Clean Agent System

Main components

Agent cylinders

Agent is stored as a liquefied gas under nitrogen superpressurisation, typically around 25 bar for FM-200, in cylinders sized to the protected volume. Cylinder banks are weighed or level-checked at survey, since a partially discharged cylinder looks externally identical to a full one.

Discharge nozzles and piping

Fixed piping distributes agent from the cylinder bank to nozzles sized and positioned to reach design concentration within about 10 seconds across the whole protected volume — a slower fill lets the fire regenerate faster than the agent can suppress it.

Detection and control panel

Cross-zoned smoke or flame detection triggers the release, usually with a manual abort station and a pre-discharge alarm giving personnel time to leave before the automatic release fires.

Room integrity

The protected space itself is part of the system — door closers, damper interlocks that shut ventilation on alarm, and cable/pipe penetration seals all have to hold the agent concentration for the hold time specified in the design, usually around 10 minutes.

Selection and sizing

Sizing is a room-volume calculation against the agent's design concentration, corrected for temperature. The factors a buyer checks:

• Net protected volume including any fixed obstructions that reduce free volume
• Room integrity test result (door fan test) confirming the space holds concentration for the hold time
• Agent choice — Novec 1230 has a near-zero global warming potential against FM-200's higher GWP, increasingly relevant for newbuild specification
• Cylinder location and temperature range, since agent pressure is temperature-dependent

Regulations and class

Fixed gas fire-extinguishing systems fall under SOLAS Ch. II-2 Reg. 10 and the FSS Code, which sets the technical requirements for equivalent alternatives to CO2 systems, including clean agent. Class surveys check cylinder weight or pressure at intervals set by the classification society, generally annually as part of the fire safety survey, plus a full system function test within the survey cycle. Because clean agent systems are approved as CO2 equivalents rather than a mandated system in their own right, the flag state's acceptance letter for the specific agent and design should be kept with the ship's fire control plan.

Typical faults

• Cylinder pressure or weight loss from a slow valve seal leak — caught late, the room has no protection and nobody knows until survey or a real fire
• Door or damper interlock defeated or left in manual override — agent discharges into a room that cannot hold concentration and leaks out before suppression completes
• Detector heads fouled with dust in an engine room environment — false alarms lead crews to disable a zone rather than clean it, leaving the space unprotected
• Penetration seals broken during cable work and never reinstated — same failure mode as the door interlock, harder to spot on a walk-through

What to look for in a supplier

• FSS Code type approval for the specific agent and cylinder pressure, not a generic clean agent certificate
• Ability to supply a room integrity (door fan) test report at handover, not just the hardware
• Spare cylinder and valve availability matched to the ship's trading pattern — agent cylinders are not a shelf item in every port
• Clear documentation of design concentration and hold time calculations for the surveyor's file

A clean agent cylinder that reads full on the gauge but has lost superpressurising nitrogen through a slow leak will still discharge — just not fast enough to reach design concentration, so pressure alone is not proof the bottle will do its job.