Running head: SMOKE ALARMS 1 Smoke Alarms: Comparing the Differences in Response Times and Nuisance Alarms Chris Kasperczyk University of Cincinnati Fire Science Analytical Approaches to Public Fire Protection
SMOKE ALARMS 2 Introduction In 2005, Popular Mechanics Magazine consulted twenty-five authorities at museums and universities across the United States to select the top fifty inventions over the past fifty years. In December 2005 the results were published and noted the residential smoke alarm was ranked as one of the top fifty inventions (Hutchinson, 2005). Smoke alarms, originally known as smoke detectors, began to appear in homes during the late 1960 s. In 1970, the public acceptance of smoke alarms grew due to the availability of less expensive battery-operated devices. Throughout the 1970 s and 1980 s various surveys indicated smoke alarm installation was dramatically increasing thanks to hard-wired devices, public education and improved building codes. Although the rate wasn t as fast as previous years, installations continued to grow during the 1990 s. As of 2004, surveys indicate 96% of residential properties in the United States have at least one smoke alarm. Historically, four of every five fire deaths have occurred in U.S. homes. According to Bukowski (2003), Analysis by the National Fire Protection Association (NFPA) indicates when a fire occurs, detectors cut the chances of dying nearly in half (p. 9-79). Smoke alarms are critical for early detection of fires in the home. Their warning provides us with valuable time to safely escape a fire. Today there are three types of smoke alarms available on the market; photoelectric, ionization and a combination of the two known as a dual sensor alarm. Both ionization and photoelectric smoke alarms are effective in detecting the presence of fire and have to pass similar standards. However, there are noticeable differences in performance between the two types including operation, response time and nuisance alarms. The purpose of this paper is to compare the effectiveness of photoelectric and ionization smoke alarms.
SMOKE ALARMS 3 Discussion Photoelectric and ionization smoke alarms are similar in the fact that they operate when smoke enters the sensing chambers. However once the smoke enters the chamber their detecting mechanisms are quite different. Photoelectric smoke alarms use a light source to sense smoke. The photoelectric alarm requires a light source, typically a light-emitting diode, a lens that adjusts the light into a beam and a photoelectric sensor used as a light detector. This type of alarm relies on the small particles to enter the chamber and scatter the light to activate the alarm. When the chamber is smoke-free, the beam of light is uninterrupted and does not make contact with the light sensor, thus not activating the alarm. Once particles enter the sensing chamber, the beam of light is scattered causing the photoelectric sensor to detect the light which activates the alarm. Prior to the residential version of photoelectric smoke alarms, there were commercialgrade photoelectric smoke alarms that were operated from a fire alarm control panel. These alarms demonstrated a slow response because their designs restricted smoke entry into the sensing chamber (Bukowski, 1993). Ionization smoke alarms use ionic current as their detection mechanism. This ionic current is created in a chamber with a minute amount of a manmade element named Americum- 241 and two electrodes. The battery source for the detector applies a voltage to the plates, charging one plate positive and the other plate negative. Alpha particles constantly released by the Americum knock electrons off of the atoms in the air, ionizing the oxygen and nitrogen atoms in the chamber. The positively-charged oxygen and nitrogen atoms are attracted to the positive plate, generating a small, continuous current. When smoke enters the ionization chamber, the smoke particles attach to the ions and neutralize them, so they don t reach the plate. The drop in current between the plates triggers the alarms (Helmenstine, 2010). Although they
SMOKE ALARMS 4 were uncommon, ionization smoke alarms were used in the early 1960 s. At the time, federal regulations required that installations of ionization-type alarms be individually licensed and that alarms be tested annually for leakage of radioactive source material. After about ten years of testing data indicated that no leakage ever occurred, these regulations were withdrawn in the late 1960 s (Bukowski, 1993). Residential fires can occur any time of day or night. These fires can take the form of a smoldering or flaming fire. A smoldering fire is a slow burning, flameless form of combustion that produces a minimal amount of heat and large amounts of smoke. In comparison, a flaming fire is a free-burning fire that produces a flame, extreme heat, burns rapidly and creates minimal amounts of smoke. Both types of fires create hazardous conditions to everyone who is exposed within the structure. Hazardous conditions include poor visibility due to smoke obscuration, thermal effects including burns, irritation of the airway tract and narcosis from inhaling the toxic gases. One of the most lethal gases produced by both smoldering and flaming fires is Carbon Monoxide. In a smoldering fire, the incompleteness of the combustion process leads to high levels of Carbon Monoxide. In comparison, flaming fires produce smaller amounts of Carbon Monoxide. Over the years, studies been completed to determine how smoke alarms react to these two types of fires. In 1960, Los Angeles Fire Department performed the first experiments on the performance of residential fire detectors in smoldering and flaming fires. The smoldering test fire was conducted with an upholstered chair and used a cigarette as the ignition source. The flaming test fire was reproduced by starting a fire in containers of trash. The test devices were a photoelectric smoke detector and a spring-wound residential heat detector. According to Bukowski (1993), observations from the test are as follows:
SMOKE ALARMS 5 In slow, smoldering fires conducted during these tests: 1. Disabling and near-lethal concentrations of carbon monoxide gas were recorded prior to the sounding of heat activated alarms. 2. Temperatures within the dwellings remained near ambient until such time as the upholstered furniture being burned burst into flames. 3. Before operation of a heat-activated device, visibility within the dwelling was diminished to the point where, in bright, sunny, daylight conditions, people would be unable to rely on sight (as a means of receiving adequate warning) for evacuating the premises. 4. In all tests in which smoke detectors were used, the smoke activated device operated prior to the development of serious concentrations of carbon monoxide or smoke. In rapid-burning rubbish fires conducted during these tests: 1. Heat-activated devices operated soon after ignition of the fire and before serious carbon monoxide or smoke concentrations were in evidence. 2. Smoke devices did not respond as long as the fire was free burning (p. 50). In 1974, Factory Mutual Research Corporation performed experiments that examined the performance of smoke alarms in high-rise apartments. The purpose of these experiments was to evaluate the performance of photoelectric smoke alarms, ionization smoke alarms and heat detectors. The test area was a 753 square foot apartment with a single bedroom. Overall, there were nineteen separate tests performed. According to Bukowski (1993), pertinent conclusions reached in this study include the following:
SMOKE ALARMS 6 1. The ionization detector performed adequately in the protectable flaming fire starts and, in general, inadequately in the smoldering fire starts. 2. The photoelectric smoke detector did not perform adequately anywhere in the protectable flaming fire starts, but was adequate almost everywhere in the apartment in the smoldering fire starts of long duration (p. 53). In October of 2000, a home smoke alarm study was conducted by the National Institute of Standards and Technology (NIST). This study was similar to research conducted in 1974 by Factory Mutual known as the Indiana Dunes Tests. Similarities included the tests occurred in acquired residential structures, fire scenarios mimicked actual fatal fires, test fires were both smoldering and flaming in nature and the purpose of the tests were to evaluate the performance of photoelectric, ionization, dual sensor and aspirated smoke alarms. In addition to the smoldering and flaming fires, the NIST study also included cooking fires within these tests. These tests were conducted and evaluated over a two year period. Averill et al. (2008) indicates conclusions from the test include: Smoke alarms of either the ionization type or the photoelectric type consistently provided time for occupants to escape from most residential fires. Consistent with prior findings, ionization type alarms provided somewhat better response to flaming fires than photoelectric alarms, and photoelectric alarms (often) considerably faster response to smoldering fires than ionization type alarms (p. 259). Table 1 represents the average smoke alarm activations times from the NIST experiments that began in October of 2000.
SMOKE ALARMS 7 Research of smoke alarms has also occurred outside the United States. In 1991, Norway conducted research on the reaction times of photoelectric and ionization smoke alarms. During the testing process, researchers compared the response times of both types of alarms in flaming and smoldering fires. Fleming (2006) reports they obtained the following conclusions: The ionization detectors detected smoke from a smoldering fire much later than optical (photoelectric) detectors. When the particular conditions during the fire development are taken into consideration there are reasons to indicate that this detection principle would not provide adequate safety during this type of fire (pp. 4-5). One side effect of operating smoke alarms is the possibility of nuisance alarms. These nuisance alarms occur when the smoke alarm is exposed to a non-fire aerosol. Photoelectric and ionization smoke alarms are both susceptible to these unwanted alarms. In the residential setting, these alarms usually occur due to cooking activities or humid conditions typically found near bathrooms. Unfortunately, these nuisance alarms can lead to an unsafe practice; the resident disconnecting the power that supplies the smoke alarm in order to prevent the annoying false alarm. In fact, false alarms and nuisance activations are the leading cause for deliberately disabling smoke alarms, and may lead people to ignore its early warning of a fire (Ahrens, 2009, p. vii). Researchers conducted a study on smoke alarms in four rural Alaskan villages and published the results in 2000. The researchers chose the four villages based upon similarities in the square footage of the home, the population and the average income. The purpose of the research was to investigate nuisance alarms associated with photoelectric and ionization smoke alarms. Researchers installed new ionization smoke alarms in two of the villages while the other
SMOKE ALARMS 8 two villages received new photoelectric smoke alarms. Both styles of smoke alarms were installed near a cooking or heating source. During the installation process, residents were instructed on smoke detector maintenance, testing procedures and how to change the batteries. The residents were advised the researchers would return in six months to evaluate the smoke alarms. When the researchers returned to the homes, they interviewed the residents. Researchers asked if nuisance alarms occurred, how often, what caused the nuisance alarm and what silenced the alarm? Researchers found 81% of the ionization alarms still worked while 96% of the photoelectric alarms still functioned properly. Ninety-two percent of the homes with an ionization alarm reported at least one nuisance alarm while only 11% of the homes with a photoelectric alarm reported a nuisance alarm. Ninety-three percent of the 69 ionization nuisance alarms were due to cooking as were four of the six (67%) of the photoelectric nuisance alarms. The authors of the research state in their findings, We conclude that the incidence of nuisance alarms is much higher in small dwellings using ionization smoke alarms (Fazzini, Grossman, & Perkins, 2000). Table 2 reflects the results of nuisance alarms in this study. Part of the research conducted by NIST during their research in 2000 on the performance of residential smoke alarms included a variety of scenarios thought to produce nuisance alarms. The testing process included exposing both photoelectric and ionization smoke alarms to different non-fire aerosols. Most of the scenarios were based upon common cooking activities including; frying bacon, frying hamburgers, deep-frying potatoes, baking and broiling pizza, boiling pastas and toasting bread. The researchers also included cigarette smoking and candle burning scenarios but did not include any steam or dust exposure tests. Averill et al. (2008) document the following as an observation from the NIST analysis on nuisance alarms:
SMOKE ALARMS 9 It was observed that ionization alarms had a propensity to alarm when exposed to nuisance aerosols produced in the early stages of some cooking activities, prior to noticeable smoke production. This phenomenon could be particularly vexing to homeowners who experience such nuisance alarms (p. 250). In 2008, the United States Consumer Product Safety Commission (CPSC) conducted a test on nuisance alarm activations associated with cooking. They compared photoelectric, ionization and dual sensor alarms during a thirty day period of testing. Their test concluded any smoke alarm placed too close, less than 10 feet to 15 feet, to a cooking appliance would produce a nuisance alarm. Data obtained from the study indicates the number of nuisance alarms was highest for smoke alarms at a distance of 5 feet from the cooking appliance, with dual-sensor smoke alarms producing the most nuisance alarms (Lee, 2010, p. 12). Table 3 indicates the number of nuisance activations that occurred during the testing process by type of smoke alarm. The table reflects a decline in all types of smoke alarm nuisance alarms as the distance reaches 20 feet from the cooking source. Conclusions and Recommendations This paper discussed two types of smoke alarms that have been installed in homes across the United States since the 1960 s. The discussion concentrated on the response times and nuisance alarms associated with the use of photoelectric and ionization smoke alarms. Although this paper addresses the shortcomings of these two smoke alarms, it also points out the positive aspects of both. Regardless of the type of smoke alarm, it is difficult to quantify the number of lives both types of smoke alarms have saved. There is no doubt smoke alarms have made a significant impact on life safety.
SMOKE ALARMS 10 This paper and previous research indicates there are noticeable differences in the performance of both. Tests conducted by Los Angeles Fire Department in 1960, Factory Mutual in 1974, researchers in Norway in 1991 and NIST in 2000 all point out photoelectric alarms responded quicker to smoldering fires as opposed to flaming fires. The NIST study provided more detail regarding times of alarm activation during the tests. In smoldering tests conducted in a two-story home (Table 1), on average the photoelectric smoke alarm responded 47 to 54 minutes before the ionization alarm activated. The delayed response by ionization detectors in smoldering fires could have fatal consequences for occupants in the structure. The buildup of toxic gases could incapacitate the occupant and the amount of smoke would decrease visibility and make escape difficult. Overall, ionization smoke alarms do not appear to be effective in smoldering fires. Conversely, these same studies indicated ionization smoke alarms responded quicker to flaming fires compared to photoelectric smoke alarms. However, photoelectric smoke alarms appear to be almost as effective at detecting a flaming fire as an ionization smoke alarm. According to the NIST study in 2000, the documented times indicate on average the ionization alarm responded to a flaming fire approximately 57 to 65 seconds sooner than the photoelectric relative to the flaming fire scenario. The delay in response by the photoelectric smoke alarm isn t as significant here as the delay with the ionization in detecting a smoldering fire is, however there is still a delay in the alarm recognizing there is an active fire. Nuisance alarms have long been one of the negative side effects of smoke alarms. This paper points out ionization smoke alarms are more susceptible to these irritating false activations. In fact, this research indicates ionization smoke alarms are far more likely to produce a nuisance alarm compared to photoelectric smoke alarms. Research conducted by NIST in 2000 and by
SMOKE ALARMS 11 researchers in Alaska supports this belief. Although these false alarms are annoying for the occupants, they are very concerning for the fire service from a life safety standpoint. This is due to the fact occupants will remove the battery to eliminate the nuisance alarm. A study conducted by the United States Consumer Product Safety Commission (CPSC) in 2008 studied nuisance alarms that were associated with cooking. According to this study, records of fires that occurred from 2000-2004 indicate smoke alarms were not operating or intentionally disabled in 46% of the reported fires. Nearly all of these non-working smoke alarms were due to dead or missing batteries (Lee, 2010, p. v). Based upon the conclusions from this research, the following recommendations should occur to improve the effectiveness of smoke alarms in the residential setting. First, the fire service should educate the community about the differences in smoke alarm performance. This can be accomplished by public education events in the community and providing information on fire department websites. An opportune time to educate the public would be during fire safety week in October. During these different occasions, the fire service members should explain the how a photoelectric smoke alarm performs compared to an ionization smoke alarm in smoldering and flaming fires. Since research indicates ionization smoke alarms are relatively ineffective for smoldering fires, photoelectric smoke alarms should be strongly recommended. Ionization smoke alarms can be included within the dwelling as long as photoelectric smoke alarms are also included within the protection. This would be especially true if they are installed in a hard-wired system and interconnected with photoelectric smoke alarms. The next recommendation is the fire service should consider requiring the installation of photoelectric smoke alarms in new construction or remodel projects within the community. Although this might be a long and demanding task, the lives and property that could be saved
SMOKE ALARMS 12 from this project is worth the time. The state of Vermont is an example of a state that made changes to their smoke alarm laws. Vermont changed their state law that pertains to smoke detectors in 2008. According to Vermont.gov (2010) the Vermont General Assembly amended the smoke alarm (detector) law by requiring the photoelectric smoke alarm (detector) be installed in new single-family dwellings and dwellings that are sold or transferred after January 1, 2009. The final recommendation pertains to the prevention of nuisance alarms. The occurrence of nuisance alarms can have a detrimental effect on the purpose of the smoke alarm. Typically, people will disconnect the smoke alarm when these annoying alarms happen which eliminates the intended safety purpose of the alarm. This paper recommends the smoke alarms should not be installed near any cooking appliances and be at least twenty feet away from the appliance or a shower location. Also, ionization and dual sensor smoke alarms should not be installed near any of these locations because they are more likely to produce a nuisance alarm compared to a photoelectric smoke alarm. The installer should follow the manufacturer s installation recommendations when installing a smoke alarm. In closing, smoke alarms have saved many lives worldwide. Photoelectric and ionization smoke alarms have the same purpose, to detect and alert residents to fires. Both smoke alarms have to pass strict testing by Underwriters Laboratory (UL); however this paper indicates there is a vast difference in their effectiveness with reaction times to certain fire conditions and nuisance alarms.
SMOKE ALARMS 13 Table 1. Average time to alarm (in seconds) for several smoke alarms and fire scenarios in a two-story home (Averill, 2008, p. 243) Every Level Installation Criterion Flaming Photo Ion Dual Ion/Photo Aspirated Living Room 107 70 Bedroom 54 30 Bedroom (Door Closed) 186 164 3602 Smoldering Living Room 1542 4824 1508 1424 Living w/ac 1366 4192 2030 2072 Cooking Kitchen 880 1554 898 858 Every Level + Bedrooms Installation Criterion Flaming Photo Ion Living Room 107 70 Bedroom 54 30 Bedroom (Door Closed) 186 164 Smoldering Living Room 1542 4824 Living w/ac 1338 4192 Cooking Kitchen 880 1554 Every Room Installation Criterion Flaming Photo Ion Living Room 107 70 Bedroom 54 30 Bedroom (Door Closed) 186 164 Smoldering Living Room 1542 4824 Living w/ac 1338 4192 Cooking Kitchen 880 1290
SMOKE ALARMS 14 Alaskan Village Smoke Alarm Study Photoelectric Ionization 96.00% 81.00% 92.00% 11.00% Functioning Alarms Total Nuisance Alarms Table 2 Number of Nuisance Activations 60 50 40 30 20 10 0 Smoke Alarm Nuisance Activations All Homes, Two Manufacturers 5 ft. 10 ft. 20 ft. Ion 41 23 5 Dual 53 41 5 Photo 14 28 4 Table 3 (Lee, 2010 p. 13)
SMOKE ALARMS 15 Bibliography Ahrens, M. (2008, January). Home smoke alarms The data as context for decision. Fire Technology. doi:10.1007/s10694-008-0045-9 Ahrens, M. (2009, September). Smoke alarms in U.S. home fires. Retrieved May 4, 2010 from http://www.nfpa.org/assets/files//pdf/smokealarmsexecsum.pdf Averill, J.D., Bryner, N.P., Bukowski, R.W., Cleary, T.G., Kuligowski, E.D., Peacock, R.D., Reneke, P.A., & Walton, W.D. (2008, February). Performance of home smoke alarms: Analysis of the response of several avaialable technologies in residential fire settings. Retrieved May 9, 2010 from http://smokealarm.nist.gov/pdf_files/nist_tn_1455-1_feb2008.pdf Bukowski, R.W. (1993, January/February). Studies assess performance of residential detectors. NFPA Journal, 87(1). Retrieved May 4, 2010 from http://www.fire.state.mn.us/firewkop/firecode/smoke%20and %20Heat%20 Detector%20Study.pdf Bukowski, R.W. (Ed). (2003). Fire protection handbook (19 th ed.) (Vol. 2). Quincy, Massachusetts: National Fire Protection Association. Fazzini, T.M., Grossman, D., & Perkins, R. (2000, August). Ionization and photoelectric smoke alarms in rural Alaskan homes. Western Journal of Medicine, 173(2), 89-92. Retrieved May 17, 2010 from http://www.ncbi.nlm.nih.gov/pmc/articles/pmc1071008/
SMOKE ALARMS 16 Fleming, J.M. (2006). Photoelectric and ionization detectors - A review of the literature Re-visited. Retrieved May 12, 2010 from http://www.mass.gov/ Eeops/docs/dfs/osfm/boards/specific_meetings/j_fleming/photo_vs_ion_ revisited_2004_j_fleming.pdf Helmenstine, A.M. (2010). How do smoke detectors work? Photoelectric & ionization smoke detectors. Retrieved May 2, 2010 from http://chemistry.about.com/cs/howthingswork/a/aa071401.a.htm Hutchinson, A. (2005, December). Top 50 inventions. Popular Mechanics, 182(12), 76-84, 135. Lee, A., & Pineda, D. (2010, March). Smoke alarms Pilot study of nuisance alarms associated with cooking. Retrieved May 4, 2010 from http://www.cpsc.gov/library/foia/foia10/os/smokealarmnuisance.pdf Vermont.gov (n.d.). Smoke & CO alarms. Retrieved May 24, 2010 from http://www.dps.state.vt.us/fire/smoke/imdex.html