Choosing between wet, dry, pre-action and deluge sprinkler systems comes down to three questions: can the piping be kept above freezing, how much harm would accidental water do, and how fast can a fire spread? Wet systems are the default where piping stays above freezing, which in our engineering judgment covers most buildings in Saudi Arabia. The other three solve specific problems, at the price of delays, extra design rules and heavier maintenance.
Key takeaways
- Wet systems are the simplest and fastest; the NFPA 13 annex reserves dry systems for spaces where heat cannot prevent freezing.
- Freeze protection is needed where water-filled piping cannot stay at or above 4°C (40°F), which is typically uncommon in Saudi buildings except freezers and some unheated spaces in colder regions.
- Dry and double-interlock pre-action systems delay water and need a 30% larger hydraulic design area.
- Only double interlock needs both detection and an open sprinkler; single interlock fills the pipes on detection alone.
- Deluge systems use open outlets and wet the whole area at once, for hazards such as transformers and hangars.
In this article
- How each sprinkler system works
- Wet vs dry vs pre-action vs deluge compared
- Pre-action: single, double or non-interlock?
- Where each type fits in Saudi projects
- Design rules that change between types
- Step-by-step: choosing the sprinkler system type
- Common site mistakes
- Inspection, testing, maintenance and cost
- How AZEIDK helps
- FAQ
How each sprinkler system works
Wet pipe system
The pipes are full of water up to closed, heat-activated sprinklers. When a sprinkler opens, water discharges at once and an alarm valve or flow switch signals the fire alarm panel. Only wet systems can qualify for the NFPA 13 design area reduction for quick-response sprinklers (see our sprinkler systems guide).
Dry pipe system
The piping holds compressed air or nitrogen, and a dry pipe valve holds the water back. When a sprinkler opens, the air escapes, the valve trips and water travels to the sprinkler. Quick-opening devices speed up the trip on larger systems; the valve holds priming water, so it sits in a heated enclosure.
Pre-action system
The piping is dry and supervised with air, and a deluge-type valve, controlled by a releasing panel, admits water on a signal from a separate detection system, an open sprinkler or both, depending on the interlock type below. It guards against water from damaged pipes or sprinklers but adds components and depends on detection.
Deluge system
The pipes are empty, ending in open sprinklers or nozzles. A detection system or manual release opens the deluge valve, and every outlet flows at once. Water spray protection for equipment such as transformers is designed to NFPA 15.
Wet vs dry vs pre-action vs deluge compared
| System | How water reaches the fire | Typical use | Maintenance load |
|---|---|---|---|
| Wet | At once when a sprinkler opens | Conditioned buildings | Lowest |
| Dry | After air vents and the valve trips | Spaces below 4°C | High: valve tests, air supply, drains |
| Pre-action, single interlock | Detection fills the pipes; a sprinkler must still open | Data centers, archives, museums | High: valve plus detection |
| Pre-action, double interlock | Needs detection and an open sprinkler | Freezers | High: as dry, plus detection |
| Deluge | Detection opens the valve; all outlets flow | Transformers, hangars, flammable liquid areas | High: annual full flow test |
Pre-action: single, double or non-interlock?
NFPA 13, published by the National Fire Protection Association (NFPA), defines three types:
| Type | Water enters the pipes when | Notes |
|---|---|---|
| Single interlock | Detection operates | The San Francisco Fire Department (SFFD) accepts only this type for server rooms in buildings that need wet sprinklers |
| Double interlock | Detection operates and a sprinkler opens | Sized like a dry system; SFFD accepts it for deep-freeze facilities |
| Non-interlock | Detection or a sprinkler operates | Almost exclusively seen in the European Union, per PHCP Pros |
Double interlock gives the strongest protection against accidental water, but a 2026 PHCP Pros data center guide notes that FM Global Data Sheet 5-32 puts greater weight on reliable fire control than on preventing water exposure and cautions that pre-action delays can hurt fire control. A 2020 PHCP Pros column says pre-action may be one of the most over-specified systems, so specify double interlock only where the risk justifies it.
Where each type fits in Saudi projects
The Saudi Fire Protection Code (SBC 801), whose 2024 edition is listed by the Saudi Building Code Center, and Civil Defense set where sprinklers are required; the design follows the NFPA 13 edition named in the specification (see our NFPA 13 guide). Typical choices:
- Offices, hotels, hospitals, malls and most car parks: usually wet, after a winter design temperature check (see our car park fire protection guide).
- Freezers and cold stores: dry or pre-action systems designed for refrigerated areas, with dried air or nitrogen (see our cold storage guide).
- Data centers, archives and museums: pre-action; consider single interlock first (see our data center guide).
- Transformers, hangars and flammable liquid spill areas: deluge or water spray.
Design rules that change between types
- Water delivery (dry): NFPA 13 limits the time for water to reach the most remote sprinklers assumed open, by hazard: 15 seconds for dwelling units (one sprinkler), 60 for light hazard (one), 50 for ordinary (two), 45 for extra hazard (four) and 40 for high-piled storage (four). Outside dwelling units, systems up to 500 gallons (about 1,890 L), or 750 gallons (about 2,840 L) with a quick-opening device, are exempt. These are 2007 to 2016 edition values; the 2025 edition consolidates them in Section 8.2.4.
- Design area: dry and double-interlock systems need a 30% larger design area (Section 19.2.3.2, 2022 edition).
- System size: a single or non-interlock pre-action valve controls no more than 1,000 sprinklers (Section 7.3.2.2 in the 2007 to 2016 editions).
- Dry system sprinklers: upright, listed dry sprinklers, or pendents and sidewalls on return bends where the area stays at or above 4°C (Section 8.2.2.2, 2022 edition).
- Pitch: dry branch lines at least 4 mm/m and mains at least 2 mm/m outside refrigerated areas.
- Friction: dry steel piping uses a Hazen-Williams C of 100; the 2022 edition allows 120 with nitrogen, and the 2025 edition extends this to vapor corrosion inhibitor and vacuum systems; gridded dry systems remain prohibited (now Section 8.2.1).
- Supervision: pre-action piping and detection are supervised above 20 sprinklers (2007 edition; confirm in the adopted edition), and since 1 January 2021 the 2019 edition requires a trouble signal when a releasing solenoid is removed.
Step-by-step: choosing the sprinkler system type
- Confirm where sprinklers are required and which NFPA 13 edition applies.
- Check whether every space stays at or above 4°C; if so, start from a wet system.
- Assess whether the damage accidental water would cause justifies pre-action.
- Choose single interlock unless freezing or the risk analysis calls for double interlock.
- Check whether fast, area-wide fires call for deluge or water spray.
- Run hydraulic calculations with the right design area, C-factor and delivery time.
- Coordinate detection and the releasing panel with the fire alarm design (see our fire detector selection guide).
Common site mistakes
- Water left in dry or pre-action piping after hydrostatic or trip tests, causing corrosion or ice plugs.
- Low points without accessible auxiliary drains, or drains missing from the maintenance log.
- Standard pendents on a dry system, or dry sprinklers in 90-degree elbows, which the NFPA 13 annex rules out.
- A compressor that runs often: Fire Engineering notes it should run only a few times in 24 hours, so frequent cycling points to a leak.
- Unsupervised or removed releasing solenoids, and partial trips recorded as full-flow tests.
Inspection, testing, maintenance and cost
Wet systems carry the lightest NFPA 25 routine of the four types. The valve tests below are from the 2017 edition text as quoted by QRFS and the National Fire Sprinkler Association (NFSA); confirm them in the adopted edition (see our NFPA 25 guide). The 2026 edition is now current; NFSA’s summary of proposals for it includes annual internal inspection of all dry, pre-action and deluge valves.
| Test | Dry pipe | Pre-action | Deluge |
|---|---|---|---|
| Priming water level | Quarterly | Quarterly | Per adopted edition |
| Valve trip test | Annually, in warm weather | Annually | Annually, full flow |
| Full-flow trip test | Every 3 years and after alterations | Every 3 years | Annually |
| Quick-opening device | Quarterly | If fitted (double interlock): per adopted edition | Not applicable |
| Low air pressure alarm | Annually | Quarterly | Not applicable |
| Auxiliary drains | After each operation and before freezing weather | Same | Same |
Detection and releasing devices are also tested under NFPA 72, which requires the system to be secured from accidental release during testing, including disconnecting releasing solenoids. For dry systems, NFPA 25 requires records of trip and water delivery times for full-flow trip tests.
Cost follows the system type, valves, air supply, detection and hydraulic demand (larger design areas and deluge flow enlarge pipes, pumps and tanks), plus heated valve rooms and lifetime testing.
How AZEIDK helps
Through our fire fighting systems solutions, AZEIDK covers automatic sprinkler systems, fire pumps, valves and pipes, and foam and deluge systems based on project requirements, with engineering design and calculations, supply, installation, testing and commissioning, Civil Defense approval support and annual maintenance contracts, backed by 16+ years in the Saudi market.
Our supply scope includes TYCO sprinklers, among them Series DS-1 dry sprinklers for freeze-prone areas; American Fire Control (AFC), including the ACV-300 Series wet alarm valve and OS&Y (outside screw and yoke) gate valves; and KDI UL listed and FM approved pipes.
FAQ
Which sprinkler system is the most reliable?
A wet pipe system: water is already at every sprinkler, with no valve to trip or detection to depend on. The NFPA 13 annex reserves dry systems for places where heat cannot prevent freezing, and, as PHCP Pros summarizes it, FM Global Data Sheet 5-32 puts reliable fire control ahead of preventing water exposure.
Does every pre-action system need two events?
No. Only double interlock waits for both detection and a sprinkler opening. A single interlock system fills the pipes on detection, then water flows only from sprinklers opened by heat. A non-interlock system admits water on detection or an open sprinkler, whichever comes first.
How long can a dry system take to deliver water?
NFPA 13 limits the time for water to reach the most remote one, two or four sprinklers assumed open, by hazard: 15 seconds for dwelling units, 60 for light, 50 for ordinary, 45 for extra hazard and 40 for high-piled storage. Outside dwelling units, systems up to 500 gallons, or 750 gallons with a quick-opening device, are exempt.
Does a car park in Saudi Arabia need a dry system?
Only if water-filled piping there cannot be kept at or above 4°C (40°F). Wet systems generally suit Saudi car parks, but check winter design temperatures for open or unheated car parks in northern and high-altitude regions. Whether a car park needs sprinklers at all is set by SBC 801 and Civil Defense requirements.
Should dry and pre-action systems use nitrogen?
They can be pressurized with compressed air or nitrogen. Nitrogen reduces corrosion, and the 2022 edition of NFPA 13 lets nitrogen-filled systems use a C-factor of 120 instead of 100 in hydraulic calculations, which can reduce pipe sizes. The nitrogen supply then needs maintaining so that assumption holds.
Need the right sprinkler system for your project? Send our engineers your drawings and operating conditions for a review of system type and calculations. Contact the AZEIDK team
