Fire Alarm and Life Safety Systems
Core concepts
Fire alarm work demands knowledge of initiating devices (smoke, heat, duct, waterflow, tamper), notification appliances (horns, strobes, speakers), and the circuit classes that govern survivability. Understand Class A versus Class B signaling line circuits, the difference between conventional zones and addressable devices, and the purpose of the control unit's alarm, supervisory, and trouble signals. Know that NAC circuits are power-limited and supervised, that end-of-line devices terminate Class B circuits, and that notification appliance circuits must produce adequate candela and sound pressure. Understand interface with suppression systems, elevator recall, and door release.
Traps to expect
Questions test whether you know that a trouble signal is not an alarm, that a supervisory signal (valve tamper, low air) is distinct from both, and that silencing a signal does not reset the system. Another trap is mixing up Class A (redundant path, survives a single open) with Class B (single path, EOL supervised). Watch for items on spacing of smoke detectors versus strobe coverage, and on whether a duct detector substitutes for area detection.
Worked example
A 120 ft hallway needs smoke detection. With a 30 ft listed spacing and 15 ft from walls, detectors can be placed at 15 ft, 45 ft, 75 ft, and 105 ft from one end - four detectors, each within 15 ft of a wall or another detector. Rule of thumb: for smooth ceilings, detector spacing equals the listed spacing, but always keep the first detector within half the spacing from the end wall.