FM200 vs CO2 Suppression Systems: Which One Belongs in Your Room?

The deciding question: will people be in the room?

Start every suppression decision with occupancy, not price. Total-flooding CO2 works by displacing oxygen and typically needs a concentration of roughly 34% or more in the room. That concentration is lethal to anyone inside. FM200 (HFC-227ea) works at roughly 7–8.5% and is designed so that, at normal design concentrations, it can be used in normally occupied spaces.

So the rule of thumb most designers follow is:

• Normally occupied rooms (server rooms with technicians, control rooms, archives with staff, bank operations rooms): FM200 or another clean agent.
• Normally unoccupied rooms that people only enter for maintenance (switchgear rooms, transformer rooms, generator and turbine enclosures, cable tunnels): CO2 can be considered, with strict life-safety controls.

If a room is "sometimes occupied" and you cannot guarantee evacuation and lock-out procedures, treat it as occupied.

How each agent puts out a fire

FM200 extinguishes mainly by absorbing heat from the flame and interrupting the combustion reaction. Because it works at a relatively low concentration, there is still breathable oxygen in the room. It discharges in about 10 seconds and leaves no residue.

CO2 extinguishes mainly by smothering: it reduces the oxygen level below what the fire needs, with some cooling effect. It also leaves no residue and is electrically non-conductive. However, the discharge is very cold and produces a dense white fog, which reduces visibility and can cause thermal shock to some sensitive equipment. CO2 is heavier than air, so it can collect in basements, pits and trenches next to the protected room.

Both are covered by recognised standards: NFPA 2001 and ISO 14520 for clean agents such as FM200, and NFPA 12 for carbon dioxide systems.

Side-by-side comparison

The table shows why the choice is rarely about effectiveness. Both extinguish electrical fires well. The trade-off is life safety and equipment sensitivity against agent cost and refill convenience.

Life-safety precautions every CO2 system needs

If you choose CO2, the life-safety design is not optional. Ask your designer to show how each of the following is provided:

1. Lock-out (isolation) valve – a manual valve that physically prevents discharge into the room while people are working inside, with a clear lock-out procedure.
2. Pre-discharge alarm and time delay – sirens and flashing beacons that operate before discharge, with enough delay for people to leave.
3. Warning signs – at every entrance and inside the room, stating that the room is protected by CO2 and must be evacuated when the alarm sounds.
4. Odoriser – many designs add a scent to the CO2 so that leaks or discharges can be noticed.
5. Status indication – a panel or lamp outside the door showing whether the system is in automatic or manual mode.
6. Safe re-entry – after discharge, nobody enters until the room is ventilated; responders who must enter use self-contained breathing apparatus.
7. Low areas checked – adjacent pits, trenches and basements where CO2 can settle need to be assessed and signed.
8. Training – everyone with access to the room is trained on the alarm, the lock-out procedure and the evacuation route.

A CO2 system without these controls is a hazard in itself. If any of them cannot be guaranteed, choose a clean agent instead.

Where each system fits

Kitchens are excluded from both CO2 and FM200 total flooding. Cooking-oil fires can re-ignite once a gas agent disperses because the oil stays above its auto-ignition temperature. Kitchen hoods use a pre-engineered wet chemical system, backed up by K-type (Class F) portable extinguishers; see fire extinguisher types.

Cost and lifecycle considerations

Up-front cost. CO2 agent is inexpensive, but a CO2 system needs more high-pressure cylinders, a heavier manifold and more pipework for the same room. FM200 agent costs more per kilogram, but needs fewer cylinders and less space. For small and medium rooms FM200 often ends up competitive; for large unoccupied volumes CO2 is usually cheaper.

Room sealing. Both systems need a reasonably tight room. CO2 designs for deep-seated fires may require extended hold times, which makes sealing even more important.

Maintenance. Both need periodic inspection, cylinder weighing or level checking, detector testing and functional testing of the release circuit. High-pressure cylinders also need periodic hydrostatic testing at the intervals set by the applicable standard.

After a discharge. CO2 cylinders can be refilled quickly by local gas suppliers. FM200 refills depend on a supplier who stocks the agent and can recharge the specific cylinder type, so ask about refill lead time before you buy.

How Safety Plus supplies and installs suppression systems

Safety Plus supplies and installs both FM200 and CO2 fire suppression systems. A typical scope includes:

• Site survey: room dimensions, occupancy, hazards, openings and penetrations.
• Design: agent quantity, cylinder sizing, pipe routing and nozzle layout, with calculations.
• Detection and control: detectors, releasing panel, manual release, abort or lock-out, sirens and beacons. See fire alarm and detection.
• Installation of cylinders, brackets, manifold, pipework and nozzles.
• Testing and commissioning, followed by handover documents and user training.

Where the project also needs full fire protection engineering, Safety Plus provides project engineering coordination and technical consultancy. Explore fire suppression systems and CO2 and other extinguishers. Still comparing clean agents? Read Novec 1230 vs FM200. Share your room drawings via request a quote.

Frequently asked questions

Sources

• National Fire Protection Association (NFPA)
• International Organization for Standardization (ISO)
• Occupational Safety and Health Administration (OSHA)