Case study: Sprinklers and smoke detection

Robert G. Bill Jr. and Hsiang-Cheng Kung conducted 12 fire tests in 1989 (article: Evaluation of an Extended Coverage sidewall Sprinkler and Smoke Detectors in a Hotel Occupancy) to evaluate the performance of an extended-coverage horizontal sidewall sprinkler with a fast-response link and the performance of smoke detectors. Eight of the tests were flaming fire tests using a bed or chair as the source, and four tests were conducted with a smoldering combustion in a bed.

A common type of high-rise building use is residential group R-1, so the results of this study are applicable when studying trends in high-rise fire-detection methods. Per the International Fire Code (IFC), high-rise group R-1-type occupancies shall be provided with both an automatic sprinkler system and single- and multiple-station smoke alarms in sleeping areas and in every room in the path of the means of egress from the sleeping area to the door leading from the sleeping unit.

The tests where the fire originated from the flaming chair resulted in the smoke detectors activating at a gas temperature of 100°F and an obscuration of 15%/ft. The activation of the smoke detector occurred approximately 3 minutes before sprinkler activation. For this specific case, smoke detectors provide occupants sufficient egress time to exit the space, and the smoke detector provides early enough detection that manual firefighting is a possibility.

During the tests, the sprinklers were able to suppress the fires in the guest rooms. Although smoke detectors do provide earlier warning to occupants, sprinklers are still a critical aspect in the fire protection design and provide an important function to providing safety to occupants and the building.

James A. Milke, PhD, A.J. Campanella, Cathleen T. Childers, and Brittany D. Wright published a study titled “Performance of Smoke Detectors and Sprinklers in Residential and Health-Care Occupancies,” which compiled data from several research groups, including Bill and Kung, and compiled the data to determine the relative performance of smoke detectors and sprinklers in one- and two-family dwellings, hotels, and institutional occupancies. They found the number of fires determined to be too small for operation was fewer for smoke detectors than for sprinklers. This finding indicates that smoke detectors are capable of responding to smaller fires than sprinklers, which agrees with the finding in the study performed by Bill and Kung in 1989.

Milke’s team also found that the casualties from fires judged to be too small for operation were 15.5 times more frequent for fires too small for sprinkler activations, versus fires too small for smoke-detector activation. In summary, smoke detectors respond quicker than sprinklers and provide occupants a greater amount of time to egress, which results in far fewer casualties.

While sprinklers primarily function to contain a fire to the room of origin, smoke detectors provide warning to occupants to allow sufficient time for them to safely egress the building. Automatic sprinklers can provide a warning to occupants via a waterflow detector, which is connected to the building’s fire alarm system. However, studies have shown that smoke-detector response time is quicker to detect fires in the incipient stages.

The primary goal for safe egress is to provide occupants a large available safe egress time (ASET) as compared with the required safe egress time (RSET). Based on the studies referenced above, smoke detectors provide a level of protection that increases the ASET for building occupants.

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