Residential Fires are Changing
Prepared by Past Chief Thomas Bartsch, VSFD
There has been a steady change in the residential fire
environment over the past several decades.
These changes include larger homes, more open floor
plans and volumes, increased synthetic fuel loads and new
construction materials.
This also means shorter escape times for occupants as the
egress routes may be compromised earlier due to lack of
compartmentation.
Underwriters Laboratories
Home Size and Geometry
Home Size and Geometry
New home design changes;
• Larger home footprints.
• Open floor plan concepts.
• More unventilated attics.
• Increasingly airtight construction.
• Increased concealed space.
• Variety in plans and construction types.
Home Size and Geometry
Many modern-day homes are larger than homes built
before 1980.
Homes have increased in average area from approximately
1500 sq. ft. in 1973 to over 2500 sq. ft. in 2008.
Twenty-six percent of homes constructed in 2008 were
larger than 3,000 sq. ft.
In addition to increased area, more homes are being built
with two stories.
Home Size and Geometry
Newer homes tend to incorporate features such as taller
ceilings, open floor plans, two-story foyers and great
rooms.
These features remove compartmentation, add volume and
can contribute to rapid smoke and fire spread.
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.
Home Contents
Home Contents
Building Contents have changed significantly in recent
years, contributing to the decrease in time to untenable
(life threatening) conditions.
These changes include:
• increased use of more flammable synthetic materials
such as plastics and textiles,
• increased quantity of combustible materials,
• the use of goods with unknown composition and
uncertain flammability behavior.
Home Contents
Home Contents have transitioned from being primarily of
natural materials (wood, wool and cotton) to being
dominated by synthetic materials.
Hydrocarbon and synthetics such as polyurethane foam
have replaced cotton as the padding found in upholstered
furniture, which have significantly higher heat release
rates.
Home Contents
The shift to synthetic materials speeds up the stages of fire
development creating an increased potential for ventilationlimited fire conditions prior to fire department arrival.
A single upholstered chair can provide enough energy to
take a 10 x 12 room to flashover. A sofa can provide 3X the
energy of a single chair.
Construction Materials
Construction Materials
Construction materials such as;
• New engineered products.
• Combustible exterior finishes.
• Green or environmentally sustainable building
materials.
• Energy efficient windows and insulation.
Construction Materials
Life and fire safety are not part of the construction material
selection of builders, using less material and being more
affordable are.
Such as dimensional lumber floor system (Legacy)
compared to wood “I” joist (Modern)
Engineered wood floor assemblies have the potential to
collapse very quickly under well ventilated fire conditions.
Construction Materials
Changes in wall linings (unrated Gypsum board) 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. (Legacy used lathe and plaster)
Changes in structural components have removed the mass
of the components which allows them to collapse
significantly earlier.
When it comes to lightweight construction there is no
margin of safety.
The Changing Fire Scene
The Changing Fire Scene
LEGACY Content fires:
Primarily consist of natural fiber contents such as
wood, wools and cottons. These fires have a relatively
low heat release rate when compared to hydrocarbon
based products.
MODERN Content fires:
Fires that involve hydrocarbon and synthetic based
contents such as foam rubber, nylon, rayon and
polypropylene. These fires have a relatively high heat
release rate when compared to the natural fiber
products found in legacy fires.
Legacy Content Fires
Legacy Content fires will
remain in the Decay Stage if
no additional oxygen is
added to the fire area.
Legacy Content fires develop slower, but have enough
oxygen to support continuous combustion and create
enough pressure to force smoke from the building,
including around doors and windows.
Legacy Content Fires
The smoke being pushed out of the fire compartment by
the pressure of the fire clearly indicates the presence of a
fire.
Flames venting from the windows of a Legacy Content
fire, besides identifying the location of the fire, usually
facilitates extinguishment of the fire since the fire is
already vented.
Modern Content Fires
Modern Content fires
rapidly consume the
available oxygen within the
fire area and enter into an
earlier oxygen limited Decay
Stage.
Modern Content fires rapidly consume more of the
available oxygen within the fire area creating conditions
favorable to a possible ventilation induced flashover.
Modern Content Fires
Modern Content fires rapidly react to ventilation and the
in-flow of additional oxygen.
Modern Content fires want 4 to 5 times the amount of air
as a Legacy Content fire and quickly become ventilationlimited fires due to their higher fuel load.
Modern Content Fires
While in the Decay Stage, the Modern Content fire may
no longer have enough pressure to push smoke from the
fire area or building.
With Modern Content fires, the assumption, that the
absence of smoke pushing from a building is a positive
sign, is no longer accurate.
Modern Content Fires
Modern Content fires require the control of ventilation to
prevent the potential escalation of interior fire conditions.
With Modern Content fires, heavy flames out the window
are usually an indicator of high heat and smoke conditions
within the interior, including areas remote from the fire.
Modern Content fires generate a greater volume of heat
and smoke that may overwhelm the ventilation point(s).
Impact on Firefighting
Operational Time Frames
Impact on Firefighting Operational Time Frames
The most significant impact of the changing residential fire
environment on our firefighting tactics is the dramatic shift
of the safe operational timeline.
Operational timeframe begins with our arrival on the scene
and ends when the fire is placed under control.
To compare the Modern and Legacy content fire
environment, it is important to examine the time prior to
fire department arrival.
Impact on Firefighting Operational Time Frames
Modern versus Legacy fire timelines
Impact on Firefighting Operational Time Frames
The UL Modern Content room test flashed over in 3:40
minutes and the UL Legacy Content room test flashed over
in 29:30 minutes.
Other UL tests have shown:
 Unprotected Modern floor system (engineered wood “I” joist)
collapsed in 6:00 minutes and adding a layer of gypsum
board increased the collapse time to 26:43 minutes.
 Unprotected Legacy floor system (dimensional lumber 2 by 10)
collapsed in 18:35 minutes, and adding a layer of plaster
and lath increased the collapse time to 79:00 minutes.
Fire Dynamics
Fire Dynamics
Modern Content and Legacy Content fires demonstrate
very different fire behavior.
UL tests have shown that Modern Content fires transition
to flashover in less than 4 minutes while the fastest
Legacy Content fire to achieve flashover did so at in over
29 minutes.
Fire Dynamics
The Modern Content fire, in most cases, has either
transitioned to flashover prior to our arrival or became
ventilation-limited and is waiting for a ventilation opening
to increase in burning rate.
This transition has a substantial impact on occupant and a
firefighter safety. This change leads to faster fire
propagation, shorter time to flashover, rapid changes in
fire dynamics, and shorter escape times.
Fire Dynamics
It also highlights that the operational timeframe begins
after 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 department operations.
Fire Dynamics
Fast fire propagation, and rapidly changing fire conditions
should be expected in the Modern content fire.
In a Legacy Content fire, arriving at the 8 minute mark, it
would still be in the Growth Stage and less volatile.
Firefighters may not be in the house yet or may be just
entering to search for occupants.
Fire Dynamics
In the Modern Content fire, a FD arriving at the 8 minute
mark, collapse is possible as soon as 1:30 minutes later.
The Legacy Content fire collapse hazard begins 40
minutes after arrival of firefighters.
FD Operations
Door Control
Door control is a temporary action, if you limit the air inlet
you limit the fire’s ability to grow.
Door control does not completely cut off the oxygen supply,
it slows it, which slows fire growth and delays flashover.
Air is feeding the fire, the clock is ticking, get water on the
fire or it will grow to an untenable condition.
Door Control
The door should be controlled until water is applied to the
fire. Once water goes on the fire, the door may be fully
opened to ventilate.
The simple action of door control after forcing entry until
the coordinated attack will limit the air to the fire and slow
the potential rapid fire progression.
Reading Smoke
“Reading smoke conditions is a very important
component of size-up.”
Do not get complacent if there is nothing showing on
arrival.
In many UL experiments, the smoke color changed
from black to grey as the fire became ventilation-limited
and the pressure within the house decreased, ten
seconds later there was no visible smoke showing at all.
Reading Smoke
Modern Content fires generate greater volumes of smoke
until the fire is extinguished.
Modern Content fires enter an early Decay Stage due to the
limited available oxygen, producing heavy smoke and
varying heat conditions.
Smoke is not always an indicator of what is happening
within the structure. Little or no smoke showing does not
mean that conditions are safer than having fire showing.
Reading Smoke
Little or no smoke showing could mean a fuel-limited fire
that is producing little smoke or it could mean a ventilationlimited fire that is in the initial Decay Stage and starved for
air.
If smoke and fire are venting downward, horizontally or
pulsing from an opening in the building, this indicates the
fire conditions may be wind-impacted.
Consider treating every fire like it is ventilation-limited
until proven otherwise.
Flow Path
Flow paths can be defined as the movement of heat and
smoke from the higher air pressure within the fire area to all
other lower air pressure areas both inside and outside of a
fire building.
As the heated fire gases are moving towards the low
pressure areas, the energy of the fire is entraining oxygen
towards the fire, as the fire is rapidly consuming the
available oxygen in the area.
Flow Path
A Flow Path is changed with:
• ventilation and not water application and
• with water application
Flow paths and timing are very important to understanding
fire dynamics and the impact of firefighter tactics on the
fire ground. The closer the air is provided to the seat of the
fire, the faster it will intensify.
Limiting flow paths until water is ready to be applied is
important to limiting heat release and temperatures.
Ventilation
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
FF’s or unplanned ventilation (e.g., failure of a window or a
door opened by occupant or a neighbor) heat release will
increase, potentially resulting in flashover conditions.
Ventilation
Modern Content fires rapidly react to ventilation and the
in-flow of additional oxygen.
These ventilation induced fire conditions are sometimes
unexpectedly swift, and provide little time for firefighters
to react and respond.
Therefore, ventilation should be controlled and
communicated between interior and exterior members
and coordinated by the IC or appropriate officer inside the
fire area to be vented.
Ventilation
UL tests, on average, showed timeframes until conditions
become untenable,
• 100 seconds for the one-story 1200 ft2 test house and
• 200 seconds for the two-story 3200 ft2 test house.
• In many of the experiments from the onset of
firefighter untenability until flashover was less than 10
seconds.
These times are very conservative, fire is going to respond
faster to additional ventilation opening because the
temperatures are going to be higher.
Ventilation
UL tests have shown that the time between tactical
ventilation and flashover are 2 minutes for the Modern
Content fire and over 8 minutes in the Legacy content fire.
In the Legacy Content fire, you have more time to recover
from poorly venting times or uncoordinated attack prior to
flashover, 8 minutes.
The time to recover in the Modern Content fire was
approximately 2 minutes.
Ventilation
Remember - Forcing the front door is ventilation.
If you notice a rapid in-rush of air or a tunneling effect, it
could indicate a ventilation-limited fire.
Air is feeding the fire and there is little time before either
the fire gets extinguished or it grows until a untenable
condition exists.
Ventilation
Fire showing does not mean that the fire is vented; it means
that it is venting and still remains ventilation-limited. The
fire is burning outside of the window because there is no
air available inside to burn.
Other areas within the fire compartment can be “underventilated”, and additional venting creates a flow path
allowing the heated gases to ignite and flashover.
Ventilation
“Every new ventilation opening provides a new flow path
to the fire.”
Primary importance during VEIS is closing the door to the
room. This eliminates the impact of the open vent and
increases tenability for potential occupants and firefighters
while the smoke ventilates from the now isolated room.
Ventilation
Closing a door between the occupant and the fire or a FF
and the fire, can increase the chance of survivability.
If you are searching ahead of a hoseline or become
separated from your crew and conditions deteriorate, then
a good choice of actions would be to get in a room with a
closed door until the fire is knocked down or escape out of
the room’s window with more time provided by the closed
door.
Ventilation
It is of paramount importance that horizontal and vertical
ventilation must be coordinated.
Operations conducted in the flow path can place firefighters
at significant risk due to the increased flow of fire, heat, and
smoke toward their position.
In ventilation, “Timing is Everything”.
Summary
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.
“You are not fighting your
grandfather’s fire anymore.”
Referenced Material:
UL “Impact of Ventilation on Fire Behavior in Legacy and Contemporary
Residential Construction”, Steve Kerber PE
UL “Study of the Effectiveness of Fire service Vertical Ventilation and Suppression
Tactics in Single Family Homes”, Steve Kerber, PE
UL “Analysis of Changing Residential Fire Dynamics”, Steve Kerber, PE
USFA “Changing Severity of Home Fires Workshop Report”.
FDNY “Firefighting Procedures, Ventilation”
A special THANK YOU to Dave Walsh, Program Chair-Fire Science, Dutchess
Community College for his comments and suggestions.
THANK YOU