What is the difference between a deluge system and a standard sprinkler system?

In a standard wet or dry pipe sprinkler system, each head is individually heat-actuated — only the heads directly over the fire open. In a deluge system, all heads are permanently open and connected to a dry pipe. When the detection system (heat, smoke, or flame detectors) triggers the deluge valve, water flows through every head simultaneously across the entire protected zone. This delivers a much higher water density over a much larger area much faster — appropriate for rapidly spreading fires involving flammable liquids or high fire loads.

Where are deluge systems typically installed?

Deluge systems are used where standard sprinkler response would be too slow or where simultaneous protection of a large area is required: aircraft hangars (ICAO and CAA requirement), transformer bays, LPG and LNG storage facilities, chemical process areas, munitions stores, and some paint spray booths. They are also used as foam deluge systems — where the agent is a foam-water mixture rather than water alone — for flammable liquid hazards.

What activates a deluge system?

A deluge system is activated by a dedicated detection system — typically heat detectors, flame detectors, or a combination — that is separate from the sprinkler heads themselves. When the detectors trigger, they open a deluge valve (also called a deluge release valve) which allows pressurised water into the pipe system and through all open heads. Most systems include a manual release option and a time-delay/abort function to prevent accidental discharge.

Is a deluge system the same as a foam suppression system?

No — but deluge systems can use foam as their agent. A foam deluge system uses the same open-head, simultaneous-discharge principle but injects foam concentrate into the water supply upstream of the deluge valve. The resulting foam-water solution is discharged through the open heads to form a foam blanket over flammable liquid surfaces. This is the standard protection for aircraft hangars, fuel storage bunds, and some chemical process areas.

What standard governs deluge systems in the UK?

The primary standard for deluge and pre-action sprinkler systems in the UK is BS EN 12845 (fixed firefighting systems — automatic sprinkler systems), supplemented by Loss Prevention Standard LPS 1124 for specific applications. For foam deluge systems, BS EN 13565-2 applies. All systems must be designed and installed by a competent specialist contractor and commissioned with a full flow test.

⚠ Emergency: If a deluge system discharges — evacuate immediately, do not re-enter until system is reset and all-clear given.

Glossary — Fire Suppression

Deluge System

A deluge system is a fixed fire suppression system in which all sprinkler heads are permanently open. Activation of the detection system opens a deluge valve, causing water (or foam-water mixture) to flow simultaneously through every head in the protected zone. Used where rapid, total-area coverage is required — typically high-hazard industrial and aviation applications.

Fixed suppression High-hazard occupancies BS EN 12845

Key distinction

Unlike wet or dry pipe sprinkler systems — where only the heads directly above a fire activate — a deluge system discharges through all heads simultaneously across the entire protected zone. This delivers a far higher water application rate and provides coverage before a fire has time to spread, making it appropriate for flammable liquid fires and other rapidly spreading hazards.

Suppression system comparison

System type	Heads	Activation	Coverage	Typical application
Wet pipe sprinkler	Closed (heat-activated individually)	Individual heads open at fusible link/bulb temperature	Only heads over fire	Offices, hotels, shops, residential
Dry pipe sprinkler	Closed (heat-activated individually)	Pressure loss opens dry valve; individual heads activate	Only heads over fire	Cold stores, car parks, unheated buildings
Deluge system	Open (all open permanently)	Detection system opens deluge valve; all heads discharge together	Entire protected zone simultaneously	Aircraft hangars, transformer bays, chemical stores, LNG facilities
Pre-action system	Closed (heat-activated)	Two-step: detection then sprinkler head activation	Only activated heads	Server rooms, museums, libraries

How a deluge system works

The pipe system is dry (unpressurised) during standby. All sprinkler heads are open — there is no fusible element or glass bulb. A separate detection system (typically linear heat detectors, UV/IR flame detectors, or a combination) monitors the protected area. When detectors trigger, a signal opens the solenoid-controlled deluge valve. Water enters the pipe system and flows simultaneously through all open heads, applying a uniform water density across the entire protected floor area.

Foam deluge systems

For flammable liquid hazards, a foam concentrate injection system upstream of the deluge valve adds foam solution to the water supply. The foam-water mixture is discharged through the open heads to form a foam blanket that suppresses vapour release and seals the fuel surface from oxygen. Aircraft hangar systems typically use aqueous film-forming foam (AFFF) or fluoroprotein foam. See our fire suppression systems glossary entry for a full overview of fixed suppression types.

Interaction with fire compartmentation

Deluge systems protect specific hazard areas — they do not substitute for fire compartmentation of the building as a whole. The protected zone must still be enclosed by fire-resistant construction appropriate to the risk. Service penetrations through compartment walls must be fire stopped to prevent spread of fire or smoke to adjacent areas in the event of suppression failure.

Maintenance requirements

Deluge systems require quarterly functional tests of the detection and valve systems and an annual full flow test. The water supply (tank capacity, pump performance) must be verified annually against the system design. Foam concentrate must be sampled and tested periodically to confirm it remains within specification.

Frequently asked questions

FAQ

Deluge System

Suppression system comparison

How a deluge system works

Foam deluge systems

Interaction with fire compartmentation

Maintenance requirements

Related entries

Frequently asked questions

Frequently asked questions