Once a survey has settled that a room needs gaseous suppression rather than water (we covered that decision in gas suppression vs sprinklers for data centres), a second fork opens immediately: inert gas or chemical agent?

On paper they look interchangeable. Both are clean agents designed to BS EN 15004. Both leave no residue, conduct no electricity and are safe for occupied spaces at design concentration. Both will put the fire out. But they are very different systems to own, and the differences sit in the plant room, in the discharge itself, in what happens after a discharge, and in where the chemistry is heading over the next decade.

This is how we walk clients through the choice.

What the two families actually are

Inert gas systems put a fire out by taking its oxygen away. IG-55 is a 50/50 blend of argon and nitrogen, two gases already in the air around you. On discharge it lowers the oxygen in the protected space from around 21% to roughly 12-13%: too little to sustain combustion, but calculated under BS EN 15004 so occupants can still evacuate safely. There is no fog, no corrosive by-product and no thermal shock to hot equipment. The gas simply disperses when you ventilate.

Chemical agents (the halocarbon clean agents) extinguish by soaking up heat and interrupting the combustion reaction. The two you will meet in UK buildings are FK-5-1-12, best known under its former 3M brand name Novec 1230, and FM-200, the trade name for HFC-227ea. Both are stored as liquid and discharge as gas, which is the root of most of their practical advantages.

Space and weight: the first practical filter

Because chemical agents are stored as liquid, they protect a given room from far fewer cylinders than an inert system, and the bank usually sits inside or beside the protected space. Where every square metre of plant room is spoken for (server rooms, comms suites, control rooms, small data floors), that compactness is often what makes suppression viable at all.

Inert gas is stored as compressed gas, so the same room needs a larger cylinder bank. The counterweight is that inert gas travels well in pipework: the cylinders can sit well away from the space they protect, in a basement store or plant area where floor space is cheaper and floor loading is easier to accommodate. If the only place a cylinder bank can live is beside the racks, chemical agent usually wins this round; a remote store makes the inert footprint problem largely disappear.

Discharge: ten seconds versus a minute

Chemical agents reach extinguishing concentration in around ten seconds, fast enough to stop a fire in sensitive electronics before it becomes an insurance claim. Inert systems are given around sixty seconds to reach design concentration under BS EN 15004. In practice, detection speed matters more than agent speed for the slow, smouldering faults that start most electronics fires, but the discharge dynamics differ in a way that affects the building.

Pushing a room full of gas into a sealed enclosure raises its pressure, and conventional inert discharges arrive with an aggressive initial surge that forces large pressure-relief vents on the room. This is where hardware choice matters: Gemini installs Fike ProInert, an IG-55 system with a pressure-regulating discharge valve that feeds the agent in at a controlled, steady rate. Peak pressures drop, relief venting shrinks, and retrofitting into a finished building gets simpler. Chemical agents, discharging a smaller volume, place lower venting demands on the enclosure to begin with.

Room integrity: the test both must pass

Neither family works if the room leaks. The agent has to stay at concentration long enough to make sure the fire is dead, typically ten minutes, and the only way to prove the enclosure can do that without discharging a cylinder is a door-fan integrity test to Annex E of BS EN 15004-1 and ISO 14520-1.

That applies at commissioning, at least annually, and after any work that touches the fabric: new cable penetrations, replaced doors, moved partitions, changes above the ceiling. Most insurers treat current integrity test records as a condition of cover. Whichever agent you choose, budget for the testing regime; a suppression system over a leaking enclosure is a very expensive alarm.

After the discharge: refill logistics

This is the question buyers ask least and owners care about most, and it is where the two families have diverged sharply.

Refilling an inert system is a logistics exercise, not a procurement gamble. Argon and nitrogen are naturally occurring industrial gases; recharge is about cylinders, transport and recommissioning rather than sourcing a specialist chemical.

Chemical agents now carry supply-chain questions. FM-200 sits inside the GB and EU F-gas quota regimes, which progressively cut the volume of hydrofluorocarbons that can be produced or imported, and that keeps pushing recharge costs and lead times in one direction: up. FK-5-1-12 remains available, but 3M, the company that made the Novec brand famous, has ended its PFAS production entirely; generic supply continues from other manufacturers with listed hardware, including Kidde’s Fluoro-K and Fike’s SF 1230, but the recharge supply chain has concentrated into fewer hands. If you run a chemical-agent system today, confirm your recharge route in writing before you need it.

The environmental direction of travel

Inert gas has no environmental question to answer: zero global warming potential, zero ozone depletion potential, no fluorinated chemistry facing regulatory pressure.

The fluorinated agents are living under two regimes at once. FM-200 is a potent greenhouse gas caught by the F-gas phasedown. FK-5-1-12 is a fluoroketone that falls within the scope of the broad PFAS restrictions being assessed under UK and EU chemicals regulation, with the combined ECHA opinions expected to reach the European Commission by the end of 2026 and the socio-economic committee already signalling that use-specific derogations, not a blanket ban, are the likely shape of the outcome.

To be clear: none of this bans anything today. Existing systems remain lawful to use, maintain and recharge, and panic replacement is the wrong response. But for a system you are specifying now, with a long service life ahead of it, the direction of travel belongs in the decision. We set out the full regulatory picture, and a stewardship checklist for existing estates, in PFAS and clean agent suppression: what operators should do in 2026.

Side by side

  • Extinguishing method: inert gas (IG-55) works by oxygen reduction; chemical agents (FK-5-1-12, FM-200) work by heat absorption.
  • Discharge time: around sixty seconds for inert gas; around ten seconds for chemical agents.
  • Cylinder count: a larger bank for inert gas; far fewer cylinders for chemical agents.
  • Cylinder location: inert cylinders can sit remote from the room; chemical banks usually sit inside or beside it.
  • Enclosure venting: inert needs relief vents, much reduced by a regulated discharge; chemical agents place lower venting demands.
  • Refill after discharge: naturally occurring industrial gases for inert; quota- and PFAS-exposed supply chains for chemical.
  • Environmental position: zero GWP and no fluorinated chemistry for inert; the F-gas phasedown (FM-200) and the PFAS assessment (FK-5-1-12) for chemical.
  • Safe for occupied spaces: yes for both, at design concentration.

Typical fit by room type

Data halls, archives, heritage stores, laboratories. Rooms with long asset lives, sustainability commitments or space for a remote cylinder bank tend towards inert gas. The zero-GWP story also travels well through planning and ESG reporting.

Tight comms rooms, control rooms, small data floors. Where the cylinder bank must live beside the kit and every square metre is committed, chemical agent compactness often decides it, specified with eyes open on the recharge supply chain.

Existing FM-200 and Novec estates. Keep maintaining them. A well-maintained chemical system remains effective, lawful and insurable, and premature replacement wastes money. The sensible triggers to reassess are end of design life, a discharge that makes recharge uneconomic, or a major refit of the protected space.

UPS, switchgear and battery rooms. The agent must be electrically safe for the equipment present, and lithium-ion thermal runaway needs its own risk assessment; gaseous suppression alone is not automatically the whole answer here.

What we would recommend

If you are specifying from scratch and the building can accommodate the cylinder bank, our default is inert gas: IG-55 with a regulated discharge valve. It has no refill supply-chain exposure, no fluorinated chemistry for a future regulator to reopen, and with controlled discharge the traditional venting penalty has shrunk. It is the specification least likely to need explaining to anyone a decade from now.

Where space rules inert out, FK-5-1-12 is still a legitimate specification, provided the recharge route is confirmed in writing at handover and the owner understands the regulatory picture they are buying into.

And whichever agent is in the cylinders: test the room integrity annually and after any works, keep the service records current, and treat the enclosure as part of the system. The gas cannot do its job if the room will not hold it.

Where Gemini stands

Gemini AMPM is agent-neutral: we design, install and maintain both families to BS EN 15004 and ISO 14520, and we recommend the right system for the room, not the one that is easiest to sell. We are an approved Fike installer and delivered IG-55 suppression at Peterborough Court & Daniel House in the City of London, and our in-house team covers the whole lifecycle: design, installation, door-fan integrity testing, servicing and post-discharge recharge.

If you are weighing up inert against chemical for a new room, or want an honest read on the estate you already own, book a survey or call 0330 043 0080.

This article is general guidance. Final specification of gas suppression systems must be undertaken by a competent designer working to BS EN 15004 and the fire risk assessment for the building.