Smoke Alarms and the Modern Residence Fire


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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. 1. Smoke Alarms and the Modern Residence FireSmoke Alarms and theModern Residence Fire:Recent Studies and Research at UL Information effective as of May 26, 2011
  2. 2. Smoke Alarms and the Modern Residence FireULs Fire Experts Research Effectivenessof Smoke Alarm TechnologyRecent research regarding the modern residence fire is providingnew insights into the advantages and limitations of currentsmoke alarm technologies. This white paper summarizesrecent and current research conducted at UL on the changingnature of residential fires and the effectiveness of smoke alarmtechnologies, and discusses the implications of this research forfuture standards development.Home smoke alarms provide a critical the focus of extensive research byfirst line of defense for occupants in scientists and engineers at UL and otherresidential settings should a fire occur. institutions. The goal of this researchTheir widespread use can be directly is to increase the understanding oflinked with the dramatic decline in deaths the range of expected conditions, e.g.,related to residential fires over the past smoke, temperature, gases in modern30+ years. During this same time period, residential fires, and to ensure thatresidences have also changed. Homes smoke alarm technologies continue tohave increased in size, the number and provide individuals with the greatestamount of furnishings and possessions possible protection in the event of a fire.have grown, and petroleum-based Smoke Alarms – A Provensynthetic materials have supplantednatural materials in furnishings and home History of Reducing Fireconstruction products. Deaths and Injuries Commercially available residential smokeThe combination of these factors detectors and smoke alarms have beenhas changed the smoke and gas largely responsible for the dramaticcharacteristics of residential fires decline in residential fire deaths andand in some cases accelerated injuries in the past 30 years. Accordingthe speed of fire growth. to research conducted by the NationalFor the past several years, the changing Fire Protection Association (NFPA) onnature of residential fires has been data collected from the U.S. Firepage 2 Information effective as of May 26, 2011
  3. 3. Smoke Alarms and the Modern Residence FireAdministration’s (USFA) National Fire recent study by the National Institute In addition, the type and quantity ofIncident Reporting System (NFIRS) of Standards and Technology (NIST) has smoke particles and gases generatedand the NFPA annual fire department shown that, even when working smoke when synthetic materials areexperience survey, home fires accounted alarms are present, the margin between ignited is characteristically differentfor 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 changehomes were equipped with smoke This trend suggests the presence of other from natural to synthetic materials inalarms. [Karter 2004, Ahrens 2007] emerging factors that have the potential home furnishings has led to the fasterBy 2009, when more than 95% of homes to impact the effectiveness of smoke development of residence fires and to thewere 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 availabledropped to 2565, a 56% decline, and residence that is challenging the adequate for safe egress from a home fire is muchinjuries dropped by more than 59% over egress time provided by smoke alarms. shorter than in the past, placing a greatera 32 year span. [Karter 2010, Ahrens burden on smoke alarms to respond at2010] While the entire reduction in The Changing Nature of the earliest possible stages of a fire. the Modern Residencedeaths is not completely attributable Smoldering fires extend the time beforeto smoke alarm use adoption, it is In a never-ending effort to reduce lethal conditions are reached but alsoa leading factor in the reduction of production costs and improve product provide more time for smoke detectiondeaths over this period of time. performance, manufacturers of home and warning to occupants. These fires furnishings are turning away fromDuring 2003-2007, roughly 1 of every are slow growing and may or may not materials like wood and natural fibers in300 households reported a fire requiring transition to rapidly growing flaming favor of high-performance, lower-costintervention by the fire service. [Ahrens fires. In a recent NIST study, initial synthetic materials. For example, most2010] Of these 385000 fires per year, smoldering phases lasted anywhere from upholstered furniture available todaythe 4% of households that do not have 30 to 120 minutes before fire conditions utilizes polyurethane foam for paddingsmoke alarms account for 31% of fires became untenable. [Bukowski 2004] and synthetic fabric covers, replacingand 40% of deaths. [Ahrens 2010] natural padding materials like cotton, While NFPA studies have determinedFurthermore, another 30% of deaths down and feathers, and cover materials that more than 25% of home fireoccur in households with installed, made of cotton, wool, linen or silk. deaths involve an extended initialviable smoke alarms that were disabled smoldering phase, it is estimated While these material changes can leador were otherwise not working. [Ahrens that roughly 3% of the deaths involve to products that are easier to clean2010] By providing occupants with fires that did not transition from and more resistant to normal wearadvanced notice of the threat of a fire and smoldering to flaming. [Hall 2000] and tear, they also react differentlyadditional time to escape, the presence when exposed to an ignition source. Smoke Detection Technologiesof working smoke alarms is often the Studies by UL researchers have founddifference between escaping a home fire Today’s residential smoke alarms are that synthetic materials typically ignitewithout injury and succumbing to it. largely based on one of two prevailing faster, burn more intensely, release detection technologies: photoelectric orIn the context of these statistics, it is their fire-enabled energy faster, and ionization. Ionization-based smoke alarmsunderstandable that significant public create greater amounts of smoke than operate by monitoring a small currentsafety efforts are focused on ensuring natural materials. [Fabian 2007] created by ionized air between electricallythat working smoke alarms are installed charged plates; smoke particles willin 100% of homes. But at least onepage 3 Information effective as of May 26, 2011
  4. 4. Smoke Alarms and the Modern Residence Firereduce the current. A photoelectric- device, in order to provide individualsbased smoke alarm, on the other hand, with the earliest possible warning UL currently recommendsdetects the scattering or obscuration of and the longest possible escape time, the use of both photoelectriclight caused by smoke particulates. In regardless of the type of fire encountered. and ionization smoke alarmsboth cases, the units trigger when the At the same time, ongoing studies in residential settings, orsignal crosses a set threshold value. are providing researchers with a the use of smoke alarmsResearch has shown that each smoke more advanced understanding of the incorporating both types ofalarm technology has unique advantages characteristics of various types ofunder certain fire conditions. In controlled fires, along with their smoke and gas these sensing technologiesexperiments, smoke alarms based on byproducts, leading to the development in a single device, in order toionization technology tend to activate of more complex and detailed fire provide individuals with themore quickly than those based on profiles that can be integrated into earliest possible warning andphotoelectric technology in flaming current fire detection technologies. the longest possible escapefires, while photoelectric alarms tend to Innovations in Smoke time, regardless of the typeactivate earlier than ionization alarmsin smoldering fires. [IAFC 2008] Alarm Technologies of fire encountered. In addition to the ionization andAdditional research by UL on individual photoelectric smoke detectionmaterials and items further clarifies technologies that have been availablethese trends even for the same material. for many years, a new generation of This research has led to someFor 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 developmentfurniture) 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 effectivelyactivated earlier; when the same to fires in the modern home. The following sections summarizepolyurethane foam was smoldered, such some of UL’s research regarding smokeas 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 beenOf course, the key challenge in selecting the types of smoke detection technologies completed, and outlines future stepsthe appropriate smoke alarm technology that can be employed in smoke alarms, for those studies still in the inability to predict the type of provided they can meet the performancehome fire that is likely to occur. For that tests specified in the standard. Similarly, Smoke Characterizationreason, 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 FireInternational Association of Fire Chiefs detection technologies that can be used. Protection Research Foundation (FPRF)(IAFC), NIST, National Association ofState 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 Smokecurrently recommend the use of both engaged in ongoing investigations Characterization Project. In that earlierphotoelectric and ionization smoke regarding the changing nature of NIST study, researchers observed aalarms in residential settings, or the use modern fires and the effectiveness of reduction in available safe egressof smoke alarms incorporating both types current smoke detection technologies. times, attributed to significantly fasterof these sensing technologies in a singlepage 4 Information effective as of May 26, 2011
  5. 5. Smoke Alarms and the Modern Residence Firefire growth caused by the types of •  The response time of photoelectric was the predominance of sub-micronmaterials used in modern furnishings. and ionization smoke alarms was sized smoke particles generated by influenced by different smoke combustion. Other studies have shownThe purpose of the UL-FPRF Smoke particle sizes and counts due to that such particles penetrate the humanCharacterization Project was to more changes in the combustion mode cardiovascular system, and can befully 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 greatereffluent characterization technology smoke alarms for flaming and high cardiovascular risks and certain types ofthat 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 causalTesting scenarios included the for lower energy non-flaming fires. relationship between sub-micron smokestandard UL 217 smoke alarm fire test •  Smoke from low energy non-flaming particles and the risk of cardiovascularprotocols, including a burning coffee fires was found to stratify with time. problems, UL partnered with the Chicagomaker, a toaster with a bypassed The full report of the Smoke Character- Fire Department and the University ofshutoff, and flaming and smoldering ization Project is publicly available at Cincinnati College of Medicine to collectupholstered furniture components. data on the smoke and gas effluents toThe 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. 6. Smoke Alarms and the Modern Residence FireAs a component of this study, •  Long-term repeated exposure In the final stages of its work, thethe combustibility, smoke and may accelerate cardiovascular Task Group is using the results of itsgas characteristics of 42 different mortality and the initiation and/ work to select the test foam materialresidential construction and furnishing or progression of atherosclerosis. and the flaming and smoldering testmaterials were characterized using protocols to be proposed to the UL The full report of this research is publiclythe methodology developed in the 217 STP. Test material specifications available on the project’s webpage atUL-FPRF Smoke Characterization and test consistency limits are now UL’s website ( This increased the number being formulated for the selected testof 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 thein the UL-FPRF Smoke Character- ization Project discussed above, development of material specificationsization Project, to the 60 smoke researchers determined that flaming and test consistency limits has beensignatures now currently identified. and non-flaming polyurethane foam the discovery that the cell size ofThe Firefighter Exposure to produces smoke with characteristics polyurethane foam (independent of theSmoke Project study produced that are different from those used to foam density) significantly impacts thethe 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 6 Information effective as of May 26, 2011
  7. 7. Smoke Alarms and the Modern Residence FireUL researchers recently completed an plastic bins, two picture frames and two toy bin, and multiple wood toys. Theinvestigation on impact of fire service glass vases on it. The right rear corner of rear wall had cotton curtains hangingventilation practices on fire growth the room had a plastic toy bin, a plastic from a metal rod and the side walls hadin modern and legacy residences. toy tub and four stuffed toys. The rear wood framed pictures hung on them. wall had polyester curtains hangingAs a part of this study the fire growth Both rooms were ignited by placing a from a metal rod and the side walls hadbehavior 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 untilin side-by-side fires. Each living room The legacy room was lined with a layer flashover. The legacy room transitioned tomeasured 12 ft. by 12 ft., with an 8 of ½ inch painted cement board and flashover in 29 minutes and 30 secondsft. ceiling and an 8 ft. wide by 7 ft. the floor was covered with unfinished whereas the modern room transitionedtall opening on the front wall. hardwood flooring. The furnishings in just 3 minutes and 30 seconds. included a cotton-covered/cotton-battingThe modern room was lined with a layer The full report of this research, Impact of filled sectional sofa, a solid wood coffeeof ½ inch painted gypsum board and Ventilation on Fire Behavior in Legacy and table, two end tables and a traditionalthe floor was covered with carpet and Contemporary Residential Construction, television stand. A cotton throw waspadding. The furnishings included a and the video showing the two burning placed on the right side of the sofa. Bothmicrofiber covered polyurethane foam rooms are publicly available on the end tables had a lamp with polyesterfilled sectional sofa, engineered wood ventilation project webpage at UL’s shade on top. Two paperback bookscoffee table, end table, television stand website ( were placed near the lamp on the leftand book case. The sofa had a polyester side of sofa and a wicker basket was Smoke Alarm Response Projectthrow placed on its right side. The end located on the floor to the right oftable had a lamp with polyester shade This study is intended to characterize the sofa at the floor level. The coffeeon top of it and a wicker basket inside it. smoke and gas conditions in various table had three hard-covered books, aThe coffee table had six color magazines, locations throughout a modern, television remote and a plant made ofa television remote and a synthetic two-story open floor plan residence to synthetic materials. The television standplant on it. The television stand had a evaluate the response rate of different had a 27 inch tube television. The rightcolor magazine and a 37 inch flat panel smoke detection technologies and front corner of the room had a woodtelevision. 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 gaspage 7 Information effective as of May 26, 2011
  8. 8. Smoke Alarms and the Modern Residence Firecomposition, reference obscuration and The ultimate goal of UL’s smoke alarmionization signals, analog photoelectric research is to provide the technologicaland ionization detector signals, and data that can help eliminate fire deathstemperature. A final report summarizing in residential dwelling units. This canthe research from this project is expected lead to advancements in product safetyto be released in the near future, and standards, model codes and regulations.will be publicly available through UL’s Achieving that goal also depends onwebsite ( having working smoke alarms installed in every home, and on continuing programsImplications that effectively educate consumersNational and local building codes and about the dangers of residence fires,regulations have been responsible for and the actions that they can take tothe almost universal installation of ensure their safety. Taken together,smoke alarms in residential structures these steps will lead to safer homes andover the past decade. These codes fewer injuries and lives lost to fire.are continually revised to reflect theknowledge gained through ongoing For more information about Smokeresearch and product development. Alarms and the Modern ResidenceBecause of these ongoing efforts, smoke Fire, please contact Tom Fabian, Ph.D.,alarms installed in today’s residences are research manager for Fire Hazard,more effective and reliable than ever. UL, and Pravin Gandhi, Ph.D., director of Global Corporate Research, UL.The studies and research efforts discussedin this white paper illustrate the extent UL and the UL logo are trademarks ofto which UL researchers are actively Underwriters Laboratories Inc.© 2011.engaged in better understanding the All rights reserved.changing nature of residence fires, andthe ramifications for smoke detectionsystems and smoke alarm technologies.As the results of this research are madeavailable, further changes to UL 217smoke alarm standard and model codescan be expected. Although the transitionof enhanced safety requirements fromproduct safety standards to codesand regulations often proceeds in aseemingly non-linear fashion, suchenhancements are also critical in ensuringthat codes and regulations providethe highest possible level of 8 Information effective as of May 26, 2011
  9. 9. Smoke Alarms and the Modern Residence FireReferences[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 Report,” UL, Northbrook, Ill., April[2] Ahrens, M., “U.S. Experience with SmokeCharacterization.pdf.) 2010. (Available at http://www. Smoke Alarms and other Fire 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 9 Information effective as of May 26, 2011