off u201d i e the fan blades decelerate and may stop rotating depending on the particular control scheme and type of sensors being used sprinklers 14 in the vicinity of fire 16 can be selectively activated individually in zone groups or all of the sprinklers can be activated together likewise the deactivation of fans 12 may be done selectively or as a group examples of sensors that can sense or react to a characteristic associated with fire 16 include but are not limited to optical detectors ionization detectors heat detectors and combinations thereof information on various types of sensors is provided herein under the section entitled u201c background u201d in the illustrated example of fig1 sensors 18 sensors 18 a and 18 b are smoke detectors e g optical ionization or any other suitable type of smoke detector that are installed near the building 39 s ceiling 20 where relatively warm smoke tends to collect during for example fire 16 in some cases sensors 18 are positioned in updrafts created by fans 12 sensor 18 a for example is positioned in an updraft 22 of fan 12 a such that sensor 18 a may quickly sense smoke 24 being drawn up by the rising current of air returning to fan 12 a in response to detecting smoke 24 from fire 16 sensors 18 provide signals 26 and or 28 signals 26 and 28 can be conveyed e g transmitted to a common controller 30 e g programmable logic controller computer processor logic circuit electromagnetic relay circuit etc that in turn provides output signals 32 and or 34 to deactivate fans 12 a and or 12 b alternatively signals 26 and or 28 may be conveyed directly.