Gas-based fire suppression for switch rooms and server rooms (FM-200, Novec 1230, inert gas)

The guide on extinguishing agents for electrical installations covers which portable agents (CO₂, powder, clean-agent portable extinguishers) are safe to use near live equipment. This article covers the fixed, room-level counterpart of that same principle: a total flooding gas suppression system, as commonly installed in switch rooms, UPS rooms, data centres and server rooms, designed and installed per NEN-EN 15004 (which mirrors the international ISO 14520 series).

Why a gas system for these spaces

Water sprinklers and dry-chemical powder both extinguish effectively, but both leave a room unusable afterwards for electrical equipment: water causes short circuits and corrosion, and powder residue is electrically conductive and highly abrasive to contacts and bearings. A total-flooding clean-agent (or inert-gas) system extinguishes without leaving a residue and without requiring the room to be de-energised first for the agent itself to be safe to discharge — the property that makes it the standard choice for rooms containing energised switchgear, UPS systems and server racks.

Two extinguishing principles

Halocarbon clean agents (HFC-227ea, known by the trade name FM-200, and FK-5-1-12, known as Novec 1230) extinguish primarily by chemically interrupting the combustion reaction, at a design concentration in the range of roughly 7–9 % by volume for a typical Class A (surface) hazard such as electronic equipment.
Inert gases (nitrogen IG-100, argon-based blends, or the nitrogen/argon/CO₂ blend IG-541) extinguish by reducing the oxygen concentration in the room below the level that sustains combustion, which requires a much higher design concentration (room oxygen typically reduced to roughly 12–15 %) and therefore a correspondingly larger volume of stored gas.

Design concentration, discharge time and hold time

Three parameters, all set in NEN-EN 15004, together determine whether a system actually extinguishes a fire:

Design concentration — the minimum agent concentration the system must achieve throughout the protected volume.
Discharge time — total flooding systems are designed to reach that design concentration very quickly (on the order of seconds) after activation, so the fire does not have time to grow before the extinguishing concentration is reached.
Hold time (soak time) — the design concentration must be maintained for a specified period after discharge, to prevent re-ignition of any still-hot material once the discharge itself has finished.

Achieving the hold time depends entirely on the physical integrity of the room: any significant leakage path (unsealed cable penetrations, gaps around doors, suspended-ceiling voids) lets the agent dilute below the design concentration before the hold time has elapsed. This is verified with a room integrity (door-fan) test: a calibrated fan pressurises or depressurises the room while measuring leakage, to confirm the enclosure will actually retain the design concentration long enough — a test that must be repeated whenever the room's physical boundary is altered (new cable routes, new penetrations, a suspended-ceiling change), not only at initial commissioning.

FM-200 versus Novec 1230: safety margin and environmental impact

Both are halocarbon clean agents with a similar extinguishing mechanism, but they differ on two points relevant to system choice:

Safety margin for occupied spaces: Novec 1230 has a considerably higher No Observed Adverse Effect Level (NOAEL) than HFC-227ea, giving a larger safety margin between the normal design concentration and the concentration at which physiological effects begin — relevant for a normally-occupied server or switch room.
Environmental impact: HFC-227ea has a high Global Warming Potential and a long atmospheric lifetime; Novec 1230 has a Global Warming Potential close to zero and a short atmospheric lifetime. This difference, combined with the EU F-gas Regulation's phase-down of HFCs, is a practical reason new installations increasingly specify Novec 1230 or an inert-gas system over HFC-227ea.

CO₂ total flooding: effective, but not for occupied rooms

CO₂ total flooding is highly effective but extinguishes by reducing oxygen to a concentration that is itself an asphyxiation hazard to people in the room — well above the concentration tolerable for continued human presence. It requires a pre-discharge alarm with a mandatory evacuation delay, positive means of preventing re-entry during discharge, and is therefore mostly reserved for normally unoccupied enclosures rather than a routinely staffed switch room or server room.

Post-discharge safety: decomposition products

When a halocarbon clean agent is exposed to an actual flame or a very hot surface during extinguishing, it can partially decompose into toxic by-products, including hydrogen fluoride (HF) — a corrosive, toxic gas. The room must be ventilated and, where the fire involved higher temperatures or was not extinguished immediately, checked for HF before personnel re-enter without respiratory protection — a step that is separate from, and in addition to, the normal electrical isolation (lock-out/tag-out) that must precede any manual intervention in the room afterwards.

Relationship to NEN 3140

A gas suppression system is a passive, reactive layer of protection against a fire that has already started; it does not replace the preventive measures that reduce the chance of an electrical fire starting in the first place — periodic thermographic inspection, secure connections, and the regular NEN 3140 inspection of the installation itself. The two regimes serve different purposes and neither substitutes for the other, the same relationship the ATEX periodic inspection guide describes for an explosion-protection regime running alongside the ordinary electrical inspection.

Practical relevance

For a new or refurbished switch room, UPS room or server room, agent selection (halocarbon versus inert gas, and which halocarbon), room integrity verification at commissioning and after any later penetration, and a documented post-discharge re-entry procedure are all part of the fire-protection design — not an afterthought bolted onto the electrical design once the room layout is already fixed.

Common mistakes

Specifying CO₂ total flooding for a normally-occupied switch or server room without the mandatory pre-discharge evacuation sequencing — an asphyxiation risk to anyone still inside.
Not repeating the room-integrity (door-fan) test after later cable routing changes or other penetrations of the room boundary — the design concentration can leak away before the required hold time has elapsed, allowing re-ignition.
Treating gas suppression as a substitute for preventive electrical maintenance (thermographic inspection, secure connections, RCD testing) rather than as a last-resort layer behind that prevention.
Re-entering the room immediately after discharge without checking for hydrogen fluoride decomposition products, particularly after a fire that reached higher temperatures before being extinguished.