Suppression is what you fit where a sprinkler is the wrong answer. A server room cannot be flooded. A deep fat fryer cannot be put out with water. A listed interior may not tolerate the pipework. Each of those has its own fixed system, and each is chosen for the hazard rather than for the building as a whole.
Kitchen hood suppression
A commercial kitchen with a deep fat fryer or a range under an extraction canopy is the commonest case. Nozzles in the canopy and over the appliances discharge a wet chemical agent, the gas or electrical supply to the appliances is shut off automatically, and the extraction is dealt with. It is the only practical answer to a fryer fire, because the fire is in a bath of oil above its auto-ignition temperature and cooling it is the whole problem.
Gas suppression
Inert gases or chemical clean agents flood a sealed room and put out the fire without leaving residue on the equipment. They are used over data rooms, switch rooms and archives. The room has to hold the agent long enough to work, which is why a room integrity test matters and why a gas system defeated by a new cable penetration is a common and expensive finding.
Water mist
Very fine droplets that cool and displace oxygen locally using a fraction of the water a sprinkler uses. It suits places where water damage is the concern or where a tank and pump for a sprinkler system will not fit, including heritage buildings and small plant rooms. It is a designed system rather than a product, and a mist system installed without a design is not a system.
Inspection, and the special failure modes
All fixed suppression is inspected and serviced on a schedule by a competent contractor, and each type adds its own failure mode. Kitchen systems need the nozzles cleaned of grease and the fuel shutoff proved. Gas systems need the room integrity retested when the room changes and the cylinders weighed. Mist systems need their nozzles clear and their pumps proved. None of that is visible from the room it protects.
Questions people ask about fire suppression systems
What is a fire suppression system?
A fixed system that discharges an agent automatically onto a defined hazard: wet chemical over a kitchen range, gas into a sealed room, or water mist where water damage or space rules out sprinklers.
Does a commercial kitchen need suppression?
Where there is a deep fat fryer or a significant range under a canopy it is normally the only practical answer, and insurers commonly require it.
Is gas suppression safe for people in the room?
Modern agents are designed to be used in occupied spaces at the design concentration, with alarms and a delay before discharge. The room must still be evacuated on the alarm.
How often is a suppression system serviced?
On a schedule set by the system standard and the manufacturer, by a competent contractor, with kitchen nozzles cleaned, fuel shutoff proved, and gas cylinders weighed and room integrity retested when the room changes.