Current smoke alarms pass life-saving tests


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A report from the Commerce Department's National Institute of Standards and Technology (NIST) today stated that both types of commercially available home smoke alarms (also called smoke "detectors") consistently provide people enough time to escape most residential fires. It stressed the need for immediate response to an activated alarm and showed that individuals caught in a flaming fire (as opposed to a smoldering fire) have an average of three minutes from an alarm's first warning to escape.

"The three-minute escape window for flaming fires differs from the 17 minutes NIST recorded in its seminal smoke alarm tests in the 1970s," said Richard Bukowski, the NIST researcher who conducted both studies. "It confirms what fire scientists have recognized for some time: fires today seem to burn faster and kill quicker because the contents of modern homes (such as furnishings) can burn faster and more intensely."

"Our new research, however, proves that even with a three-minute warning, smoke alarms still offer enough time to save your life," Bukowski stressed. "When the alarm sounds, it is important that everyone just get out of the house."

Smoke alarms are of two types--ionization and photoelectric.* Some combination models are sold.

According to the two-year NIST home smoke alarm performance study, ionization smoke alarms respond faster to flaming fires, while photoelectric smoke alarms respond quicker to smoldering fires. The report concluded that, despite these differences, the placement of either alarm type on every level of the house provided the necessary escape time for the different types of fires examined. The researchers determined the necessary escape times by considering the time that the alarms sounded in various locations and the development of untenable (unsurvivable) conditions.

The tests also showed how closed bedroom doors and proper placement of smoke alarms affect one's chances of survival. In both cases, the time to escape untenable conditions was increased, providing that the individual was not in the room where the fire originated.

* Ionization alarms work on the principle that as smoke particles enter the alarm's sensing chamber, the particles reduce the electric current flow in the alarm. Photoelectric alarms use light to detect the presence of smoke particles, with the particles scattering the light toward a sensor.

The new smoke alarm data are expected to be useful in considering programs and legislation to install interconnected smoke alarm systems (where one alarm sets off all other alarms connected to it within a building) in older homes. Major U.S. housing codes have required interconnected smoke alarms, including alarms in bedrooms, since 1993. However, most homes built before that date are not so equipped.

The NIST report also looked at the interaction of smoke alarms and residential sprinklers of the type increasingly being required in new homes. The tests reaffirmed earlier findings that smoke alarms of either type will activate faster than sprinklers, although sprinklers, once activated, can stop a major home fire quickly. The NIST report also noted that sprinklers activated well after smoke alarms and after heat alarms. The report concluded that "while these sprinklers have an outstanding record of saving lives and property, the later activation times imply that residential sprinkler installations should always include smoke alarms (as currently required in National Fire Protection Association Standards 13D and 13R) to provide greater escape time for those capable of escaping."

To further investigate the results of an earlier study by the U.S. Consumer Product Safety Commission (CPSC), NIST also looked into "nuisance" or false alarms, usually activated by cooking fumes. Such false alarms are of concern because inconvenienced individuals sometimes disconnect the smoke detectors, leaving the area without devices capable of detecting authentic fires. The NIST tests showed that normal cooking activities cause nuisance alarms in both photoelectric and ionization type alarms. Neither type of detector was demonstrably better in reducing nuisance alarms. The test data, however, are expected to be useful in the design of next-generation "smart" units that will use computer-chip evaluation of multiple fire conditions to accurately distinguish unwanted fire conditions from nuisance conditions.

The recent NIST tests were similar in many respects to the 1975-1976 NIST tests that produced the first data on record to clearly demonstrate the potential of smoke alarms to save lives. The NIST fire engineers tested the ionization and photoelectric alarms in fire tests conducted within a controlled laboratory setting as well as in two homes---a manufactured home and a three-bedroom, two-story brick house. The layout of the manufactured home also was considered representative of apartments and condominiums of about 100 square meters (or about 1,000 square feet). Groups of alarms were located in the room of fire origin, in at least one bedroom and in a central location on each floor. The researchers used actual furnishings and household items for fire sources and tested smoke alarms bought in retail stores.

Source: Eurekalert & others

Last reviewed: By John M. Grohol, Psy.D. on 21 Feb 2009
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