The National Fire Protection Association (NFPA) lays out several types of fire alarm systems and fire suppression systems. For instance, the NFPA 72 doesn't show what type of fire alarm system is needed for an "occupancy"; the NFPA 72 only shows that if smoke detectors are needed, smoke detectors have to be installed in a certain way.
Occupancy, and the type of fire alarm system that should be installed, is determined by the NFPA 101 or the International Building Code. These books show that one type of occupancy, for instance a gas or petrol station, requires a totally different type of fire alarm system than an apartment building.
The books also indicate that for some types of occupancy, total coverage by smoke detectors is required, and pull stations are required at all exits . . . except if the building has total coverage by a sprinkler system. In some occupancies with total coverage by a sprinkler system, except for any needed smoke control, and except for a single pull station in a normally occupied area, there is no need for smoke detectors or pull stations.
You can add to the various requirements above the requirements of the various Authorities Having Jurisdiction (AHJs). See:
Just Who Is the Authority Having Jurisdiction (AHJ)?
There are many reasons to install smoke detectors above a false ceiling; there are many more reasons not to install smoke detectors above a false ceiling. The requirements, though, have to be taken on a building-by-building basis; you will find that there isn't a blanket rule that covers every situation.
I know that this isn't what you wanted to hear, and I wish I could help you with specific information, but there are just too many factors involved for me to be of any help.
Douglas Krantz
