Guide · Clean agent suppression

Sizing a clean agent system: room volume, temperature and enclosure integrity

A clean agent system is sized from the room, not from a catalogue. Four things decide the quantity and the hardware: how big the protected volume really is, how cold the room gets, how well it holds the agent in, and how the system is detected and released.

1. Is clean agent the right answer?

Clean agent is for rooms where a sprinkler discharge would cause more loss than the fire: server rooms and data centres, electrical switchrooms, control rooms, telecom facilities, archives and records. The agent is electrically non-conductive and leaves no residue to clean up. Where water is acceptable, it is usually the cheaper and simpler answer — and we will say so.

Our systems are designed to NFPA 2001, the standard for clean agent fire extinguishing systems.

2. Net room volume

The agent has to fill the protected volume, so the quantity starts with an honest volume: length × width × height of the room. Two points change the number:

• Voids. A raised floor or a space above a false ceiling is part of the protected volume if it is to be protected — and it usually should be, because it carries cabling and detection. Decide this at the start; either the void is protected with the room or it is sealed off from it.
• Solid structure. Permanent solid structure that agent cannot enter may be deducted from the volume. Movable equipment, furniture and racks may not.

3. Minimum temperature

Agent vapour behaves like a gas: the colder the room, the denser the vapour, and the more agent by weight is needed to reach the same concentration. Quantity is therefore worked out for the lowest temperature the room will see — not the temperature on the thermostat. An unheated store room, a plant room in winter or a room served by a cold air-conditioning stream can all set a lower design temperature than the room’s normal condition.

4. Design concentration and the quantity calculation

The design concentration is set by the standard for the agent and the hazard. The agent quantity then follows from the volume, the minimum temperature and that concentration, using the agent manufacturer’s design data. Those figures are issued with the quotation and the technical documentation for your room; they are not printed here, because a figure taken from the wrong pressure, temperature or agent is exactly how a system ends up undersized.

Note also that the maximum charge of a cylinder is the cylinder volume at its filling rate. The design quantity for your room will usually be less.

5. Enclosure integrity

The agent must stay at its design concentration for the hold time the standard requires, which a leaky room cannot do. The usual leak paths are gaps under and around doors, cable and pipe penetrations, and ventilation ducts. Three things follow:

• Sealing. Penetrations are sealed and doors made to close properly.
• Ventilation. Air handling is shut down and dampers close when the system releases.
• Pressure relief. The discharge raises the room pressure briefly, so a room that is very tight needs a relief vent, and a room that is very leaky needs sealing — an enclosure integrity test shows which.

Integrity testing and relief-vent sizing are quoted with the system.

6. Detection and release

Release is normally interlocked to cross-zoned detection: two independent detectors must operate before the agent is released, and a manual abort inside the protected room stops it. The discharge delay is set to suit the evacuation time for the space. Discharge time is 10 seconds or less.

7. Pipe network or cabinet

	Engineered pipe network	Cabinet system
Suits	Larger rooms, several rooms from one cylinder bank, or cylinders outside the protected space	A single server room, switchroom or store where running pipework is not worth the disruption
Storage pressure	4.2 MPa	2.5 MPa
Cylinders	40 to 180 litres	40 to 180 litres
Coverage per system	Up to 800 m² and 3,600 m³	Up to 500 m² and 1,600 m³ per unit

Both are available with FM-200 (HFC-227ea) or Novec 1230. The full model tables are on the clean agent suppression page.

What to send us

• The room dimensions — length, width and height — and any raised floor or ceiling void.
• The lowest temperature the room is expected to reach.
• What is in it: racks, switchgear, records.
• The openings: doors, ducts and cable or pipe penetrations.
• How many rooms, and whether they could share one cylinder bank.

We will size the system and issue the technical documentation with our quotation.