What’s Best for Smoldering Smoke?

Does smoke always rise?  No.  Weak plume smoke doesn’t have the thermal inertia to reach ceiling detectors.  Before flames erupt, smoldering smoke from incipient fires drifts much more randomly.  (See “Tanaka” quote below)

Ceiling smoke alarms are primary detectors.  Many installations use secondary point detectors to detect the smoldering problem earlier, instead of waiting for the smoke to eventually reach the ceiling.  (See “Fox” quote below)  

The Smoke Shutoff™ is intended to be used as a secondary point detector, stopping these smoldering fires before flames erupt or before the smoke itself kills.

Smoldering fires are the leading cause of fire deaths in the United States (Hall 2004)

The Smoke Shutoff™ uses photoelectric detection because it is superior to ionization detectors for detecting smoldering smoke.  (NFPA link).  Nearly all the smoke detectors on Home Depot and Lowe’s shelves are ionization because those units can be made for about $5 less than photoelectric.  Fortunately, quality Kidde and First Alert photoelectric or combo (both photo and ionization) are available on Amazon and other mail order catalogs. 

References:

Takeyoshi Tanaka, Disaster Prevention Research Institute, Kyoto University, Gokasho, Uji, Japan says

A hot upper layer pre-established under the ceiling of a room in a house due to a solar load in the summer or room heating in the winter may cause problems for fire detection by ceiling-mounted smoke detectors. A weak plume from a smoldering fire may be pushed back down by the hot layer, and be unable to reach a ceiling-mounted detector. LINK

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Peter Fox of Airsense Technology

It was recognised many years ago that the relatively cool smoke produced by the early stage of electrically initiated fires travels on the air currents generated by the air conditioning system, rather than being able to rise by thermal buoyancy to the ceiling, where conventional type smoke detectors are installed...

Primary detection offers an extremely efficient method of protecting an area subject to high air movement. But if the air handling system is switched off, detection will suffer – any smoke will rise to the ceiling in the normal way. Consideration should therefore be given to installing secondary detection either through conventional point detectors… LINK

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             J. R. Hall, 2004, The Smoking-Material Fire Problem,
             Fire Analysis and Research Division of The National Fire Protection
             Association, Quincy, MA (USA). November 2004.