Churn (≤140%)
12.6 bar
Figure 3-0 · The fire-protection chain. Each box is a section below. (Original schematic.)
This is life-safety, code-driven design
Fire protection is the least "free" discipline: it follows the fire code and the Authority Having Jurisdiction (Civil Defense) almost literally. The numbers here teach the method — the governing values are set by the adopted NFPA editions referenced in SBC 801 and by the AHJ. Constants, symbols & conversions used in the worked examples
| Symbol / constant | Value | What it is |
|---|---|---|
| ρ (water) / g | 1000 kg/m³ / 9.81 m/s² | For the pump-power formula. |
| η (eta) | 0.75 typical | Pump efficiency (decimal). |
| 1 gpm | = 3.785 L/min | US gallons/min → litres/min (NFPA uses gpm). |
| 100 psi | ≈ 6.9 bar ≈ 70 m head | Required residual at the top hose valve. |
| 1 m³/s | = 1000 L/s | Flow conversion. |
| COP (in heat-rejection) | — | Chiller efficiency (not fire — referenced from HVAC where relevant). |
Key formulas: water reserve V = design flow × duration · pump power P = ρ·g·Q·H ÷ η · sprinkler head flow Q = K·√P · demand = density × design area
3.1 Fire strategy & design criteria
Role: the fire strategy defines hazard classification, what systems are required, water demand, durations, and the zoning concept — agreed with the AHJ before sizing anything.
| Input | Typical (tall mixed-use) | Source |
|---|---|---|
| Occupancy hazard | Light (hotel rooms/residential) to Ordinary (retail, BOH, car park) | NFPA 13 |
| Systems required | Full sprinklers + standpipes + fire pumps + special hazards | SBC 801 / NFPA 1 |
| Water-supply duration | Sprinkler 30–60 min; standpipe per code; combined per AHJ | NFPA 13/14 |
| Min residual at top hose valve | 6.9 bar (100 psi) for 65 mm; 4.5 bar (65 psi) for 40 mm | NFPA 14 |
Code
SBC 801 (Saudi Fire Code), NFPA 1; classification NFPA 13; life safety/egress NFPA 101; AHJ = Saudi Civil Defense (DGCD).FIRE-WATER STORAGE→pumps→zoning→standpipes/sprinklers→head
3.2 Fire-water storage
Role: a dedicated reserve — never shared below draw-off with domestic water — sized for the worst-case simultaneous demand × required duration. In a tall building, tanks are distributed up the tower so each zone's pumps have suction.
Worked example 3.2 · Fire reserve volume
Given: design demand (sprinkler + inside/outside hose) = 2,500 gpm = 9,460 L/min = 157.7 L/s; required duration 60 min.
Reserve = 9,460 × 60 = 567,600 L = ~568 m³.
~568 m³ dedicated fire reserve (often split between a ground tank and high-level tanks per zone). Confirm demand & duration with the AHJ — they govern.
Code
Tanks: NFPA 22; private mains NFPA 24; dedicated reserve & duration: NFPA 13/14, SBC 801.3.3 Fire pumps
Role: provide the rated flow at the rated pressure for the most demanding zone. Listed fire pumps follow a defined performance curve and are arranged with a jockey pump (holds standby pressure) and usually a diesel + electric duty/standby pair. Tall buildings use series / zoned pumping.
The NFPA 20 pump curve
A listed fire pump must deliver: ≤140% of rated pressure at churn (0 flow), 100% at rated flow, and ≥65% of rated pressure at 150% of rated flow. The design point and the building demand must sit under this curve.
NFPA 20 fire-pump performance envelope
A fire pump must hold a defined curve: churn (shut-off) ≤ 140% of rated pressure, 100% at the rated point, and ≥ 65% of rated pressure at 150% of rated flow. Set the rated duty to read the curve in real units.
The pump's 100% duty flow — the system is sized at this point.
Rated discharge pressure at the duty flow.
Flow at 150%
225 L/s
Pressure at 150%
5.9 bar
Envelope
Pump pressure vs flow scaled to your rated duty; the three marked points are the NFPA 20 envelope limits.
Worked example 3.3 · Fire-pump duty & power for a zone
Given: zone demand Q = 9,460 L/min = 0.158 m³/s; required head = static lift 120 m + friction 25 m + 70 m (≈6.9 bar residual) = 215 m (~21 bar); pump efficiency η = 0.75.
Hydraulic power: P = ρgQH ÷ η = 1000 × 9.81 × 0.158 × 215 ÷ 0.75 = 444 kW.
~444 kW fire-pump (electric + diesel standby). Keep zone working pressure under the NFPA 14 limit (350 psi / 24 bar) — if exceeded, add another pumping stage / zone higher up.
In the software
Run the network demand & residuals in a hydraulic calc tool (PIPENET Sprinkler/Spray, Elite Fire, HASS, AFT). Select the listed pump from the manufacturer against the NFPA 20 curve; verify the design and 150% points and the zone max pressure. Code
Fire pumps: NFPA 20; standpipe pressure limit: NFPA 14; controllers & power: NFPA 20 / NFPA 110.3.4 Zoning the fire riser
Role: as with domestic water, the standpipe/sprinkler riser is split into pressure zones so no component exceeds its rating. Zones are fed by series pumps + break tanks, with PRVs on hose valves where static pressure is too high (NFPA 14 limits outlet pressures).
Key takeaway
NFPA 14 caps system pressure at ~350 psi (24 bar) and hose-valve outlet pressure (PRV needed above ~100–175 psi). These two limits set how tall each fire zone can be — typically ~20–25 floors. Code
Zoning, max pressures, PRV on hose valves: NFPA 14; pumps in series: NFPA 20.pumps→STANDPIPES + HOSE
3.5 Standpipes & fire-brigade hose valves
Role: wet vertical pipes with hose-valve outlets at every floor/stair so firefighters get water at height without dragging hose up the building. Class I (fire-brigade 65 mm), II (occupant 40 mm — now rare), or III (both).
Worked example 3.5 · Standpipe demand (NFPA 14)
Given: a multi-standpipe building. NFPA 14: 500 gpm for the first (most remote) standpipe + 250 gpm each additional, capped at 2,500 gpm; min 100 psi residual at the topmost 65 mm outlet.
3 standpipes → 500 + 250 + 250 = 1,000 gpm; large buildings reach the 2,500 gpm cap.
Design the pumps/risers for the capped demand at 100 psi residual at the highest outlet — the controlling case for fire-pump head.
Code
Standpipes: NFPA 14 (flow, residual pressures, outlet locations); SBC 801; AHJ hose-valve requirements.risers→SPRINKLERS→head (room)
3.6 Sprinkler systems & the head in the room
Role: automatic detection + suppression at the ceiling of (almost) every space. Wet-pipe is standard in conditioned towers. Designed by the density/area method (or full hydraulic calc): a design density (mm/min) over the most hydraulically demanding area.
| Hazard | Density | Design area |
|---|---|---|
| Light (hotel room, residential, office) | ~4.1 mm/min (0.10 gpm/ft²) | ~140 m² (1,500 ft²) |
| Ordinary Group 1 (retail, BOH) | ~6.1 mm/min (0.15 gpm/ft²) | ~140 m² |
| Car park / storage | Ordinary 2 / special | per NFPA 13 |
Worked example 3.6 · Sprinkler demand (density/area)
Given: Ordinary Hazard Gp 1: density 6.1 mm/min over design area 140 m².
Sprinkler flow at the area = 6.1 L/min·m² × 140 m² = 854 L/min (≈ 226 gpm) at the head, before adding hose allowance.
Add inside+outside hose allowance (e.g. +950 L/min) and solve the network by hydraulic calc → required source flow & pressure.
~854 L/min over the remote area + hose; head spacing ≤ 12–21 m² coverage each; the hydraulic calc proves the most remote head still gets its minimum pressure (~0.5 bar).
In the software
Build the sprinkler network in PIPENET (Sprinkler/Spray), Elite Fire or HASS: enter K-factors, densities, design area & pipe layout; the tool runs the NFPA 13 area/density hydraulic calc and proves the most-remote-area pressure/flow. Model layout in Revit. Code
Sprinklers: NFPA 13 (densities, spacing, hydraulic calc); ITM later: NFPA 25; under SBC 801.3.7 Special-hazard suppression
| System | Where | Code |
|---|---|---|
| Clean-agent gaseous (e.g. inert/HFC, novel agents) | IT/data, telecom, major electrical & control rooms (no water) | NFPA 2001 |
| Wet-chemical hood suppression | Commercial/hotel kitchens (grease) | NFPA 17A / NFPA 96 |
| Water mist | Selected atria/machinery/heritage spaces | NFPA 750 |
| Foam | Fuel/generator day-tank rooms | NFPA 11 |
| Portable extinguishers | Everywhere as backup | NFPA 10 |
Code
NFPA 2001, 17A, 96, 750, 11, 10 — all under SBC 801 & Civil Defense approval.3.8 Valves, accessories & the fire-brigade interface
- Alarm/control valves (wet alarm valve, flow switches, tamper switches) — initiate alarm & monitor each zone (interfaced to fire alarm, Module 5).
- PRVs on hose valves/sprinkler zones — keep outlet pressures within NFPA 14/13 limits.
- Fire Department Connection (FDC) — lets the brigade pump into the system from outside.
- Test & drain, check valves, isolation (supervised) valves, pressure gauges.
Code
Valve supervision & FDC: NFPA 13/14; monitoring interface: NFPA 72.3.9 Installation, accessories & field tricks
| Item | Field rule / trick |
|---|---|
| Seismic bracing & sway restraint | NFPA 13 requires lateral/longitudinal bracing & flexible couplings — vital on tall buildings (SBC 301). |
| Listed components only | Every pipe, fitting, valve, head must be UL/FM listed for fire service; AHJ rejects non-listed. |
| Pitch & drainage | Pitch pipes to drains; auxiliary drains at trapped sections. |
| Head clearance & obstruction rules | Keep heads clear of obstructions and within distance-to-ceiling rules — coordinate with HVAC/lighting in BIM. |
| Hydrostatic test 200 psi / 2 h | NFPA 13/14 require a 200 psi (or +50 psi over working) 2-hour test before acceptance. |
| Spare heads & wrench cabinet | Provide the code spare-head cabinet at handover. |
| Firestopping at penetrations | Tested/listed firestop at every rated-barrier crossing. |
Code
Bracing & testing: NFPA 13/14; listing: UL/FM; seismic: SBC 301; firestop: UL systems / NFPA 101.3.10 Testing & commissioning (with the AHJ)
- Hydrostatic & flush of all piping; fire-pump acceptance test (churn, rated, 150% points witnessed) per NFPA 20.
- Main drain & flow-switch tests; alarm/monitoring verified to the fire-alarm panel (Module 5).
- Integrated cause-and-effect test with smoke control, lifts & alarm, witnessed by Civil Defense before occupancy.
Code
Acceptance: NFPA 13/14/20; integrated test: NFPA 4; AHJ sign-off: Civil Defense / SBC 801.Terms & abbreviations
Plain-English meaning of the fire-protection terms used in this module.
| Term | What it means (plain English) |
|---|---|
| AHJ | Authority Having Jurisdiction — here, Saudi Civil Defense, who approve & inspect fire systems. |
| Hazard classification | How combustible a space is (Light / Ordinary / etc.) — sets sprinkler density. |
| Sprinkler | A ceiling head that opens at a set temperature and sprays water on the fire automatically. |
| Density / area method | Designing sprinklers by a water density (mm/min) applied over the most demanding floor area. |
| K-factor | A sprinkler head's flow constant — relates flow to pressure (Q = K√P). |
| Standpipe | A wet vertical pipe with hose-valve outlets so firefighters get water on every floor. |
| Hose valve / FDC | Hose valve = firefighter's outlet on a standpipe; FDC = Fire Department Connection, where the brigade pumps water in from outside. |
| Fire pump | The pump providing fire-system flow & pressure; follows the NFPA 20 performance curve. |
| Churn / rated / 150% points | Three points on the pump curve: no flow (churn), design flow (rated), and overload (150% flow). |
| Jockey pump | A small pump that maintains standby pressure so the main fire pump doesn't start needlessly. |
| PRV | Pressure-Reducing Valve — keeps hose-valve/sprinkler pressures within code limits in tall zones. |
| Residual pressure | The pressure still available at the topmost outlet during flow (e.g. 100 psi / 6.9 bar required). |
| gpm / psi | US units common in NFPA: gallons per minute (flow), pounds per square inch (pressure). 100 psi ≈ 6.9 bar. |
| Wet-pipe system | Sprinkler pipework permanently filled with water (standard in heated/cooled buildings). |
| Clean agent | A gas (not water) that suppresses fire in IT/electrical rooms without damaging equipment (NFPA 2001). |
| Listed (UL/FM) | Components tested & approved by UL or FM for fire service — the AHJ requires listed parts. |
| Cause-and-effect | The matrix defining what each alarm triggers (alarms, smoke control, lift recall, etc.). |
| ITM | Inspection, Testing & Maintenance (NFPA 25) — keeping the system working after handover. |
References & software map
| Task | Software | Code |
|---|---|---|
| Sprinkler/standpipe hydraulic calc | PIPENET (Sprinkler/Spray), Elite Fire, HASS | NFPA 13/14 |
| Fire-pump selection & curve check | Manufacturer tools (against NFPA 20 curve) | NFPA 20 |
| Surge / transient on tall risers | AFT Impulse / Bentley HAMMER | engineering practice |
| Layout & coordination | Revit MEP + Navisworks | NFPA 13 obstruction rules |
- SBC 801 — Saudi Fire Code (adopts NFPA by reference); NFPA 1 Fire Code.
- NFPA 13 (sprinklers), 14 (standpipes), 20 (pumps), 22 (tanks), 24 (mains), 25 (ITM).
- NFPA 2001, 17A, 96, 750, 11, 10 (special hazards & extinguishers); NFPA 4 (integrated test).
- NFPA 101 (life safety); Saudi Civil Defense (DGCD) requirements; UL/FM listings.
Note
Worked numbers teach the method; fire design is governed by the NFPA editions referenced in SBC 801 and by the AHJ. Confirm all values with the code and Civil Defense.