The Evolution of Smoke Alarms and Detectors and the New UL Standard: Are We Progressing?

By Brittany Brown

EVERY YEAR, hundreds of thousands of fires occur across the United States. Despite not being the number one type of fire encountered, residential fires account for the largest number of civilian fire fatalities—more than 75% of all civilian fire deaths.¹ The five leading causes of fires within residential homes are cooking, heating equipment, electrical distribution and lighting equipment, intentional fire setting, and smoking material. Cooking, however, remains the leading cause of home fires, with smoking materials resulting in the greatest number of home fire deaths.² The primary cause of death or symptoms leading to death in 89% of these civilian fire fatalities can be attributed to thermal burns and smoke inhalation.³ Thirty years ago, occupants had between 14 and 17 minutes to escape a fire. Now, due to the number of synthetic materials, occupants only have two to three minutes.⁴

Studies have shown that having an operational smoke alarm/detector can almost double your odds of surviving a home fire and could lessen the annual home fire fatality rate by more than 37%.⁵ Research has shown that 41% of all civilian fire fatalities were in residential structures without smoke alarms/detectors, with an additional 16% of these fatalities in residential structures with smoke alarms/detectors that failed to operate.6 In homes with large enough fires to activate them, it was found that these smoke alarms/detectors did activate 89% of the time.⁶ In an assessment of all residential fire fatalities, of those that included smoke alarms, 73% of the fatalities in these home fires did have a smoke alarm that operated, yet a fatality still occurred. This notion begs the question: Are smoke alarms effective enough at early identification of fire growth and development to give occupants enough time to safely egress based on the evolution of new synthetic fuels?

Fire Death Causation and Human Behavior

The most notable factor contributing to fire fatalities is fire pattern effects: Victims are entrapped or their vision is blocked by smoke or flames and they cannot physically escape because of smoke.³ It should be noted that most fire fatality victims are asleep, almost 46%, during the initiation of the fire event. This and a lack of adequate early notification are the leading contributing factors relating to residential fire fatalities.³ The byproducts of combustion, predominantly carbon monoxide, hydrogen cyanide, and other noxious gases, physically and mentally inhibit victims’ ability to escape because of simple and complex asphyxiation and through the alteration of cognitive processes.

As the fire event unfolds, the following actions take place in sequence in some capacity: The fire event begins, and the victims detect that something is occurring and become alarmed, at which point they seek information.⁷ After this action, they then make the decision to evacuate not physically yet but mentally. They then work to prepare, protect others, and then protect themselves. This is when the movement period begins.⁷ This thought process is known as their timeline regarding preevacuation and movement, the decision process that occurs during the fire event. In cases where there is a smoke alarm/detector, the device operating may be what initiates the detection phase—the victim becomes alarmed and seeks more information. All of this occurs before evacuation.⁷ It is important to understand this analysis of human behavior in fire, as it directly impacts victim survivability. It is also important to assess whether smoke alarms/detectors are indicating early enough to allow this human behavior to occur while still allowing for occupant egress before cognitive impediments are reached due to the volatility of new home furnishings.

Smoke Inhalation and Fire Death

The primary cause of death or symptoms leading to death in 89% of these civilian fire fatalities can be attributed to thermal burns and smoke inhalation.³ Within this 89%, there are three physiological types of injuries leading to death due to smoke inhalation: thermal injury predominantly to the upper airway, chemical injury to the upper and lower respiratory tract, and systematic effects of toxic gases such as carbon monoxide and hydrogen cyanide.⁸ Within this assessment, asphyxia from carbon monoxide toxicity is the main cause of rapid death in fire victims, with thermal and chemical injuries impacting the upper and lower respiratory tract, initiating the cycle of respiratory distress and resulting in edema formulation.⁸

These injuries occur due to incomplete combustion processes, as matter is broken down by the effects of heat alone through pyrolysis, which precedes combustion, and molecular bonds are broken.⁹ These molecules, broken from their bonds, form new molecular bonds and present as carbon monoxide, carbon dioxide, hydrogen cyanide, nitrous oxide, and other compounds.¹⁰

These new molecular compositions can act as chemical or simple asphyxiants or simply become oxygen depletion/replacement agents. The respiratory system cannot process these compounds, and breathing them in can cause irritation and edema as well as airway occlusion and eventually asphyxiation.¹¹ Carbon monoxide impacts the body’s ability to oxygenate. This eventually leads to simple asphyxiation. ⁸ These gases also highly impact decision-making processes, causing internal mental lags, confusion, and disorientation, overall impeding or halting the evacuation decision process.⁷

These byproducts of combustion are buoyant due to differential thermal layers and usually rise, congruent with fire dynamics and the fire plume. As a fire continues to grow within a residence, fuel packagers are consumed and broken down into these new gases, ultimately causing an oxygen-deficient environment to exist.⁹ This is one of the reasons smoke alarms are mounted on the ceiling. As these particles rise, they encounter the smoke alarm/ detector, which processes the particles depending on the type of smoke alarm (photoelectric/ ionization). At this time, if the particle sizes of the byproducts of combustion are sufficient, the smoke alarm will activate or the smoke detector will initiate a signal to the fire alarm control panel to ensure communication to notification devices.⁹

UL and Updated Requirements

ANSI/UL 217 and ANSI/UL 268 have been modified to address the more than 350 technical changes required for manufacturers to update smoke alarms and smoke detectors to maintain their UL Listing. Research conducted by the National Institute of Standards and Technology (NIST) and the National Fire Protection Association (NFPA) demonstrated the need for smoke alarm and detection changes based on more specific testing done on home furnishings, including flaming polyurethane foam and smoldering polyurethane foam tests.¹²

These tests revealed that smoke produced from burning or smoldering foam and plastics generates a smoke aerosol that differs in terms of color, quantity, and mean diameter of particulates from what previous smoke alarms/detectors could effectively detect.¹² The new UL standards account for this evolution in home furnishing hazards with an algorithm-based detection method based on particulate size and density to better assess false alarms like cooking steam to ensure greater consistency of activation. During a study of residential home fires that occurred between 2009 and 2013 where a smoke alarm was present but did not activate, it was noted that 46% of these cases could be attributed to missing or disconnected batteries.¹³ The owner/ operator purposefully disconnected the batteries likely due to nuisance alarms.¹³ The new standard hopes to lessen these nuisance alarms as well as target based on particulate size, smoldering, and flaming polyurethane fires faster, to allow for earlier detection.¹² These standards were initially supposed to be enacted in April 2020 but, due to the global pandemic, were pushed back to allow for manufacturers to comply during this unsteady economic environment.

Smoke Alarm Activation

As fuel packages have changed in the past 20 years, smoke alarms and smoke detectors have as well. In fact, UL 217 and UL 268 are on their eighth and seventh and editions, respectively.¹² Are these changes sufficiently correlative to the degree and type of fuel load present in most residential structures? And can that be assessed quantitively and qualitatively?

With the delay in the enactment of the new ANSI/UL 217 and 268 for manufacturers to comply with updated standards, it is unlikely that any data will be available anytime soon. Smoke alarms used in residential structures have a lifespan of 10 years, assuming that they are maintained properly. This means that most residential households may not reap the benefits of the newly designed smoke alarms/detectors for at least 10 years, assuming that at the end of their usable life cycle existing smoke alarms/detectors are replaced with those complying with UL 217 or UL 268. From there, data could be assessed as to whether there is a discernable decrease in residential fire fatalities that could be related to more timely activation of smoke alarms based on particulate size and type and better maintenance due to fewer nuisance alarms.

From there, the data must be assessed to adequately determine whether these changes are truly effective from quantitative and qualitative analyses on whether there is a decrease in residential fire deaths and if the changes in smoke alarms/detectors can be attributed as correlative. Issues associated with reporting, misreporting, and incomplete or inaccurate data associated with the compilation of residential structure fire injuries, deaths, and incidents will likely impact the reliability of data acquisition, which inherently is a challenge.

Another variable to account for is the inclusion of 10-year sealed lithium-type batteries in both ionization and photoelectric smoke alarms. Smoke alarms with batteries that are not removable—in fact, sealed—may sway home fire fatality statistics as well by prohibiting the removal of batteries and specifically addressing the 46% of the time where a smoke alarm was present but did not activate due to the removal of batteries.¹³ The introduction of the technology, and associated legislation updates in multiple states including California, Florida, Georgia, Illinois, Louisiana, Maine, Maryland, Massachusetts, New Jersey, New York, North Carolina, Oregon, and Vermont, which all in some facet require the installation or sale of these specific smoke alarms, will unintentionally jilt the potential statistical significance of the new UL standards for these smoke alarms. In short, the evolving technology of smoke alarms/detectors is moving in a positive direction, quantitatively and qualitatively. This remains to be seen, as corroborated by data, but it is likely that a potential decrease in home fire fatalities may occur because of these technological changes in both the design of the devices themselves and associated progressive legislation in specific states. As hazards evolve, correlative technology must evolve as well—in this case, whether the new UL standards will be able to adequately address nuisance alarms while also activating faster based on the fuel package such as polyurethane foam. It is likely that when these new smoke alarms/detectors are phased in, they will create fewer nuisance alarms, resulting in fewer owner/operator modifications, including the removal of the batteries. However, the inclusion of sealed battery smoke alarms specifically may also address this issue, with an inability to target extrapolated data regarding nuisance alarms.

It is likely that with continued synthetic fuels present in residential structures, the issue of smoke inhalation will continue to present as the leading cause of death in home fires. This number will likely increase as different synthetic fuels are developed and sold throughout the United States. The human process and methodology for assessing danger, such as in the case of a house fire, will remain the same. The timeliness of detection, such as in the case of an activating smoke alarm/detector, has the potential to allow for quicker harzard assessment and correlative action, giving victims an opportunity t0 escape faster before they are subject to toxic gas injuries.

She has served primarily as a fire marshal, training officer, and firefighter working in New Mexico, Texas, Kentucky, and now Colorado. Brown is pursuing a PhD in forensics from Oklahoma State University and has a master’s in systems engineering from Embry-Riddle Aeronautical University. She previously served as a university professor at Eastern Kentucky University, College of Justice and Safety, working primarily within fire protection, safety, and engineering technologies. Brown is an advisory board member for the Vision 20/20 Strategy 1, Leadership Team; a committee member for the Fire, Performance, and Wildland Interface Code Interpretation Committee for the International Code Council (ICC) and IBC-FS Fire Safety Committees; a subject matter expert for the National Association of Certified Engineering Technologies (NICET) for Fire Alarm Systems; and a member of IFSTA Fire Protection, Detection, and Suppression Systems Validation Committee, 6th Edition.

ENDNOTES

1. “Topical Fire Report Series: Civilian Fire Fatalities in Residential Buildings (2017-2019).” U.S. Fire Administration, vol. 21, no. 3, 2021, usfa.fema.gov.
2. Aherns, Marty, and Radhika Maheshwari. “Home Structure Fires.” NFPA, 2020, nfpa.org.
3. “Fire in the United States 2008-2017.” U.S Fire Administration, 2019, fema.gov.
4. Mulvihill, Keith. “How a House Fire Spreads.” This Old House, 11 Aug. 2024, bit.ly/3Ct2xie.
5. Runefors, Marcus, et al. “How Could the Fire Fatalities Have Been Prevented? An Analysis of 144 Cases During 2011–2014 in Sweden.” Journal of Fire Sciences, vol. 34, no.6, 2016, pp. 515-527, bit.ly/3URbJDm.
6. Aherns, Marty.”Smoke Alarms in U.S. Home Fires.”NFPA 2021. nfpa.org.
7. Society of Fire Protection Engineers. SFPE Guide to Human Behavior in Fire, 2nd Edition. Springer, 2019, bit.ly/496RzLH.
8. Gupta, Kapil, et al. “Smoke Inhalation Injury Etiopathogenesis, Diagnosis, and Management.” Indian Journal of Critical Care Medicine,vol.22,no.3,2018.pp. 180-188,ijccm.org.
9. “NFPA 921: Guide for Fire and Explosion Investigations.” NFPA, 2021, bit.ly/3AxYPDs.
10. DeHaan, John, and David Icove. Kirk’s Fire Investigation, 7^th Edition. Pearson, bit.ly/3USuaYj.
11. “House Fires: The Fatal Danger Beyond the Flames.”Cleveland Clinic, 2 Nov. 2021, bit.ly/40KDpNT.
12. D. Kaiser. “Smoke Alarms and Smoke Detectors– New and Revised Requirements.” UL Research Institutes (Archived), 2020, ul.org.
13. McGree, Tucker. “Smoke Alarms in US Home Fires.” NFPA, bit.ly/3USHJqS.

BRITTANY BROWN has been serving in the public safety industry for almost 20 years in both the fire service and the United States Air Force.