Smoke Alarm Presence and Performance in U.S. Home Fires

The vast majority of U.S. homes have at least one smoke alarm. For smoke alarms to be effective, they must have a functional power source, be close enough to the smoke to activate, they must be heard, and occupants must take appropriate action. In homes with smoke alarms and fires considered large enough, the alarms operated 83% of the time. Analyses of data from the U.S. Fire Administration’s National Fire Incident Reporting System and the National Fire Protection Association’s fire department survey showed that in 2003 to 2006, no smoke alarms were present in 31% of reported home fires and 40% of home fire deaths. Smoke alarms were present but failed to operate in 9% of the reported fires and 23% of the deaths. Thirty-seven percent of the deaths resulted from the 47% of fires with operating smoke alarms. Circumstances of the fire, the detection equipment, and occupant characteristics must be considered when evaluating smoke alarm performance. Hardwired smoke alarms operated more often than alarms powered by batteries alone. Victims of fatal fires with working smoke alarms were more likely than victims of fires without working smoke alarms to have been in the area of origin when the fire began; fighting the fire; unable to act; or at least 65 years old; and less likely to have been sleeping. Findings from the Consumer Product Safety Commission’s 2004 to 2005 Residential Fire Survey provide background about smoke alarms in the general population and in unreported fires.     

Enclosure smoke filling revisited

Building fires go through a series of stages. They start with a fire plume/ceiling jet period during which buoyant fire gases rise to the ceiling and spread radially beneath the ceiling. A second stage, the enclosure smoke-filling period, follows; this second stage is the subject of this paper. It has been more than 20 yr since Zukoski first addressed the smoke filling stage of enclosure fires in terms of thermodynamic control volume concepts and fire plume entrainment, yet his analysis remains pertinent. This paper reviews and extends fire modeling concepts related to enclosure smoke filling developed by Zukoski. The mass-based analysis of Zukoski is recast in terms of the volumetric flow rates typically used for ventilation system design; it is extended to consider global average temperature rise and the effects of oxygen consumption on the maximum global average temperature rise that can be achieved in a closed-room fire. A spreadsheet template is developed to compare hand calculations based on a global analysis with numerical smoke filling calculations. Results of this comparison suggest that there is little difference in conditions predicted with the global hand calculations and the numerical smoke filling calculations; consequently, the hand calculations are suitable for preliminary fire hazard analyses.     

The trouble with fire intensity

The author discusses the inadequacies and limitations of the term “fire intensity” as it is used to describe the severity of forest fires and suggests that the term “fire front power” is more appropriate. General Physical Scientist, Southeastern Forest Experiment Station, USDA, Forest Service, Macon, Georgia.     

Thermally-Induced Failure of Smoke Alarms

Smoke alarms are relied upon to notify building occupants of a fire, and the performance of these devices in the fire environment is critical for the safe evacuation of the building occupants. Development of smoke detection technology has focused primarily on the activation time of the smoke alarm and the amount of escape time they will provide. The growth rate of fires in industrial and residential settings has increased significantly in the past four decades, often attributed to the construction and materials of modern-day furnishings and contents compared to that in the 1970s. This changes the thermal environment smoke alarms are exposed to and raises the question whether they are able to alert the occupants before failing due to heat exposure. Research by Ashley et al. in 2005 showed that approximately 30 s of sounding time is necessary to reliably awaken a sleeping occupant and initiate egress. As research has primarily focused on the activation of smoke alarms, there is a gap in the industry knowledge of the thermally induced failure in these devices. Experiments using two different smoke alarm designs were performed in a heated tunnel with induced airflow. The alarms were heated until they reached a code-mandated audibility failure criterion of less than 5 dB above ambient levels, as well as complete cessation of the audible alarm sound during experimental testing. For these samples, reduction in sound signal started to occur at a component temperature of 56°C, and all alarms had stopped sounding when heated to 144°C. The results of a plunge heating test were used to compute a generalized two-stage Response Time Index for the thermal response of each type of smoke alarm. The output data from the NIST Home Smoke Alarm Tests performed in 2008 were used to calculate the estimated time when the smoke alarm would have thermally failed during those tests. The calculations showed that in the scenarios analyzed, both smoke alarm designs tested would provide more than the 30 s required, before reduced audibility or failure occurs. The failure of both alarm designs in just over 3 min shows that more research is needed applying this methodology to a wider range of alarm models and fire scenarios to ensure that smoke alarms are able to provide adequate protection in modern fires.

     

Interactions Between Human Behaviour and Technology: Implications for Fire Safety Science

Here we present a number of studies showing how human behaviour may influence the effectiveness of fire safety equipment. The paper initially focuses on smoke alarms and first reviews studies on the waking effectiveness of smoke alarms, including the increased waking effectiveness of a low frequency 520 Hz square wave. Section 2.2 presents research on the impact of changes in the open or shut status of doors and windows on alarm performance. When all doors were closed, the average alarm volume in other rooms fell to a mere 36 dBA. Time for alarm activation by smoke was very strongly influenced by shutting interconnecting doors. The analysis in Sect. 2.3, using detailed coroner’s files, suggests that for many fire fatalities a smoke alarm is likely to have been irrelevant to whether or not a person died in the fire. Part 3 presents research examining the use of fire extinguishers and fire blankets by older adults. Blanket use was more successful than the fire extinguisher, with 22% of participants unable to remove the fire extinguisher safety tag. We conclude that any new fire safety technologies or developments need to explicitly take into account human factors in their design. Further, consideration must be made about whether a new product is likely to be located, installed, available, maintained and/or appropriately used by the people who are most at risk. The paper closes with a discussion of some preventative strategies.     

Performance of Dual Photoelectric/Ionization Smoke Alarms in Full-Scale Fire Tests

Data from two full-scale residential smoke alarm fire test series were analyzed to estimate the performance of dual sensor photoelectric/ionization alarms as compared to co-located individual photoelectric and ionization alarms. Dual alarms and aggregated photoelectric and ionization alarm responses were used to estimate dual alarm performance. It was observed that dual alarms with equivalent or higher sensitivity settings performed better than individual photoelectric or ionization alarms over a range of flaming and smoldering fire scenarios. In one test series, dual alarms activated 539 s faster than ionization alarms and 79 s faster than photoelectric alarms on average. In another test series, individual alarm sensor outputs were calibrated against a reference smoke source in terms of light obscuration over a path length (percent smoke obscuration per unit length) so that alarm thresholds could be defined by the sensor outputs. In that test series, dual alarms, with individual sensor sensitivities equal to their counterpart alarm sensitivities, activated 261 s faster on average than ionization alarms (with sensitivity settings of 4.3%/m smoke obscuration for the ionization sensors) and 35 s faster on average than the photoelectric alarms (with sensitivity settings of 6.6%/m, for the photoelectric sensors.) In cases where an ionization sensor was the first to reach the alarm threshold, the dual alarm activated 67 s faster on average than the photoelectric alarm. While in cases were a photoelectric sensor was the first to reach the alarm threshold, the dual alarm activated 523 s faster on average than the ionization alarm. Over a range of ionization sensor settings examined, dual alarm response was insensitive to the ionization sensor setting for initially smoldering fires and fires with the bedroom door closed, while dual alarm response to the kitchen fires was very sensitive to the ionization sensor setting. Tests conducted in the National Institute of Standards and Technology (NIST) fire emulator/detector evaluator showed that the ionization sensors in off-the-shelf ionization alarms and dual alarms span a range of sensitivity settings. While there appears to be no consensus on sensitivity setting for ionization sensors, it may be desirable to tailor sensor sensitivities in dual alarms for specific applications, such as near kitchens where reducing nuisance alarms may be a goal, or in bedrooms where higher smoke sensitivity may be a goal.     

Field test and evaluation of residential sprinkler systems: Part III

A series of full-scale fire tests utilizing prototype “quick-response” sprinklers was conducted in a two-story residence in Los Angeles, CA, and a mobile home in Charlotte, NC. A prime objective of the program was to test the performance of alternative sprinkler designs to “control” the development of fire in single-family dwellings and mobile homes. Part of the mobile home test series focused on a study of the comparative activation times of sprinklers and smoke detectors installed in the same areas under a variety of test conditions. The results of that phase of the test program are given here. National Fire Protection Association REFERENCE: Cote, arthur E., “Field Test and Evaluation of Residential Sprinkler Systems”, Fire Technology, Vol. 20, No. 2, May 1984, p. 41. Mr. Cote is Assistant Vice President (Engineering & Technical Services) for the NFPA. He served as project manager for the test series insofar as the NFPA had overall management responsibilities for the program.     

Fire development in a 1/3 train carriage mock-up

To study what parameters that control the initial fire spread and the development to local flashover in a metro carriage, a total of six fire tests were conducted in a mock-up of a metro carriage that is about 1/3 of a full wagon length. They were carried out under a large scale calorimeter in a laboratory environment. The focus was on the initial fire development in a corner scenario using different types of ignition source that may lead to a fully developed fire. The ignition sources used were either a wood crib placed on a corner seat or one litre of petrol poured on the corner seat and the neighbouring floor together with a backpack. The amount of luggage and wood cribs in the neighbourhood of the ignition source was continuously increased in order to identify the limits for flashover in the test-setup. The tests showed that the combustible boards on parts of the walls had a significant effect on the fire spread. In the cases where the initial fire did not exceed a range of 400–600 kW no flashover was observed. If the initial fire grew up to 700–900 kW a flashover was observed. The maximum heat release rate during a short flashover period for this test set-up was about 3.5 MW. The time to reach flashover was highly dependent on the ignition type: wood cribs or backpack and petrol. A full developed carriage fire was achieved as a result of intense radiation from the flames and ceiling smoke layer. This was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was, leading to a ceiling flame. In such cases, the seats alone did not contain sufficient fuel for the fire to spread within the train, and additional fuel (luggage) is required near the seats. For fully developed carriage fires, the fire starting on the seat in the corner spread to the opposite seat on the same side of the aisle, then horizontally spread to seats on the other side of the aisle, and finally a longitudinal flame spread along the carriage was observed. When and where the fire stopped or whether it reached a fully developed stage was mostly dependent on the amount of fire load nearby the ignition source and how strong the vertical flame spread on the high pressure laminate boards mounted to walls and ceiling above the ignition source was.     

Human awakening and subsequent identification of fire-related cues

Twenty-four college-age male subjects, employed for one night each, were evaluated on their ability to awaken and then identify fire cues. Twelve subjects were exposed to smoke alarm warning signals of three intensities, while the second twelve subjects were exposed to a smoke odor, a heat presentation, and a single smoke alarm warning signal. Subjects were, in all cases, awakened by alarms that reached their ears at signal/noise ratios of 34 dB. They were considerably less likely to be awakened by heat, the smoke odor, and alarm sounds that reached their ears at signal/noise ratios of 10 dB or less. Upon awakening, subjects repeatedly failed to correctly label radiant heat presentations and smoke alarm warnings as fire cues. Reference: Kahn, Michael J., “Human Awakening and Subsequent Identification of Fire-Related Cues,” Fire Technology, Vol. 20, No. 1, February 1984, p. 20.     

Home Smoke Alarms: The Data as Context for Decision

Considerable attention has been devoted to how home smoke alarms could be more effective at preventing fire deaths. The death rate per 100 reported home fires is half as high in homes with working smoke alarms compared to homes without this protection. This paper summarizes what is known about the performance and effectiveness of home smoke alarms and of victim characteristics in home fires with and without operating smoke alarms based on statistical analysis of actual fire experience data. Special studies on other factors affecting smoke alarm performance, audibility, and nuisance alarms are also discussed. The paper also identifies several questions that cannot, at present, be conclusively addressed.     

Full-scale experimental study on smoke flow in natural ventilation road tunnel fires with shafts

Three full-scale burning tests were conducted in a natural ventilation city road tunnel with shafts. Fire sources were placed to be at different locations but its peak release heats were all around 5 MW. Results showed that large amounts of smoke and heat were released through shafts. The maximum smoke temperatures under the ceiling were below than 100 °C, and being lower than 110 °C at the safe height farther 3 m away from fires. The maximum smoke spreading horizontal lengths were less than 240 m both in the upwind and downwind. During the late stages, many smoke particles descended from the ceiling and downdraught occurred at shafts due to low smoke temperatures, but the visibility was not very bad and people needn’t evacuate. All These results are valuable for fire protection and construction of natural ventilation road tunnel with shafts.     

A Physical Model and Improved Experimental Data Correlation for Wind Induced Flame Drag in Pool Fires

The flames over a burning liquid fuel are observed to spill over the downwind edge of the liquid pool in a wind. Empirical correlations in the literature relate the total base dimension of the fire (diameter + the spill over) with the wind Froude number. This leads to erroneous and physically incorrect (negative) value for the flame spillover at low wind speeds and/or in large diameter fires. The data from laboratory scale (0.1–0.6 m) to field scale (up to 35 m) fires of different hydrocarbon fuels on the wind induced flame “drag” or “spillover” were re-examined. The ratio of the flame spillover distance with the pool diameter is seen to vary in direct proportion to the square root of the Froude number but with different proportionality constants for different fuels. A physical model was developed to analyze the phenomena that occur at the base of a pool fire subject to a wind. This model indicates that the non-dimensional downwind flame spillover distance is directly proportional to the square root of the Froude number, inversely proportional to the square root of the dimensionless heat of combustion of the fuel and directly proportional to the 1/4th power of the ratio of vapor density to air density. Available experimental data are synthesized into a single correlation when plotted on the basis of the non-dimensional parameters from the model. This correlation includes the Froude number, the Damkohler number (dimensionless heat of combustion of the fuel), the wind flow Reynolds number and the fuel vapor-to-air density ratio.     

Fire detection using smoke and gas sensors

Fire detection systems located in aircraft cargo compartments are currently based only on smoke detectors. They generate about 200 false alarms per year for US registered aircraft. The number of false alarms is growing as more planes are outfitted with smoke detectors and air travel expands. Moreover, the survivability of an aircraft in a fire scenario depends on the early detection of the fire. A fire detection system is developed based on the simultaneous measurements of carbon monoxide, carbon dioxide, and smoke. The combination of the rates of rise of smoke and either carbon monoxide or carbon dioxide concentration provides a potential fire alarm algorithm to increase the reliability of aircraft smoke detectors, and to reduce the time to alarm. The fire detection system with the alarm algorithm detected fires that were not alarmed by smoke sensors, and alarmed in shorter times than smoke sensors operating alone.     

Experimental study on transverse smoke temperature distribution in road tunnel fires

To assess the impact of smoke on the ceiling in tunnel fires, the smoke temperature under the ceiling was studied experimentally with small-scale experiments. This study focused on the transverse smoke temperature distribution in road tunnel fires as the longitudinal one has been widely researched. Comparison for the transverse and longitudinal smoke temperature distributions near the fire was conducted and the difference was researched. A correlation determining the transverse smoke temperature distribution under the ceiling was developed by taking the fire location into account.     

Thirty-three Years of Regulating Fire Protection at Commercial U.S. Nuclear Power Plants: Dousing the Flames of Controversy**

This article focuses on what have been, and may continue to be, the more controversial aspects of fires at commercial nuclear power plants regulated by the U.S. Nuclear Regulatory Commission. Examining what has transpired in fire protection regulation since the 1975 fire at Browns Ferry Unit 1, which first focused attention on the potential hazard of fire at commercial nuclear power plants, we offer a personal perspective as to whether or not the “the flames of controversy” have been “doused.” We show that significant progress has been made while speculating whether these “flames” may ever truly be extinguished, or only kept under control. No core damage accident has ever occurred at a commercial nuclear power plant due to fire.

Sprinkler performance tests—The extended coverage panacea

Performance testing of multiple extended coverage sidewall sprinklers indicates that these sprinklers, installed on spacings that are multiples of specified room areas with ceiling heights up to 9 ft, perform comparably to single sprinkler per room installations under fire conditions. Underwriters Laboratories Inc. Note: Mr. Suchomel and Mr. Castino are Associate Managing Engineer and Managing Engineer of the Laboratories' Fire Protection Department. Mr. Castino presented this paper, under the title “Fire Performance Tests of Sprinklers Under Simulated Field Installation Conditions—The Extended Coverage Panacea,” at the NFPA Fall Meeting on November 12, 1979 in Phoenix, Arizona.     

Full-scale experiment and CFD simulation on smoke movement and smoke control in a metro tunnel with one opening portal

Three full-scale model experiments were conducted in a unidirectional tube, which is a part of a metro tunnel with one end connected to an underground metro station and the other end opened to outside in Chongqing, PR China. Three fire HRRs, 1.35 MW, 3 MW and 3.8 MW were produced by pool fires with different oil pan sizes in the experiments. Temperature distributions under the tunnel ceiling along the longitudinal direction were measured. At the same time, CFD simulations were conducted under the same boundary conditions with the experiments by FDS 5.5. In addition, more FDS simulation cases were conducted after the FDS simulation results agreed with the experimental results. The simulation results show that the smoke temperature and the decay rate of the temperature distribution under the tunnel ceiling along the longitudinal direction increase as HRR increases. The smoke exhausts effectively from the tunnel under mechanical ventilation system, whether the emergency vent is activated as a smoke exhaust or an air supply vent. The operation mode of the mechanical ventilation system depends on the evacuation route.     

Studies on buoyancy driven two-directional smoke flow layering length with combination of point extraction and longitudinal ventilation in tunnel fires

This paper investigates the buoyancy-driven smoke flow layering length (both upstream and downstream) beneath the ceiling with combination of point extraction and longitudinal ventilation in tunnel fires. A theoretical model is developed based on previous back-laying model with only longitudinal ventilation, with modified actual heat release rate, as well as modified upstream and downstream opposing longitudinal air flow velocities by the induced flow velocity due to point extraction. Experiments are carried out in a reduced scale model tunnel with dimensionless of 72 m×1.5 m×1.3 m. A LPG porous gas burner is used as fire source. The smoke flow layering length both upstream and downstream are identified based on temperature profiles measured along the ceiling, for different experiment conditions. CFD simulations with FDS are also performed for the same scenarios. Results show that with combination of point extraction and longitudinal ventilation, the smoke flow layering length is not symmetric where it is longer downstream than that upstream. The upstream smoke layering length decreases, while the downstream layering length increases with increase in longitudinal ventilation velocity; and they both decrease with increase in point extraction velocity. The predictions by the proposed theoretical model agree well with the measurements and simulation results.     

Impact of Air Velocity on the Detection of Fires in Conveyor Belt Haulageways

A series of large-scale experiments were conducted in an above-ground fire gallery using three different types of fire-resistant conveyor belts and four air velocities for each belt. The goal of the experiments was to understand and quantify the effects of air velocity on the detection of fires in underground conveyor belt haulageways and to determine the rates of generation of toxic gases and smoke as a fire progresses through the stages of smoldering coal, flaming coal, and finally a flaming conveyor belt. In the experiments, electrical strip heaters, imbedded approximately 5 cm below the top surface of a large mass of coal rubble, were used to ignite the coal, producing an open flame. The flaming coal mass subsequently ignited 1.83-m-wide conveyor belts located approximately 0.30 m above the coal surface. Gas samples were drawn through an averaging probe for continuous measurement of CO, CO₂, and O₂ as the fire progressed. Approximately 20 m from the fire origin and 0.5 m below the roof of the gallery, two commercially available smoke detectors, a light obscuration meter, and a sampling probe for measurement of total mass concentration of smoke particles were placed. Two video cameras were located upstream of the fire origin and along the gallery at about 14 m and 5 m in order to detect both smoke and flames from the fire. This paper discusses the impact of ventilation airflow on alarm times of the smoke detectors and video cameras, CO levels, smoke optical densities and smoke obscuration, total smoke mass concentrations, and fire heat release rates, examining how these various parameters depend upon air velocity and air quantity, the product of air velocity, and entry cross-section.     

Field test and evaluation of residential sprinkler systems: Part II

A series of National Fire Protection Association full-scale tests involving sprinkler installations was conducted in a two-story residence in Los Angeles, CA, and in a mobile home in Charlotte, NC. Previous laboratory tests, including full-scale room fire tests, had indicated that a prototype “quick-response” sprinkler was effective in controlling residential home fires. More full-scale fire tests under less controlled and more operational conditions were considered necessary to confirm or deny this conclusion. Part I of this three-part series (November 1983) explained the objectives of the tests and the test procedures that were to be followed. This second part describes the criteria used to evaluate the effectiveness of sprinkler systems using the “quick response” sprinkler in the series of seventy-six tests and the results of those tests. Part III will cover that phase of the test program that focused on a comparison of sprinkler and smoke detector activation times in the mobile home test structure. National Fire Protection Association Mr. Cote is Assistant Vice President (Engineering & Technical Services) for the NFPA. He served as project manager for the test series insofar as the NFPA had overall management responsibilities for the program. Reference: Cote Arthur E., “Field Test and Evaluation of Residential Sprinkler Systems: Part II” Fire Technology, Vol. 20, No. 1, February 1984, p. 48.