Dry Chemical System

What a fixed dry chemical system is for

Portable extinguishers cover a fire a crew member can reach and fight directly; a fixed dry chemical system is built for spaces where a fire can spread faster than a hand extinguisher can control it, or where crew access is limited during a fire, such as a galley deep-fat range hood and duct, a paint locker, or a helicopter deck fuelling point. Rather than relying on someone carrying an extinguisher to the seat of the fire, the system discharges powder automatically or by remote pull station through fixed piping and nozzles aimed directly at the hazard.

Main components

Powder storage cylinders

One or more pressure vessels hold the dry chemical charge, usually a sodium or potassium bicarbonate based powder chosen for the fire class expected in that space, kept dry and free-flowing by a moisture-tight fill and periodic condition checks.

Expellant gas cylinder

A separate cylinder of nitrogen or CO2 provides the propelling gas, either stored ready-connected or released by a pilot cylinder that then pressurises the main powder cylinders, depending on system design.

Fixed piping and discharge nozzles

Sized and positioned during design to deliver a calculated powder density across the protected area or directly onto specific equipment, such as a fryer or duct opening, within seconds of activation.

Detection and release station

Heat or flame detectors trigger automatic release in unmanned or high-risk spaces; a manual pull station, always provided as a backup, lets crew release the system from outside the protected space.

Selection and sizing

The system is engineered to the specific hazard, not sold as a fixed capacity unit:

• Protected area or volume, and whether the hazard is a local point source such as a fryer versus a whole enclosure such as a paint locker.
• Powder type matched to the expected fire class, since bicarbonate powders suited to class B fires differ from the ammonium phosphate powders used for combined class A/B/C risk.
• Discharge time and powder quantity calculated to achieve extinguishing concentration before the fire can regrow, typically within ten to thirty seconds.
• Detection method appropriate to the space, balancing fast response against false discharge risk from normal galley heat.

Regulations and class

SOLAS Chapter II-2 requires fixed fire-extinguishing arrangements for galley ranges with deep-fat cooking equipment and for certain other specific hazards, and sets performance criteria the system's design must meet rather than mandating one brand or layout. Class societies require the system design to be approved against a recognised standard before installation, and periodic servicing, weighing of powder cylinders, and pressure testing of expellant gas cylinders at intervals set by the equipment standard, commonly aligned with the vessel's fire equipment survey cycle.

Typical faults

What to look for in a supplier

• Approval to service the specific system brand and design, since powder chemistry and cylinder hardware are not interchangeable between manufacturers.
• Documented weighing and condition checks of powder cylinders at every service, not just a visual inspection.
• Ability to pressure test and, where due, hydrostatically retest the expellant gas cylinders on the same visit.
• Familiarity with galley hood and duct nozzle layouts specifically, since misaimed nozzles are a common installation-era defect that only shows up at commissioning test.

Ask for the actual discharge test result, not just a service sticker, whenever the system is due; a system that passes a static weight and pressure check can still fail to reach the fryer surface if a nozzle was reaimed or blocked during galley cleaning.