Today, strobe coverage dictates all. The size and physical floor plan determine the amount of strobes. Correct me if I’m wrong, but I recall reading that there must be one strobe per every 20’ x 20’ area. My high school has TEN SpectrAlert Advances, 5 P2R’s on High Volume Temporal, and 5 SR remote strobes (I can’t remember the candela settings) in the dining room, and a P2R and SR in the serving line. As for the kitchen, I’ve never been in there so I have no clue. The rest of the school has a mix of SpectrAlert Advance P2R’s, SR’s, PC2R’s, and SCR signals run by the semi-reliable Silent Knight IFP-2000 installed when the school was built in 2009. That cafeteria gets rather LOUD during fire drills. :lol:
As for grandfather clauses, if the existing layout, wiring, etc. does not change, the existing coverage (or lack thereof) is deemed sufficient unless the AHJ says otherwise. My 6th grade middle school only had one System Sensor MA sounder in the dining room set on Swept Frequency, run by an ESL 1500, and the roar of 200 talking middle schoolers proved no match for the obnoxious whine of Swept Frequency. My 7th/8th grade middle school only had one Wheelock 34T in the dining room and only one in the kitchen, but the both of them did their job WELL during a mid-lunch malfunction of the fault-ridden Fire-Lite MS-5210UD that controlled them.
I think it also probably depends on the installer. The Simplex/Standard Electric Time and ESL (the latter two now Fire-Lite) systems in schools I’ve been a student in, both old and new, seemed to use the least amount of signals possible, while the EST and Silent Knight systems seem to have signals EVERYWHERE. One of my elementary schools had 6 EST Genesis horn/strobes per hallway, plus in every classroom and bathroom, while the other two I went to had TrueAlerts or 2901-9838+4903-9101 horn/strobe-plates spaced well apart. The school with TrueAlerts had 4 per hallway, with remote strobes in every classroom/bathroom, and 2 horn/strobes in the Cafeteria (4020 system installed in 2001), and the school with 9838+9101’s had 2 per hallway and 1 in the rather small Cafeteria (4005 system installed in 1990 as a 4002).
So basically…size of the room, strobe coverage concerns, and installer/AHJ preferences.