Recent research regarding the modern residence fire is providing new insights into the advantages and limitations of current smoke alarm technologies. This white paper summarizes recent and current research conducted at UL on the changing nature of residential fires and the effectiveness of smoke alarm
technologies, and discusses the implications of this research for future standards development.
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Smoke Alarms and the Modern Residence Fire
1. Smoke Alarms and the Modern Residence Fire
Smoke Alarms and the
Modern Residence Fire:
Recent Studies and Research at UL
Information effective as of May 26, 2011
2. Smoke Alarms and the Modern Residence Fire
UL's Fire Experts Research Effectiveness
of Smoke Alarm Technology
Recent research regarding the modern residence fire is providing
new insights into the advantages and limitations of current
smoke alarm technologies. This white paper summarizes
recent and current research conducted at UL on the changing
nature of residential fires and the effectiveness of smoke alarm
technologies, and discusses the implications of this research for
future standards development.
Home smoke alarms provide a critical the focus of extensive research by
first line of defense for occupants in scientists and engineers at UL and other
residential settings should a fire occur. institutions. The goal of this research
Their widespread use can be directly is to increase the understanding of
linked with the dramatic decline in deaths the range of expected conditions, e.g.,
related to residential fires over the past smoke, temperature, gases in modern
30+ years. During this same time period, residential fires, and to ensure that
residences have also changed. Homes smoke alarm technologies continue to
have increased in size, the number and provide individuals with the greatest
amount of furnishings and possessions possible protection in the event of a fire.
have grown, and petroleum-based
Smoke Alarms – A Proven
synthetic materials have supplanted
natural materials in furnishings and home
History of Reducing Fire
construction products. Deaths and Injuries
Commercially available residential smoke
The combination of these factors
detectors and smoke alarms have been
has changed the smoke and gas
largely responsible for the dramatic
characteristics of residential fires
decline in residential fire deaths and
and in some cases accelerated
injuries in the past 30 years. According
the speed of fire growth.
to research conducted by the National
For the past several years, the changing Fire Protection Association (NFPA) on
nature of residential fires has been data collected from the U.S. Fire
page 2 Information effective as of May 26, 2011
3. Smoke Alarms and the Modern Residence Fire
Administration’s (USFA) National Fire recent study by the National Institute In addition, the type and quantity of
Incident Reporting System (NFIRS) of Standards and Technology (NIST) has smoke particles and gases generated
and the NFPA annual fire department shown that, even when working smoke when synthetic materials are
experience survey, home fires accounted alarms are present, the margin between ignited is characteristically different
for 5865 deaths and more than 31000 available and safe egress times has shrunk from that of natural materials.
injuries in 1977, when only 22% of over the past 30 years. [Bukowski 2004]
The seemingly insignificant change
homes were equipped with smoke
This trend suggests the presence of other from natural to synthetic materials in
alarms. [Karter 2004, Ahrens 2007]
emerging factors that have the potential home furnishings has led to the faster
By 2009, when more than 95% of homes to impact the effectiveness of smoke development of residence fires and to the
were equipped with smoke alarms, the alarms in home fires. Most notably, it more rapid onset of untenable conditions.
annual death rate from home fires had is the changing nature of the modern As such, the amount of time available
dropped to 2565, a 56% decline, and residence that is challenging the adequate for safe egress from a home fire is much
injuries dropped by more than 59% over egress time provided by smoke alarms. shorter than in the past, placing a greater
a 32 year span. [Karter 2010, Ahrens burden on smoke alarms to respond at
2010] While the entire reduction in The Changing Nature of the earliest possible stages of a fire.
the Modern Residence
deaths is not completely attributable
Smoldering fires extend the time before
to smoke alarm use adoption, it is In a never-ending effort to reduce
lethal conditions are reached but also
a leading factor in the reduction of production costs and improve product
provide more time for smoke detection
deaths over this period of time. performance, manufacturers of home
and warning to occupants. These fires
furnishings are turning away from
During 2003-2007, roughly 1 of every are slow growing and may or may not
materials like wood and natural fibers in
300 households reported a fire requiring transition to rapidly growing flaming
favor of high-performance, lower-cost
intervention by the fire service. [Ahrens fires. In a recent NIST study, initial
synthetic materials. For example, most
2010] Of these 385000 fires per year, smoldering phases lasted anywhere from
upholstered furniture available today
the 4% of households that do not have 30 to 120 minutes before fire conditions
utilizes polyurethane foam for padding
smoke alarms account for 31% of fires became untenable. [Bukowski 2004]
and synthetic fabric covers, replacing
and 40% of deaths. [Ahrens 2010]
natural padding materials like cotton, While NFPA studies have determined
Furthermore, another 30% of deaths down and feathers, and cover materials that more than 25% of home fire
occur in households with installed, made of cotton, wool, linen or silk. deaths involve an extended initial
viable smoke alarms that were disabled smoldering phase, it is estimated
While these material changes can lead
or were otherwise not working. [Ahrens that roughly 3% of the deaths involve
to products that are easier to clean
2010] By providing occupants with fires that did not transition from
and more resistant to normal wear
advanced notice of the threat of a fire and smoldering to flaming. [Hall 2000]
and tear, they also react differently
additional time to escape, the presence
when exposed to an ignition source. Smoke Detection Technologies
of working smoke alarms is often the
Studies by UL researchers have found
difference between escaping a home fire Today’s residential smoke alarms are
that synthetic materials typically ignite
without injury and succumbing to it. largely based on one of two prevailing
faster, burn more intensely, release
detection technologies: photoelectric or
In the context of these statistics, it is their fire-enabled energy faster, and
ionization. Ionization-based smoke alarms
understandable that significant public create greater amounts of smoke than
operate by monitoring a small current
safety efforts are focused on ensuring natural materials. [Fabian 2007]
created by ionized air between electrically
that working smoke alarms are installed
charged plates; smoke particles will
in 100% of homes. But at least one
page 3 Information effective as of May 26, 2011
4. Smoke Alarms and the Modern Residence Fire
reduce the current. A photoelectric- device, in order to provide individuals
based smoke alarm, on the other hand, with the earliest possible warning UL currently recommends
detects the scattering or obscuration of and the longest possible escape time, the use of both photoelectric
light caused by smoke particulates. In regardless of the type of fire encountered. and ionization smoke alarms
both cases, the units trigger when the
At the same time, ongoing studies in residential settings, or
signal crosses a set threshold value.
are providing researchers with a the use of smoke alarms
Research has shown that each smoke more advanced understanding of the
incorporating both types of
alarm technology has unique advantages characteristics of various types of
under certain fire conditions. In controlled fires, along with their smoke and gas
these sensing technologies
experiments, smoke alarms based on byproducts, leading to the development in a single device, in order to
ionization technology tend to activate of more complex and detailed fire provide individuals with the
more quickly than those based on profiles that can be integrated into earliest possible warning and
photoelectric technology in flaming current fire detection technologies.
the longest possible escape
fires, while photoelectric alarms tend to
Innovations in Smoke time, regardless of the type
activate earlier than ionization alarms
in smoldering fires. [IAFC 2008]
Alarm Technologies of fire encountered.
In addition to the ionization and
Additional research by UL on individual photoelectric smoke detection
materials and items further clarifies technologies that have been available
these trends even for the same material. for many years, a new generation of
This research has led to some
For example, when polyurethane foam smoke detection technologies are
important findings that will guide
(used in mattresses and upholstered being developed in industry. The goal
future UL Standards development
furniture) was ignited with a cigarette of these efforts is to produce a smoke
activities involving smoke alarms.
lighter to flame, the ionization alarms alarm that reacts more effectively
activated earlier; when the same to fires in the modern home. The following sections summarize
polyurethane foam was smoldered, such some of UL’s research regarding smoke
as from a cigarette, the photoelectric In an effort to promote innovation of new
alarms and modern residence fires,
alarm activated earlier. [Fabian 2007] smoke detection technologies, the UL 217
details the key recommendations
smoke alarm standard does not restrict
produced by the studies that have been
Of course, the key challenge in selecting the types of smoke detection technologies
completed, and outlines future steps
the appropriate smoke alarm technology that can be employed in smoke alarms,
for those studies still in progress.
is the inability to predict the type of provided they can meet the performance
home fire that is likely to occur. For that tests specified in the standard. Similarly, Smoke Characterization
reason, nationally recognized fire safety the NFPA 72 National Fire Alarm Code Project [Fabian 2007]
organizations including NFPA, USFA, does not place restrictions on the smoke In 2006 in conjunction with the Fire
International Association of Fire Chiefs detection technologies that can be used. Protection Research Foundation (FPRF)
(IAFC), NIST, National Association of
State Fire Marshals (NASFM) and UL all Research by UL of the NFPA, and as a follow up to a
Researchers at UL have been actively 2004 NIST study, UL initiated a Smoke
currently recommend the use of both
engaged in ongoing investigations Characterization Project. In that earlier
photoelectric and ionization smoke
regarding the changing nature of NIST study, researchers observed a
alarms in residential settings, or the use
modern fires and the effectiveness of reduction in available safe egress
of smoke alarms incorporating both types
current smoke detection technologies. times, attributed to significantly faster
of these sensing technologies in a single
page 4 Information effective as of May 26, 2011
5. Smoke Alarms and the Modern Residence Fire
fire growth caused by the types of • The response time of photoelectric was the predominance of sub-micron
materials used in modern furnishings. and ionization smoke alarms was sized smoke particles generated by
influenced by different smoke combustion. Other studies have shown
The purpose of the UL-FPRF Smoke
particle sizes and counts due to that such particles penetrate the human
Characterization Project was to more
changes in the combustion mode cardiovascular system, and can be
fully characterize the products of both
(flaming versus non-flaming). subsequently absorbed into the body.
flaming and non-flaming combustion
Throughout their professional careers,
on a variety of products and materials • Commercially available ionization
firefighters are exposed to intense heat,
typically found in residential settings. smoke alarms triggered earlier than
smoke particulate and fire gas effluents.
This study used smoke particle and gas commercially available photoelectric
Firefighters also have a history of greater
effluent characterization technology smoke alarms for flaming and high
cardiovascular risks and certain types of
that had not been previously available energy non-flaming (toaster) fires.
cancers than the general population.
for commercial testing purposes.
• Photoelectric alarms triggered earlier
In 2007 to further investigate the causal
Testing scenarios included the for lower energy non-flaming fires.
relationship between sub-micron smoke
standard UL 217 smoke alarm fire test
• Smoke from low energy non-flaming particles and the risk of cardiovascular
protocols, including a burning coffee
fires was found to stratify with time. problems, UL partnered with the Chicago
maker, a toaster with a bypassed
The full report of the Smoke Character- Fire Department and the University of
shutoff, and flaming and smoldering
ization Project is publicly available at Cincinnati College of Medicine to collect
upholstered furniture components.
http://www.nfpa.org/assets/files//PDF/ data on the smoke and gas effluents to
The Smoke Characterization Project study which firefighters are exposed during
Research/SmokeCharacterization.pdf.
produced the following key findings: routine firefighting operations, as well
• Synthetic materials ignite faster, burn Firefighter Exposure to Smoke as contact exposure from contaminated
Particulates [Fabian 2010] personal protective equipment. This
more intensely and create greater
amounts of smoke and other types One of the key observations noted in the research was funded by a grant from U.S.
of gases than natural materials. UL-FPRF Smoke Characterization Project Department of Homeland Security (DHS).
page 5 Information effective as of May 26, 2011
6. Smoke Alarms and the Modern Residence Fire
As a component of this study, • Long-term repeated exposure In the final stages of its work, the
the combustibility, smoke and may accelerate cardiovascular Task Group is using the results of its
gas characteristics of 42 different mortality and the initiation and/ work to select the test foam material
residential construction and furnishing or progression of atherosclerosis. and the flaming and smoldering test
materials were characterized using protocols to be proposed to the UL
The full report of this research is publicly
the methodology developed in the 217 STP. Test material specifications
available on the project’s webpage at
UL-FPRF Smoke Characterization and test consistency limits are now
UL’s website (www.ul.com/fireservice).
Project. This increased the number being formulated for the selected test
of measured smoke signatures from Smoke Alarm Fire Tests protocols generated by the Task Group.
the 18 materials, originally completed
In the UL-FPRF Smoke Character- One unanticipated issue in the
in the UL-FPRF Smoke Character-
ization Project discussed above, development of material specifications
ization Project, to the 60 smoke
researchers determined that flaming and test consistency limits has been
signatures now currently identified.
and non-flaming polyurethane foam the discovery that the cell size of
The Firefighter Exposure to produces smoke with characteristics polyurethane foam (independent of the
Smoke Project study produced that are different from those used to foam density) significantly impacts the
the following key findings: evaluate smoke alarms under UL 217. smoke build-up rate, particularly for the
slower smoldering fire test protocol.
• Concentrations of combustion products Accordingly, in 2008, UL formed a Task
To address this issue, the Task Group is
were found to vary tremendously from Group under the UL 217 Standards
currently pursuing two approaches:
fire to fire, depending on the size, the Technical Panel (STP), to develop
chemistry of materials involved, and appropriate tests for flaming and 1) Develop test material specifications and
the ventilation conditions of the fire. non-flaming polyurethane foam. test consistency limits for a range of
The objective of the Task Group is commercially available foams meeting
• The type and quantity of smoke
to expand the number of smoke the test material property targets
particles and gases generated
signatures to which smoke alarms
depended on the chemistry and 2) Develop a standard reference for
are evaluated under the standard.
physical form of the materials polyurethane foam
being burned. However, synthetic To date, the Task Group has established
Once the material properties (chemistry,
materials produced more smoke target performance criteria for the new
density, indentation load density, cell
than natural materials. fire tests that will not inadvertently
size, etc.) have been established, the
cause an increase in nuisance alarm
• Combustion of the materials generated proposed test protocols will be repeated
frequency. UL has also investigated
asphyxiants, irritants, and airborne 30 times to establish the test consistency
the smoke produced by samples of
carcinogenic byproducts that could limits, and the Task Group will submit
commercially available foams used in
be potentially debilitating. the developed test protocols (including
mattresses and upholstered furniture,
test sample specifications) to the UL
• Multiple asphyxiants, irritants and covering a range of densities.
217 STP for review and consideration.
carcinogenic materials were found
In addition, the Task Group has
in smoke during both suppression Comparison of Modern and Legacy
investigated how sample size, geometry,
and overhaul phases. Carcinogenic Home Furnishings [Kerber 2010]
density, mode of combustion, and
chemicals may act topically,
mode of heating impacts smoke Funded through an Assistance to
following inhalation, or following
particle size, count distribution and Firefighters Grant from the U.S.
dermal absorption, including from
smoke concentration build-up rates. Department of Homeland Security,
contaminated equipment.
page 6 Information effective as of May 26, 2011
7. Smoke Alarms and the Modern Residence Fire
UL researchers recently completed an plastic bins, two picture frames and two toy bin, and multiple wood toys. The
investigation on impact of fire service glass vases on it. The right rear corner of rear wall had cotton curtains hanging
ventilation practices on fire growth the room had a plastic toy bin, a plastic from a metal rod and the side walls had
in modern and legacy residences. toy tub and four stuffed toys. The rear wood framed pictures hung on them.
wall had polyester curtains hanging
As a part of this study the fire growth Both rooms were ignited by placing a
from a metal rod and the side walls had
behavior in modern and legacy lit stick candle on the right side of the
wood framed pictures hung on them.
furnished living rooms was examined sofa. The fires were allowed to grow until
in side-by-side fires. Each living room The legacy room was lined with a layer flashover. The legacy room transitioned to
measured 12 ft. by 12 ft., with an 8 of ½ inch painted cement board and flashover in 29 minutes and 30 seconds
ft. ceiling and an 8 ft. wide by 7 ft. the floor was covered with unfinished whereas the modern room transitioned
tall opening on the front wall. hardwood flooring. The furnishings in just 3 minutes and 30 seconds.
included a cotton-covered/cotton-batting
The modern room was lined with a layer The full report of this research, Impact of
filled sectional sofa, a solid wood coffee
of ½ inch painted gypsum board and Ventilation on Fire Behavior in Legacy and
table, two end tables and a traditional
the floor was covered with carpet and Contemporary Residential Construction,
television stand. A cotton throw was
padding. The furnishings included a and the video showing the two burning
placed on the right side of the sofa. Both
microfiber covered polyurethane foam rooms are publicly available on the
end tables had a lamp with polyester
filled sectional sofa, engineered wood ventilation project webpage at UL’s
shade on top. Two paperback books
coffee table, end table, television stand website (www.ul.com/fireservice).
were placed near the lamp on the left
and book case. The sofa had a polyester
side of sofa and a wicker basket was Smoke Alarm Response Project
throw placed on its right side. The end
located on the floor to the right of
table had a lamp with polyester shade This study is intended to characterize
the sofa at the floor level. The coffee
on top of it and a wicker basket inside it. smoke and gas conditions in various
table had three hard-covered books, a
The coffee table had six color magazines, locations throughout a modern,
television remote and a plant made of
a television remote and a synthetic two-story open floor plan residence to
synthetic materials. The television stand
plant on it. The television stand had a evaluate the response rate of different
had a 27 inch tube television. The right
color magazine and a 37 inch flat panel smoke detection technologies and
front corner of the room had a wood
television. The book case had two small assess the benefits of having alarms in
multiple locations. The various scenarios
investigated in this project include
cooking in the kitchen, e.g., making toast,
frying bacon, a cooking oil fire, smoldering
and flaming upholstered furniture fires
in the two-story family room, smoldering
and flaming upholstered furniture
fires in a den, and mattress fires in the
bedrooms. The standard test protocols
found in UL 217 to evaluate smoke alarms
were also conducted in the living room.
UL is currently analyzing the recorded
data, including smoke particle size
and count distribution, effluent gas
page 7 Information effective as of May 26, 2011
9. Smoke Alarms and the Modern Residence Fire
References
[1] Karter, M.J., “Fire Loss in the United [6] Fabian, T.Z, and Gandhi, P.D., “Smoke [9] Fabian, T.Z., Borgerson, J., Kerber,
States During 2003,” NFPA Fire Characterization Project: Technical S.I., Baxter, C.S., Ross, C.S., Lockey,
Analysis and Research Division, Report," UL, Northbrook, Ill., April J.E., and Dalton, J.M., “Firefighter
Quincy, Mass., October 2004. 2007. (Available at http://www. Exposure to Smoke Particulates: Final
nfpa.org/assets/files//PDF/Research/ Report,” UL, Northbrook, Ill., April
[2] Ahrens, M., “U.S. Experience with
SmokeCharacterization.pdf.) 2010. (Available at http://www.
Smoke Alarms and other Fire
ul.com/global/documents/offerings/
Detection/Alarm Equipment," NFPA [7] Hall, J.R. Unpublished NFIRS national
industries/buildingmaterials/
Fire Analysis and Research Division, estimates statistics cited in A brief
fireservice/WEBDOCUMENTS/EMW-
Quincy, Mass., April 2007. history of home smoke alarms,
2007-FP-02093.pdf.)
presentation to National Fire
[3] Karter, M.J., “Fire Loss in the United
Protection Association conference, [10] Kerber, S., “Impact of Ventilation
States During 2009," NFPA Fire
Denver, Colo., May 2000. on Fire Behavior in Legacy and
Analysis and Research Division,
Contemporary Residential
Quincy, Mass., August 2010. [8] “Smoke Alarms: Ionization and
Construction," UL, Northbrook, Ill.,
Photoelectric Technology," Position
[4] Ahrens, M., “Home Structure Fires,” December 2010.
Paper, International Association of
NFPA Fire Analysis and Research
Fire Chiefs, Fairfax, Va., April 2008.
Division, Quincy, Mass., March 2010.
[5] Bukowski, R.W. et al., “Performance
of Home Smoke Alarms—Analysis
of the response of several available
technologies in residential fire
settings," NIST Technical Note 1455,
National Institute of Standards and
Technology, Gaithersburg, Md., July
2004, Reissued 2008.
page 9 Information effective as of May 26, 2011
