When the ignition source is positioned directly beneath
smoke detectors and sprinklers, the smoke flow effect is
generally greater than the temperature rise effect with the
result that the smoke detectors will activate first. Sprinklers will
not activate until the glass temperature sensing bulb senses that
the temperature has reached 69 C - 150 C. Because of the
locations of movable and fixed fire loads as well as the fire
spread pattern and ventilation effects, smoke detectors do not
necessarily activate sooner than sprinklers. Appropriate sprinkler
or smoke detector location planning consistent with
different situations (interior decoration, room layout, and
opening design) is the key to performance-based fire safety
design.