The Short Answer
Use a clean agent system for spaces that are normally occupied, such as data centres, control rooms, and offices with sensitive equipment, because clean agents are designed to be safe for people at their working concentrations. Use CO2 mainly for normally unoccupied hazards, such as certain machinery spaces and enclosures, because CO2 suppresses fire by lowering oxygen to levels that are dangerous to people. Occupancy is the single question that decides most of these choices.
How Each System Works
Clean agents, meaning halocarbons such as FM-200 and Novec 1230 and inert gas blends, suppress fire by absorbing heat or by gently reducing oxygen to a level that still supports life at design concentration. CO2 suppresses fire by displacing oxygen substantially, which is highly effective but creates an atmosphere people cannot breathe. Clean agents fall under NFPA 2001; CO2 systems fall under NFPA 12. Both are gas suppression systems and both leave no residue, but they achieve suppression in fundamentally different ways.
Occupant Safety: The Deciding Factor
This is the difference that usually decides the choice. Clean agents are formulated and designed so that people can be present during and after discharge at design concentrations, which is why they are the standard for occupied IT and control spaces. CO2 is not; its use requires strict safeguards, including pre-discharge alarms, time delays, pneumatic sirens, and lock-off provisions, and it is confined to spaces where people are not normally present. For any regularly occupied space, a clean agent is almost always the correct answer, and treating this as the first filter avoids specifying an unsafe system.
Residue, Equipment, and Recovery
Both agents are clean and leave no residue, so both protect electronics well and allow relatively quick recovery after a discharge. Clean agent systems are the standard choice around live IT and control equipment because they combine no residue with occupant safety, so staff can respond and equipment can return to service without a cleanup. CO2 also leaves no residue, but its safety constraints limit where it can be used regardless of how clean it is.
Cost and Space
CO2 can be cost-effective for suitable unoccupied hazards and is a mature, well-understood technology. Clean agents typically cost more per protected volume, but they remove the occupant-safety constraint, which is decisive for most modern facilities. Storage space differs by agent: halocarbon clean agents are compact, inert gas blends need more cylinders, and CO2 storage depends on the hazard. These practical factors feed into the design once the safety question has been settled.
Which Should You Choose
Start with occupancy. If people can be present, choose a clean agent designed to NFPA 2001. If the space is reliably unoccupied and the safeguards can be enforced, CO2 may suit. For a data centre or control room, the answer is almost always a clean agent, as explained in our server room fire suppression guide. SFFECO manufactures gas suppression systems and can advise on the right agent, then design, supply, install, and commission it for your facility.
