FPAS Fire Systems Design (FSD) cheat sheet

Detector spacing is governed by the listed coverage area, ceiling height, beam pockets, and ventilation; a single area-per-detector rule cannot be applied across all detector types.

Keep point detectors at least 0.5 m from walls and clear of air diffusers; the manufacturer's installation instructions set the final clearance.

Alarm audibility: at least 65 dBA at occupied locations or 5 dBA above ambient, whichever is higher; sleeping areas commonly require 75 dBA at the pillow.

Secondary battery capacity: C = I_standby × t_standby + I_alarm × t_alarm, with t_standby typically 24 h and t_alarm 5 min; apply battery derating and ageing factors.

Supervised detection circuits must annunciate open-circuit and short-circuit faults; end-of-line devices or addressed loop isolation provide fault discrimination.

Smoke detectors are generally unsuitable in dusty, steam-laden, or cooking environments; use heat or alternative detection matched to the expected fire signature.

A sprinkler flow switch or pressure switch used as a fire alarm input must be monitored and assigned an alarm zone that identifies the water flow location.

Cross-zoning requires two independent detector alarms before a suppression release or a high-level alarm, reducing false discharges.

Design density formula: Q = ρ × A, where Q is minimum sprinkler flow in L/min, ρ is density in mm/min or L/min/m², and A is the design area of operation in m².

Sprinkler discharge formula: Q = K√P, where Q is flow in L/min, K is the listed K-factor, and P is pressure in bar for metric K-factors.

Select the sprinkler temperature rating above the maximum ambient temperature; ordinary-rated 68°C heads are common for occupied spaces with moderate ceilings.

A wet-pipe alarm valve flow switch should actuate on a single sprinkler flow; the inspector's test valve simulates the hydraulically most remote sprinkler.

Calculate pump head as elevation pressure plus pipe friction loss plus residual pressure at the most remote sprinkler; include backflow and valve losses.

Use Hazen-Williams for water pipe friction: h = 10.67 L Q^1.85 / (C^1.85 d^4.87), with consistent SI units.

A sprinkler system must have a main drain, alarm test valve, and pressure gauge to verify supply and alarm operation.

Do not reduce pipe size below the minimum listed for the sprinkler and occupancy; hydraulic calculations, not pipe-size rules, govern.

Hydrant design must satisfy simultaneous flow at the design number of hydrants, with residual pressure at the most remote hydrant not below the local code minimum.

Pump head equals static elevation plus friction loss plus residual pressure; include hose and hydrant valve losses.

Hazen-Williams friction formula h = 10.67 L Q^1.85 / (C^1.85 d^4.87) applies to hydrant mains and hose reel pipework.

Hose reels are typically 30 m long with 19 mm or 25 mm hose; the reel must reach all parts of the protected area without passing through fire doors.

Each hydrant should have a valve, non-return arrangement where required, drain, and a compatible fire brigade coupling.

Booster connections must be accessible to fire brigades and marked with the system type and pressure rating.

Hydrant ring mains require sectional valves so isolation does not remove more than the permitted number of hydrants.

Flow testing records should include static pressure, residual pressure, flow rate, and pump status.

Total-flooding agent mass: m = (V/S) × C/(100−C), where V is enclosure volume, S is specific volume, and C is design concentration in percent.

Design concentration equals extinguishing concentration multiplied by a safety factor; clean-agent Class B designs commonly use a 1.2 safety factor.

For occupied spaces, the design concentration should not exceed the agent's NOAEL; if it does, provide pre-discharge warning and timed egress.

Clean-agent total-flooding discharge is typically 10 s; inert-gas systems often use 60–120 s to limit pressure and noise.

Enclosure integrity testing with a door fan verifies that the room can hold the design concentration for the required hold time.

CO2 total-flooding systems must not be used in normally occupied spaces because of asphyxiation risk.

Cross-zoned detection and a pre-discharge delay allow investigation and evacuation before agent release.

Pressure relief vents must be sized to prevent enclosure overpressure during agent discharge.

Extinguisher rating codes such as 2A:10B:C indicate Class A water-equivalent rating, Class B test-fire size, and electrical non-conductivity.

Water extinguishers are unsuitable for live electrical equipment and cooking-oil fires; Class F wet chemical agents saponify hot oils.

CO2 extinguishers are effective on electrical fires but have limited cooling; in confined spaces, discharge can reduce oxygen.

Dry-powder extinguishers leave residue that can damage electronics; clean-agent extinguishers are preferred for sensitive equipment.

Mount portable extinguishers with the carrying handle not more than 1.5 m above the floor and the label visible.

Class D metal fires require specially formulated dry powders; water, foam, and CO2 are generally ineffective or dangerous.

Travel distance to an extinguisher depends on occupancy hazard and extinguisher class; check the applicable code for the maximum distance.

An extinguisher is only suitable for a fire class shown on its label; never use a lower-rated extinguisher than the hazard requires.