FPAS Fire Systems Design (FSD) common mistakes
FPAS Fire Systems Design (FSD) · Understand the traps and how to avoid them.
Laying out smoke detectors on a uniform maximum-spacing grid without checking detector technology, ceiling height, beams, ceiling pockets, air movement, or obstructions.
Candidates memorise a spacing table and apply it to every room instead of treating spacing as a starting point that depends on the listed coverage and the actual ceiling geometry.
What to do instead
Select the detector type first, then apply the manufacturer's listed coverage and the adopted standard's corrections for height, beams, ventilation and obstructions; mark each detector's actual coverage on the plan and check it against the ceiling section.
Producing a device schedule and floor plan but no complete input/output matrix or cause-and-effect chart for sprinkler flow switches, suppression releases, door releases, air-handling shutdown and staged evacuation.
The candidate treats the alarm system as a set of devices rather than a sequence of causes and effects, so interfaces are left implicit and omissions are not visible.
What to do instead
Build a cause-and-effect matrix listing every initiating device/input against every output and required response, then trace each row to a physical device, address and cable route on the design.
Sizing sprinkler mains and branches by nominal pipe-size rules or by copying a typical layout instead of performing a hydraulic calculation for the required density and remote area.
Rule-of-thumb sizing is faster and familiar, and candidates underestimate how K-factor, pressure, elevation and friction loss change the required pipe sizes.
What to do instead
Calculate the remote-area demand from the design density and assumed operating area, select sprinkler K-factors, sum friction and elevation losses to the supply point, and compare the result with the available water supply curve.
Omitting sprinklers or failing to check coverage beneath ducts, mezzanines, storage racks, canopies and other obstructions.
The candidate designs only from the reflected ceiling plan and does not review building sections, so hidden combustible or obstruction conditions are missed.
What to do instead
Review architectural and services sections alongside the plan, apply the standard's obstruction and clearance rules, and add sidewall, intermediate or additional sprinklers where the obstruction prevents adequate water distribution.
Sizing hydrant mains, pumps and tanks from floor area or hydrant count without a worst-case hydraulic calculation that includes simultaneous hydrant and hose-reel demand, friction loss and elevation.
Candidates use simple occupancy-based rules and forget that the highest or most remote outlet, not the nearest one, governs the design.
What to do instead
Identify the worst-case hydrant/hose-reel operating combination, calculate flow and pressure at the most remote outlet including friction and elevation, and plot the demand against the pump and water-supply curves.
Showing hose-reel coverage as a radius circle on the plan without tracing the actual hose path around walls, corners and doors, or checking residual pressure at the nozzle.
A scaled radius looks adequate on paper, but hose cannot travel through walls and pressure losses along the hose and pipework reduce nozzle performance.
What to do instead
Trace the hose route from each reel around actual obstructions, confirm the required reach is achieved, locate reels near exits and protected routes, and verify nozzle pressure at the worst-case reel.
Calculating gaseous agent quantity from room volume alone, ignoring enclosure leakage, ventilation, temperature, altitude and the required design concentration and hold time.
The volume formula is simple and memorable, while enclosure integrity and site conditions require additional checks that candidates often skip.
What to do instead
Use the correct design concentration for the hazard, adjust agent quantity for actual volume, temperature and altitude, classify and seal enclosure leakage, verify hold time by door-fan or enclosure-integrity test, and provide pressure relief.
Designing the suppression system in isolation without coordinating detection, pre-discharge alarms, abort switches, HVAC shutdown, dampers, door holders and post-discharge ventilation.
The candidate treats the agent cylinder and nozzles as the whole system and does not consider the sequence required for safe and effective discharge.
What to do instead
Prepare a suppression cause-and-effect matrix covering detection, warning, time delays, abort, shutdown of air movement, closure of openings, discharge and post-discharge ventilation, and show each interface on the design.
Selecting portable extinguishers by agent colour or by counting one per room rather than matching the extinguisher class and rating to the hazard and checking travel distance.
Candidates rely on familiar labels and simple counts and do not verify whether the extinguisher is suitable for electrical equipment, cooking oils, flammable liquids or ordinary combustibles.
What to do instead
Classify each area's fire hazard, select an extinguisher with the correct class and rating, verify electrical safety and special-hazard suitability, and lay out extinguishers against the required travel distance and access requirements.
Specifying extinguisher locations without mounting heights, signage, access clearances, anti-tamper measures or a maintenance and recharge schedule.
The candidate focuses on the number and type of extinguishers and treats installation and upkeep details as someone else's responsibility.
What to do instead
Add a location schedule giving mounting height, signage, access and bracket type, check that each unit is visible and unobstructed, and include inspection, testing and recharge requirements in the design documentation.