Automatic sprinkler systems are the most widely used fire suppression systems in buildings. In Saudi Arabia they are required under the Saudi Fire Code, SBC 801, which refers to NFPA 13 for design and installation. This guide is a complete reference: system types, the network’s components in order from the water source to the sprinkler, how hazards are classified, and how the system is tested and maintained. Each component has a detailed guide in our technical library.
Key points
- Four main types: wet, dry, pre-action and deluge. Wet is the most common.
- Each sprinkler operates on its own when heat reaches it; they do not all open together (except in a deluge system).
- Hazard classification (light, ordinary, extra) sets the water density and the area each sprinkler protects.
- Every valve and fitting in the network is required to be listed or approved for fire protection use.
How the system works
The pipes are full of water under pressure (in a wet system). Each sprinkler is closed by a heat-sensitive element: a glass bulb or a fusible link. When the temperature rises above the sprinkler’s rating, the element breaks and water flows from that sprinkler only. The flow trips the water flow indicator or alarm valve, which signals the control panel, and the pumps start as pressure falls.
System types and when each is used
| System | What the pipes hold | Typical use |
|---|---|---|
| Wet | Water at all times | Most buildings: offices, residential, retail |
| Dry | Compressed air or nitrogen | Areas exposed to freezing, such as cold stores |
| Pre-action | Air, filled with water after a detector signal | Computer rooms and archives, where accidental discharge must be avoided |
| Deluge | Empty, with open sprinklers | High hazards needing immediate full coverage, such as fuel stations and transformers |
Components from the tank to the sprinkler
- Water source: a fire water tank or the public main, with inlet and suction connections and an anti-vortex plate at the suction outlet.
- Pump room: a main pump, a standby pump and a jockey pump, with isolation valves, check valves and a pressure relief valve.
- Isolation valves: OS&Y gate valves or butterfly valves with supervisory switches, so their position is always known. See OS&Y vs NRS and butterfly valves in fire protection.
- Check valve prevents water returning to the source. See the check valves guide.
- Alarm station: a wet alarm check valve or a water flow indicator on each floor, with supervisory switches.
- Risers, mains and branch lines: usually grooved fittings and couplings from 2″ upwards and threaded fittings in small sizes. See rigid vs flexible couplings.
- Sprinklers: type and K-factor are chosen by hazard. Work out the flow with the sprinkler flow calculator.
Hazard classification
NFPA 13 classifies occupancies by the quantity of combustibles and how fast fire spreads; the classification sets the required water density and the design area:
- Light hazard: offices, classrooms, hospitals, residential.
- Ordinary hazard, in two groups: car parks and restaurants usually in group 1, shops and light storage in group 2.
- Extra hazard: areas with flammable liquids and some industries.
The final classification and the system calculations are the responsibility of the project’s approved designer.
Testing before handover
Warning
Every valve and fitting in the network must withstand the test pressure, not just the working pressure. Check each component’s rated working pressure in the model table before approval.
The network is hydrostatically tested at a pressure above the working pressure for a period set in NFPA 13, with no pressure loss or leakage; alarm devices and pumps are then operated and every control valve is checked.
Periodic maintenance
After handover, inspection, testing and maintenance follow NFPA 25: regular visual checks of valve positions and supervisory switches, tests of flow indicators and alarm devices, and pump tests. A control valve left closed by mistake is one of the best-known causes of sprinkler failure in a fire, which is why supervisory switches exist.
MECH products for each stage
MECH supplies gate, butterfly and check valves, alarm stations, water flow indicators, and grooved fittings and couplings that are UL Listed and FM Approved depending on model and size. Browse the products and open each model’s table for sizes, working pressure and certificates.
Frequently asked questions
Do all sprinklers operate in a fire?
No. In wet, dry and pre-action systems only the sprinklers that the heat reaches operate. Only in a deluge system are the sprinklers open, so they all discharge together.
What is the difference between wet and dry systems?
A wet system’s pipes are full of water, so it acts immediately. A dry system’s pipes hold compressed air and it is used where water could freeze; there is a short delay before water reaches the sprinkler.
Who decides the system type and hazard classification?
The project’s approved designer, under SBC 801 and NFPA 13, with review by the consultant.
References
- SBC 801 — Saudi Fire Code.
- NFPA 13 — Standard for the Installation of Sprinkler Systems.
- NFPA 20 — Standard for the Installation of Stationary Pumps for Fire Protection.
- NFPA 25 — Standard for the Inspection, Testing, and Maintenance of Water-Based Fire Protection Systems.
This guide is a general introduction. Design, calculations and component selection are the responsibility of the project’s approved designer.