I HAD A QUESTION ON HAVING 2 SMOKE DETECTORS TO SET OFF NOTIFICATION DEVICES. WHAT IS THE RULE ON HAVING TO SET OFF 2 DETECTORS BEFORE THE ALARMS SOUNDS??? THANKS
Most jurisdictions want notification devices to begin evacuation on the first detector. Some allow you to wait for a second (cross zone) to do other actions such as release a suppression agent, etc.
Many addressable smoke detectors can also wait to activate alarm after a short period of "verification" that the smoke is still there.
That is normally only used for suppression systems so as to be sure of a fire before dumping water or chemical on computers and such.
I have done it in production areas. An example was a building that made the crystal wafers that computer chips are made out of. They want to make very sure there is a fire before they shut down production and evacuate a building. It was allowed by the AHJ in that case.
Also, when you cross zone detectors you need to cut the normal spacing in half and be sure to have at least 2 detectors in every area.