conditions that firefighters are going
as the start of the operational timeframe
standard response times for different
legacy fire timelines shows the hazard
location on the fire development timeline
to firefighters. It also highlights that
legacy fires.
potential flashover. In many cases this
means that if sufficient ventilation is
available the fire will spread significantly
prior to fire service arrival. If sufficient
ventilation is not available the fire will
become ventilation limited and be very
sensitive to initial fire service operations.
The potential for fast fire propagation,
and rapidly changing fire conditions
should be expected in the modern fire
page 17
to be faced with today and into the
future have been significantly impacted
by the ever changing fire environment.
As society continues to make changes to
building materials as a result of the desire
to be environmentally conscience and
to increase profit the fire environment
is going to continue to change and if the
current trends continue it will not be in
favor of firefighter safety. Therefore it
new fire environment and its impact
component of this is understanding the
conditions they are arriving to are very
different than several generations ago.
Fire conditions can change rapidly due
to the under ventilated fire conditions
and floor systems can collapse quickly
and with little warning. While operating
conditions need to be constantly
monitored to understand the impact of
the tactics used and the potential need
to change them. Ultimately, if the fire
environment has changed tactics need
to change or be reevaluated to have the
greatest opportunity to be most effective
on today’s fires.
Suggestions for
Future Research
Research should be conducted to examine
the impact of changing fuel loads in
full-scale structures especially how it
pertains to fire service operations. The
impact of ventilation is key to this fire
development as well. Experiments need
to focus on fire department tactics to
make sure that they are still relevant with
this evolving fire environment.
Analysis of Changing Residential Fire Dynamics
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UL and the UL logo are trademarks of UL LLC © 2012. No part of this document may be copied or distributed without the prior written
consent of UL LLC 2012.
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