They suppress fire without leaving residue and without reducing oxygen to a level people cannot survive.

Design concentrations are set below levels considered hazardous for the brief exposure during evacuation.

That combination is what distinguishes them from CO2, which is lethal at working concentrations.

No residue means sensitive electronics are not damaged by the suppression itself.

Discharge is fast, typically completed in seconds.

Data halls, control rooms, switch rooms and archives are the usual applications.

It is how well the room holds the agent, and the design assumes concentration is held for a specified period after discharge.

A room that leaks loses concentration quickly and the fire can re-establish.

Suppressing a fire briefly is not the same as extinguishing it.

Integrity is proven at commissioning by a fan pressurisation test rather than by inspection.

Cable penetrations, ductwork, door seals and building works all degrade it over time.

Retesting after alterations is the control, and alterations in these rooms are constant.

A rapid gaseous discharge into a sealed room raises pressure sharply enough to damage its construction.

Damaged walls or ceilings then destroy the integrity the system depended on.

Pressure relief vents are sized as part of the system design.

They must not themselves become a leakage path that defeats the hold time.

This requirement is frequently overlooked in retrofits into existing rooms.

Both over-pressure and under-pressure can occur depending on the agent and discharge rate.

Specific agents have been restricted or phased down in various markets, and the position differs by jurisdiction and continues to change.

The driver is global warming potential rather than fire performance.

That makes long-term availability a commercial consideration when specifying.

Recharge cost after a discharge can rise sharply as an agent becomes restricted.

Alternative agents and inert gas systems are the usual substitutions.

The current regulatory position should be established locally rather than assumed from practice elsewhere.

Typically within seconds, and the discharge time is a designed parameter rather than a product property.

Fast discharge achieves concentration before the fire grows significantly.

It also limits the time occupants are exposed to the discharge itself.

Discharge produces noise and turbulence that can affect sensitive equipment, particularly hard drives.

Nozzle placement and discharge rate are calculated for the specific enclosure.

Hold time after discharge is the separate parameter that enclosure integrity governs.

Pre-discharge alarms, a time delay, manual hold or abort facilities and clear signage - the specifics vary by market.

Occupants need warning and time to leave before discharge.

Manual hold devices let someone in the room delay discharge while evacuating.

Interlocks with ventilation and door closers are part of holding the concentration.

Signage at entrances warns anyone approaching that a system is installed.

Requirements differ between jurisdictions and are part of the design rather than optional additions.

Agent quantity verification, cylinder inspection, detection and release testing, and periodic integrity retesting.

Agent quantity is checked by weight or pressure depending on the system.

Cylinders are subject to periodic pressure testing under separate pressure equipment rules.

Detection and release must be proven end to end rather than by tripping the valve manually.

Integrity retesting after room alterations is the item most often omitted.

Who may do this work, how often, and what they must record all come from the local standard.