Essential Points: Fire Risk Analysis & Sprinkler System Design

1. Risk Analysis Summary

Building Risk Category: High-riser
Occupancy Type: Office areas
Occupancy Characteristic: A (BS 9999)
Combustible Materials: Low/limited combustibility construction materials + Wooden/plastic furniture, papers, cardboard
Fire Load: Medium
Fire Growth Rate: Category 2 (0.012kW/s²)
Original Risk Profile: A2 → Improved to A1 with automatic sprinkler system
Containment Measures: Compartmentation, Fire-stop materials, Fire dampers
Fire Resistance: 2-hour (shafts, load-bearing walls), 1-hour (compartment walls)
Sprinkler System: Required

Hazard Class: Ordinary Hazard (OH) per BS EN 12845
Hazard Group: OH III (due to 44.45m height difference between highest & lowest sprinkler)
Number of Installations: 1 (height difference < 45m)
Installation Type: Wet pipe system (no frost risk, ambient temp < 95°C)
Total Protected Area: 41,598 m²

Parameter	Specification	Standard Reference
Max spacing between sprinklers	4m x 4m grid	BS EN 12845, Table 19
Max area coverage per sprinkler	12 m²	BS EN 12845, Table 19
Min spacing between sprinklers	2m	BS EN 12845, Clause 12.3
Design Density	5 mm/min (5 l/min/m²)	BS EN 12845, Table 3
Assumed Max Area of Operation (AMAO)	216 m²	BS EN 12845, Clause 13.4.3.1
Min sprinkler discharge pressure	0.35 bar	BS EN 12845, Clause 13.4.4
Min distance from walls	102 mm	NFPA 13:2002, Clause 8.6.3.3

Type: Automatic, Glass bulb
Standard: BS EN 12259-1:1999
Pattern: Spray (pendent concealed for ceilings), Conventional (upright for no ceilings/voids), Flat spray (above open cell ceilings)
K-factor: 80 (Nominal), Tolerance: 76 to 84
Orifice Size: 15mm
Thread Size: 15mm
Temperature Rating: 68°C (Red bulb)
Thermal Sensitivity: Quick Response

Voids above ceiling (>0.8m height) require sprinkler protection. Classified as Ordinary Hazard 1 (OH1).

Total area (41,598 m²) > 12,000 m² → Zoning applied per Annex D of BS EN 12845.
Each floor is a separate zone.
Max protected area per zone (floor): 6,411 m².
Each zone has: Subsidiary stop valve, Flow switch, Test valve, Drain valve, Pressure gauge.
All critical valves have supervisory switches monitored by the Fire Alarm Control Panel (FACP).

Riser, Arm, Drop pipes: 25mm diameter (for a single sprinkler).
Range Pipes: Sized using pre-calculated tables (BS EN 12845, Table 30).
Distribution Pipes (Downstream of Design Point): Pre-calculated tables (BS EN 12845, Table 31).
Distribution Pipes (Upstream of Design Point): Hydraulic calculation to limit friction loss to 0.5 bar + static head gain at 1000 l/min flow.
Design Points are located at the node feeding the 18th sprinkler.
Hazen-Williams formula used for hydraulic calculations (C=120 for galvanized steel).