Detectors in the Spotlight

James Milke, Ph.D., P.E., is professor and associate chair of the Fire Protection Engineering department of the University of Maryland. Milke and his staff reviewed several past studies conducted over several years to examine the comparative operation of smoke detectors and sprinklers over a wide range of data. Milke presented the results in a report at the Automatic Fire Alarm Association’s (AFAA) annual meeting in April and followed it up with a presentation at the AFAA breakfast at the National Fire Protection Association (NFPA) annual conference in Las Vegas in June.

As we all know, the primary purpose of smoke alarms and detectors is to provide early warning to afford more time to escape a fire situation. Fire sprinklers provide the suppression feature for facility fire protection to reduce the fire size and keep it from spreading. Together, they can improve fire protection for both the building and the occupants. The review assessed the response time or the period between activation and the available safe egress time. This review focused on the percentage of fires too small to activate the respective devices and the casualty rates (fatal and nonfatal).
Marty Ahrens, NFPA, conducted the “Home Structure Fires” study, which found 96 percent of homes have at least one smoke alarm, and only 31 percent have a smoke alarm in all bedrooms. Her analysis found that the fire death rate in homes without a working smoke alarm was approximately double the fire death rate for homes with working smoke alarms. John Hall, NFPA, conducted a study, “U.S. Experience with Sprinklers and Other Automatic Fire Extinguishing Equipment.” He concluded that the fire death rate was approximately 80 percent lower in units with sprinklers (in addition to the smoke alarms). Both found that around 5 percent of the fires in residences were judged to be too small to activate smoke alarms, while 54 percent were too small to activate sprinklers.

In another study, Jennifer Flynn’s “U.S. Structure Fires in Nursing Homes,” 72 percent of reported fires in nursing homes and 78 percent of reported fires in hospitals and hospices were deemed too small to activate sprinklers.

As part of this report, the University of Maryland team reviewed about 197,000 National Fire Incident Reporting System (NFIRS) fire incidents from 2003–2007 in one-, two- and multifamily dwellings; commercial residential facilities; and healthcare facilities. They found a range of 38–65 percent of fires were too small to activate sprinklers, while only a range of 9–13 percent of fires were too small to activate smoke detectors. They discovered fire incidents with fires too small to activate sprinklers where smoke detectors were not installed produced a ratio of 4.1 for one- and two-family and multiresidential, 15.5 for commercial residential, and 2.9 for healthcare occupancies. This indicates the chance of sustaining a casualty is 15.5 times higher if no smoke detectors are installed for fires too small to activate sprinklers. Where both smoke detectors and sprinklers were installed, smoke detectors alerted occupants in approximately 94 percent of the incidents where sprinklers did not operate in commercial residential occupancies, and in 100 percent of the cases in healthcare occupancies. This clearly shows the value of having both smoke detectors and sprinklers to improve life safety. Casualty rates were reduced significantly when both types of devices were installed. This shows the value of the sprinklers keeping the fire from spreading. The significant difference in casualty rates in the “too small” fires indicates the potential contribution of smoke detectors to fire safety in sprinklered buildings.

This is only a brief description of the report to show the value of smoke detectors and sprinklers. Since each perform different functions, it is important each occupancy be reviewed to determine the best fire protection for that facility. In general, smoke detection is installed to provide earlier warning of a fire situation to increase egress time for occupants, and sprinklers are installed to protect the property by suppressing the fire and reducing fire spread to other parts of the building. Monitoring of both types of systems provides faster fire department response, which saves the lives of occupants and reduces property damage. It also provides a higher level of safety for fire fighters. A copy of this report is available for download at

In future articles, I will discuss the value of different types of smoke detection, including technological improvements, and I will analyze the use of new technology for monitoring fire alarm and sprinkler systems.

HAMMERBERG is currently the president/executive director of the Automatic Fire Alarm Association Inc. headquartered in Jasper, Ga. He serves on a number of NFPA committees, including the NFPA 72 Technical Correlating Committee and the Protected Premises Technical Committee. He can be reached at

About the Author

Thomas P. Hammerberg

Life Safety Columnist
Thomas P. Hammerberg, SET, CFPS is president of Hammerberg & Associates Inc. He serves as Director of Industry Relations for the Automatic Fire Alarm Association (AFAA) Inc. and represents the association on a number of NFPA committees, including the...

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