Fire Alarm System Fundamentals, Classifications, and Design Principles
Classifying a system
Know the vocabulary used to describe systems: conventional (zone) versus addressable versus analog addressable; single-stage versus two-stage signaling (alert then general alarm, usually with voice); tone-only versus voice evacuation; protected-premises systems versus systems that report to a supervising station; automatic versus manual initiation. Design starts with the occupancy and the code trigger, then moves to a sequence-of-operations matrix: what initiates, what sounds, what shunts or releases, what notifies, and in what order.
Design principles
Detector type follows the expected fire signature: photoelectric for smoldering fires, ionization or beam for fast flaming fires, heat where smoke detection is unsuitable, air sampling for special hazards. Layouts must satisfy spacing rules, stay out of dead-air spaces, and be checked for NAC voltage drop and battery capacity. Coverage decisions (full versus selective) come from the occupancy chapter of the code, not from the panel's capabilities.
Worked example
A 60 ft by 80 ft office with a smooth 10 ft ceiling and listed smoke spacing of 30 ft. Every point must be within 0.7 x 30 = 21 ft of a detector. A 3 by 5 grid gives 20 ft by 16 ft spacing; the half-diagonal is sqrt(10^2 + 8^2), about 12.8 ft, well inside 21 ft. Fifteen detectors satisfy the rule.
Trap
Addressability does not change spacing requirements. A common distractor implies that addressable devices give better coverage; they give better identification, not more area per device.