Fire detection, alarm and life safety electrical systems
Domain 8: Fire detection, alarm and life safety electrical systems
This domain tests detection, alarm and interfacing as a life-safety system. You must apply the relevant fire code, design survivable circuits, and prove cause-and-effect operation.
Core rules
- Select detection by space and fire risk: smoke, heat, beam, aspirating or multi-criteria; respect spacing and detector coverage.
- Define zones, alarm sound pressure, visual alarms and accessibility requirements for hearing-impaired occupants.
- Use fire-rated cable and survivable routes for circuits that must operate during fire; separate fire alarm from other services.
- Write a cause-and-effect matrix for sounders, dampers, door holders, lifts, HVAC shutdown and suppression interfaces.
- Provide battery standby for quiescent and alarm loads, including ageing and charger capacity.
- Commission by 100% device test where required, loop test and interface test; record results.
Worked example
A fire panel draws 2 A quiescent for 24 h and 5 A in alarm for 0.5 h. Required capacity = (2 × 24) + (5 × 0.5) = 48 + 2.5 = 50.5 Ah. Apply a 1.25 ageing/design factor: 50.5 × 1.25 = 63.1 Ah. Select a battery of at least 63 Ah, then verify charger rating and end-voltage. The alarm load is not continuous for 24 h.
Traps
- Using non-fire-rated cable for critical alarm circuits.
- Omitting cause-and-effect interfaces.
- Calculating battery capacity with alarm current for the full standby period.
- Ignoring sound pressure or visual alarm coverage.