Project Inputs
Example Data Table
| Scenario | Floors | Floor Area | Smoke Spacing | Heat Spacing | Egress Length | Exits | Output (Total Devices) |
|---|---|---|---|---|---|---|---|
| Office block | 3 | 1,200 m2 | 9 m | 10.5 m | 200 m | 4 | — |
| Warehouse | 1 | 2,500 m2 | 10 m | 12 m | 140 m | 2 | Depends on settings |
| Residential mid-rise | 8 | 900 m2 | 8 m | 10 m | 260 m | 6 | Depends on settings |
Formula Used
- Total area = Floors × Floor area (unless total area is provided).
- Effective coverage factor = Obstruction factor × Height derate.
- Detector coverage (approx.) = Spacing² × Effective coverage factor.
- Detector count = ceil(Assigned area ÷ Coverage per detector).
- Call points (planning) = ceil(Egress length ÷ (2× travel distance)) + Exits.
- Notification appliances (planning) = ceil(Total area ÷ (Spacing² × 0.85)).
- Audibility (simplified) Predicted SPL = SPL@1m − 20·log10(distance).
- Loops (rule-of-thumb) = ceil(Initiating devices ÷ Devices per loop).
- Panels (rule-of-thumb) = ceil(All devices ÷ Devices per panel).
- Alarm current = (Horns×mA) + (Strobes×mA), then add margin.
- Battery (simplified) = (Standby Ah + Alarm Ah) × 1.25 reserve.
How to Use This Calculator
- Select your unit system, then enter floors and area.
- Set ceiling height and obstruction factor for realistic coverage.
- Adjust smoke/heat spacing and the coverage mix for your risk profile.
- Enter egress length, travel distance, and exit count to estimate call points.
- Set notification spacing and audibility inputs to check sound assumptions.
- Review the results summary above the form after calculating.
- Export CSV/PDF to document scenarios and share with the team.
Fire Alarm Device Planning Notes
1) Define the protected footprint
Start with verified floor count and total area. For multi-storey projects, distribute devices by floor and confirm special rooms, shafts, and atriums. This tool uses total area to estimate baseline counts, then adjusts coverage using spacing and a practical obstruction factor.
2) Detector coverage assumptions
Detector quantity is driven by effective coverage (spacing squared). A 9 m smoke spacing implies about 81 m2 before derating. If obstructions and high ceilings reduce effectiveness to 0.85, coverage becomes 68.9 m2, increasing device count by roughly 17%. Use smoke/heat percentage to reflect real hazard zoning.
3) Manual call points along egress
Manual call points are estimated from egress length and maximum travel distance. With 200 m of travel path and a 30 m travel target, the run spacing becomes 60 m, producing about 4 devices, plus exits. Always place devices at exits and stair doors as required by local authority.
4) Notification and audibility check
Notification appliances are planned by area coverage and spacing. Audibility is checked using a simple 20·log10(distance) drop from the device output at 1 m. For example, a 90 dB device at 10 m predicts about 70 dB. If ambient is 60 dB and margin is 15 dB, the 75 dB target requires closer spacing or higher output.
5) Loops, panels, and power budgeting
The calculator provides rule-of-thumb planning counts for addressable loops and control panels using user-set capacities. Power sizing uses horn/strobe current draws with a margin, then estimates battery capacity from standby hours and alarm minutes with a reserve factor. Replace these assumptions with manufacturer data during detailed design and commissioning.
FAQs
1) Is this output a final code-compliant design?
No. It is a planning estimate for early sizing, comparisons, and documentation. Final layouts must follow applicable codes, authority requirements, and manufacturer listings.
2) Why do counts change when I adjust obstruction factor?
Obstructions reduce effective coverage. Lower factors shrink coverage per device, so more detectors and appliances are required to protect the same area.
3) How should I choose smoke and heat percentages?
Use them to represent zoning decisions. Higher smoke share suits occupied spaces; higher heat share suits dusty, steamy, or high-nuisance areas. Normalize helps when totals are not 100%.
4) What does the audibility PASS/REVIEW mean?
It compares predicted sound level at a worst-case distance with a target above ambient. REVIEW means assumptions may not meet audibility; revise spacing, outputs, or zones.
5) Can I model strobes separately from horns?
Yes. Set horn share to control the split of appliances. Enter distinct mA values for horns and strobes to refine alarm current and battery planning.
6) How do loops and panels get calculated?
They are computed by dividing initiating devices and total devices by your capacity settings, then rounding up. Treat this as early planning, not a hardware submittal.
7) Why does imperial mode still show some results in metric?
Inputs and labels switch to ft and ft2, while internal calculations use meters for consistency. The summary area converts back for display, but coverage values remain in m2.